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Advanced alkaline water electrolysis

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Advanced alkaline water electrolysis

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... For instance, one possible competing reaction in the CVE system is the water electrolysis reaction (Eq. 5) (Marini et al., 2012). ...
... As illustrated in Eq. 5, theoretically the water electrolysis reaction can take place when the applied bias voltage is higher than 1.23 V (Weller et al., 2014). In practice, due to the overpotentials on the electrode/solution interfaces, as well as the ohmic drop of the reaction solution, the bias voltage required for water electrolysis is often higher than 2.0 V (Marini et al., 2012). Therefore, in the CVE U extraction experiments, water electrolysis might occur as the side reaction when higher bias voltages (3.0 V and 4.0 V) were applied, resulting in increased electricity consumption. ...
Article
Removing and recovering uranium (U) from U-mining wastewater would be appealing, which simultaneously reduces the adverse environmental impact of U mining activities and mitigates the depletion of conventional U resources. In this study, we demonstrate the application of a constant-voltage electrochemical (CVE) method for the removal and recovery of U from U-mining wastewater, in an ambient atmosphere. The effects of operation conditions were elucidated in synthetic U-bearing water experiments, and the cell voltage and the ionic strength were found to play important roles in both the U extraction kinetics and the operation cost. The mechanistic studies show that, in synthetic U-bearing water, the CVE U extraction proceeds exclusively via a single-step one-electron reduction mechanism, where pentavalent U is the end product. In real U-mining wastewater, the interference of water matrices led to the disproportionation of the pentavalent U, resulting in the formation of tetravalent and hexavalent U in the extraction products. The U extraction efficacy of the CVE method was evaluated in real U-mining wastewater, and results show that the CVE U extraction method can be efficient with operation costs ranging from $0.55/kgU ~ $64.65/kgU, with varying cell voltages from 1.0 V to 4.0 V, implying its feasibility from the economic perspective.
... This asbestos diaphragm act as a semipermeable membrane that is used to separate the compartments of the cell as mentioned above, one of the most significant merit of this membrane is that it wouldn't allow the gases to pass through it so we can easily collect the produced gases from their respective compartments. However, alkaline electrolysis has many disadvantages, such as low current densities (below 400 mA/cm 2 ), poor operating pressure, the electrolytes used are corrosive, the crossover of gases, and low energy efficiency [102]. A marigold-shaped N-rGO-MoS 2 -Ni(OH) 2 nanocomposite prepared by a two-step hydro-thermalized process was recently introduced for the outstanding enhanced electro-catalytic activity [103]. ...
Article
With the increase in world population, the corresponding energy demand is also rising at a fast pace. The exploitation and usage of fossil fuels in transportation and energy generation is increasing the concentration of global greenhouse gases (GHGs) and polluting the environment. To achieve pledges of the ‘Paris Agreement’ and check global warming, there is a crucial need to reduce our dependence on fossil fuels and switch to cleaner and greener fuel sources. Hydrogen is a clean fuel since its exhaust is only water after combustion. Hydrogen may be a promising alternative to fossil fuels due to its high calorific value. However, there are still several hurdles and challenges in the commercialization of hydrogen for the transportation and energy generation sectors. This study reviews the current trends in hydrogen production, storage, and its applications and their status with reference to India. Infrastructure development, delivery, legislation, cost, and widespread acceptance are all identified as barriers to the commercialization of hydrogen-powered vehicles in India. It further outlines the challenges and techno-economic hurdles in attaining the hydrogen economy.
... The OH ion move toward the anode under the sway of an electric charge. At the anode, it splits into ½ of O 2 and one molecule of water [23,64,74]. In 2005 Penn state university and Wageningen University, two research organizations introduced a new novel electrolysis technique in which organic matter was used and called microbial electrolysis cell [23,[75][76][77]. ...
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The depletion of conventional energy reserves, that is: fossil fuels, has sparked a lot of interest in hydrogen as a clean energy source. Hydrogen as a fuel possesses enormous energy density, carbon-free by-products, and storable nature. Water splitting is a carbon-neutral process for sustainable hydrogen production. However, the process needs high-performance, stable, and low-cost catalysts to be kinetically and economically competent. A wide variety of catalysts have been researched for the purpose of efficient generation of hydrogen using the process of water splitting. Tungsten carbide is a stable and electrochemically active material that exhibits low Tafel slopes and overpotentials comparable to benchmark catalyst Platinum at operationally relevant current densities. This review article aims to discuss the progress that has been made by Tungsten carbide and its hybrids for water-splitting. Starting with the synthesis strategies and their effects on the structure and properties, particular consideration has been devoted to prevalent approaches that can improve the catalytic properties of the hybrids for the overall process. An insight to the future consideration for catalytic enhancement that is noteworthy for researchers and industrialists alike is also discussed to sort out the best class of materials in accordance with hydrogen production techniques.
... The reaction of the hydrogen fuel cell and the combustion of hydrogen are zero carbon emissions. Hydrogen can be used in heating systems, power generation systems (Chapman et al., 2019;Berger et al., 2020), industrial processes, and hydrogen fuel cell vehicles (Ramachandran and Menon, 1998;Marini et al., 2012;Zuo et al., 2021). It can be applied in many ways in the future (Jin et al., 2021;Liu et al., 2021;Zhang et al., 2021). ...
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The uncertainty and volatility of renewable energy generation lead to large amounts of abandoned electricity. The electricity-hydrogen coupling microgrid (EHCM) consists of the proton exchange membrane electrolytic cell (PEMEC), liquid organic hydrogen carrier (LOHC) hydrogen storage, proton exchange membrane fuel cell (PEMFC). The structure helps to increase the utilization of wind and photovoltaic power. The scheduling of an EHCM is very challenging. This paper proposes the optimal operation of a microgrid considering the uncertainty of wind speed, light, and the coupling of electricity and hydrogen. The electricity-hydrogen coupling model and hydrogen market model are constructed. The microgrid provides ancillary services to the grid while meeting hydrogen demand. The above model is solved using a two-stage optimization method with time scales of day-ahead and intra-day. Finally, taking the IEEE 33-node microgrid as an example, the effectiveness of the proposed model is verified. The results of the case show that the proposed method can obtain more benefits and reduce carbon emissions.
... Alkaline electrolysis has some disadvantages: low operating pressure, limited current density, and low energy efficiency (Marini et al., 2012;Rand andDell, 2008;Zeng and Zhang, 2010). The increment of pressure benefits to avoid a compressing process for the gas product storage which is leads to the reducing the gas storage volume to reasonable capacity. ...
Article
Hydrogen is a clean alternative fuel without carbon gas emission. This paper presents a critical evaluation of the different methods available for generating hydrogen from various feedstocks. The advantages and disadvantages of each process are discussed deeply by recent literatures. Steam reforming of fossil fuels (SRF) has been proved as an attractive method and commercialized on the larger scale. However, CO2 emission that produced during the process is critical issue by this method and therefore, CO2 capture, and storage/utilization technology are required. Besides, water splitting can produce ultra-purity hydrogen and oxygen as byproduct, but this method cannot be competed with SRF because of its expensive costs. The only possible to reduce this gap is by using solar energy with low-cost as energy source for water splitting and carbon taxes are imposed by the government to support research and development. Hydrogen production derived from biomass through gasification and pyrolysis currently shown an economic visibility and expected compete with available technology in the future. Moreover, by utilizing membrane reactor and integrated with a cheaper solar energy could significantly improve biomass-to-hydrogen conversion.
... [37] However, PGM electrocatalysts have been sometimes used on both anode and cathode or just on a single electrode to improve the hydrogen production capacity. [38] For anode porous transport layer (PTL), the preferred material in alkaline electrolytes is nickel foam while for the cathode PTL, due to the less extreme conditions, both carbon cloth/paper and nickel foam can be used. In A-WE, the PTLs contribute only 8 % of the overall stack cost. ...
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As highlighted by the recent roadmaps from the European Union and the United States, water electrolysis is the most valuable high‐intensity technology for producing green hydrogen. Currently, two commercial low‐temperature water electrolyzer technologies exist ‐ alkaline water electrolyzer (A‐WE) and proton exchange membrane water electrolyzer (PEM‐WE). However, both have major drawbacks. A‐WE shows low productivity and efficiency, while PEM‐WE uses a significant amount of critical raw materials. Lately, the use of anion‐exchange membrane electrolyzers (AEM‐WE) has been proposed to overcome the limitations of the current commercial systems. AEM‐WE could become the cornerstone to achieve an intense, safe and resilient green hydrogen production to fulfill the hydrogen targets to achieve the 2050 decarbonization goals. Here we discuss the status of AEM‐WE development, with a focus on the most critical aspects for research and highlighting the potential routes for overcoming the remaining issues. The mini‐review closes with the future perspective on the AEM‐WE research indicating the targets to be achieved.
... The need to switch over to an ecofriendly alternate energy production strategy which does not carry over negative impacts of carbonaceous fuels arises in the present scenario [2][3][4]. Numerous pioneering ideas have been proposed to meet the situation such as electrocatalysis, fuel cells and solar electric systems [5][6][7]. Among these, researchers have found that H 2 is a viable solution for sustainable and eco-friendly production of energy, which will help to make the earth green again [5,8,9]. ...
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Creation of an economic and efficient electrocatalyst for water splitting is of prime importance to develop renewable energy technologies. The spinel oxides of first row transition metals are widely employed for the application of OER due to their excellent stability in neutral and alkaline medium. This study reveals the magnetic properties and electrocatalytic OER activity of spinel ferrites, cobalt ferrite and nickel ferrite nanoparticles synthesised by a novel method (Patent No: 360528). Lime fruit extract was used as the medium for the sol–gel auto combustion synthesis of ferrite nanoparticles. X-ray diffraction studies revealed the crystallization of ferrites in cubic spinel structure. The Fourier transform infrared spectral study gives characteristic vibration bands of ferrites. XPS spectrum confirms the presence and oxidation states of elements in the samples. Vibrating Sample Magnetometer measurements illustrate the ferromagnetic nature of the sample. Saturation magnetization, magnetic remanence and the coercivity determined from the hysteresis loop are found to be in good agreement with the reported values. Under basic conditions, the electrode modified with nanoparticles exhibited an enhanced electrocatalytic OER activity. The overpotential corresponding to 10 mA cm⁻¹ was found to be 410 and 530 mV versus RHE for CFL and NFL, respectively. Besides, the electrode possesses excellent stability for several OER cycles without loss of activity.
