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Progress toward Commercial Application of Electrochemical Carbon Dioxide Reduction

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Abstract

Climate change is one of the greatest challenges facing humanity, and our continued sustainable development requires a portfolio of solutions to ultimately reduce the use of fossil fuels and decrease the concentration of carbon dioxide in our atmosphere. Chemistry is central to tackling this issue, and of the pathways to transform carbon dioxide into value-added compounds, single-step electrically driven chemical methods have attracted substantial interest in the last decade. This review places emphasis on the barriers that chemists must overcome to realize this technology and enable commercial use of electrochemical carbon dioxide reduction. We outline design strategies for gas-diffusion electrodes and electrolyzers that follow fundamental principles of catalysis to bridge the gap between catalyst discovery and integrated system engineering. These should address both technical (thermodynamic and kinetic) and practical (infrastructural) hurdles to implementation. We conclude by discussing how these approaches can be improved to help achieve a carbon-neutral economy.

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... 25 Technical (thermodynamic and kinetic) and practical (infrastructural) hurdles in industrialized eCO 2 RR have also been discussed. 26 Some targeted strategies were put T A B L E 1 Summary of potential products in industrial eCO 2 RR, as well as their corresponding catalyst, current density (j), Faraday efficiency (FE), cell type, electrolyte, cathode potential, and references (Ref forward to bridge the gap between lab and industry. This review focuses on recent research on advancing industrial applications of eCO 2 RR. ...
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Recently, research on the electrocatalytic CO2 reduction reaction (eCO2RR) has attracted considerable attention due to its potential to resolve environmental problems caused by CO2 while utilizing clean energy and producing high‐value‐added products. Considerable theoretical research in the lab has demonstrated its feasibility and prospect. However, industrialization is mandatory to realize the economic and social value of eCO2RR. For industrial application of eCO2RR, more criteria have been proposed for eCO2RR research, including high current density (above 200 mA cm−2), high product selectivity (above 90%), and long‐term stability. To fulfill these criteria, the eCO2RR system needs to be systematically designed and optimized. In this review, recent research on eCO2RR for industrial applications is summarized. The review starts with focus on potential industrial catalysts in eCO2RR. Next, potential industrial products are proposed in eCO2RR. These products, including carbon monoxide, formic acid, ethylene, and ethanol, all have high market demand, and have shown high current density and product selectivity in theoretical research. Notably, the innovative components and strategy for industrializing the eCO2RR system are also highlighted here, including flow cells, seawater electrolytes, solid electrolytes, and a two‐step method. Finally, some instructions and possible future avenues are presented for the prospects of future industrial application of eCO2RR. Electrocatalytic carbon dioxide reduction (eCO2RR) is important for alleviating energy and environmental issues. Extending current research on eCO2RR to future industrial production is an effective way to realize its economic value. This review focuses on the possible industrial catalysts, potential industrial products, and inspiring innovative strategies and presents an outlook on the future industrial application of eCO2RR.
... Over the past decades, the electrochemical reduction of carbon dioxide (CO 2 ) into industrially valuable products has become one of the most promising for valorizing anthropogenic CO 2 emissions, while providing a means of energy storage for intermittent renewable sources, such as wind and solar [1][2][3][4][5]. One of the interesting target products for CO 2 reduction is formate, as it has the potential to generate the highest revenue per mole of electrons consumed [6]. Although the electrochemical reduction of CO 2 into valuable products is promising, product separation remains a challenge as most of the dissolved products are present at low concentrations (mostly in the millimolar to nanomolar concentration range) along with a significant excess of electrolyte anions [7][8][9]. ...
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The selective separation of ions is a major technological challenge having far-ranging impacts from product separation in electrochemical production of base chemicals from CO2 to water purification. In recent years, ion-selective electrochemical systems leveraging redox-materials emerged as an attractive platform based on their reversibility and remarkable ion selectivity. In the present study, we present an ultrasound-intensified fabrication process for polyvinyl ferrocene (PVF)–functionalized electrodes in a carbon nanotube (CNT) matrix for selective electro-adsorption of formate ions. To this end, a response surface methodology involving the Box–Behnken design with three effective independent variables, namely, PVF to CNT ratio, sonication duration, and ultrasonic amplitude was applied to reach the maximum formate adsorption efficiency. The fabricated electrodes were characterized using cyclic voltammetry, X-ray diffraction, Raman spectroscopy, and scanning electron microscopy (SEM). SEM images revealed that an optimized ultrasonic amplitude and sonication time provided remarkable improvements in electrode morphology. Through a sedimentation study, we qualitatively demonstrate that the main optimized conditions improved PVF/CNT dispersion stability, consequently providing the highest number of active surface sites for adsorption and the highest adsorption efficiency. The highest percentage of active electrode surface sites and the maximum adsorption efficiency were 97.8 and 90.7% respectively at a PVF/CNT ratio of 3, ultrasonication time of one hour, and 50% ultrasonic amplitude.
... Because of the high surface energy of the intermediates on SACs, incomplete electron transfer occurs, resulting in CO along with limited formation of C2+ hydrocarbons [353]. Furthermore, the formation of unwanted products on the cathode continues to be a barrier to the commercialization of CO2RR [354,355]. In general, SACs form a uniform coordinating environment with novel electronic properties of metal centers and exhibit exceptional selectivity in numerous catalytic processes [356][357][358][359][360]. Numerous studies have been conducted to investigate SACs' potential to enhance the electrocatalytic reduction process and improve product selectivity [361,362]. ...
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ABSTRACT With the disruptive carbon cycle being blamed for global warming, the plausible electrocatalytic CO2 reduction reaction (CO2RR) to form valuable C2+ hydrocarbons and feedstock is becoming a hot topic. Cu-based electrocatalysts have been proven to be excellent CO2RR alternatives for high energy value-added products in this regard. However, the selectivity of CO2RR to form C2+ products via Cu-based catalysts suffers from a high overpotential, slow reaction kinetics, and low selectivity. This review attempts to discuss various cutting-edge strategies for understanding catalytic design such as Cu-based catalyst surface engineering, tuning Cu bandgap via alloying, nanocatalysis, and the effect of the electrolyte and pH on catalyst morphology. The most recent advances in in situ spectroscopy and computational techniques are summarized to fully comprehend reaction mechanisms, structural transformation/degradation mechanisms, and crystal facet loss with subsequent effects on catalyst activity. Furthermore, approaches for tuning Cu interactions are discussed from four key perspectives: single-atom catalysts, interfacial engineering, metal-organic frameworks, and polymer-incorporated materials, which provide new insights into the selectivity of C2+ products. Finally, major challenges are outlined, and potential prospects for the rational design of catalysts for robust CO2RR are proposed. The integration of catalytic design with mechanistic understanding is a step forward in the promising advancement of CO2RR technology for industrial applications.
... 3 Work also continues on the development of electrochemical reduction technologies for the direct conversion of atmos-pheric CO 2 into other C1 compounds. 4,5 As these technologies develop further, it is likely that atmospheric CO 2 will become an abundant source of methanol in the future. Further, compared to other gaseous C1 compounds (carbon monoxide, CO 2 , methane, etc.), methanol provides a convenient liquid feedstock for large-scale transport and industrial fermentation. ...
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The global expansion of biomanufacturing is currently limited by the availability of sugar-based microbial feedstocks, which require farmland for cultivation and therefore cannot support large increases in production without impacting the human food supply. One-carbon feedstocks, such as methanol, present an enticing alternative to sugar because they can be produced independently of arable farmland from organic waste, atmospheric carbon dioxide, and hydrocarbons such as biomethane, natural gas, and coal. The development of efficient industrial microorganisms that can convert one-carbon feedstocks into valuable products is an ongoing challenge. This review discusses progress in the field of synthetic methylotrophy with a focus on how it pertains to the important industrial yeast, Saccharomyces cerevisiae. Recent insights generated from engineering synthetic methylotrophic xylulose- and ribulose-monophosphate cycles, reductive glycine pathways, and adaptive laboratory evolution studies are critically assessed to generate novel strategies for the future engineering of methylotrophy in S. cerevisiae.
... Among these, electrocatalytic CO 2 reduction reaction (CO 2 RR) has been regarded as one of the most attractive methods to address the issue of renewable utilization of CO 2 (Kuhl et al., 2012;Kondratenko et al., 2013;Al-Omari et al., 2018;Bushuyev et al., 2018;Chen et al., 2018;Tackett et al., 2019;Zhang M.-D. et al., 2020;Franco et al., 2020;Sun et al., 2020;Yang et al., 2020;Liang et al., 2021). ...
