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Comparative life cycle analysis of electrolyzer technologies for hydrogen production: Manufacturing and operations

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... To elucidate the complex interplay among these factors, numerous mechanistic and regression models have been developed [22]. To address this need, this paper proposes an efficiency model for PEM electrolyzers, grounded in the understanding of how power and temperature influence efficiency [23]. ...
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In the design and synthesis of energy systems, mathematical tools such as optimization algorithms are often used. While using them, environmental indicators are increasingly used as optimization criteria to exploit the possible environmental benefits of these systems. The problem is that the high number of environmental indicators poses a problem for optimization algorithms in terms of convergence, computational time and visualization. In this paper, this problem is addressed through a many-objective search of solutions using a state-of-the-art evolutionary algorithm, NSGA-III. Furthermore, the performance of this algorithm is tested using different settings in the PCA-based objective reduction framework. The original 14 indicators are reduced to seven, four, three and two, which reveal important insights about the use of NSGA-III, objective reduction and a combination of the two. It was found that by using objective reduction, the performance of NSGA-III can be further improved in terms of the quality of solutions and computational time. However, beyond a certain point, further objective reduction leads to a trade-off between solution quality and computational time. For this case study, the best quality solutions were obtained in the PCA reduction procedure when the CUT value was maintained at 99.99% without additional reduction in the last step, using a correlation matrix. The algorithms were applied to a real-life sizing case study involving hydrogen production from polymer-electrolyte-membrane (PEM) water electrolysis, for which the demand is furnished by the electricity spot market, solar photovoltaics (PV) or wind turbine in Marseille, France. These results will be useful for future applications of many-objective optimization and objective reduction. They will also be practical for including environmental indicators in the many-objective search for solutions.
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The electrochemical oxygen evolution reaction (OER) is a fundamental anodic semi-reaction used in the hydrogen energy industry. Herein, we report a novel NiFe-layered double hydroxide (NiFe-LDH)-based hybrid catalyst for the OER, which is promoted by the two-step hydrothermal loading of carbon sphere (CS) onto NiFe-LDH sheets, named as [email protected] The effects of hydrothermal carbonization (HTC) parameters (such as hydrothermal time and glucose concentration) and the loading ratio of CSs on [email protected] were investigated. The results showed that the two-step hydrothermal synthesis significantly inhibited the interference of the carbonized substances on the lattice formation of NiFe-LDH and successfully achieved a firm combination. By adjusting the HTC process, the surface characteristics and graphitization degree of the carbonized microspheres can be effectively controlled, leading to increased OER performance of [email protected] Thus, under the optimal process parameters (5 h, 0.6 M, and 5 mL), [email protected] exhibited an excellent overpotential of 292 mV at 50 mA cm⁻² and 372 mV at 100 mA cm⁻² for the OER. The outstanding OER performance of [email protected] is attributed to the excellent morphology control of the composite, abundant functional groups, and suitable graphitization degree of the hydrothermally carbonized CS, as well as the synergistic effect between the CSs and NiFe-LDH.
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Hydrogen has been considered as a clean energy carrier by generating electricity via fuel cells without carbon dioxide emissions; however, in the current stage, most hydrogen is produced by a steam methane reforming, emitting carbon dioxide as a byproduct, together. In this context, a green hydrogen production system, which is consisted of water electrolysis and a renewable energy plant, should be expanded to prepare for the upcoming hydrogen society in the future. A techno-economic analysis is carried out for green hydrogen production based on seasonal solar radiation data in the case of the single and the hybrid system, which is designed as only alkaline water electrolyzer and a combination of alkaline water electrolyzer and energy storage system. In addition, a carbon footprint analysis was performed to quantify the carbon dioxide emissions for the proposed systems. And the optimal scale of alkaline water electrolyzer and energy storage system is figured out via a genetic algorithm considering a carbon tax on emitted carbon dioxide. Based on itemized cost estimation results, 6.55 and 6.88 USD kgH2⁻¹ of unit hydrogen production costs were obtained for the case of a hybrid and a single system, respectively. Further, the results present that the hybrid system is preferred when Li-ion battery costs decrease to under 79.67 USD kWh⁻¹. In addition, the capital cost is a crucial factor to figure out the optimized AWE scale and ESS capacity that set the optimized size is important to minimize the unit hydrogen production cost. Finally, the effort to reduce the capital cost to produce the green hydrogen is necessary when increasing trend of carbon dioxide tax is considered.