... Electrolysis is a non-spontaneous chemical decomposition technique in an electrolyzer (electrolyte, anode-cathode electrodes and separator,) when an electric current is transmitted to an ion-containing solution [110]. Alkaline water electrolysis, Solid oxide electrolysis (SOES), PEM electrolysis, High-temperature water electrolysis are the various methods that could be used for hydrogen production using electrolysis [111][112][113][114][115][116]. The alkaline water and PEM electrolyzers operate at moderate temperatures (373 K), but the SOSE electrolyzer operates at high temperatures (800-1273 K) [116]. ...
Article
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Hydrogen as an energy carrier can provide a long term solution to the problem of sustainable supply of cleaner and environmentally friendly fuel. Hydrogen finds extensive use s in petroleum, chemical synthesis and treated as a zero-emission fuel for transportation as well. It could also be used to produce power. Especially, in the remote areas away from main cities where electrification cost would be significantly higher. A hydrogen based decenteralized system could be developed where the “surplus” power generated by a renewable source could be stored as chemical energy in the form of hydrogen. 80% of the whole hydrogen produced is by steam methan reforming at an energy efficiency of 74–85%. However, steam methane reforming and other fossil fuel based technologies are neither green nor sustainable. Hydrogen, could only be counted as a renewable and clean fuel if the required power to produce hydrogen comes from a renewable source such as wind or solar power. Using a renewable source, hydrogen could be produced by electrolysis, biohydrogen, thermochemical cycles, photocatalysis, and plasmolysis. Amongst hydrogen production technologies, electrolysis contributes the highest 4% of the total world’s energy demand. The production cost and energy efficiency estimated for electrolysis are 10.3 $/kg and 52%, respectively. Electrolysis, an energy-intensive process for hydrogen production, is still confronting challenges to manifest itself economically. While, the production rate of 20 g/kWh with predicated cost and efficiency 0.09 €/kWh or 6.36 $/kg and 79.2%, respectively, has been reported that depicts plasmolysis competitive on par with electrolysis with the advantage of low power consumption, reduced equipment size and principle cost. This review highlights the current status, potential, and challenges of both renewable and non-renewable hydrogen production. A new strategy for simultaneous hydrogen production and separation by microplasmas and microbubble mediated mass transfer has been proposed. A decenterlaized system for hydrogen generation by combining the proposed strategy with solar energy has been suggested to reduce the carbon footprints.
... The intermediate M À O either recombines with another M À O to release O 2 gas or forms M À OOH upon reacting with OH À , followed by decomposition into O 2 . [52,[101][102][103] However, the M À O bonding interactions in M À OH, M À O, and M À OOH intermediates are a few key parameters in electrocatalytic OER performance. [52] Furthermore, it is difficult to precisely determine the reaction kinetics and RDS of the OER owing to the multiple electron transfer pathways and intermediates. ...
Article
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Hydrogen is regarded as the cleanest and highest energy‐density fuel as an alternative energy resource. Water electrolysis is useful for producing ultrapure hydrogen (>99.9%), and alkaline water electrolysis is industrially adopted for large‐scale hydrogen production. However, the anodic oxygen evolution reaction (OER) remains as the bottleneck for achieving efficient hydrogen generation because of its multielectron pathways and sluggish kinetics. Additionally, the OER is crucial for other renewable energy conversion and storage systems, such as CO2 reduction and metal–air batteries. In this regard, high‐performing, durable, and cost‐effective electrocatalysts are essential for achieving the desired hydrogen production efficiency. Recently, transition metal carbonate hydroxides (TMCHs) have been investigated as electrocatalysts for alkaline water splitting because of their layered structure, rich redox properties, and high accessibility to electrolytes. Furthermore, the electronic, morphological, and structural modulations in mixed TMCHs, due to the presence of multiple metal centers, offer more accessible active sites for the OER. Considering these aspects, the present review focuses on the application of mixed transition metal carbonate hydroxide (MTMCH)‐based nanostructured electrocatalysts to OER in alkaline media. This review will benefit the understanding and evaluation of OER activity and the development of MTMCH‐based electrocatalysts for practical application to the OER. Status of the recent developments involving various improvement strategies and future perspectives on the mixed transition metal carbonate hydroxide electrocatalysts for oxygen evolution reaction in alkaline media are discussed.
... There are various technologies for water electrolysis that differ in materials, operating temperature, electrolytes, and catalysts. Among the low temperature operating technologies, alkaline electrolyzers (AE) are already industrially widespread and mature [5][6][7]. In particular, membrane-based alkaline electrolyzers (AEM) represent the most interesting technology, thanks to the characteristics of compactness, ease of use, low maintenance, and high pressure performance [8,9]. ...
Article
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Nanostructured cobalt oxide powders as electro catalysts for the oxygen evolution reaction (OER) in an alkaline membrane electrolysis cell (AME) were prepared by flame spray synthesis (FS); an AME’s anode was then produced by depositing the FS prepared cobalt oxide powders on an AISI-316 sintered metal fiber by the electrophoretic deposition (EPD) method. FS powders and the composite electrode were characterized by SEM, XRD, and XPS analysis. The electrode showed an increase in the OER catalytic activity in a KOH 0.5 M solution with respect to commercial materials commonly applied in alkaline electrolysis, demonstrating that the flame spray synthesis of nanoparticles combined with the electrophoretic deposition technique represent an effective methodology for producing an anodic catalyst for alkaline membrane electrolyzers.
... Apart from the joined advanced on membranes and electrodes, a combined-design cell was proposed by Marini et al 219 in 2012. It consisted on two cell designs: a zero-gap configuration and an anion exchange membrane (AEM), similar to PEM cells from the point of view of structural configuration. ...
Article
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Water‐based hydrogen production is currently an attractive research field, as it provides a greener method to produce hydrogen than existing alternatives. Green hydrogen is expected to progressively replace fossil fuels, which are highly harmful environmentally. This paper presents a critical analysis over time of the main water splitting technologies currently in use for sustainable hydrogen production. As a result of the critical analysis, all the studied techniques have been ordered chronologically in the way that it is possible to understand how new materials have driven to new techniques, more efficient and less expensive. This allows having a complete vision of these technologies. A high level of maturity has been reached in electrolysis, while other techniques still have a long way to go, although many improvements and relevant advancements have been made over the years. The paper offers a global and comparative vision of each technology. From this, it is possible to identify the different paths where efforts are needed to make water‐based hydrogen production a mature, stable and efficient technology. Critical analysis over time of hydrogen production techniques based on water splitting. Chronological revision about photolysis, thermolysis and electrolysis. Historical achievements and current advances are presented. Technical comparison of water splitting‐based hydrogen production alternatives. Qualitative discussion over advantages and disadvantages of water splitting techniques.
... Of all the available techniques, alkaline and polymer electrolyte membrane (PEM) electrolyzers are found to be the superior ones for the production of H 2 via water splitting in which the latter has been better acclaimed for its lower ohmic losses and higher yield. [17,18] However, an inherent limitation of PEM electrolyzers is the use of acidic membranes, which requires expensive catalysts like platinum, ruthenium, and iridium for their operation. [14] Water splitting in alkaline or PEM electrolyzers evolves H 2 at the cathode and oxygen at the anode at the standard reaction potential of 1.23 V, [18] which suggests that the splitting process is a strongly uphill reaction. ...
Article
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Electrochemical reforming of alkaline ethanol has been found to be an attractive single‐step method at room temperature and pressure for hydrogen (H2) production especially when the electrical energy has been supplied through non‐fossil fuel resources. In the present study, we employ solar panels to generate and allow a low‐voltage current to flow into screen‐printed electrodes with milli‐scale spacing to produce a high‐intensity electric field, which eventually engenders electrolysis of ethanol alkaline solution into H2. The portable, eco‐friendly, and economic proof‐of‐concept prototype using screen‐printed gold electrodes and alkaline ethanol shows a facile pathway to produce H2 under atmospheric conditions. Remarkably, introduction of gold nanoparticles (Au NPs) into the electrolyte with diameters ranging from 20 nm – 100 nm shows an enhanced capacity of the electrolyzer to produce H2 under an illumination equivalent to the solar irradiance. The Plasmonic Au NPs enhance the ion transport in the electrolyte under photonic excitation, which eventually facilitates a faster electro‐oxidation of the ethanol alkaline electrolyte. In a way, the solar irradiance serves dual purposes – generation of high‐intensity electric field in the electrolyte through the screen‐printed electrodes and Plasmonic effects through Au NPs for a faster rate of H2 production. The results show current densities as high as 135 A m‐2, 240 A m‐2, and 118 A m‐2 with independent variations in sizes of Au NPs, wavelength of solar radiation, and irradiance of light, respectively. Furthermore, a high Faradaic efficiency (FE) of ∽82% was obtained for the electrolyte solution containing Au NPs of an average diameter of 50 nm. Integration of multiple screen‐printed electrodes shows further enhancement of H2 throughput, leaving a niche for the prototype to scale‐up H2 production with very large‐scale integration of such electrodes. This article is protected by copyright. All rights reserved.
... Anion exchange membranes (AEMs) are ion conducting materials used in several applications like anion exchange membrane fuel cells (AEMFCs) [1][2][3][4], water electrolysers [5], water treatments, and redox flow batteries [6,7]. AEMFCs are promising to decrease the cost of fuel cell devices because less expensive and more abundant electrocatalytic materials, such as nickel, iron, silver, or carbon nanotubes, can catalyze the oxygen reduction reaction (ORR) in basic conditions [8]. ...
Article
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In this work we report the synthesis of poly(vinylbenzylchloride-co-hexene) copolymer grafted with N,N-dimethylhexylammonium groups to study the effect of an aliphatic backbone without ether linkage on the ionomer properties. The copolymerization was achieved by the Ziegler–Natta method, employing the complex ZrCl4 (THF)2 as a catalyst. A certain degree of crosslinking with N,N,N′,N′-tetramethylethylenediamine (TEMED) was introduced with the aim of avoiding excessive swelling in water. The resulting anion exchange polymers were characterized by 1H-NMR, FTIR, TGA, and ion exchange capacity (IEC) measurements. The ionomers showed good alkaline stability; after 72 h of treatment in 2 M KOH at 80 °C the remaining IEC of 76% confirms that ionomers without ether bonds are less sensitive to a SN2 attack and suggests the possibility of their use as a binder in a fuel cell electrode formulation. The ionomers were also blended with polyvinyl alcohol (PVA) and crosslinked with glutaraldehyde. The water uptake of the blend membranes was around 110% at 25 °C. The ionic conductivity at 25 °C in the OH− form was 29.5 mS/cm.