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CO2 emission caused by fuel combustion and human activity has caused severe climate change and other subsequent pollutions around the world. Carbon neutralization via various novel technologies to alleviate the CO2 level in the atmosphere has thus become one of the major topics in modern research field. These advanced technologies cover CO2 capture, storage and conversion, etc., and electrocatalytic CO2 reduction reaction (CO2RR) by heterogeneous catalysts is among the most promising methods since it could utilize renewable energy and generate valuable fuels and chemicals. Covalent organic frameworks (COFs) represent crystalline organic polymers with highly rigid, conjugated structures and tunable porosity, which exhibit significant potential as heterogeneous electrocatalysts for CO2RR. This review briefly introduces related pioneering works in COF-based materials for electrocatalytic CO2RR in recent years and provides a basis for future design and synthesis of highly active and selective COF-based electrocatalysts in this direction.
... The alarmingly rising level of CO 2 in the atmosphere has aggravated the greenhouse effect, raising serious concerns about the ecological, social, and sustainability problems across the globe. Electrochemical reduction of CO 2 is a promising way to fulfill the carbon neutral goal and at the same time to generate valuable chemical feedstocks [1][2][3][4][5][6][7][8]. Among the various chemical products from CO 2 reduction reaction (CO 2 RR), formic acid (HCOOH) is a key chemical of great industrial significance as well as an important hydrogen carrier for energy storage and conversion [9,10]. ...
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For electrochemical CO2 reduction to HCOOH, an ongoing challenge is to design energy efficient electrocatalysts that can deliver a high HCOOH current density (JHCOOH) at a low overpotential. Indium oxide is good HCOOH production catalyst but with low conductivity. In this work, we report a unique corn design of In2O3-x@C nanocatalyst, wherein In2O3-x nanocube as the fine grains dispersed uniformly on the carbon nanorod cob, resulting in the enhanced conductivity. Excellent performance is achieved with 84% Faradaic efficiency (FE) and 11 mA cm-2 JHCOOH at a low potential of - 0.4 V versus RHE. At the current density of 100 mA cm-2, the applied potential remained stable for more than 120 h with the FE above 90%. Density functional theory calculations reveal that the abundant oxygen vacancy in In2O3-x has exposed more In3+ sites with activated electroactivity, which facilitates the formation of HCOO* intermediate. Operando X-ray absorption spectroscopy also confirms In3+ as the active site and the key intermediate of HCOO* during the process of CO2 reduction to HCOOH.
... Notably, some CCS operations are already able to meet both criteria, transforming captured CO 2 permanently into minerals underground at a cost lower than the current price of CO 2 emission allowance in Europe (Esrafilzadeh et al., 2019;Snaebjö rnsdó ttir et al., 2020). For CU, the initial targets should be CO 2 -derived products with a large profit margin (Chen et al., 2018) instead of those having the larger market, because this can catalyze the fast diffusion of CCUS technologies. Among these products, carbon nanotubes (CNTs) synthetized using electricity coming from solar cells (Johnson et al., 2017;Licht et al., 2016;Ren and Licht, 2016) can represent an economic stepping stone because of their large potential profit margin (100 000-400 000 $ t À1 ). ...
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The 2021 Intergovernmental Panel on Climate Change (IPCC) report, for the first time, stated that CO2 removal will be necessary to meet our climate goals. However, there is a cost to accomplish CO2 removal or mitigation that varies by source. Accordingly, a sensible strategy to prevent climate change begins by mitigating emission sources requiring the least energy and capital investment per ton of CO2, such as new emitters and long-term stationary sources. The production of CO2-derived products should also start by favoring processes that bring to market high-value products with sufficient margin to tolerate a higher cost of goods. In this Perspective, we revisit the 2018 IPCC timetables for committed decarbonization considering the necessity for CO2 removal, with a focus on its economic viability. Thereby, we suggest a CO2 removal schedule, conceived to be energetically and economically sustainable, that adheres to the best-case pathway presented in the 2018 IPCC report.
... The growing CO 2 emissions and increasing atmospheric CO 2 concentration necessitate the exploration of economically viable approaches to achieving CO 2 capture, storage, conversion, and utilization [1][2][3][4][5][6][7]. Converting CO 2 into value-added chemicals (e.g., CO, CH 4 , light olefins, alcohol, and aromatics) is attracting enormous attention, especially the electrochemical CO 2 reduction using solar-or wind-based renewable electricity, which can mitigate the CO 2 emissions while manufacturing carbon-containing chemicals with a reduced carbon footprint [8][9][10][11][12][13]. Current efforts to electrochemically convert and utilize CO 2 center around high-temperature (>700 • C) oxygen-ion solid oxide electrolysis cells (O-SOECs) [14][15][16] for synthesizing carbon monoxide (CO) or syngas (a mixture of CO and H 2 ) and low-temperature (<100 • C) proton exchange membrane (PEM) and anion exchange membrane (AEM) CO 2 electrolyzers that produce chemicals beyond syngas, such as ethylene, methanol, formate acid, and dimethyl ether [17][18][19]. ...
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Protonic ceramic electrochemical cells (PCECs) are solid-state electrochemical devices that employ proton-conducting oxides as electrolytes, which offer a promising approach for electrification of chemical manufacturing, including CO2 reduction to produce value-added chemicals (e.g., CO). The primary advantage of PCECs is their intermediate operating temperatures (300-600 °C), which thermodynamically and kinetically favor the CO2 reduction chemistry at the negative electrode. However, the conventional negative electrodes of PCECs, such as BaZr0.8-xCexY0.2O3-δ-Ni or BaZr0.8-xCexY0.1Yb0.1O3-δ-Ni, cannot reduce CO2 to either CH4 or CO with a selectivity of >99%, leading to the production of a CO and CH4 mixture. Herein, an oxide-supported in-situ exsolved Ni-Fe alloyed nanoparticle electrocatalyst, Sr2Fe1.4Mo0.5O6-δ-Ni0.175 (SFM-Ni0.175), is first employed as the negative electrode of PCECs. The PCECs equipped with this new negative electrode selectively favor the CO2-to-CO conversion. A selectivity of ~100% toward CO has been demonstrated over a wide range of operating temperatures (400-600 °C) and applied potentials/current densities. The negative electrode demonstrated in this work fully suppresses the CH4 production. In situ diffuse reflectance infrared spectroscopy (DRIFTS) was performed to probe the CO2 reduction mechanisms over both SFM-Ni0.175 and the traditional negative electrode (BCZYYb7111+Ni), which indicates SFM-Ni0.175 inhibits the formation of formate species, leading to selective production of CO. This work validates that PCECs equipped with the rationally designed negative electrode can selectively manufacture chemicals.
... 35 For example, electrolyte cations affect the double electrical layer, thus enabling the possibility to regulate the reaction rates and selectivity of the CRR. 37 To date, excellent reviews on the design of electrocatalysts and reaction cells for CRR have been published [38][39][40][41][42][43] ; a comprehensive review focusing on tuning the catalyst microenvironment to promote the CRR is therefore timely. ...
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Abstract Converting CO2 into high‐value fuels and chemicals by renewable‐electricity‐powered electrochemical CO2 reduction reaction (CRR) is a viable approach toward carbon‐emissions‐neutral processes. Unlike the thermocatalytic hydrogenation of CO2 at the solid‐gas interface, the CRR takes place at the three‐phase gas/solid/liquid interface near the electrode surface in aqueous solution, which leads to major challenges including the limited mass diffusion of CO2 reactant, competitive hydrogen evolution reaction, and poor product selectivity. Here we critically examine the various methods of surface and interface engineering of the electrocatalysts to optimize the microenvironment for CRR, which can address the above issues. The effective modification strategies for the gas transport, electrolyte composition, controlling intermediate states, and catalyst engineering are discussed. The key emphasis is made on the diverse atomic‐precision modifications to increase the local CO2 concentration, lower the energy barriers for CO2 activation, decrease the H2O coverage, and stabilize intermediates to effectively control the catalytic activity and selectivity. The perspectives on the challenges and outlook for the future applications of three‐phase interface engineering for CRR and other gas‐involving electrocatalytic reactions conclude the article.
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Developing robust electrocatalyst and advanced devices is important for electrochemical carbon dioxide (CO2) reduction toward the generation of valuable chemicals. We present herein a carbon-confined indium oxides electrocatalyst for stable and efficient CO2 reduction. The reductive corrosion of oxidative indium to metallic state during electrolysis could be prevented due to carbon protection, and the applied carbon layer also optimizes the reaction intermediate adsorption, which enables both high selectivity and activity for CO2 reduction. In a liquid-phase flow cell, the formate selectivity exceeds 90% in a wide potential window from -0.8 V to -1.3 V vs. RHE. The continuous production of ~ 0.12 M pure formic acid solution is further demonstrated at a current density of 30 mA cm-2 in a solid-state electrolyte mediated reactor. This work provides significant concepts in the parallel development of electrocatalysts and devices for carbon-neutral technologies.