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Ammonia (NH3) is an attractive carbon-free fuel, though it often requires the addition of a promoter such as hydrogen (H2) to ensure efficient and complete combustion. Herein, we describe the construction and operation of a catalytic membrane reformer (CMR) for the efficient generation of H2/NH3fuel mixtures. A fraction of the ammonia is decomposed, and the released hydrogen is extracted through a membrane, where it combines with the remaining ammonia, which is used as a sweep gas. The use of ammonia as a sweep stream increased hydrogen recovery by as much as 60% and reduced the CMR operating temperature to as low as T = 350 °C. Dynamic control of the H2/NH3ratio is achieved by adjusting the sweep flowrate, and the rejection of N2enhances fuel quality. The use of the sweep enables high H2recovery under isobaric operation, producing high-pressure H2/NH3fuel mixtures without the need for compression. A simple reactor model was developed that accurately captures reformer performance across the range of operating conditions explored, and the excellent durability of the CMR was demonstrated through nominally unchanged performance over >1500 h of operation. This compact reformer provides on-demand generation of H2/NH3fuel mixtures from a single fuel source that may serve as drop-in replacements for hydrocarbons to provide clean combustion with minimal equipment modification. Finally, the CMR concept may be applied for hydrogen enrichment of other fuels, and we successfully demonstrate the generation of H2/CH4mixtures using methane as the sweep gas.
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Green hydrogen produced by water electrolysis is one of the most promising technologies to realize the efficient utilization of intermittent renewable energy and the decarbonizing future. Among various electrolysis technologies, the emerging anion-exchange membrane water electrolysis (AEMWE) shows the most potential for producing green hydrogen at a competitive price. In this review, we demonstrate a comprehensive introduction to AEMWE including the advanced electrode design, the lab-scaled testing system establishment, and the electrochemical performance evaluation. Specifically, recent progress in developing high activity transition metal-based powder electrocatalysts and self-supporting electrodes for AEMWE is summarized. To improve the synergistic transfer behaviors between electron, charge, water, and gas inside the gas diffusion electrode (GDE), two optimizing strategies are concluded by regulating the pore structure and interfacial chemistry. Moreover, we provide a detailed guideline for establishing the AEMWE testing system and selecting the electrolyzer components. The influences of the membrane electrode assembly (MEA) technologies and operation conditions on cell performance are also discussed. Besides, diverse electrochemical methods to evaluate the activity and stability, implement the failure analyses, and realize the in-situ characterizations are elaborated. In end, some perspectives about the optimization of interfacial environment and cost assessments have been proposed for the development of advanced and durable AEMWE.
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Hydrogen imports are considered as a promising pillar for the defossilisation of the German energy system. One of the main concerns when discussing hydrogen solutions is its environmental performance, especially with regard to its greenhouse gas emissions. While a large number of life cycle assessments (LCA) helps to thoroughly understand the impacts of domestic hydrogen production, the assessment of international supply chains remains scarce. On that account, this study performs a comparative LCA of liquefied hydrogen imports from Chile, Canada and Morocco to Germany in a cradle-to-gate approach. A scenario and sensitivity analysis allows to analyse the main drivers on the ecological meaningfulness and to derive recommendations for the establishment of renewable hydrogen supply chains. The results show that the import of renewable hydrogen can outperform domestic production in some cases. In the defined base case, the global warming potential of hydrogen delivered to the German gas grid ranges from 1.505 to 2.457 kgCO2eq/kgH2 or 45.2 to 73.7 gCO2eq/kWhH2,LHV for wind-based imports. Domestically produced hydrogen from wind shows emissions of 1.989 kgCO2eq/kgH2 or 59.7 gCO2eq/kWhH2,LHV. Results for hydrogen produced by solar PV range from 3.787 to 4.008 kgCO2eq/kgH2 or 113.6 to 120.3 gCO2eq/kWhH2,LHV for imports (5.195 kgCO2eq/kgH2 or 155.9 gCO2eq/kWhH2,LHV for domestic production). However, while for domestic hydrogen electrolysis is by far the predominant process step, the entire process chain needs to be taken into consideration for importing cases (e.g. the shipping distance and fuel, the electricity source for hydrogen liquefaction).