Article
Anionic electrolyzers are expected to play a major role in the future massive production of green hydrogen. In this context, anionic membranes are still a bottleneck for their low conductivity and insufficient long-term chemical stability. In this paper we discussed and demonstrated the use of chemically modified, Aquivion®-based anionic membranes for water electrolysis. The membranes were subjected to different ageing treatments up to 3M at 80°C and showed better performance and durability than commercial AemionTM. Current density around 130 mA cm⁻² at 2 V were obtained with nickel foam as a benchmark electrode material.
Article
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Hydrogen is nowadays considered a favorable and attractive energy carrier fuel to replace other fuels that cause global warming problems. Water electrolysis has attracted the attention of researchers to produce green hydrogen mainly for the accumulation of renewable energy. Hydrogen can be safely used as a bridge to successfully connect the energy demand and supply divisions. An alkaline water electrolysis system owing to its low cost can efficiently use renewable energy sources on large scale. Normally organic/inorganic composite porous separator membranes have been employed as a membrane for alkaline water electrolyzers. However, the separator membranes exhibit high ionic resistance and low gas resistance values, resulting in lower efficiency and raised safety issues as well. Here, in this study, we report that zirconia toughened alumina (ZTA)–based separator membrane exhibits less ohmic resistance 0.15 Ω·cm2 and low hydrogen gas permeability 10.7 × 10−12 mol cm−1 s−1 bar−1 in 30 wt.% KOH solution, which outperforms the commercial, state-of-the-art Zirfon® PERL separator. The cell containing ZTA and advanced catalysts exhibit an excellent performance of 2.1 V at 2000 mA/cm2 at 30 wt.% KOH and 80 °C, which is comparable with PEM electrolysis. These improved results show that AWEs equipped with ZTA separators could be superior in performance to PEM electrolysis.
Article
Seven nickel electrodes with aligned porous structure of different thicknesses (i.e., 100, 250, 400, 500, 600, 850, and 1100 μm) were fabricated via freeze casting, and the effect of the electrode thickness on hydrogen evolution reaction (HER) was experimentally studied. The polarization curves of the porous electrodes were obtained by linear sweep voltammetry (LSV) in a 1 M KOH solution. The results show that, in the lower current density zone, the overpotential decreases with the increasing thickness of the aligned porous electrode. At higher current density, the overpotential presents a relative complex variation with the electrode thickness. For a thicker porous electrode, its electrochemically active surface area (ECSA) undoubtedly increases. Nevertheless, its bubble removal ability decreases due to deeper porous channels, which adversely affects the HER performance. It is also found that while the aligned pore orientation of the electrode is parallel to gravity direction, the electrode with a thickness of 400 μm has a trade-off between the ECSA and bubble removal ability and shows optimal performance.
Article
In this study, zero energy building (ZEB) with four occupants in the capital and most populated city of Iran as one of the biggest greenhouse gas producers is simulated and designed to reduce Iran's greenhouse emissions. Due to the benefits of hydrogen energy and its usages, it is used as the primary energy storage of this building. Also, the thermal comfort of occupants is evaluated using the Fanger model, and domestic hot water consumption is supplied. Using hydrogen energy as energy storage of an off-grid zero energy building in Iran by considering occupant thermal comfort using the fanger model has been presented for the first time in this study. The contribution of electrolyzer and fuel cell in supplying domestic hot water is shown. For this simulation, Trnsys software is used. Using Trnsys software, the transient performance of mentioned ZEB is evaluated in a year. PV panels are used for supplying electricity consumption of the building. Excess produced electricity is converted to hydrogen and stored in the hydrogen tank when a lack of sunrays exists and electricity is required. An evacuated tube solar collector is used to produce hot water. The produced hot water will be stored in the hot water tank. For supplying the cooling load, hot water fired water-cooled absorption chiller is used. Also, a fan coil with hot water circulation and humidifier are used for heating and humidifying the building. Domestic hot water consumption of the occupants is supplied using stored hot water and rejected heat of fuel cell and the electrolyzer. The thermal comfort of occupants is evaluated using the Fanger model with MATLAB software. Results show that using 64 m² PV panel power consumption of the building is supplied without a power outage, and final hydrogen pressure tank will be higher than its initial and building will be zero energy. Required hot water of the building is provided with 75 m² evacuated tube solar collector. The HVAC system of the building provided thermal comfort during a year. The monthly average of occupant predicted mean vote (PMV) is between −0.4 and 0.4. Their predicted percentage of dissatisfaction (PPD) is lower than 13%. Also, supplied domestic hot water (DHW) always has a temperature of 50 °C, which is a setpoint temperature of DHW. Finally, it can be concluded that using the building's rooftop area can be transformed to ZEB and reduce a significant amount of greenhouse emissions of Iran. Also, it can be concluded that fuel cell rejected heat, unlike electrolyzer, can significantly contribute to supplying domestic hot water requirements. Rejected heat of electrolyzer for heating domestic water can be ignored.
Chapter
Pumped hydro storage (PHS) is the most mature energy storage technology and has the highest installed generation and storage capacity in the world. Most PHS plants have been built with the objective to store electricity generated from inflexible sources of energy such as coal and nuclear in daily storage cycles. However, with the rapid reduction in price of batteries and their ability to decentralize energy storage, future PHS plants are expected to have monthly, seasonal, and pluriannual storage cycles, combined with existing hydropower dams downstream and provide water management services. This chapter gives an overview of different arrangements of PHS plants, their challenges and benefits for supporting the shift to a more sustainable world.
Article
A water electrolysis cell based on anion exchange membrane (AEM) and critical raw materials-free (CRM-free) electrocatalysts was developed. A NiFe-oxide electrocatalyst was used at the anode whereas a series of metallic electrocatalysts were investigated for the cathode, such as Ni, NiCu, NiMo, NiMo/KB. These were compared to a benchmark Pt/C cathode. CRMs-free anode and cathode catalysts were synthetized with a crystallite size of about 10 nm. The effect of recirculation through the cell of a diluted KOH solution was investigated. A concentration of 0.5-1 M KOH appeared necessary to achieve suitable performance at high current density. Among the CRM-free cathodes, the NiMo/KB catalyst showed the best performance in the AEM electrolysis cell achieving a current density of 1 A cm⁻² at about 1.7-1.8 V/cell when it was used in combination with a NiFe-oxide anode and a 50 µm thick Fumatech FAA-3-50® hydrocarbon membrane. Durability tests showed an initial decrease of cell voltage with time during 2000 h operation at 1 A cm⁻² until reaching a steady state performance with an energy efficiency close to 80%. An increase of reversible losses during start-up and shutdown cycles was observed. Appropriate stability was observed during cycled operation between 0.2 and 1 A cm⁻²; however, the voltage efficiency was slightly lower than in steady-state operation due to the occurrence of reversible losses during the cycles. Post operation analysis of electrocatalysts allowed getting a better comprehension of the phenomena occurring during the 2000 h durability test.
Article
Due to the threat of climate change, renewable feedstocks & alternative energy carriers are becoming more necessary than ever. One key vector is hydrogen, which can fulfil these roles and is a renewable resource when split from water using renewable electricity. Electrolyzers are often not designed for variable operation, such as power from sources like wind or solar. This work develops a framework to optimize the design and operation of a large-scale electrolyzer hub under variable power supply. The framework is a two-part optimization, where designs of repeated, modular units are optimized, then the entire system is optimized based on those modular units. The framework is tested using a case study of an electrolyzer hub powered by a Dutch wind farm to minimize the levelized cost of hydrogen. To understand how the optimal design changes, three power profiles are examined, including a steady power supply, a representative wind farm power supply, and the same wind farm power supply compressed in time. The work finds the compressed power profile uses PEM technology which can ramp up and down more quickly. The framework determines for this case study, pressurized alkaline electrolyzers with large stacks are the cheapest modular unit, and while a steady power profile resulted in the cheapest hydrogen, costing 4.73 €/kg, the typical wind power profile only raised the levelized cost by 2%–4.82 €/kg. This framework is useful for designing large-scale electrolysis plants and understanding the impact of specific design choices on the performance of a plant.
Chapter
The development of green and sustainable processes is a central focus of modern heterogeneous catalysis and its applications in a multitude of fields such as the generation of biofuels, water and air remediation, synthesis of commodity chemicals, hydrogen generation, and carbon dioxide reduction. This chapter focuses on the fundamentals and applications of three emerging branches of heterogeneous catalysis: catalytic conversion of biomass to biofuels, electrocatalysis, and photocatalysis. The use of biomass is widely contemplated as a potential route for the sustainable production of fine chemicals, commodity materials, and fuels. This research line is particularly relevant in the transportation fuel sector that is strongly dependent on petroleum. In this area the depletion of worldwide reserves, uncertainty in crude oil prices, and concern over emission problems have compelled the scientific community to widen the search for alternative fuels complying with the stringent sustainability criteria. A great advantage of biomass fuel over the other renewable energy options for transportation such as hydrogen fuel cells is the possibility to produce liquid biofuels such as bioethanol and biodiesel. These do not entail extensive variations of the traditional transport infrastructure and the internal combustion engine. Catalytic processes are increasingly applied to the production of biofuels, playing a crucial role in improving product quality and achieving mild operational conditions compared to uncatalyzed reactions. Electrocatalysis is a subclass of heterogeneous catalysis involving redox reactions through the direct transfer of electrons between an electrode (i.e., the catalyst) and electrolyte. Electrocatalysis is a key discipline for the development of a multitude of electrochemical processes including energy storage, fuel cells, organic electrosynthesis, and hydrogen generation. Depending on the electrochemical device involved, the catalytic reaction can convert chemical energy into electrical energy or vice versa. The first kind of reaction occurs in fuel cells and batteries, while the second one aims to convert the oxidized product back to its reusable form through an electricity input. This chapter will cover the fundamentals of two important electrocatalytic processes: electrochemical splitting of water into O2 and H2, and reduction of CO2 into value-added fuels. Photocatalysis relies on the unique properties of semiconductor catalysts to harvest incident light and generate electron–hole pairs. Electrons and holes that reach the catalyst surface trigger the reduction and oxidation reaction, respectively. Photocatalysis is a rapidly expanding technology with a high potential for a wide range of industrial applications which include mineralization of organic pollutants, remediation of water and air, and production of renewable fuels and organic synthesis. From the point of view of pollutant degradation, photocatalysis is a viable alternative to energy- and cost-intensive traditional methods such as adsorption, reverse osmosis, and ultrafiltration among others. One of its key advantages lies in the possibility to mineralize organic pollutants completely to form harmless products using only atmospheric oxygen and light under mild reaction conditions. After covering the fundamentals of photocatalysis, this chapter will focus on two important applications: wastewater treatment and organic synthesis.