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The efforts required to achieve the climate targets set in the Paris Agreement and the associated transition of energy generation and supply necessitate the implementation of new energy technologies. In addition, the remaining carbon budgets involved in reaching these targets require early and effective action. Therefore, policy- and decision-makers must rely on comprehensive assessments to identify the economic viability and effectiveness of climate change mitigation of emerging energy technologies. Thus, they must be able to set supportive measures and regulations or decide on corresponding investments. In terms of the energy transition, apart from electrification, the demand for renewable gases, such as hydrogen or synthetic natural gas (SNG), is substantial. Therefore, power-to-gas (PtG) is a fundamental cornerstone of future renewable and sustainable energy systems. However, the corresponding technologies are still in a relatively early stage of technological maturity, especially regarding implementations at industrial scale. On one hand, this leads to hesitancy in their implementation, while on the other, the hydrogen demand of >1500 TWh/a identified for the EU suggests an early and rapid expansion of capacities. Hence, this thesis provides a prospective techno-economic assessment (TEA) of today’s most promising and mature PtG technologies to estimate their short- and long-term competitiveness, allowing for the identification of the required measures. To estimate the development of technology costs, economies of scale were considered by implementing a disaggregated experience curve model. This model allows for an effective assessment of scaling effects over all investigated technologies. In addition, it shows the importance of considering spillover learning effects between technologies to avoid overestimating the individual effects of technological learning. According to these investigations, the technology costs for PtG applications are expected to decrease by 30–75 % solely through technological learning induced by the non-energetic industrial demand for hydrogen by 2050. With the additional consideration of increasing system scales above 50 MW, overall cost reductions for all technologies are calculated with >75 %. Consequently, the product generation costs for hydrogen and SNG from PtG were found to decrease significantly for corresponding large-scale implementations. Depending on the source of electricity, hydrogen production costs are evaluated to reach values well below 100 €/MWh H₂ in the long term. Owing to the additional efforts required for the methanation process, the identified general production costs for SNG relate to approximately 150 €/MWh SNG. However, in that context, the elaborated assessments show that significantly better performance can be achieved if synergistic effects between the processes are appropriately utilized. Therefore, an integrated system within an industrial application scenario can achieve an effective product cost of <50 €/MWh SNG. Furthermore, studies have shown that the competitiveness of PtG is widely affected by its consideration as an integral part of future energy systems, and thus, its capabilities regarding sector coupling. The utilization of byproducts, namely oxygen and waste heat, not only contributes to the economic viability of the process but can also have a significant impact on systemic energy efficiency by reducing diverse supply efforts. Finally, the elaborated assessment methods and performed analysis also represent a generic outline of the capabilities of prospective techno-economic methods to identify the potential of early-stage technologies to contribute to the energy transition. Therefore, these methods allow for early identification of the technical and economic risks involved, as well as potential bottlenecks regarding resource and demand potentials, thus enabling the establishment of effective measures.
Article
Climate change damage induced by growing carbon dioxide (CO2) emissions has rapidly fostered research on capturing, utilizing, and converting CO2 into valuable C1 and C2 chemicals. In particular, electrochemical reduction of CO2 into formic acid and ethylene is a promising way to recycle the wasted CO2 gas, provided that this process is environmental sustainable and economic feasible compared to conventional processes. Here we review electrocatalysts for the production of formic acid and ethylene by electrochemical CO2 reduction. We discuss the optimization of catalysts by structural engineering, construction of metal alloys, development of metal and non-metal composites, defect engineering single-atom catalyst schemes, and metal-functional polymers. We also present life cycle and economic assessments of electrochemical CO2 reduction. Actually, due to the lack of material recycling, and to disadvantages of high electricity consumption, insufficient catalytic performance, and durability, current electrochemical CO2 reduction is still inferior to the conventional process.
Article
To improve the atomic utilization of metals and reduce the cost of industrialization, the one-step total monoatomization of macroscopic bulk metals, as opposed to nanoscale metals, is effective. In this study, we used a thermal diffusion method to directly convert commercial centimeter-scale Ni foam to porous Ni single-atom-loaded carbon nanotubes (CNTs). As expected, owing to the coating of single-atom on porous, highly conductive CNT carriers, Ni single-atom electrocatalysts (Ni-SACs) exhibit extremely high activity and selectivity in CO2 electroreduction (CO2RR), yielding a current density of > 350 mA/cm2, a selectivity for CO of > 91% under a flow cell configuration using a 1 M potassium chloride (KCl) electrolyte. Based on the superior activity of the Ni-SACs electrocatalyst, an integrated gas-phase electrochemical zero-gap reactor was introduced to generate a significant amount of CO current for potential practical applications. The overall current can be increased to 800 mA, while maintaining CO Faradaic efficiencies (FEs) at above 90% per unit cell. Our findings and insights on the active site transformation mechanism for macroscopic bulk Ni foam conversion into single atoms can inform the design of highly active single-atom catalysts used in industrial CO2RR systems.
Chapter
Surface Organometallic Chemistry is a branch of chemistry that deals with well-defined catalysts and bridges the gap between homogeneous and heterogeneous catalysts. Surface organometallic chemistry is based on a single-site approach where a catalyst can be targeted by stitching surface organometallic fragment (SOMF) or surface coordination fragments (SCF) on the surface called the “predictive approach.” The objective is to enter into a catalytic cycle through a presumed intermediate through SOMF or SCF. In this book chapter, the recent advances of surface organometallic catalysts are documented through various catalytic reactions. Additionally, solid-state NMR of many surface organometallic complexes were given to describe how important is solid-state NMR for the characterization of surface organometallic complexes thoroughly.
Article
Photoelectrochemical CO2 reduction reaction (PEC CO2RR) is a promising technology which offers the possibility of a carbon‐neutral solar fuel production via artificial photosynthesis. The challenging proton‐coupled multielectron transfers with high energy barriers in CO2RR however pose as a huge hindrance to the technology, which demands strict specifications in the design of photocathode materials so as to improve PEC performances. This review underscores effective design strategies and current material progress for the judicious assembly of photocathode materials for CO2RR. The review begins with elucidating the fundamental principles of CO2 reduction process and photocathode electrochemistry. Based on these, the design criteria and trade‐offs in the design of PEC CO2RR photocathodes are highlighted. The various promotive strategies for photocathodes and their underlying rationales such as doping, defect engineering, nanostructuring, cocatalyst loading, passivation, heterojunction formation, and innovative multijunction configurations are further outlined and design propositions in the area are provided. Following that, various photocathode semiconductor materials categorized into photovoltaic (PV) grade (silicon, III–V semiconductors, chalcogenides) and non‐PV grade (metal oxides) materials are summarized and extensively discussed, along with their recent advances. Finally, perspectives on the design of photocathodes for CO2RR and new paradigms in the field are put forward. Photoelectrochemical (PEC) CO2 reduction is an attractive carbon‐neutral strategy as it has the potential for selectivity tuning, design flexibility, and the utilization of sustainable solar energy. Particularly, this review covers the design and current development of photocathodes, which mark an important avenue for the overall broad realization of PEC CO2 reduction to solar fuels in the future.
Article
C2H4 is an essential precursor for synthesis of a range of industrial chemicals while contributing ∼150 Mt of CO2e emissions per year. C2H4 synthesis via electrochemical CO2 reduction reaction (CO2RR) is an attractive approach to reduce carbon emissions. The lower single-pass conversion (<10%) of the state-of-the-art CO2 electrolyzers contributes significantly to the cost of post-CO2RR separation of products, rendering even processes with high CO2RR current densities unfit for scaling up. Here, we develop an aqueous flow-through electrochemical cell to enhance the activity and selectivity of C2H4 on a three-dimensional (3D) Cu mesh electrode by applying square-wave oscillating potentials. A high C2H4 faradaic efficiency of ∼58%, C2H4 current density of 306 mA/cm², and gaseous C2H4 purity of ∼52 wt % without CO2 in the product stream are obtained. Integrating the 3D Cu mesh catalyst in a photovoltaic (PV) electrolyzer yields a solar-to-carbon (STC) efficiency of ∼10% with a solar-to-C2H4 efficiency of ∼4%.
Article
Metal-organic framework (MOF) based single-atom catalysts (SACs) with distinctive features are emerging extraordinary materials in the electrochemical field in the latest years. MOF has the virtues of functional tunability, high surface areas, and well-defined pores structures, while SAC possesses the advantages of maximum atom utilization, special electronic characteristics, and quantum size effects. By combining the merits of both, MOF-based SACs exhibit huge potential in electrocatalytic CO2 reduction reactions (CO2RR) and, more generally, in the field of electroreduction reactions. In this review, the diverse fabrication strategies and principles of MOF-based SACs, including MOF-immobilized SACs and MOF-derived SACs, and the corresponding representative samples of each strategy are systematically introduced and summarized. Then, insights into the mechanisms and pathways of electrochemical CO2RR are discussed. In addition, we illustrate elaborately the recent progress of MOF-derived SACs for electrocatalytic CO2RR to valuable chemicals/fuels according to the classification of catalytic products, C1, C2, and C2+ species. At last, the current challenges and future development directions of MOF-based SACs toward electrochemical CO2RR are proposed. We hope that this review would be helpful in rational designing MOF-based SACs with higher efficiency, selectivity, and long-term durability for the electrocatalytic CO2RR and/or a wider range of electrochemical applications in the future.