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Power-to-methane (PtM) systems may allow fluctuations in the renewable energy supply to be smoothed out by storing surplus energy in the form of methane. These systems work by combining the hydrogen produced by electrolysis with carbon dioxide from different sources to produce methane via the Sabatier reaction. The present work studies PtM systems based on the CO2 supplied by the chemical looping combustion (CLC) of biomass (PtM-bioCLC). Life- cycle- assessment (LCA) was performed on PtM-bioCLC systems to evaluate their environmental impact with respect to a specific reference case. The proposed configurations have the potential to reduce the value of the global warming potential (GWP) climate change indicator to the lowest values reported in the literature to date. Moreover, the possibility of effectively removing CO2 from the atmosphere through the concept of CO2 negative emissions was also assessed. In addition to GWP, as many as 16 LCA indicators were also evaluated and their values for the studied PtM-bioCLC systems were found to be similar to those of the reference case considered or even significantly lower in such categories as resource use-depletion, ozone depletion, human health, acidification potential and eutrophication. The results obtained highlight the potential of these newly proposed PtM schemes.
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The gravimetric H2 densities and the heats of combustion of tanks stored ammonia (ammonia storage tanks) were similar to those of the liquid H2 tanks at the weight of 20–30ton, although the gravimetric H2 density of liquid H2 is 100 wt%. The volumetric H2 densities and the heats of combustion of ammonia storage tanks were about 2 times higher than those of liquid H2 tanks at 1–4 × 10⁴ m³. Gray ammonia is synthesized from hydrogen through process known as steam methane reforming, nitrogen separated from air and Haber-Bosch process. Blue ammonia is the same as gray ammonia, but with CO2 emissions captured and stored. Green ammonia is produced by reacting hydrogen produced by electrolysis of water and nitrogen separated from air with Haber-Bosch process using renewable energies. The energy efficiencies of gray, blue and green ammonia were better than those of liquid hydrogen and methylcyclohexane (MCH) with high H2 density and similar to the efficiency of H2 gas. The energy efficiencies of ammonia decreased in the order, gray ammonia > blue ammonia > green ammonia. The production costs of green hydrogen energy carried increased in the order, ammonia < liquid H2<MCH. The amounts of energy consumption by N2 production and Haber-Bosch process were below 10% compared with the value of H2 production from water electrolysis.
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A profound transformation of the global energy system is needed to meet the goals of the Paris Agreement. In this context, governments, businesses, energy organizations, and research institutes are exploring the opportunities that green hydrogen could offer to achieve net-zero targets for energy-related carbon dioxide (CO2) emissions. There is currently a significant political and commercial momentum for clean hydrogen development, with a fast-growing number of policies and projects around the world. This study aims to provide new insights into the use of renewable energy sources to produce hydrogen via water electrolysis processes. The objective is to present a comparative synthesis of the three most developed water electrolysis technologies: Alkaline Water Electrolysis, Proton Exchange Membrane and Solid Oxide Electrolysis.
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The vigorous development of two-dimensional (2D) materials brings about numerous opportunities for lithium-ion batteries (LIBs) due to their unique 2D layered structure, large specific surface area, outstanding mechanical and flexibility properties, etc. Modern technologies for production of 2D materials include but are not limited to mechanochemical (solid-state/liquid-phase) exfoliation, the solvothermal method and chemical vapor deposition. In this review, strategies leading to the production of 2D materials via solid-state mechanochemistry featuring traditional high energy ball-milling and Sichuan University patented pan-milling are highlighted. The mechanism involving exfoliation, edge selective carbon radical generation of the 2D materials is delineated and this is followed by detailed discussion on representative mechanochemical techniques for tailored and improved lithium-ion storage performance. In the light of the advantages of the solid-state mechanochemical method, there is great promise for the commercialization of 2D materials for the next-generation high performance LIBs.
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The spike in energy prices and feared natural gas supplies shortage during the winter of 2021/2022 indicate a limited ability of existing energy measures to deliver energy security for the European Union. Moreover, the lack of a common external energy security policy made it difficult for the EU to assume a common energy position towards Russiaʼs invasion of Ukraine in February 2022. While the pace of decarbonisation needs to increase for the EU to achieve its 2050 goals, the Union must support its member states' energy security (including its external dimension) during the transition period, until it will be provided by domestic low-carbon energy sources.