Thesis
This thesis deals with the development of highly active and stable anodes for electrocatalytic water oxidation under near-neutral pH conditions, based on nickel or cobalt or nickel/iron oxide nanoparticules embedded into a poly(pyrrole-alkylammonium) matrix. Prepared by an all-electrochemical procedure, these nanocomposite materials are highly nanostructured with sizes of metal oxide particle between 20 and 30 nm, which are well dispersed into the polypyrrole film, conferring a great electroactive surface area and thus a high electrocatalytic activity towards water oxidation at near neutral pH of 9.2. These performances place these nanocomposite based electrodes among the most active anodes described in the literature employing either nickel or cobalt or nickel/iron oxide at pH 9.2. In addition, when the nanocomposite material is electrodeposited on porous ITO, the physisorption of the nanocomposite film is considerably enhanced and consequently its catalytic activity is very stable beyond 24 h of electrolysis. This work demonstrates the beneficial role of positively charged polypyrrole matrix in the preparation of small particles of metal oxide and in the achievement of highly stable and active anodes for water oxidation.
Chapter
Hydrogen production via electrolysis of water (water splitting reaction) is a means of storing excess electrical energy produced by renewable energy sources. This hydrogen gas may be used directly to produce power via combustion or recombination with oxygen in a fuel cell; it may be injected into the natural gas network; and it may be used as a transport fuel or as a chemical intermediate. The main methods of hydrogen production via electrolysis are described: alkaline, proton exchange membrane, and solid-oxide. The materials of construction and the advantages and disadvantages of each system are considered. Methods of storing the hydrogen produced via electrolysis are presented along with the integration of production and storage into large-scale demonstration projects. Finally, selected emerging technologies are considered with respect to how they address shortcomings with the current technology.
Thesis
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This PhD aimed at studying the influence of a radio frequency alternating magnetic field (AMF) on the water splitting reaction in alkaline media (KOH, 1 mol/L). The objective of this approach was to heat the catalyst at a very local scale to enhance water electrolysis, without heating the electrolyte and the other cell component, especially to limit their degradation and provide the energy exactly where it is needed: on the catalyst active sites. The heat stems from (a priori) hysteresis losses of ferromagnetic nanoparticles submitted to an AMF. In such respect, the work consisted in a first place of finding non-PGM materials (especially FeNi- and Ni-based) which are fast water splitting catalysts, as well as magnetically sensitive materials. Thus, several electrochemical tests (cyclic voltammetry, durability tests, Identical Location TEM) were conducted, as well as magnetic characterization (VSM, SAR), without an AMF application in first instance, then with it. The magnetic field proved to influence both the charge-transfer kinetics and the mass-transport kinetics (cyclic voltammetry, chronopotentiometry, Tafel, open-circuit voltage analysis), and that the heating came also from eddy current generation in the electrode support (non-graphitized carbon felt). No influence on the thermodynamics was concluded. In parallel, a bibliographic survey permitted to account for the various effects which can occur in an electrochemical system submitted to a magnetic field. Thus, Lorentz, Kelvin, spin polarization, as well as Soret, Marangoni and Maxwell stress effects were evaluated in the system. No influence of a Lorentz or spin polarization effects was observed, but the others are likely to intervene. Then, post mortem analyses (ILSEM, XRD, ETEM) allowed to study the influence of the temperature and of a reductive/oxidant atmosphere on the best catalyst (FeNi3@Ni). Finally, preliminary experiments were conducted to take benefit from the eddy current as main heating source. The efficiency of the system is also discussed.
Article
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Developing new strategies to advance the fundamental understanding of electrochemistry is crucial to mitigating multiple contemporary technological challenges. In this regard, magnetoelectrochemistry offers many strategic advantages in controlling and understanding electrochemical reactions that might be tricky to regulate in conventional electrochemical fields. However, the topic is highly interdisciplinary, combining concepts from electrochemistry, hydrodynamics, and magnetism with experimental outcomes that are sometimes unexpected. In this review, we survey recent advances in using a magnetic field in different electrochemical applications organized by the effect of the generated forces on fundamental electrochemical principles and focus on how the magnetic field leads to the observed results. Finally, we discuss the challenges that remain to be addressed to establish robust applications capable of meeting present needs by overcoming existing limitations.
Article
The development of alkaline membranes with high conductivity and stability is a significant challenge for the commercial application of advanced alkaline water electrolysis. In this study, a novel anion exchange membrane (AEM) was fabricated by quaternary ammonium poly (n‐methyl‐piperidine‐co‐p‐terphenyl) (QAPPT) and Ni‐Fe layered double hydroxide (LDH) synthesis for advanced alkaline water electrolysis. The uniform dispersion of Ni‐Fe LDH in the QAPPT/Ni‐Fe LDH composite membrane was confirmed by scanning electron microscopy, showing that Ni‐Fe LDH provides the composite membrane with high OH− conductivity and tensile strength. Among different membrane samples, the QAPPT/3% Ni‐Fe LDH composite membrane exhibited the best conductivity with 217.6 mS cm−1 at 80°C. Furthermore, the QAPPT/3% Ni‐Fe LDH composite membrane showed outstanding electrolysis performance of 1 A cm−2 at the voltage of 1.824 V at 60°C. According to a long‐term stability test, conducted at 500 mA cm−2 for more than 87 h, the QAPPT/3% Ni‐Fe LDH composite membrane achieved satisfactory electrolysis voltage. This study's results show that QAPPT/Ni‐Fe LDH composite membranes have excellent application prospects in advanced alkaline water electrolysis. A novel anion exchange membrane based on QAPPT and Ni‐Fe LDH was prepared for advanced alkaline water electrolysis. The introduction of Ni‐Fe LDH provides QAPPT/Ni‐Fe LDH composite membranes with excellent hydroxide conductivity and durability. The QAPPT/3% Ni‐Fe LDH composite membrane exhibits excellent electrolysis performance with the current density of 1 A cm−2 at the voltage of 1.824 V at 60°C.
Article
The energy crisis and depletion of non-renewable energy resources have been promoted as a result of the drastic rise of world pollution and the energy demand. Facile production of hydrogen through water splitting has become a popular alternative source of energy owing to the numerous environmentally friendly and economic benefits it provides. Additionally, it is preferred due to the depletion of non-renewable energy resources, pollution caused by the burning of non-renewable energy resources, and climate change. Hydrogen fuel is generated from water by virtue and acts as clean energy without contributing to carbon emissions. Various types of water-splitting methods such as electrolytic, thermochemical, mechanocatalytic, plasmolytic, photocatalytic, and photoelectrocatalytic can be applied for obtaining hydrogen and oxygen. This review highlights the multifunctional materials used in photoelectrochemical water splitting and their superior properties for producing carbon-free energy from water. The multifunctional materials help reduce aqueous protons to hydrogen and oxidize water to oxygen during the splitting of water. In this paper, a wide class of materials such as carbon materials, metal-organic frameworks, perovskites, and semiconducting oxides is discussed for efficient hydrogen production. Different types of water-splitting methods and multifunctional materials with varying properties can lead to improved results. The review sheds light upon the hydrogen economy and future prospects, elucidating the selection of multifunctional materials for efficient hydrogen production.
Article
The hydrogen oxidation (HOR) and evolution reactions (HER) under alkaline conditions are sluggish when compared to activity at low pHs. The consequence is that when catalysts are employed in anion exchange membrane fuel cells and water electrolysers, high loadings of precious metals are required to achieve the necessary performance. Strong metal-support interactions can be exploited to enhance the activity and stability of metal nanoparticles. This usually occurs through strong electronic coupling. Here, a series of transition metal nanoparticle electrocatalysts (Pd, Ir, Ru and Rh) with a metal loading of 10wt%, were prepared using two supports; carbon and carbon-CeO2 (50:50). Each material is characterized using XRD, XPS, TEM and electrochemical tests, EIS and tafel analysis is performed in order to understand the HER and HOR activities. The presence of CeO2 enhances the activity of Pd, Ir and Rh. Ruthenium has superior activity in term of mass activity, specific activity and i0, both for HER and HOR. The HOR/HER exchange current (i0) of Ru/C has an average value of 106 A gMetal⁻¹. Importantly, EIS and capacitance measurements show that CeO2 promotes catalyst utilization and lowers ionic resistance.
Article
Electrocatalytic water splitting is an important method to produce green and renewable hydrogen (H2). One of the hindrances for wide applications of electrocatalysis in H2 production is the lack of freshwater resources. Comparatively, seawater splitting has become an effective approach for large-scale H2 production due to its abundant reserves. However, the increased complexity of seawater content emerged more problems in electrocatalytic seawater splitting. Recently, various strategies have been reported on improving the performance of electrocatalysts applied in seawater. Herein, this review firstly analyzed the mechanisms and challenges of electrocatalytic seawater splitting to evolve H2, and summarized the recent progress on H2 production in electrocatalytic seawater splitting. Furthermore, suggestions for future work have been provided for guidance.
Article
The chlorine evolution reaction holds a core role in the chemical industries and water‐treatment plants. To overcome the high power input supplied for Cl2 generation at an industrial scale an efficient and durable electrocatalyst is always on hunt. Double perovskite oxides have been used previously for oxygen evolution reaction (OER) and have shown outstanding results on the ground of dual surface active site mechanism. Here, La2CoMnO6 (LCMO) are explored for the electrochemical Cl2 and O2 generation. The electrocatalytic studies are performed in 5 m NaCl (pH ≈ 2.2) for chlorine evolution reaction (CER) and 1 m KOH (pH = 13.5) for OER. The LCMO shows enhanced catalytic activity with onset and overpotential of 75 and 280 mV for CER. Further, the kinetics of the catalytic reaction is determined by the Tafel slope values that is calculated to be 44 mV dec−1 for CER. The interfacial charge transfer resistance value at 11 Ω tells the insight mechanism by facilitating more interaction between electrode‐electrolyte interfaces. In addition to this, wettability analysis of LCMO shows a contact angle as low as 23°. The present study paves a way for double perovskites to be used as an electro‐catalyst for the chlor‐alkali process. Excellent electrochemical performance of lanthanum cobalt manganese oxide‐based double perovskite system towards chlorine and oxygen evolution is reported.
Article
The development of clean and renewable new energy to solve the shortage of fossil energy and environmental pollution is an important research direction in the future. Hydrogen energy has been regarded as a kind of future energy because of its excellent characteristics of pollution-free and high calorific value. In addition, the electrolyzed water technology can also be combined with renewable energy sources such as solar energy to achieve complete recycling of hydrogen energy. In actual production, the realization of efficient water splitting relies to a large extent on the low-cost, high-activity and durable hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) reaction catalysts. Recently, heteroatom-doped transition metal-based water electrolysis catalyst materials have shown excellent electrocatalytic performance and durability for HER and OER, showing great potential for replacing precious metal-based catalysts. This article reviews the application of heteroatom doping strategies in transition metal-based catalytic materials and their latest research progress. First, summarize the internal relationship of heteroatom doping strategy to the morphology and catalytic activity of electrolyzed water catalytic materials. Then, the preparation process of heteroatom-doped transition metal-based catalytic materials for water electrolysis and the reasons for the improved performance and related mechanisms are discussed. Finally, the opportunities and challenges for the future development of heteroatom-doped transition metal-based catalytic materials are emphasized from the perspectives of catalytic mechanism and improvement measures.