Article
Bismuth‐oxygen moieties are beneficial for high‐efficiency CO 2 RR producing formate, however, the preservation of bismuth‐oxygen moietyis challenging while applying a cathodic potential. This work reports preparation of ultrathin Bi 2 O 2 O/Bi 2 O 2 (OH)(NO 3 ) nanosheets (BiON‐uts) via in‐situ tailoring hydrogen bonds in Bi 2 O 2 (OH)(NO 3 ) precursor. The BiON‐uts exhibits a formate faradaic efficiency of 98% with higher partial current density than that of most reported Bi‐based catalysts. Mechanistic studies demonstrate that the ultrathin nanosheet morphology facilitates ion‐exchange reaction between BiON‐uts and electrolyte to produce Bi 2 O 2 CO 3 intermediate, and adsorption reaction of CO 2 with surface Bi 2 O 2 O. DFT calculations reveal that the rate‐limiting first electron transfer is effectively improved because of the high electron affinity of Bi 2 O 2 CO 3 . More importantly, high‐efficiency CO 2 RR in turn protects bismuth‐oxygen moieties from being reduced and thus helps to maintain excellent CO 2 RR activity. This work offers an interactive mechanism of CO 2 RR promotion and bismuth‐oxygen moiety preservation, opening up new opportunities for developing high‐performance catalysts.
Article
While it is well recognized that mass transfer is an important factor in electrochemical reactions, the influence of mass transfer, especially of the convection on the electrochemical CO2 reduction has not been investigated. In this study, we focused on the influence of convection in a flow cell system using a boron-doped diamond electrode. The results clearly showed that convection improved the product selectivity and electrode potentials in CO2 reduction. It suggested that convection controls CO2 mass transfer in a flow cell system and influences the reactivity of electrochemical CO2 reduction.
Article
Direct reduction of gas-phase CO2 to renewable fuels and chemical feedstock without any external energy source or rare-metal catalyst is one of the foremost challenges. Here, using density functional theory and ab initio molecular dynamics (AIMD) simulations, we predict Ti2C(OH)2 MXene as an efficient electron-coupled proton donor exhibiting simultaneously high reactivity and selectivity for CO2 reduction reaction (CRR) by yielding valuable chemicals, formate, and formic acid. This is caused by CO2 spontaneously crossing the activation barrier involved in the formation of multiple intermediates. Metallic Ti2C(OH)2 contains easily donatable protons on the surface and high-energy electrons near the Fermi level that leads to its high reactivity. High selectivity arises from low activation barrier for CRR as predicted by proposed mechanistic interpretations. Furthermore, H vacancies generated during the product formation can be replenished by exposure to moisture, ensuring the uninterrupted formation of the products. Our study provides a single-step solution for CRR to valuable chemicals without necessitating the expensive electrochemical or low-efficiency photochemical cells and hence is of immense interest for recycling the carbon.
Article
Fabricating single‐atom electrodes via atomic dispersion of active metal atoms into monolithic metal supports is of great significance to advancing the lab‐to‐fab translation of the electrochemical technologies. Here, we report an inherent oxide anchoring strategy to fasten ligand‐free isolated Ru atoms on the amorphous layer of monolithic Ti support by regulating the electronic metal‐support interactions. The prepared Ru single atom electrode exhibited exceptional electrochemical chlorine evolution activity, three orders of magnitude higher mass activity than that of commercial dimensionally stable anode, and also selectively reduced nitrate to ammonia with an unprecedented ammonia yield rate of 22.2 mol g −1 h −1 at −0.3 V. Furthermore, the Ru single atom monolithic electrode can be scaled up from 2 × 2 cm to 25 × 15 cm at least, thus demonstrating great potential for industrial electrocatalytic applications.
Article
Fabricating single‐atom electrodes via atomic dispersion of active metal atoms into monolithic metal supports is of great significance to advancing the lab‐to‐fab translation of the electrochemical technologies. Here, we report an inherent oxide anchoring strategy to fasten ligand‐free isolated Ru atoms on the amorphous layer of monolithic Ti support by regulating the electronic metal‐support interactions. The prepared Ru single atom electrode exhibited exceptional electrochemical chlorine evolution activity, three orders of magnitude higher mass activity than that of commercial dimensionally stable anode, and also selectively reduced nitrate to ammonia with an unprecedented ammonia yield rate of 22.2 mol g −1 h −1 at −0.3 V. Furthermore, the Ru single atom monolithic electrode can be scaled up from 2 × 2 cm to 25 × 15 cm at least, thus demonstrating great potential for industrial electrocatalytic applications.
Article
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The carbon dioxide reduction reaction (CO2RR) is a promising route to convert CO2 into value‐added chemicals and fuels by utilizing renewable electrical energy, mitigating the greenhouse effect and depletion of fossil fuels for sustainability. Electrocatalyst plays a critical role in CO2RR whereas their rational design for achieving high activity, durability, and selectivity toward specific products confronts great challenge. In this review, rational CO2RR electrocatalyst design as well as essential understanding of nanomaterials in atomic‐, nanoscale‐, and microscale‐level are highlighted. Besides, basic concepts and setup factors related to CO2RR are systematically outlined to provide a clear and comprehensive understanding as guidance. More importantly, the authors discuss and try to uncover the electrocatalyst structure–function relationship with the assistance of electrokinetic studies, in situ characterizations, and computational techniques. Finally, current challenges and prospects are offered to shed light on future design of advanced CO2RR electrocatalysts. Rational electrocatalyst design understanding for the reduction of CO2 from atomic‐, nanoscale‐, and microscale‐level in this review are highlighted. In combination with advanced characterizations and theoretical calculations, this paper aims to establish the possible electrocatalyst structure–function relationship, providing guidelines for future study direction.
Article
Modeling of CO2 electroreduction reactor (CO2ECR) is highly demanded for rapid design of industrial processes, while facing challenges in practical applications. Herein, a kinetics-mass transport model is proposed, which can well balance the competition between HCOO⁻ produce and H2 evolution, and be easily integrated into Aspen HYSYS as a user defined module for CO2ECR process design. By considering both cathode potential and CO2 concentration in flow channel, optimal regions of the key parameters can be simulated to achieve high efficiency of CO2 electroreduction, i.e., about 80 % for both HCOO⁻ Faraday efficiency and CO2 conversion with slightly compressed pure CO2 feedstock of 300 kPa. By increasing anode flow rates, the lean streams with H2 concentration of around 50 % achieve nearly the maximum H2 utilization, which is attractive due to the possible reduction of purification cost.
Chapter
The electrochemical reduction of carbon dioxide leads to the formation of valued chemicals; hence, it holds great potential in reducing atmospheric CO2 concentration and can also be considered as the most feasible solution to the quest for sustainable energy resources. Metal–organic frameworks (MOFs), because of their large surface area, high porosity, easily tunable morphology, and atomically dispersed active sites, are preferred as an electrocatalyst for the reduction of CO2. In order to boost their catalytic activity, conductivity and number and types of active centers of MOFs can be varied by tuning their structure or by making their hybrids with other materials. MOFs also can be used as precursors for the formation of extraordinarily efficient carbon-based single-atom catalysts. This chapter briefly reviews the catalytic behavior of pristine MOFs, their hybrids, and carbon-based single-atom catalysts derived from MOFs for the electroreduction of CO2. Also, challenges and potential directions for improvement are highlighted.
