CO2 electroreduction to ethylene via hydroxide-mediated copper catalysis at an abrupt interface
18 May 2018-Science (American Association for the Advancement of Science)-Vol. 360, Iss: 6390, pp 783-787
TL;DR: 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).
Abstract: Carbon dioxide (CO 2 ) 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 CO 2 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 CO 2 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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TL;DR: It is hypothesized that high cathode alkalinity, driven by both initial electrolyte conditions and cathode half-reactions, promotes carbonate formation and precipitation which, in turn, facilitates electrolyte permeation and offers an opportunity to design electrodes with greater carbonation tolerance to improve device longevity.
Abstract: Managing the gas-liquid interface within gas-diffusion electrodes (GDEs) is key to maintaining high product selectivities in carbon dioxide electroreduction. By screening silver-catalyzed GDEs over a range of applied current densities, an inverse correlation was observed between carbon monoxide selectivity and the electrochemical double-layer capacitance, a proxy for wetted electrode area. Plotting current-dependent performance as a function of cumulative charge led to data collapse onto a single sigmoidal curve indicating that the passage of faradaic current accelerates flooding. It was hypothesized that high cathode alkalinity, driven by both initial electrolyte conditions and cathode half-reactions, promotes carbonate formation and precipitation which, in turn, facilitates electrolyte permeation. This mechanism was reinforced by the observations that post-test GDEs retain less hydrophobicity than pristine materials and that water-rinsing and drying electrodes temporarily recovers peak selectivity. This knowledge offers an opportunity to design electrodes with greater carbonation tolerance to improve device longevity.
182 citations
TL;DR: In this article, a comprehensive overview of recent advances in tuning CO2 reduction electrocatalysis via morphology and interface engineering is provided; the relationship between the properties of engineered catalysts and their CO2RR performance is highlighted to reveal the activity-determining parameters and underlying catalytic mechanisms.
Abstract: Electrochemical reduction of CO2 into value-added fuels and chemicals driven by renewable energy presents a potentially sustainable route to mitigate CO2 emissions and alleviate the dependence on fossil fuels. While tailoring the electronic structure of active components to modulate their intrinsic reactivity could tune the CO2 reduction reaction (CO2RR), their use is limited by the linear scaling relation of intermediates. Due to the high susceptibility of the CO2RR to the local CO2 concentration/pH and mass transportation of CO2/intermediates/products near the gas–solid–liquid three-phase interface, engineering catalysts’ morphological and interfacial properties holds great promise to regulate the CO2RR, which are irrelevant with linear scaling relation and possess high resistance to harsh reaction conditions. Herein, we provide a comprehensive overview of recent advances in tuning CO2 reduction electrocatalysis via morphology and interface engineering. The fundamentals of the CO2RR and design principles for electrode materials are presented firstly. Then, approaches to build an efficient three-phase interface, tune the surface wettability, and design a favorable morphology are summarized; the relationship between the properties of engineered catalysts and their CO2RR performance is highlighted to reveal the activity-determining parameters and underlying catalytic mechanisms. Finally, challenges and opportunities are proposed to suggest the future design of advanced CO2RR electrode materials.
182 citations
TL;DR: Li et al. as mentioned in this paper presented a real-time, in-depth, and overall review of the latest research progress concerning CO2 reduction/evolution reaction mechanisms in Li-CO2/O2 and Li−CO2 electrochemical systems.
Abstract: With ever-increasing demand for balancing CO2 emissions and maximizing electrical energy supplies, Li–CO2 electrochemistry, coupled with dual characteristics of advanced energy storage and effective CO2 fixation, has been attracting considerable attention from researchers. Herein, we offer a real-time, in-depth, and overall review of the latest research progress concerning CO2 reduction/evolution reaction mechanisms in Li–CO2/O2 and Li–CO2 electrochemical systems. Meanwhile, affecting factors on the reaction pathways and the identification of discharge products are summarized and discussed. Then, Li anode/electrolyte interface construction, electrolyte properties and selection of cathode materials/catalysts and design strategy, especially their effect on the performance of Li–CO2/O2 and Li–CO2 batteries, are explored and possible solutions and suggestions are provided. Building on an in-depth understanding of Li–CO2 electrochemistry, novel flexible Li–CO2 batteries and key factors are summarized. Furthermore, based on advanced research progress in the past several years, we identify the main problems, controversies, and challenges currently existing in various battery components that remain to be addressed to design more practicable Li–CO2/O2 and Li–CO2 batteries. Finally, future research directions and opportunities are presented.
181 citations
TL;DR: An atypical and stable OBC catalyst with a hierarchical pore and nanograin-boundary structure was constructed and was found to exhibit efficient CO2RR for production of ethylene, providing insight into the synthesis and structural characteristics of OBC, as well as its interplay with ethylene selectivity.
Abstract: Oxygen-bearing copper (OBC) has been widely studied for enabling the C-C coupling of the electrocatalytic CO2 reduction reaction (CO2RR) since this is a distinctive hallmark of strongly correlated OBC systems and may benefit many other Cu-based catalytic processes. Unresolved problems, however, include the instability of and limited knowledge regarding OBC under realistic operating conditions, raising doubts about its role in CO2RR. Here, an atypical and stable OBC catalyst with a hierarchical pore and nanograin-boundary structure was constructed and was found to exhibit efficient CO2RR for the production of ethylene with a Faradaic efficiency of 45% at a partial current density of 44.7 mA cm-2 in neutral media, and the ethylene partial current density is nearly 26 and 116 times that of oxygen-free copper (OFC) and commercial Cu foam, respectively. More importantly, the structure-activity relationship in CO2RR was explored through a comprehensive analysis of experimental data and computational techniques, thus increasing the fundamental understanding of CO2RR. A systematic characterization analysis suggests that atypical OBC (Cu4O) was formed and that it is stable even at -1.00 V [(vs the reversible hydrogen electrode (RHE)]. Density functional theory calculations show that the atypical OBC enables control over CO adsorption and dimerization, making it possible to implement a preference for the electrosynthesis of ethylene (C2) products. These results provide insight into the synthesis and structural characteristics of OBC as well as its interplay with ethylene selectivity.
181 citations
TL;DR: The history of its development and its fundamental mechanisms, cathode materials, oxygen-ion-conducting electrolyte materials, and anode materials are highlighted, and fuel-assisted SOECs with low-cost fuels applied to the anode to decrease the overpotential and electricity consumption are introduced.
Abstract: High-temperature CO2 electrolysis in solid-oxide electrolysis cells (SOECs) could greatly assist in the reduction of CO2 emissions by electrochemically converting CO2 to valuable fuels through effective electrothermal activation of the stable CO bond. If powered by renewable energy resources, it could also provide an advanced energy-storage method for their intermittent output. Compared to low-temperature electrochemical CO2 reduction, CO2 electrolysis in SOECs at high temperature exhibits higher current density and energy efficiency and has thus attracted much recent attention. The history of its development and its fundamental mechanisms, cathode materials, oxygen-ion-conducting electrolyte materials, and anode materials are highlighted. Electrode, electrolyte, and electrode-electrolyte interface degradation issues are comprehensively summarized. Fuel-assisted SOECs with low-cost fuels applied to the anode to decrease the overpotential and electricity consumption are introduced. Furthermore, the challenges and prospects for future research into high-temperature CO2 electrolysis in SOECs are included.
180 citations
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