Article
Renewable electricity from splitting water to produce hydrogen is a favorable technology to achieve carbon neutrality, but slow anodic oxygen evolution reaction (OER) kinetics limits its large-scale commercialization. Electron spin polarization and increasing the reaction temperature are considered as potential ways to promote alkaline OER. Here, it is reported that in the alkaline OER process under an AC magnetic field, a ferromagnetic ordered electrocatalyst can simultaneously act as a heater and a spin polarizer to achieve significant OER enhancement at a low current density. Moreover, its effect obviously precedes antiferromagnetic, ferrimagnetic, and diamagnetic electrocatalysts. In particular, the non- corrected overpotential of the ferromagnetic electrocatalyst Co at 10 mA cm−2 is reduced by a maximum of 36.6% to 243 mV at 4.320 mT. It is found that the magnetic heating effect is immediate, and more importantly, it is localized and hardly affects the temperature of the entire electrolytic cell. In addition, the spin pinning effect established on the ferromagnetic/paramagnetic interface generated during the reconstruction of the ferromagnetic electrocatalyst expands the ferromagnetic order of the paramagnetic layer. Also, the introduction of an external magnetic field further increases the orderly arrangement of spins, thereby promoting OER. This work provides a reference for the design of high-performance OER electrocatalysts under a magnetic field.
Article
Bifunctional electrode of hydrogen evolution reactions (HER) and oxygen evolution reactions (OER) is extremely attractive as it can simplify the water electrolysis system. Here we report a general and scalable strategy to prepare stable and efficient bifunctional electrode, based on a novel hierarchical porous structure constructed by conductive electrocatalyst. Our method involves the construction of 3D monolithic structure and its surface reconstruction by chemical etching process. This strategy produces an advanced 3D hierarchical porous Fe/Ni‐P‐B@MS electrode containing well‐defined macropores (>100 µm) at the inter‐wire space and mesopores (<100 nm) distributed uniformly over the entire catalyst surface. This highly efficient bifunctional electrode requires only 79 and 279 mV to reach 100 mA cm ‐2 toward HER and OER in 1.0 M KOH. An alkaline electrolyzer consisted of this electrode provides 100 mA cm −2 at a low cell voltage of 1.61 V and survives at large current density of 800 mA cm ‐2 for over 140 h without apparent degradation. This work provides a new perspective for the rational design of transition metal based bifunctional electrode with outstanding performance.
Article
Electrocatalysts play a central role in electrochemical water splitting to store renewable energy in the chemical fuel of hydrogen. Nanoporous metal electrodes are promising to boost hydrogen production efficiency while challenging in synthesis. Here, a phosphorus-doping assisted electrochemical etching strategy is developed to construct highly nanoporous surfaces on metal electrodes, leading to a remarkable catalytic performance for overall water splitting under lab-level or industrial electrolysis conditions. Specifically, the nanoporous FeCoNiCu foil shows 46 times higher electrochemical surface area, lowering the overpotentials by 102 mV for oxygen evolution reaction and 157 mV for hydrogen evolution reaction. The viability of the strategy is further demonstrated in the prevailing industrial electrodes of nickel meshes, enabling a cell voltage of only 1.931 V under the harsh industrial electrolytic condition (80 °C, 30 wt% KOH, and a current density of 500 mA cm⁻²). It is 126 mV lower than that of a bare nickel mesh-based electrolyzer and corresponds to a ∼4% improvement in energy-conversion efficiency. This work offers a facile and ease-to-scale-up approach for the upgrading of widespread metal electrodes, possessing great prospects in energy conversion and storage devices including electrolyzers, fuel cells, batteries, and supercapacitors.
Article
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This Review provides an overview of the emerging concepts of catalysts, membranes, and membrane electrode assemblies (MEAs) for water electrolyzers with anion-exchange membranes (AEMs), also known as zero-gap alkaline water electrolyzers. Much of the recent progress is due to improvements in materials chemistry, MEA designs, and optimized operation conditions. Research on anion-exchange polymers (AEPs) has focused on the cationic head/backbone/side-chain structures and key properties such as ionic conductivity and alkaline stability. Several approaches, such as cross-linking, microphase, and organic/inorganic composites, have been proposed to improve the anion-exchange performance and the chemical and mechanical stability of AEMs. Numerous AEMs now exceed values of 0.1 S/cm (at 60-80 °C), although the stability specifically at temperatures exceeding 60 °C needs further enhancement. The oxygen evolution reaction (OER) is still a limiting factor. An analysis of thin-layer OER data suggests that NiFe-type catalysts have the highest activity. There is debate on the active-site mechanism of the NiFe catalysts, and their long-term stability needs to be understood. Addition of Co to NiFe increases the conductivity of these catalysts. The same analysis for the hydrogen evolution reaction (HER) shows carbon-supported Pt to be dominating, although PtNi alloys and clusters of Ni(OH)2 on Pt show competitive activities. Recent advances in forming and embedding well-dispersed Ru nanoparticles on functionalized high-surface-area carbon supports show promising HER activities. However, the stability of these catalysts under actual AEMWE operating conditions needs to be proven. The field is advancing rapidly but could benefit through the adaptation of new in situ techniques, standardized evaluation protocols for AEMWE conditions, and innovative catalyst-structure designs. Nevertheless, single AEM water electrolyzer cells have been operated for several thousand hours at temperatures and current densities as high as 60 °C and 1 A/cm2, respectively.
Article
Developing inexpensive and efficient electrocatalysts for hydrogen evolution reaction (HER) in both acidic and alkaline mediums is of great significance to the hydrogen energy industry. Hereby, we prepared a mixture of precursors with homogeneous composition by using the chelating ability of soybean protein isolate (C and N source) and phytic acid (dopant and phosphating agent) with cobalt ions, and achieved one-step synthesis and construction of Co2P/N–P co-doped porous carbon composite by carbonization at 800 °C. The as-synthesized Co2P/NPPC-800 electrocatalyst exhibits low HER overpotentials of 121 and 125 mV at 10 mA cm⁻² in 0.5 M H2SO4 and 1.0 M KOH, which are close to those of the commercial Pt/C catalyst. Additionally, the NPPC substrate surrounding the Co2P could diminish the corrosion during the HER, and Co2P/NPPC-800 displays good stability and durability. Furthermore, this work offers a convenient synthesis strategy for phosphide/doped porous carbon composites in other electrochemical energy technologies.
Article
The development of extremely efficient, low-cost, and stable electrocatalysts is required for the sluggish oxygen evolution reaction. Strontium telluride multi-skinned nano balls deposited on glassy carbon (SrTe/GC) were fabricated using the hydrothermal technique and were characterized via different analytical instruments. The fabricated SrTe/GC nanoballs underwent electrochemical measurement, achieving a low overpotential of 268 mV at 10 mA/cm2 with a smaller Tafel slope of 25 mV/dec. The fabricated material also exhibited excellent stability for 24 h with no decline in current density. Hence, this study shows that strontium telluride could function as an extraordinarily efficient and stable electrocatalyst in future energy conversion applications.
Article
Here, we report the hydrogen evolution performance of a series of electrocatalysts with positive hydrogen adsorption energy ΔG H* (Ni 2 P, Ag, and Cu) could be enhanced by introducing LaNi 5 as a...
Article
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Replacing fossil fuels with energy sources and carriers that are sustainable, environmentally benign, and affordable is amongst the most pressing challenges for future socio-economic development. To that goal, hydrogen is presumed to be the most promising energy carrier. Electrocatalytic water splitting, if driven by green electricity, would provide hydrogen with minimal CO2 footprint. The viability of water electrolysis still hinges on the availability of durable earth-abundant electrocatalyst materials and the overall process efficiency. This review spans from the fundamentals of electrocatalytically initiated water splitting to the very latest scientific findings from university and institutional research, also covering specifications and special features of the current industrial processes and those processes currently being tested in large-scale applications. Recently developed strategies are described for the optimisation and discovery of active and durable materials for electrodes that ever-increasingly harness first-principles calculations and machine learning. In addition, a technoeconomic analysis of water electrolysis is included that allows an assessment of the extent to which a large-scale implementation of water splitting can help to combat climate change. This review article is intended to cross-pollinate and strengthen efforts from fundamental understanding to technical implementation and to improve the 'junctions' between the field's physical chemists, materials scientists and engineers, as well as stimulate much-needed exchange among these groups on challenges encountered in the different domains.
Article
Electrochemical water splitting is one of the most reliable approaches for environmental-friendly hydrogen production. Because of their stability and abundance, Mn-based materials have been studied as electrocatalysts for the oxygen evolution reaction (OER), which is a more sluggish reaction in the water splitting system. To increase the OER activity of Mn, it is imperative to facilitate the structural change of Mn oxide to the active phase with Mn³⁺ species, known as the active site. Here, we present the relationship between the electronic conductivity in the catalyst layer and the formation of the Mn active phase, δ-MnO2, from wrinkled Mn(OH)2. Mn(OH)2 has poor conductivity, and it disrupts the oxidation reaction toward MnOOH or δ-MnO2. Adjacent conductive carbon to Mn(OH)2 enabled Mn(OH)2 to be oxidized to δ-MnO2. Furthermore, after repetitive cyclic voltammetry activation, the more conductive environment resulted in a higher density of δ-MnO2 through the irreversible phase transition, and thus it contributes to the improvement of the OER activity.
Article
As a hydrogen fuel for real-time production without storage, HHO has great research prospect and significance. In this paper, we conducted experiments on a spark ignition (SI) engine which has two independent fuel supply systems to compare two combination modes of gasoline port injection plus HHO (GPI + HHO) and gasoline direct injection plus HHO (GDI + HHO) at different HHO flow rate, λ, engine speed and load. The results show that, in both modes, HHO addition increases the maximum cylinder pressure and torque. With the increase of HHO flow rate, the flame development period and flame propagation period shorten, the crank angle corresponding to the maximum cylinder pressure is closer to top dead center. In addition, GDI + HHO mode has better engine performance. HHO has a significant effect on improving combustion stability. Especially at λ = 1.4, as HHO flow rate increases from 0 to 16 L/min, the coefficient of indicated mean effective pressure variation of GPI + HHO and GDI + HHO mode decreases by 69.17% and 58.29%, respectively. Moreover, HHO addition improves HC and CO emissions but increases NOx emissions. CO and HC emissions of GDI + HHO mode are the lowest under all conditions, and reaching the lowest value when HHO flow rate = 16 L/min. Besides, GDI + HHO mode not only has lower NO emissions under normal working conditions (λ = 1) but also can maintain a better combustion environment under lean-burn conditions (λ = 1.2, 1.4). In general, the application of HHO as fuel in engine can improve combustion and emission characteristics and GDI + HHO mode is the best combination of gasoline and HHO.