Article
Electrochemical conversion of carbon dioxide into fuel and chemicals with added value represents an appealing approach to reduce the greenhouse effect and realize a carbon-neutral cycle, which has great potential in mitigating global warming and effectively storing renewable energy. The electrochemical CO 2 reduction reaction (CO 2 RR) usually involves multiproton coupling and multielectron transfer in aqueous electrolytes to form multicarbon products (C 2+ products), but it competes with the hydrogen evolution reaction (HER), which results in intrinsically sluggish kinetics and a complex reaction mechanism and places higher requirements on the design of catalysts. In this review, the advantages of electrochemical CO 2 reduction are briefly introduced, and then, different categories of Cu-based catalysts, including monometallic Cu catalysts, bimetallic catalysts, metal-organic frameworks (MOFs) along with MOF-derived catalysts and other catalysts, are summarized in terms of their synthesis method and conversion of CO 2 to C 2+ products in aqueous solution. The catalytic mechanisms of these catalysts are subsequently discussed for rational design of more efficient catalysts. In response to the mechanisms, several material strategies to enhance the catalytic behaviors are proposed, including surface facet engineering, interface engineering, utilization of strong metal-support interactions and surface modification. Based on the above strategies, challenges and prospects are proposed for the future development of CO 2 RR catalysts for industrial applications. Graphical Abstract
Article
CO2 electroreduction is one of the most potential ways to realize CO2 recycle and energy regeneration. The key to promote this technology is the development of high-performance electrocatalysts. However, the rational design of electrocatalysts with highly catalytic activity and products selectivity toward CO2 reduction reaction (CO2RR) remains a challenging task. Herein, we developed a machine learning (ML) model to achieve efficient exploration of electrocatalysts for CO2RR by combining with density functional theory (DFT). The results show that the electron numbers of the d orbital is the most important descriptor and the support vector regression (SVR) has the best predictive performance. The coefficient of determination (R²) and mean squared error (MSE) are 0.9193 and 0.0162, respectively. Based on the well-trained model, the overpotential of [email protected]2 is successfully predicted to be 0.477 V and it shows the best electrocatalytic performance for CO2RR. DFT calculation results show that *COOH → *CO is the potential-limiting step of CO2-to-CO electroreduction for [email protected]2. The DFT-calculated overpotential is 0.481 V, which is consistent with the ML-predicted results. This work provides a convenient machine learning model for the effective theoretical design and screening of CO2-to-CO electrocatalysts.
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International guidelines have progressively addressed global warming which is caused by the greenhouse effect. The greenhouse effect originates from the atmosphere’s gases which trap sunlight which, as a consequence, causes an increase in global surface temperature. Carbon dioxide is one of these greenhouse gases and is mainly produced by anthropogenic emissions. The urgency of removing atmospheric carbon dioxide from the atmosphere to reduce the greenhouse effect has initiated the development of methods to covert carbon dioxide into valuable products. One approach that was developed is the photocatalytic transformation of CO2. Photocatalysis addresses environmental issues by transferring CO2 into value added chemicals by mimicking the natural photosynthesis process. During this process, the photocatalytic system is excited by light energy. CO2 is adsorbed at the catalytic metal centers where it is subsequently reduced. To overcome several obstacles for achieving an efficient photocatalytic reduction process, the use of metal-containing polymers as photocatalysts for carbon dioxide reduction is highlighted in this review. The attention of this manuscript is directed towards recent advances in material design and mechanistic details of the process using different polymeric materials and photocatalysts.
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Solar-powered electrochemical production of hydrogen through water electrolysis is an active and important research endeavor. However, technologies and roadmaps for implementation of this process do not exist. In this perspective paper, we describe potential pathways for solar-hydrogen technologies into the marketplace in the form of photoelectrochemical or photovoltaic-driven electrolysis devices and systems. We detail technical approaches for device and system architectures, economic drivers, societal perceptions, political impacts, technological challenges, and research opportunities. Implementation scenarios are broken down into short-term and long-term markets, and a specific technology roadmap is defined. In the short-term, the only plausible economical option will be photovoltaic-driven electrolysis systems for niche applications. In the long term, electrochemical solar-hydrogen technologies could be deployed more broadly in energy markets but will require advances in the technology, significant cost reductions, and/or policy changes. Ultimately, a transition to a society that significantly relies on solar-hydrogen technologies will benefit from continued creativity and influence from the scientific community.
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Engineering copper-based catalysts that favour high-value alcohols is desired in view of the energy density, ready transport and established use of these liquid fuels. In the design of catalysts, much progress has been made to target the C-C coupling step; whereas comparatively little effort has been expended to target post-C-C coupling reaction intermediates. Here we report a class of core-shell vacancy engineering catalysts that utilize sulfur atoms in the nanoparticle core and copper vacancies in the shell to achieve efficient electrochemical CO2 reduction to propanol and ethanol. These catalysts shift selectivity away from the competing ethylene reaction and towards liquid alcohols. We increase the alcohol-to-ethylene ratio more than sixfold compared with bare-copper nanoparticles, highlighting an alternative approach to electroproduce alcohols instead of alkenes. We achieve a C2+ alcohol production rate of 126 ± 5 mA cm⁻² with a selectivity of 32 ± 1% Faradaic efficiency. © 2018 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.
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Carbon dioxide (CO2) electroreduction could provide a useful source of ethylene, but low conversion efficiency, low production rates, and low catalyst stability limit current systems. Here we report that a copper electrocatalyst at an abrupt reaction interface in an alkaline electrolyte reduces CO2 to ethylene with 70% faradaic efficiency at a potential of −0.55 volts versus a reversible hydrogen electrode (RHE). Hydroxide ions on or near the copper surface lower the CO2 reduction and carbon monoxide (CO)–CO coupling activation energy barriers; as a result, onset of ethylene evolution at −0.165 volts versus an RHE in 10 molar potassium hydroxide occurs almost simultaneously with CO production. Operational stability was enhanced via the introduction of a polymer-based gas diffusion layer that sandwiches the reaction interface between separate hydrophobic and conductive supports, providing constant ethylene selectivity for an initial 150 operating hours.
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Non-noble metal oxides consisting of CuO and TiO2 (CuO/TiO2 catalyst) for CO2 reduction were fabricated using a simple hydrothermal method. The designed catalysts of CuO could be in situ reduced to a metallic Cu-forming Cu/TiO2 catalyst, which could efficiently catalyze CO2 reduction to multi-carbon oxygenates (ethanol, acetone, and n-propanol) with a maximum overall faradaic efficiency of 47.4% at a potential of −0.85 V vs. reversible hydrogen electrode (RHE) in 0.5 M KHCO3 solution. The catalytic activity for CO2 electroreduction strongly depends on the CuO contents of the catalysts as-prepared, resulting in different electrochemistry surface areas. The significantly improved CO2 catalytic activity of CuO/TiO2 might be due to the strong CO2 adsorption ability.
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Copper electrodes have been shown to be selective toward the electroreduction of carbon dioxide to ethylene, carbon monoxide, or formate. However, the underlying causes of their activities, which have been attributed to a rise in local pH near the surface of the electrode, presence of atomic-scale defects, and/or residual oxygen atoms in the catalysts, etc., have not been generally agreed on. Here, we perform a study of carbon dioxide reduction on four copper catalysts from -0.45 to -1.30 V vs. reversible hydrogen electrode. The selectivities exhibited by 20 previously reported copper catalysts are also analyzed. We demonstrate that the selectivity of carbon dioxide reduction is greatly affected by the applied potentials and currents, regardless of the starting condition of copper catalysts. This study shows that optimization of the current densities at the appropriate potential windows is critical for designing highly selective copper catalysts.
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The successful transition to a low-carbon economy hinges on innovative solutions and collaborative action on a global scale. Sustainable entrepreneurship is thereby recognized as a key driver in the creation and transformation of ecologically and socially sustainable economic systems. The purpose of this article is to contribute to this topic by understanding commercialization barriers for strong sustainability-oriented new technology ventures and to derive recommendations to overcome them. A qualitative multilevel approach is applied to identify barriers and drivers within the internal dynamic capabilities of the organization and within the organization’s external stakeholders. A model of barriers has been developed based on semi-structured interviews with new carbon dioxide utilization ventures and associated industry players in Canada, the USA, and the European Economic Area. Resulting recommendations to facilitate the (re-)design of a dedicated support system are proposed on four levels: (a) actors, (b) resources, (c) institutional settings, and (d) the coordination of the support system.
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Transition-metal-based molecular complexes are a class of catalyst materials for electrochemical CO2 reduction to CO that can be rationally designed to deliver high catalytic performance. One common mechanistic feature of these electrocatalysts developed thus far is an electrogenerated reduced metal center associated with catalytic CO2 reduction. Here we report a heterogenized zinc-porphyrin complex (zinc(II) 5,10,15,20-tetramesitylporphyrin) as an electrocatalyst that delivers a turnover frequency as high as 14.4 site(-1) s(-1) and a Faradaic efficiency as high as 95% for CO2 electroreduction to CO at -1.7 V vs the standard hydrogen electrode in an organic/water mixed electrolyte. While the Zn center is critical to the observed catalysis, in situ and operando X-ray absorption spectroscopic studies reveal that it is redox-innocent throughout the potential range. Cyclic voltammetry indicates that the porphyrin ligand may act as a redox mediator. Chemical reduction of the zinc-porphyrin complex further confirms that the reduction is ligand-based and the reduced species can react with CO2. This represents the first example of a transition-metal complex for CO2 electroreduction catalysis with its metal center being redox-innocent under working conditions.
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Can a solid foundation for the future adaptation of solar fuels be built today? Component technologies developed to efficiently generate fuel from sunlight are finding innovative pathways to commercialization in established markets.
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The solar-driven electrochemical reduction of CO2 to fuels and chemicals provides a promising way for closing the anthropogenic carbon cycle. However, the lack of selective and Earth-abundant catalysts able to achieve the desired transformation reactions in an aqueous matrix presents a substantial impediment as of today. Here we introduce atomic layer deposition of SnO2 on CuO nanowires as a means for changing the wide product distribution of CuO-derived CO2 reduction electrocatalysts to yield predominantly CO. The activity of this catalyst towards oxygen evolution enables us to use it both as the cathode and anode for complete CO2 electrolysis. In the resulting device, the electrodes are separated by a bipolar membrane, allowing each half-reaction to run in its optimal electrolyte environment. Using a GaInP/GaInAs/Ge photovoltaic we achieve the solar-driven splitting of CO2 into CO and oxygen with a bifunctional, sustainable and all Earth-abundant system at an efficiency of 13.4%.
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Electrochemical reduction of CO2 into carbon-based products using excess clean electricity is a compelling method for producing sustainable fuels while lowering CO2 emissions. Previous electrolytic CO2 reduction studies all involve dioxygen production at the anode, yet this anodic reaction requires a large overpotential and yields a product bearing no economic value. We report here that the cathodic reduction of CO2 to CO can occur in tandem with the anodic oxidation of organic substrates that bear higher economic value than dioxygen. This claim is demonstrated by 3 h of sustained electrolytic conversion of CO2 into CO at a copper–indium cathode with a current density of 3.7 mA cm–2 and Faradaic efficiency of >70%, and the concomitant oxidation of an alcohol at a platinum anode with >75% yield. These results were tested for four alcohols representing different classes of alcohols and demonstrate electrolytic reduction and oxidative chemistry that form higher-valued carbon-based products at both electrodes.
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Electrochemical carbon dioxide reduction to fuels presents one of the great challenges in chemistry. Herein we present an understanding of trends in electrocatalytic activity for carbon dioxide reduction over different metal catalysts that rationalize a number of experimental observations including the selectivity with respect to the competing hydrogen evolution reaction. We also identify two design criteria for more active catalysts. The understanding is based on density functional theory calculations of activation energies for electrochemical carbon monoxide reduction as a basis for an electrochemical kinetic model of the process. We develop scaling relations relating transition state energies to the carbon monoxide adsorption energy and determine the optimal value of this descriptor to be very close to that of copper.
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Solar fuel generation through electrochemical CO2 conversion offers an attractive avenue to store the energy of sunlight in the form of chemical bonds, with the simultaneous remediation of a greenhouse gas. While impressive progress has been achieved in developing novel nanostructured catalysts and understanding the mechanistic details of this process, limited knowledge has been gathered on continuous-flow electrochemical reactors for CO2 electroreduction. This is indeed surprising considering that this might be the only way to scale-up this fledgling technology for future industrial application. In this review article, we discuss the parameters that influence the performance of flow CO2 electrolyzers. This analysis spans the overall design of the electrochemical cell (microfluidic or membrane-based), the employed materials (catalyst, support, etc.), and the operational conditions (electrolyte, pressure, temperature, etc.). We highlight R&D avenues offering particularly promising development opportunities together with the intrinsic limitations of the different approaches. By collecting the most relevant characterization methods (together with the relevant descriptive parameters), we also present an assessment framework for benchmarking CO2 electrolyzers. Finally, we give a brief outlook on photoelectrochemical reactors where solar energy input is directly utilized.
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High-temperature solid oxide electrolysis cells (SOECs) are advanced electrochemical energy storage and conversion devices with high conversion/energy efficiencies. They offer attractive high-temperature co-electrolysis routes that reduce extra CO2 emissions, enable large-scale energy storage/conversion and facilitate the integration of renewable energies into the electric grid. Exciting new research has focused on CO2 electrochemical activation/conversion through a co-electrolysis process based on the assumption that difficult C[double bond, length as m-dash]O double bonds can be activated effectively through this electrochemical method. Based on existing investigations, this paper puts forth a comprehensive overview of recent and past developments in co-electrolysis with SOECs for CO2 conversion and utilization. Here, we discuss in detail the approaches of CO2 conversion, the developmental history, the basic principles, the economic feasibility of CO2/H2O co-electrolysis, and the diverse range of fuel electrodes as well as oxygen electrode materials. SOEC performance measurements, characterization and simulations are classified and presented in this paper. SOEC cell and stack designs, fabrications and scale-ups are also summarized and described. In particular, insights into CO2 electrochemical conversions, solid oxide cell material behaviors and degradation mechanisms are highlighted to obtain a better understanding of the high temperature electrolysis process in SOECs. Proposed research directions are also outlined to provide guidelines for future research.
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Two original series of carbon gels doped with different cobalt loadings and well-developed mesoporosity, aerogels and xerogels, have been prepared, exhaustively characterized, and tested as cathodes for the electro-catalytic reduction of CO2 to hydrocarbons at atmospheric pressure. Commercial cobalt and graphite sheets have also been tested as cathodes for comparison. All of the doped carbon gels catalyzed the formation of hydrocarbons, at least from type C1 to C4. The catalytic activity depends mainly on the metal loading, nevertheless, the adsorption of a part of the products in the porous structure of the carbon gel cannot be ruled out. Apparent faradaic efficiencies calculated with these developed materials were better that those obtained with a commercial cobalt sheet as a cathode, especially considering the much lower amount of cobalt contained in the Co-doped carbon gels. The cobalt-carbon phases formed in these types of doped carbon gels improve the selectivity to C3-C4 hydrocarbons formation, obtaining even more C3 hydrocarbons than CH4 in some cases.
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Carbon dioxide capture, utilization and storage (CCUS) –including conversion to valuable chemicals-is a challenging contemporary issue having multi-facets. The prospect to utilize carbon dioxide (CO2) as a feedstock for synthetic applications in chemical and fuel industries -through carboxylation and reduction reactions-is the subject of this review. Current statute of the heterogeneously catalyzed hydrogenation, as well as the photocatalytic and electrocatalytic activations of conversion of CO2 to value-added chemicals is overviewed. Envisaging CO2 as a viable alternative to natural gas and oil as carbon resource for the chemical supply chain, three stages of development; namely, (i) existing mature technologies (such as urea production), (ii) emerging technologies (such as formic acid or other single carbon (C1) chemicals manufacture) and (iii) innovative explorations (such as electrocatalytic ethylene production) have been identified and highlighted. A unique aspect of this review is the exploitations of reactions of CO2 –which stems from existing petrochemical plants-with the commodity petrochemicals (such as, methanol, ethylene and ethylene oxide) produced at the same or nearby complex in order to obtain value-added products while contributing also to CO2 fixation simultaneously. Exemplifying worldwide ethylene oxide facilities, it is recognized that they produce about 3 million tons of CO2 annually. Such a CO2 resource, which is already separated in pure form as a requirement of the process, should best be converted to a value-added chemical there avoiding current practice of discharging to the atmosphere. The potential utilization of CO2, captured at power plants, should also been taken into consideration for sustainability. This CO2 source, which is potentially a raw material for the chemical industry, will be available at sufficient quality and at gigantic quantity upon realization of on-going tangible capture projects. Products resulting from carboxylation reactions are obvious conversions. In addition, provided that enough supply of energy from non-fossil resources, such as solar [1], is ensured, CO2 reduction reactions can produce several valuable commodity chemicals including multi-carbon compounds, such as ethylene and acrylic acid, in addition to C1 chemicals and polymers. Presently, there are only few developing technologies which can find industrial applications. Therefore, there is a need for concerted research in order to assess the viability of these promising exploratory technologies rationally.
Article
For the upscaling of the electrochemical conversion of CO2 to CO using Ag catalyst in water, gas diffusion electrodes (GDE) are needed for a sufficient supply of CO2 to obtain currents in the 100 mA cm⁻² range. The effects of an upscale of one order of magnitude starting with 10 cm² GDE size are presented. The penetration of electrolyte through the GDE needs to be regulated to balance the positive effects (avoid salt deposition) and the detrimental impacts (access blocking of CO2 to the GDE). Using a control of the partial pressure at the GDE to monitor the electrolyte penetration and enhancing CO2 feed by recirculation and turbulence promoters at the larger GDE. The first step of scale-up could be achieved without loss in performance. With three-compartment cells and 0.4 M K2SO4 electrolytes, the process is run at a current density of 150 mA cm⁻² over a couple of hundred hours with a Faradaic efficiency for CO (FECO) of approximately 60% on 100 cm² electrode area. It is discussed how to improve the performance by a management of the perspiration rate through the GDE to lay the scientific foundations for an industrial use of this technology.