Article
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Developing new strategies to advance the fundamental understanding of electrochemistry is crucial to mitigating multiple contemporary technological challenges. In this regard, magnetoelectrochemistry offers many strategic advantages in controlling and understanding electrochemical reactions that might be tricky to regulate in conventional electrochemical fields. However, the topic is highly interdisciplinary, combining concepts from electrochemistry, hydrodynamics, and magnetism with experimental outcomes that are sometimes unexpected. In this review, we survey recent advances in using a magnetic field in different electrochemical applications organized by the effect of the generated forces on fundamental electrochemical principles and focus on how the magnetic field leads to the observed results. Finally, we discuss the challenges that remain to be addressed to establish robust applications capable of meeting present needs by overcoming existing limitations.
Article
We report the influence of duty cycle in the range 30-70%, on NiMo alloys prepared on 316 L stainless steel/Ni by pulsed electrodeposition and the characterization of their composition, morphology, and electrocatalytic activity towards hydrogen evolution reaction in alkaline medium. The morphology and Mo content were affected by varying the duty cycle between 70% and 30%, obtaining twice the Mo content and a more globular structure in the NiMo alloys prepared with a 30% duty cycle. The material presented a crystalline structure with peaks corresponding to the Ni (111) and (200) planes, which are independent of the duty cycle used. The cyclic voltammetry analysis showed a remarkable increment of the exchange current density when increasing the Mo content. This effect was attributed to changes in the electronic structure related to the nanostructure of the material. All the NiMo alloys analyzed showed activation to hydrogen evolution reaction after ageing, being that obtained at 30% duty cycle the one that showed the highest one. By analysis of electrochemical impedance spectroscopy, we found for duty cycle 70% a behaviour similar to that of NiMo synthesized by direct current techniques. In that catalyst, two processes were observed at different potentials while the NiMo30% catalyst shows several electrochemical processes occurring.
Chapter
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This chapter presents a review of electrode materials used for the hydrogen evolution reactions and a comparison of their electrocatalytic activities. The introduction presents a brief definition of various thermodynamic water electrolysis potentials. In general, there are two ways to improve the performance of electrode materials: (1) use of electrode materials characterized by higher intrinsic activity i.e., higher exchange current density and (2) use of electrodes characterized by large real surface area. Both methods are used in practice. In this chapter various electrode materials are reviewed: smooth metals, alloys, intermetallic compounds and composites, Raney type materials (Raney Ni, Zn, etc.), oxides, carbides, sulfides, borides, phosphides, amorphous and nano-crystalline materials etc., Among the most active materials are noble metals, doped Raney-type alloys, IrO2/Ru2O, sulfides, borides, and Ni/Mo based alloys. Unfortunately, noble metals are very expensive and easily poisoned and their activity decreases with time. Although many materials may still be improved and optimized there is a need to study the detailed mechanism and kinetics of the HER on these materials and the relation between the geometric (surface roughness) and intrinsic electrocatalytic properties.
Article
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The kinetics of the hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER) on polycrystalline platinum [Pt(pc)] and high surface area carbon-supported platinum nanoparticles (Pt/C) were studied in 0.1 M KOH using rotating disk electrode (RDE) measurements. After corrections of noncompensated solution resistance from ac impedance spectroscopy and of hydrogen mass transport in the HOR branch, the kinetic current densities were fitted to the Butler-Volmer equation using a transfer coefficient of alpha = 0.5, from which HOR/HER exchange current densities on Pt(pc) and Pt/C were obtained, and the HOR/HER mechanisms in alkaline solution were discussed. Unlike the HOR/HER rates on Pt electrodes in alkaline solution, the HOR/HER rates on a Pt electrode in 0.1 M HClO(4) were limited entirely by hydrogen diffusion, which renders the quantification of the HOR/HER kinetics impossible by conventional RDE measurements. The simulation of the hydrogen anode performance based on the specific exchange current densities of the HOR/HER at 80 degrees C illustrates that in addition to the oxygen reduction reaction cell voltage loss on the cathode, the slow HOR kinetics are projected to cause significant anode potential losses in alkaline fuel cells for low platinum loadings (> 130 mV at 0.05 mg(Pt)/cm(anode)(2) and 1.5 A/cm(anode)(2)), contrary to what is reported for proton exchange membrane fuel cells.
Article
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Amorphous MoS3 particles are prepared using a simple chemical method. Several deposition techniques are developed to fabricate electrodes loaded with MoS3 particles. These electrodes are highly active for hydrogen evolution. The catalytically active species appear to be reduced molybdenum sulfide that contains disulfide ligands. The MoS3 particles are annealed to form polycrystalline and single crystalline MoS3 and MoS2 particles. These particles, as well as commercial MoS2 micro-crystals, show inferior catalytic activity compared to the amorphous MoS3 particles.
Article
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A number of nickel based materials are investigated as potential oxygen evolution catalysts under conditions close to those met in modern, high current density alkaline water electrolysers. Microelectrodes are used to avoid distortion of voltammetric data by IR drop even at the high current densities employed in such water electrolysers. High surface area nickel metal oxides prepared by cathodic deposition and mixed oxides prepared by thermal methods are considered. A mixed Ni/Fe oxide is the preferred electrocatalyst. The influence of hydroxide ion concentration and temperature on the voltammetry is defined. Preliminary stability tests in a zero gap cell with an OH(-) conducting membrane show no significant increase in overpotential during 10 days operation in 4 M NaOH electrolyte at a current density of 1 A cm(-2) at 333 K.
Article
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The pace of materials discovery for heterogeneous catalysts and electrocatalysts could, in principle, be accelerated by the development of efficient computational screening methods. This would require an integrated approach, where the catalytic activity and stability of new materials are evaluated and where predictions are benchmarked by careful synthesis and experimental tests. In this contribution, we present a density functional theory-based, high-throughput screening scheme that successfully uses these strategies to identify a new electrocatalyst for the hydrogen evolution reaction (HER). The activity of over 700 binary surface alloys is evaluated theoretically; the stability of each alloy in electrochemical environments is also estimated. BiPt is found to have a predicted activity comparable to, or even better than, pure Pt, the archetypical HER catalyst. This alloy is synthesized and tested experimentally and shows improved HER performance compared with pure Pt, in agreement with the computational screening results.
Article
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The identification of the active sites in heterogeneous catalysis requires a combination of surface sensitive methods and reactivity studies. We determined the active site for hydrogen evolution, a reaction catalyzed by precious metals, on nanoparticulate molybdenum disulfide (MoS2) by atomically resolving the surface of this catalyst before measuring electrochemical activity in solution. By preparing MoS2 nanoparticles of different sizes, we systematically varied the distribution of surface sites on MoS2 nanoparticles on Au(111), which we quantified with scanning tunneling microscopy. Electrocatalytic activity measurements for hydrogen evolution correlate linearly with the number of edge sites on the MoS2 catalyst.
Article
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We present here a critical review of several technologically important electrocatalytic systems operating in alkaline electrolytes. These include the oxygen reduction reaction (ORR) occurring on catalysts containing Pt, Pd, Ir, Ru, or Ag, the methanol oxidation reaction (MOR) occurring on Pt-containing catalysts, and the ethanol oxidation reaction (EOR) occurring on Ni-Co-Fe alloy catalysts. Each of these catalytic systems is relevant to alkaline fuel cell (AFC) technology, while the ORR systems are also relevant to chlor-alkali electrolysis and metal-air batteries. The use of alkaline media presents advantages both in electrocatalytic activity and in materials stability and corrosion. Therefore, prospects for the continued development of alkaline electrocatalytic systems, including alkaline fuel cells, seem very promising.
Chapter
In order to meet the anticipated enhanced demands for hydrogen as a chemical feedstock, as a process gas, and as a clean fuel, the development of techniques for bulk hydrogen generation from nonfossil primary energy sources is vital. With the continued increase in costs and dwindling availability of natural gas and oil, which are the major sources of hydrogen in most countries, the production of hydrogen from coal, or by water electrolysis using electricity derived from hydroelectric, nuclear, solar, geothermal, or fusion energy, will become quite attractive in the near future. Since the energy crisis of 1973, methods have been actively pursued for the production of electricity and/or heat (forms of energy which are not easily storable or transportable over long distances) from renewable sources. Even if such methods are found, there will still be a need for portable fluid fuels which will have to be manufactured on a large scale from the above-mentioned resources. Portable fuels will be most essential for transportation applications. Hydrogen, methanol, or ethanol are the most likely candidates for fluid fuels. Water electrolysis is the only proven technology for production of hydrogen from nonfossil fuel primary energy sources. Other methods such as thermochemical, photochemical, or biochemical are in the infant research stage and from an engineering and economic standpoint show little prospects of success for production of hydrogen on a commerical scale. Due to the intermittent nature of some of the renewable energy sources (solar, wind), energy storage in some other form becomes essential. Here again, electrolytic production of hydrogen is most attractive. H2 is ideal, whereas methanol or ethanol will be an alternative fuel for future transportation applications. In the nuclear, solar, or fusion era, the most convenient method of methanol production will be by the gas phase catalytic reaction of CO2 (from carbonate rocks, the atmosphere, or the ocean) and electrolytic hydrogen. Ethanol can be easily manufactured from any form of biomass.
Conference Paper
In computational mechanics, molecular dynamics (MD) and finite element (FE) analysis are well developed and most popular on microscale and macroscale analysis, respectively. MD can very well simulate the atomistic behavior, but cannot simulate macroscale length and time due to computational limits. FE can very well simulate continuum mechanics (CM) problems, but has the limitation on the atomistic level degree of freedom. Multiscale modeling is an expedient methodology with a potential to connect different levels of modeling such as quantum mechanics, molecular dynamics, and continuum mechanics. Developing nanotechnologies require a new simulation method which has both advantages of MD and FE. This paper proposes a new multiscale modeling technique to couple MD with FE. The proposed method relies on combining velocities principle. 1D wave propagation example has been used to illustrate the challenges in coupling MD with FE and to verify the proposed velocity combination approach.