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The construction of an efficient and robust catalyst for the electrochemical reduction of carbon dioxide into energy-rich products has recently received considerable attention. Herein, a Cu/TiO2 nanoparticles modified nitrogen-doped graphene (Cu/TiO2/NG) carbon material is fabricated for the selective reduction of CO2 into different alcohols. We found the Cu/TiO2/NG nanocomposite across a range of potentials for the electroreduction of CO2 exhibits dual catalytic ability, possessing an outstanding ability to produce methanol (reaching a maximum faradaic efficiency of 19.5% at a potential of −0.20 V vs. the reversible hydrogen electrode (RHE)) and a capability to produce ethanol (with a high faradaic efficiency up to 43.6% at −0.75 V vs. RHE). In addition, the Cu/TiO2/NG composite shows remarkable stability and reusability at both reductive potentials in the electrochemical process. The designed Cu/TiO2/NG composite may offer a new simple method based on earth-abundant metals to construct robust electrocatalysts for CO2 reduction.
Article
CO2 reduction conducted in electrochemical cells with planar electrodes immersed in an aqueous electrolyte is severely limited by mass transport across the hydrodynamic boundary layer. This limitation can be minimized by use of vapor-fed, gas-diffusion electrodes (GDEs), enabling current densities that are almost two orders of magnitude greater at the same applied cathode overpotential than what is achievable with planar electrodes in an aqueous electrolyte. The addition of porous cathode layers, however, introduces a number of parameters that need to be tuned in order to optimize the performance of the GDE cell. In this work, we developed a multiphysics model for gas diffusion electrodes for CO2 reduction and used it to investigate the interplay between species transport and electrochemical reaction kinetics. The model demonstrates how the local environment near the catalyst layer, which is a function of the operating conditions, affects cell performance. We also examined the effects of catalyst layer hydrophobicity, loading, porosity, and electrolyte flowrate to help guide experimental design of vapor-fed CO2 reduction cells.
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The electrochemical CO2 reduction reaction (CO2RR) can couple carbon-capture storage with renewable energy to convert CO2 into chemical feedstocks. For this process, copper is the only metal known to catalyze the CO2RR to hydrocarbons with adequate efficiency, but it suffers from poor selectivity. Copper bimetallic materials have recently shown an improvement in CO2RR selectivity compared with that of copper, such that the secondary metal is likely to play an important role in altering inherent adsorption energetics. This review explores the fundamental role of the secondary metal with a focus on how oxygen (O) and hydrogen (H) affinity affect selectivity in bimetallic electrocatalysts. Here, we identify four metal groups categorized by O and H affinities to determine their CO2RR selectivity trends. By considering experimental and computational studies, we link the effects of extrinsic chemical composition and physical structure to intrinsic intermediate adsorption and reaction pathway selection. After this, we summarize some general trends and propose design strategies for future electrocatalysts. Global consumption of fossil fuels is driving anthropogenic climate change and depleting reserves. To stem these environmental problems and secure future energy commodities, the electrochemical CO2 reduction reaction (CO2RR) presents an ideal solution because it can couple carbon-capture storage technology with renewable energy to convert atmospheric CO2 into useful chemical feedstocks. Efficient catalysts are required to drive this process with adequate energy efficiency and product selectivity. In this review, we discuss how surface and interfacial engineering can be used as a strategy for designing copper alloy and bimetallic materials for selective CO2 reduction to CO or hydrocarbons and alcohols. Developing selective catalysts is extremely important for the electrochemical reduction of CO2 to fuels. For this process, copper can produce hydrocarbon products such as methane but suffers from poor selectivity. Alloying copper with another metal could modify its inherent properties and improve its selectivity. This review explores the fundamental role of the secondary metals and whether their oxygen and hydrogen adsorption properties can determine CO2 reduction selectivity. Based on these findings, strategies for the design of selective copper-based catalysts are proposed.
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Electrodeposition of CuAg alloy films from plating baths containing 3,5-diamino-1,2,4-triazole (DAT) as an inhibitor yields high surface area catalysts for the active and selective electroreduction of CO2 to multi-carbon hydrocarbons and oxygenates. EXAFS shows the co-deposited alloy film to be homogenously mixed. The alloy film containing 6% Ag exhibits the best CO2 electrore-duction performance, with the Faradaic efficiency for C2H4 and C2H5OH production reaching nearly 60 and 25%, respectively, at a cathode potential of just –0.7 V vs. RHE and a total current density of ~–300 mA/cm2. Such high levels of selectivity at high activity and low applied potential are the highest reported to date. In-situ Raman and electroanalysis studies suggest the origin of the high selectivity towards C2 products to be a combined effect of the enhanced stabilization of the Cu2O overlayer and the opti-mal availability of the CO intermediate due to the Ag incorporated in the alloy.
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In-situ grown nanoporous Zn-Cu catalysts were prepared by simply annealing a commercial brass foil at 500 °C in air, followed by electrochemical reduction. During the annealing process, Zn preferentially melted and migrated out of the framework of the alloy to form a thin layer of ZnO on its surface. Subsequent electroreduction created nanoporous Zn-enriched surface. The Zn concentration increased from 36% to 50% by 10 min, to 81% by 3 h, and to 87% by 12 h annealing treatment while the average pore size decreased from 290 nm to 120 nm as the annealing time increased from 1 h to 12 h. Faradaic efficiency of CO2 reduction to CO and HCOOH was enhanced by nearly 4 and 6 times, respectively, as compared to untreated brass foils. The nanoporous Zn-Cu catalyst presented a stable ratio of CO/H2 and a steady working current density in a continuous electrolysis of 18 h in 0.5 M KHCO3 solution.
Article
Known catalysts for (photo)electrochemical carbon dioxide (CO2) reduction typically generate multiple products, including hydrogen, carbon monoxide, hydrocarbons, and oxygenates, making product separation a ubiquitous, yet often overlooked, challenge. Here, we review CO2 reduction products using available catalysts and discuss approaches for product separation along with estimates of separation energy requirements. We illustrate potential complexities and discuss opportunities to minimize separations by utilizing product mixtures. We also examine potential CO2 sources, their energy requirements, and net CO2 emissions. Finally, we discuss use of waste energy sources and integrate this information into an overall energy balance assessment. Using a common sustainability metric, energy return on energy investment (EROEI), we find that an EROEI of ∼2.0 may be possible, before including separation and CO2 production energy. For EROEI to remain above one (the break-even point), these additional energy requirements, including embodied energy of equipment, must be no greater than half of the product energy.
Article
The electrochemical reduction of carbon dioxide (CO2) has received significant attention in academic research, although the techno-economic prospects of the technology for the large-scale production of chemicals are unclear. In this work, we briefly reviewed the current state-of-the-art CO2 reduction figures of merit, and performed an economic analysis to calculate the end-of-life net present value (NPV) of a generalized CO2 electrolyzer system for the production of 100 tons/day of various CO2 reduction products. Under current techno-economic conditions, carbon monoxide and formic acid were the only economically viable products with NPVs of $13.5 million and $39.4 million, respectively. However, higher-order alcohols such as ethanol and n-propanol could be highly promising under future conditions if reasonable electrocatalytic performance benchmarks are achieved (e.g. 300mA/cm² and 0.5V overpotential at 70% faradaic efficiency). Herein, we established performance targets such that if these targets are achieved, electrochemical CO2 reduction for fuels and chemicals production can become a profitable option as part of the growing renewable energy infrastructure.
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Dendritic Ag (a CO2-to-CO reduction catalyst) has been synthesized on carbon paper (CP) using pulse electrodeposition to fabricate a gas diffusion electrode. A combination of sonication and pulse deposition facilitated mass transfer of Ag ions to the CP, enlarging the catalyst active surface area without significantly changing the Ag crystalline structure. The current density of CO2 reduction was proportional to the surface area of dendritic Ag. Further improvements in performance were achieved by adding polyethylene glycol to the CO2 reduction cell catholyte that removed the CO gas bubbles produced at the electrode surface. The fabrication methods presented herein suggest an effective gas diffusion electrode for application in the membrane-electrode-assembly-type single cell for electrochemical CO2 reduction.
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Low-dimensional materials and their hybrids have emerged as promising candidates for electrocatalytic and photocatalytic hydrogen evolution and CO2 conversion into useful molecules. Progress in synthetic methods for the production of catalysts coupled with a better understanding of the fundamental catalytic mechanisms has enabled the rational design of catalytic nanomaterials with improved performance and selectivity. In this Review, we analyse the state of the art in the implementation of low-dimensional nanomaterials and their van der Waals heterostructures for hydrogen evolution and CO2 reduction by electrocatalysis and photocatalysis. We explore the mechanisms involved in both reactions and the different strategies to further optimize the activity, efficiency and selectivity of low-dimensional catalysts.
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Electrochemical reduction of CO_2 to ethanol, a clean and renewable liquid fuel with high heating value, is an attractive strategy for global warming mitigation and resource utilization. However, converting CO_2 to ethanol remains great challenge due to the low activity, poor product selectivity and stability of electrocatalysts. Here, the B- and N-co-doped nanodiamond (BND) was reported as an efficient and stable electrode for selective reduction of CO_2 to ethanol. Good ethanol selectivity was achieved on the BND with high Faradaic efficiency of 93.2 % (−1.0 V vs. RHE), which overcame the limitation of low selectivity for multicarbon or high heating value fuels. Its superior performance was mainly originated from the synergistic effect of B and N co-doping, high N content and overpotential for hydrogen evolution. The possible pathway for CO_2 reduction revealed by DFT computation was CO_2→*COOH→*CO→*COCO→*COCH_2OH→*CH_2OCH_2OH→CH_3CH_2OH.
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We show that bicarbonate is neither a general acid nor a reaction partner in the rate-limiting step of CO2 reduction catalysis mediated by planar polycrystalline Au surfaces. We formulate microkinetic models and propose diagnostic criteria to distinguish the role of bicarbonate. Comparing these models with the observed zero-order dependence in bicarbonate and simulated interfacial concentration gradients, we conclude that bicarbonate is not a general acid co-catalyst. Instead, it acts as a viable proton donor past the rate-limiting step and a sluggish buffer that maintains the bulk but not local pH in CO2-saturated aqueous electrolytes.
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A simple, inexpensive, and novel method was used to prepare electrocatalysts from Cu supported on titanium dioxide (Cu/TiO2). XRD, SEM, and TEM characterizations confirmed different loadings of Cu nanoparticles (NPs) on TiO2. Cyclic voltammetry tests indicated that Cu/TiO2 exhibited lower overpotential for CO2 reduction than that of Cu NPs. Moreover, 40 wt % Cu/TiO2 exhibited the highest faradaic efficiency for ethanol (FEethanol) of 27.4%, which is approximately 10-fold higher than that for Cu NPs (FEethanol = 2.7%). The 40 wt % Cu/TiO2 electrocatalyst exhibits a stable current density of 8.66 mA/cm2 over a 25 h stability test. The high efficiency towards CO2 electroreduction to ethanol may be attributed to the synergistic effect of Cu and TiO2 NPs. This work highlights the importance of compositional effect of NPs on their catalytic activities and provides a strategy for designing efficient catalysts for CO2 electroreduction in the future. © 2017 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license.
Article
In the future, industrial CO2 electroreduction using renewable energy sources could be a sustainable means to convert CO2 and water into commodity chemicals at room temperature and atmospheric pressure. This study focuses on the electrocatalytic reduction of CO2 on polycrystalline Au surfaces, which have high activity and selectivity for CO evolution. We explore the catalytic behavior of polycrystalline Au surfaces by coupling potentiostatic CO2 electrolysis experiments in an aqueous bicarbonate solution with high sensitivity product detection methods. We observed the production of methanol, in addition to detecting the known products of CO2 electroreduction on Au: CO, H2 and formate. We suggest a mechanism that explains Au's evolution of methanol. Specifically, the Au surface does not favor C–O scission, and thus is more selective towards methanol than methane. These insights could aid in the design of electrocatalysts that are selective for CO2 electroreduction to oxygenates over hydrocarbons.
Article
The CO2 that comes from the use of fossil fuels accounts for about 65% of the global greenhouse gases emissions, and it plays a critical role in global climate changes. Among the different strategies that have been considered to address the storage and reutilization of CO2, the transformation of CO2 into chemicals or fuels with a high added-value has been considered a winning approach. This transformation is able to reduce the carbon emissions and induce a “fuel switching” that exploits renewable energy sources. The aim of this brief review is to gather and critically analyse the main efforts that have been made and achievements that have been reached in the electrochemical reduction of CO2 for the production of CO. The main focus is on the prospective of exploiting the intrinsic nature of the electrolysis process, in which CO2 reduction and H2 evolution reactions can be combined, into a competitive approach, to produce syngas. Several well-stablished processes already exist for the generation of fuels and fine-chemicals from H2/CO mixtures of different ratios. Hence, the different kinds of electrocatalysts and electrochemical reactors that have been used for the CO and H2 evolution reactions have been analysed, as well as the main factors that influence the performance of the system from the thermodynamic, kinetic and mass transport points of view.
Article
Rising levels of carbon dioxide (CO2) are of significant concern in modern society, as they lead to global warming and consequential environmental and societal changes. It is of importance to develop industries with a zero or negative CO2 footprint. Electrochemistry, where one of the reagents is electrons, is an environmentally clean technology that is capable of addressing the conversion of CO2 to value-added products. The key factor in the process is the use of catalytic electrode materials that lead to the desired reaction and product. Significant progress in this field has been achieved in the past two years. This review discusses the progress in the development of electrocatalysts for CO2 reduction achieved during this time period.
Article
Tuning the surface strain of heterogeneous catalysts represents a powerful strategy to engineer their catalytic properties by altering the electronic structures. However, a clear and systematic understanding of strain effect in electrochemical reduction of carbon dioxide is still lacking, which restricts the use of surface strain as a tool to optimize the performance of electrocatalysts. Herein, we demonstrate the strain effect in electrochemical reduction of CO2 by using Pd octahedra and icosahedra with similar sizes as a well-defined platform. The Pd icosahedra/C catalyst shows a maximum Faradaic efficiency for CO production of 91.1 % at −0.8 V versus reversible hydrogen electrode (vs. RHE), 1.7-fold higher than the maximum Faradaic efficiency of Pd octahedra/C catalyst at −0.7 V (vs. RHE). The combination of molecular dynamic simulations and density functional theory calculations reveals that the tensile strain on the surface of icosahedra boosts the catalytic activity by shifting up the d-band center and thus strengthening the adsorption of key intermediate COOH*. This strain effect was further verified directly by the surface valence-band photoemission spectra and electrochemical analysis.
Article
Tuning the surface strain of heterogeneous catalysts represents a powerful strategy to engineer their catalytic properties by altering the electronic structures. However, a clear and systematic understanding of strain effect in electrochemical reduction of carbon dioxide is still lacking, which restricts the use of surface strain as a tool to optimize the performance of electrocatalysts. Herein, we demonstrate the strain effect in electrochemical reduction of CO2 by using Pd octahedra and icosahedra with similar sizes as a well-defined platform. The Pd icosahedra/C catalyst shows a maximum Faradaic efficiency for CO production of 91.1 % at −0.8 V versus reversible hydrogen electrode (vs. RHE), 1.7-fold higher than the maximum Faradaic efficiency of Pd octahedra/C catalyst at −0.7 V (vs. RHE). The combination of molecular dynamic simulations and density functional theory calculations reveals that the tensile strain on the surface of icosahedra boosts the catalytic activity by shifting up the d-band center and thus strengthening the adsorption of key intermediate COOH*. This strain effect was further verified directly by the surface valence-band photoemission spectra and electrochemical analysis.
Article
Electrochemical reduction of CO2 has been pointed out as an interesting strategy to convert CO2 into useful chemicals. In addition, coupling CO2 electroreduction with renewable energies would allow storing electricity from intermittent renewable sources such as wind or solar power. In this work, an easy and fast method is adapted for the synthesis of pure and carbon supported Sn nanoparticles. The resulting nanoparticles have been characterized by transmission electron microscopy and their electrocatalytic properties towards CO2 reduction evaluated by cyclic voltammetry. Carbon supported Sn nanoparticles have been subsequently used to prepare Gas Diffusion Electrodes (Sn/C-GDEs). The electrodes have been characterized by scanning electron microscopy and also by cyclic voltammetry. Finally, the electrodes were tested on a continuous and single pass CO2 electroreduction filter-press type cell system in aqueous solution, to obtain formate at ambient pressure and temperature. These Sn/C-GDEs allow working at high current densities with low catholyte flow. Thus, for instance, at 150 mA cm⁻², a 70% Faradaic Efficiency (FE) was obtained with a formate concentration of 2.5 g L⁻¹. Interestingly, by increasing the current density to 200 mA cm⁻² and decreasing the flow rate, a concentration over 16 g L⁻¹ was reached. Despite the high concentrations obtained, further research is still required to keep high FE operating at high current densities.
Article
The utilization of CO2 as a feedstock requires fundamental breakthroughs in catalyst design. The efficiencies and activities of pure metal electrodes towards the CO2 reduction reaction are established, but the corresponding data on mixed-metal systems are not as well developed. In this study we show that the near-infrared driven decomposition (NIRDD) of solution-deposited films of metal salts and subsequent electrochemical reduction offers the unique opportunity to form an array of mixed-metal electrocatalyst coatings with excellent control of the metal stoichiometries. This synthetic method enabled us to develop an empirical structure–property correlation to help inform the development of optimized CO2 catalyst compositions.