Article
Carbon-supported IrO2 and RuO2 were prepared using an incipient wetness method and were then calcinated at various temperatures. IrO2/C and RuO2/C are less expensive than the conventional Pt/C material and more stable than metal Ni in an acidic electrolyte. Moreover, IrO2/C and RuO2/C are not influenced by under potential deposition (UPD) and show lower sensitivity to poisoning by Ni or Fe impurities. The physical properties of IrO2/C and RuO2/C were investigated via XRD and TEM. Cyclic voltammograms (CV) and Tafel plots were used to provide information regarding surface redox reaction and electrocatalytic activity. The activity and durability of IrO2/C and RuO2/C were studied after prolonged potential cycling between −0.3 and 0.3 VSCE. After comparison of Tafel plots of Pt/C and IrO2/C after activation, it was observed that they have similar electrocatalytic activities in a hydrogen evolution reaction (HER). A single cell test with solid polymer electrolyte (SPE) proved that the performance of IrO2/C (0.5 mg cm−2) was similar to that of Pt/C (0.5 mg cm−2).
Article
The construction and use of “dynamic potential–pH diagrams” (DPPDs), that are intended to extend the usefulness of thermodynamic Pourbaix diagrams to include kinetic considerations is described. As an example, DPPDs are presented for the comparison of electrocatalysts for wateroxidation, i.e., the oxygen evolution reaction (OER), an important electrochemical reaction because of its key role in energy conversion devices and biological systems (water electrolyses, photoelectrochemical water splitting, plant photosynthesis). The criteria for obtaining kinetic data are discussed and a 3-D diagram, which shows the heterogeneous electron transfer kinetics of an electrochemical system as a function of pH and applied potential is presented. DPPDs are given for four catalysts: IrO2, Co3O4, Co3O4 electrodeposited in a phosphate medium (Co–Pi) and Pt, allowing a direct comparison of the activity of different electrode materials over a broad range of experimental conditions (pH, potential, current density). In addition, the experimental setup and the factors affecting the accurate collection and presentation of data (e.g., reference electrode system, correction of ohmic drops, bubble formation) are discussed.
Article
Cu incorporated Co3O4 (CuxCo3−xO4, 0 ≤ x < 1) nanoparticles were prepared using a thermal decomposition method. Properties of the CuxCo3−xO4, such as morphology, particle sizes, crystallite structure and cation distribution, were characterized with SEM, TEM, XRD and EDX. The CuxCo3−xO4 particles, with various x values, were found to be cubic spinel nanoparticles, with average size of 20–30 nm. Incorporation of Cu in the spinel lattice of Co3O4 shifted the Co3+/Co4+redox peak as well as the onset point for OER to more negative potentials, which may be related to inversion of Cu2+ into the octahedral sites. Amongst all samples studied, Cu0.7Co2.3O4 was the most active for OER. The CuxCo3−xO4electrodes exhibited satisfying stability during repetitive cyclic voltammetry. A membraneelectrodeassembly, using 3 mg cm−2 Cu0.7Co2.3O4 on the anode, demonstrated, in an alkaline membranewater electrolyser, a high current density performance of 1 A cm−2 at a voltage of 1.8 V in 1 mol dm−3 KOH at 25 °C.
Article
The electrocatalytic activity of amorphous and crystalline RuO2 thin films for oxygen evolution in an aqueous solution was investigated. The RuO2 films were prepared on FTO substrates by electrodeposition or RF magnetron sputtering technique. The obtained films were annealed at various temperatures. In both cases, the as-prepared films or the 200°C annealed film had an amorphous structure, whereas the films annealed at 300°C and over were crystallized to rutile structure. The analysis of the Tafel slope indicated that the rate-determining step in the oxygen evolution reaction on the amorphous RuO2 was the combination of the adjacent Ru–OH groups, whereas that on crystalline RuO2 was the dissociation of O–H bond in Ru–OH group. The onset potentials of the amorphous RuO2 films for oxygen evolution were shifted toward the negative side by 0.06–0.03V from those for the rutile crystalline samples. The shift of the onset potential is probably attributed to the structural flexibility which is characteristic of the amorphous surface. This result suggested that the electrocatalytic activity of amorphous RuO2 for oxygen evolution was higher than that of rutile crystalline RuO2.
Article
GenHyPEM (Générateur d'Hydrogène par électrolyse de l'eau PEM «Proton Exchange Membrane») is an STREP programme (no 019802) supported by the European Commission in the course of the 6th framework research programme. This R&D project which started in October 2005, is a 2.6 M€ research effort over three years. It gathers partners from Belgium, Germany, Romania, Federation of Russia, Armenia and France. The main goal of the project is to develop low-cost and high pressure (50bar) PEM water electrolysers for the production of up to several Nm3H2/h. The purpose of this communication is to present the current status of GenHyPEM. Major results and technological achievements obtained so far in the fields of academic (electrocatalysis, polymer electrolyte) and applied (stack development and performances) research are presented. Non-noble electrocatalysts have been identified to replace platinum for the HER and stable performances have been obtained during operation at high (1Acm−2) current density, paving the way to substantial cost reductions. Prototype electrolysers producing from 0.1 to 5Nm3H2/h have been successfully developed.
Article
This article gives a critical review of the current data on the specific conductivity of aqueous potassium hydroxide (KOH) solutions. Empirical correlations relating concentration to density were developed to compare specific conductivity data given in weight percentage KOH and molarity of KOH. Available data on specific conductivity is related with respect to one another and compared to experimental data. Based on these comparisons, specific sets of reported data were used to develop an equation relating specific conductivity of aqueous KOH to temperature and concentration. This empirical correlation was developed over a molarity range of 0–12 at temperatures of 0–100∘C. The correlation has been compared with that proposed by See and White and shows greater accuracy over the concentration range modeled.
Article
The intensification of the production of hydrogen and oxygen, i.e., water electrolysis, was achieved in a centrifugal acceleration field. This was demonstrated by measuring the cell voltage and the electrode potentials for cells operated with and without centrifugal fields, as a function of current density. Under industrial electrolysis conditions, greater reductions in cell voltage and in electrode potentials were achieved at a relative acceleration rate of 190 G compared to those in stationary conditions. The relationships between the cell performance and relative acceleration rate, applied G value, for different anode materials, temperature, and NaCl concentration are reported. The data is obtained in acid, neutral, and highly alkaline electrolyte solutions using linear sweep voltammetry, galvanostatic, and potentiostatic polarization techniques. A cell voltage reduction of up to 700 mV, an anode potential reduction of up to 500 mV, and a cathode potential reduction of up to 350 mV at 3 kA m-2 are achieved at a relative acceleration rate of 190 G and 80°C, compared to those in stationary conditions. The saving in cell voltage, and thus energy consumption, are significantly larger than the small amount of energy required to rotate the cells.
Article
The cathode potential on the gas-evolving electrode in 0.5M H2SO4 solution was measured under a uniform magnetic field. The current interrupter method allowed us to study the IR-drop and the supersolubility of dissolved hydrogen gas. MHD convection by Lorenz force slightly reduced the ohmic resistance between the working and reference electrode, considerably restricted the increase of supersolubility and simultaneously promoted the mass transfer coefficient of the dissolved gas above 50mAcm−2. Moreover, the supersolubility peak position displayed a strong dependence on the current density in the intermediate current density region from 5 to 30mAcm−2. The peak location shifted toward lower current density with increasing in magnetic flux density. Our data show that applying a magnetic field has a much greater effect on the supersolubility at intermediate current density region than the mass transfer coefficient.
Article
The electrodeposition of composites consisting of a non-stoichiometric tungsten oxide matrix and either RuO2 or IrO2 dispersed particles was investigated. These materials were then tested as electrodes for both reduction (hydrogen evolution) and oxidation (oxygen evolution) reactions in acid medium. The composite deposition was carried out by cyclic voltammetry, potentiostatic or galvanostatic electrolysis of suspensions of the RuO2 or IrO2 particles in two different media described as appropriate for WO3 deposition: (i) a colloidal suspension obtained from Na2WO4 and H2SO4 or (ii) a solution obtained by dissolving W powder in aqueous H2O2. All the deposited composites were found to catalyse the hydrogen evolution reaction but none was active in oxygen evolution, presumably due to an inadequate electronic conductivity of the matrix. Such a behaviour differs from that of Pt-containing tungsten oxide electrodes which have been described as suitable anodes for the oxidation of organics.
Article
Oxygen evolution was studied on semiconducting IrxRu1 − xS2 single crystals. Degeneracy was present for all iridium-containing compounds. The catalytic current density corrected for surface roughness, within experimental error, was not strongly dependent on the iridium content. The Tafel slope, however, showed a positive linear variation between 180 and 300 mV dec−1 with increasing iridium content (0.5–50%). This catalytic behaviour already observed on mixed RuIr—oxide electrodes, with a Tafel slope by a factor of 5 lower, suggests that the catalytic sites on our semiconducting electrodes possess an oxide-like nature. Differential electrochemical mass spectroscopy (DEMS) measurements have also revealed a higher Tafel slope and that oxygen evolves at an overpotential of 0.2 V, comparable to oxide electrodes. The higher Tafel slopes observed on IrxRu1 − xS2 electrodes are discussed with respect to their semiconducting properties. Hydrogen evolution was additionally investigated.
Article
For oxygen and hydrogen evolving transparent nickel electrodes in KOH solutions, parameters characterizing the behaviour of bubbles which are adhered to the electrode surface during gas evolution, have been determined in dependence on current density, i, velocity of solution flow, v, pressure, p, temperature, T, and concentration of KOH. Based on experimental data a new basic bubble parameter, J, has been introduced, which accounts for the bubble behaviour. It has been found that J = a1ih1 and J/(J0−J) = a2vh2 where J0 = J at v = 0 ms−1 and a1,a2h1 and h2 are empirical constants; some of these depend on nature of gas evolved. Moreover, the parameter J is almost proportional to the KOH concentration, increases in a decreasing rate with increasing pressure and increases linearly with the reciprocal of the absolute temperature.
Article
This study is concerned with the hydrogen evolution reaction (HER) in several PTFE bonded Raney-Ni electrodes as function of temperature and treatments. The Mo-doped Raney-Ni catalysts are activated by hours of long cathodic polarization interleaved with few deep “charge – discharge” (polarity reversal) cycles. Moreover, the HER efficiency of the electrode requires additives which enhance conductivity and surface properties: with powders of Ni alloys (Ni–Ti, Ni–Cr, Ni–Fe) the electrode becomes also more stable, and almost insensitive to polarity reversal. The main effect of a temperature increase is the reduction of the Tafel slope, which is about 120 mV/dec at 25 °C, and about 60 mV/dec at 60 °C. A proper choice of additives yield electrodes which withstand polarity reversal and may be used in electrolysers which are intermittently operated, or have anodes which require periodic in situ re-activation by reduction.
Article
This report provides an overview of the current state of electrolytic hydrogen production technologies and an economic analysis of the processes and systems available as of December 2003. The operating specifications of commercially available electrolyzers from five manufacturers, i.e., Stuart, Teledyne, Proton, Norsk Hydro, and Avalence, are summarized. Detailed economic analyses of three systems for which cost and economic data were available were completed. The contributions of the cost of electricity, system efficiency, and capital costs to the total cost of electrolysis are discussed.
Article
Trends in electrocatalytic activity of the oxygen evolution reaction (OER) are investigated on the basis of a large database of HO* and HOO* adsorption energies on oxide surfaces. The theoretical overpotential was calculated by applying standard density functional theory in combination with the computational standard hydrogen electrode (SHE) model. We showed that by the discovery of a universal scaling relation between the adsorption energies of HOO* vs HO*, it is possible to analyze the reaction free energy diagrams of all the oxides in a general way. This gave rise to an activity volcano that was the same for a wide variety of oxide catalyst materials and a universal descriptor for the oxygen evolution activity, which suggests a fundamental limitation on the maximum oxygen evolution activity of planar oxide catalysts.
Article
This paper summarizes the thermodynamic theory of multi-electron transfer reactions and its implications for electrocatalysis. We discuss the fundamental differences between catalyzing reactions involving the transfer of one electron or no catalytic intermediates, two electron transfers with one catalytic intermediate, two electron transfer with two catalytic intermediates, and more than two electron transfers with more than one intermediate. These different classes of reactions imply different optimization problems for finding the best catalyst, dictated primarily by the thermodynamics of binding of the catalytic intermediates. The application of this theory to hydrogen evolution and oxidation, oxygen evolution and reduction, and carbon dioxide reduction, is discussed.
Article
In this study, the effects of Nafion® ionomer content in membrane electrode assemblies (MEAs) of polymer electrolyte membrane (PEM) water electrolyser were discussed. The MEAs were prepared with a catalyst coated membrane (CCM) method. The catalysts inks with Nafion ionomer could form uniform coatings deposited on the membrane surfaces. SEM and area EDX mapping demonstrated that anode catalyst coating was uniformly distributed, with a microporous structure. The contents of Nafion ionomer were optimized to 25% for the anode and 20% for cathode. A current density of 1 A cm−2 was achieved at terminal voltage 1.586 V at 80 °C in a PEMWE single cell, with Nafion 117, Pt/C as cathode, and Ru0.7Ir0.3O2 as anode.
Article
The activities of the oxygen evolution reaction (OER) on iridium-oxide- and ruthenium-oxide-based catalysts are among the highest known to date. However, the OER activities of thermodynamically stable rutile iridium oxide (r-IrO2) and rutile iridium oxide (r-RuO2), normalized to catalyst mass or true surface area are not well-defined. Here we report a synthesis of r-IrO2 and r-RuO2 nanoparticles (NPs) of 6 nm, and examine their OER activities in acid and alkaline solutions. Both r-IrO2 and r-RuO2 NPs were highly active for OER, with r-RuO2 exhibiting up to 10 A/goxide at 1.48 V versus reversible hydrogen electrode. When comparing the two, r-RuO2 NPs were found to have slightly higher intrinsic and mass OER activities than r-IrO2 in both acid and basic solutions. Interestingly, these oxide NPs showed higher stability under OER conditions than commercial Ru/C and Ir/C catalysts. Our study shows that these r-RuO2 and r-IrO2 NPs can serve as a benchmark in the development of active OER catalysts for electrolyzers, metal-air batteries, and photoelectrochemical water splitting applications.Keywords: iridium oxide; ruthenium oxide; oxygen evolution; water splitting; electrocatalysis; rutile; nanomaterials; acid; alkaline
Article
On the basis of density functional theory calculations, we compare the free energies of key intermediates in the water splitting reaction over transition metal oxide surfaces to those of the Mn cluster in photo system II. In spite of the very different environments in the enzyme system and on the inorganic catalyst surface of an acidic electrolysis cell, the thermochemical features of the catalysts can be directly compared. We suggest a simple test for a thermochemically optimal catalyst. We show that, although both the RuO2 surface and the Mn cluster in photo system II are quite close to optimal, the biological catalyst appears to be best.
Article
The dependence of the exchange current for the electrolytic evolution of hydrogen on metals (i0,H) on the work function () is analyzed on the basic of a new list offor polycrystalline surfaces. It is shown that log i0,H is linearly related toirrespective of the detailed nature of the mechanism involved in the rate determining step (rds). i0,H on sp metals depends on the sign of the surface charge. Results confirm previous suggestions that the main difference in double layer structure between sp and transition metals arises as a result of hindered rotation of water molecules on the latter. If the strength of the M−H bond is taken into consideration, then metals divide into two groups: (a) sp metals, with slow discharge at usual overvoltages, and probably slow hydrogen removal close to equilibrium, and (b) transition metals, with slow hydrogen removal as the rate determining step. Mn is anomalous and cannot be assigned to either class in correlations. Dependence of M−H bond strength onis also shown and discussed.
Article
In this paper, density functional theory (DFT) calculations are performed to analyze the electrochemical water-splitting process producing molecular oxygen (O2) and hydrogen (H2). We investigate the trends in the electro-catalytic properties of (1 1 0) surfaces of three rutile-type oxides (RuO2, IrO2, and TiO2). The two first of these oxide anodes show lower O2-evolving over-potentials than metal anodes, due to weak O binding but strong hydroxyl (HO∗) binding on the surface. Furthermore, the binding energies of O, HO, and HOO on the (1 1 0) surfaces fulfill universal linear relations similar to those found on metal surfaces.
Article
Hydrogen evolution from 0.5 M H2SO4 on Ti electrodes coated with a RuxTi1−xO2 (x=0.04–0.5) layer has been studied by potentiostatic polarisation, cyclic voltammetry and ac-impedance spectroscopy. The results indicate that after a certain activation period the performance of such an electrode coating is comparable to platinum. The addition of small amounts of sodium molybdate increased the capacitance of the electrode and a reduction of the performance was observed. Increasing the temperature of the pure electrolyte from 20 to 75 °C caused an increase in the rate of the hydrogen evolution and in addition an increase of the electrode capacitance. The electrodes have been found to be rather tolerant to chloride and Fe2+ ions, and could hence be promising candidates as catalyst materials for solid polymer water electrolysis systems. From steady state measurements the Tafel slopes were found to change from −105 mV/decade for pure titanium to about −40 mV/decade for the (RuTi)O2 coated electrodes. The exchange current densities were calculated from the steady state curves, as well as from impedance data, to be about 10−4 A cm−2 after activation.
Article
The electrocatalytic activities of two kinds of iridium oxide electrodes are studied for their ability to evolve hydrogen and oxygen in 1 M H2SO4 at room temperature. The first kind of electrode is made of anodic iridium oxide nanoparticules (AIRONP) prepared by cycling well-defined iridium metal nanoparticles supported on carbon between O2 and H2 evolution potentials. The oxidation process can be followed by cyclic voltammetry and CO oxidation experiments. From TEM observation and the knowledge of the active layer loading, the active surface area of these electrodes are estimated and their activities are presented for the two reactions. For the sake of comparison, electrodes fabricated by thermal decomposition of an iridium salt (TOIROF) have been studied. Their electroactive real surface area have been determined from voltammetric charge measurements. Beforehand, a correlation factor between the real surface area measured by gas adsorption experiments and this later parameter had been established. The mechanism for the two evolution reactions and for the two different electrodes is discussed in the light of our results and literature data.
Article
The electron occupation of orbitals in transition metal oxides guided the identification of an efficient oxygen evolution catalyst based on Earth-abundant elements.
Article
Improving the sluggish kinetics for the electrochemical reduction of water to molecular hydrogen in alkaline environments is one key to reducing the high overpotentials and associated energy losses in water-alkali and chlor-alkali electrolyzers. We found that a controlled arrangement of nanometer-scale Ni(OH)2 clusters on platinum electrode surfaces manifests a factor of 8 activity increase in catalyzing the hydrogen evolution reaction relative to state-of-the-art metal and metal-oxide catalysts. In a bifunctional effect, the edges of the Ni(OH)2 clusters promoted the dissociation of water and the production of hydrogen intermediates that then adsorbed on the nearby Pt surfaces and recombined into molecular hydrogen. The generation of these hydrogen intermediates could be further enhanced via Li+-induced destabilization of the HO–H bond, resulting in a factor of 10 total increase in activity.
Article
The efficiency of many energy storage technologies, such as rechargeable metal-air batteries and hydrogen production from water splitting, is limited by the slow kinetics of the oxygen evolution reaction (OER). We found that Ba0.5Sr0.5Co0.8Fe0.2O3–δ (BSCF) catalyzes the OER with intrinsic activity that is at least an order of magnitude higher than that of the state-of-the-art iridium oxide catalyst in alkaline media. The high activity of BSCF was predicted from a design principle established by systematic examination of more than 10 transition metal oxides, which showed that the intrinsic OER activity exhibits a volcano-shaped dependence on the occupancy of the 3d electron with an eg symmetry of surface transition metal cations in an oxide. The peak OER activity was predicted to be at an eg occupancy close to unity, with high covalency of transition metal–oxygen bonds.
Article
Scanning electron microscopy, linear sweep voltammetry, chronoamperometry, and in situ surface-enhanced Raman spectroscopy were used to investigate the electrochemical oxygen evolution reaction (OER) occurring on cobalt oxide films deposited on Au and other metal substrates. All experiments were carried out in 0.1 M KOH. A remarkable finding is that the turnover frequency for the OER exhibited by ∼0.4 ML of cobalt oxide deposited on Au is 40 times higher than that of bulk cobalt oxide. The activity of small amounts of cobalt oxide deposited on Pt, Pd, Cu, and Co decreased monotonically in the order Au > Pt > Pd > Cu > Co, paralleling the decreasing electronegativity of the substrate metal. Another notable finding is that the OER turnover frequency for ∼0.4 ML of cobalt oxide deposited on Au is nearly three times higher than that for bulk Ir. Raman spectroscopy revealed that the as-deposited cobalt oxide is present as Co(3)O(4) but undergoes progressive oxidation to CoO(OH) with increasing anodic potential. The higher OER activity of cobalt oxide deposited on Au is attributed to an increase in fraction of the Co sites present as Co(IV) cations, a state of cobalt believed to be essential for OER to occur. A hypothesis for how Co(IV) cations contribute to OER is proposed and discussed.
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