The world emits over 14 gigatons of CO2 in excess of what can be remediated by natural processes annually, contributing to rising atmospheric CO2 levels and increasing global temperatures. The electrochemical reduction of CO2 (CO2RR) to value‐added chemicals and fuels has been proposed as a method for reusing these excess anthropogenic emissions. While state‐of‐the‐art CO2RR systems exhibit high current densities and faradaic efficiencies, research on long‐term electrode durability, necessary for this technology to be implemented commercially, is lacking. Previous reviews have focused mainly on the CO2 electrolyzer performance without considering durability. In this Review, the need for research into high‐performing and durable CO2RR systems is stressed by summarizing the state‐of‐the‐art with respect to durability. Various failure modes observed are also reported and a protocol for standard durability testing of CO2RR systems is proposed.
Electroreduction of CO 2 (eCO 2 RR) is a potentially sustainable approach for carbon-based chemical production. Despite significant progress, performing eCO 2 RR economically at scale is challenging. Here we report meeting key technoeconomic benchmarks simultaneously through electrolyte engineering and process optimization. A systematic flow electrolysis studyperforming eCO 2 RR to CO on Ag nanoparticles as a function of electrolyte composition (cations, anions), electrolyte concentration, electrolyte flow rate, cathode catalyst loading, and CO 2 flow rate -resulted in partial current densities of 417 and 866 mA/cm 2 with faradaic efficiencies of 100 and 98 % at cell potentials of À 2.5 and À 3.0 V with full cell energy efficiencies of 53 and 43 %, and a conversion per pass of 17 and 36 %, respectively, when using a CsOH-based electrolyte. The cumulative insights of this study led to the formulation of system design rules for high rate, highly selective, and highly energy efficient eCO 2 RR to CO.[a] S.
The electrochemical reduction of CO 2 (ECO 2 R) is a promising method for reducing CO 2 emissions and producing carbonneutral fuels if long-term durability of electrodes can be achieved by identifying and addressing electrode degradation mechanisms. This work investigates the degradation of gas diffusion electrodes (GDEs) in a flowing, alkaline CO 2 electrolyzer via the formation of carbonate deposits on the GDE surface. These carbonate deposits were found to impede electrode performance after only 6 h of operation at current densities ranging from −50 to −200 mA cm −2 . The rate of carbonate deposit formation on the GDE surface was determined to increase with increasing electrolyte molarity and became more prevalent in K + -containing as opposed to Cs + -containing electrolytes. Electrolyte composition and concentration also had significant effects on the morphology, distribution, and surface coverage of the carbonate deposits. For example, carbonates formed in K + -containing electrolytes formed concentrated deposit regions of varying morphology on the GDE surface, while those formed in Cs + -containing electrolytes appeared as small crystals, well dispersed across the electrode surface. Both deposits occluding the catalyst layer surface and those found within the microporous layer and carbon fiber substrate of the electrode were found to diminish performance in ECO 2 R, leading to rapid loss of CO production after ∼50% of the catalyst layer surface was occluded. Additionally, carbonate deposits reduced GDE hydrophobicity, leading to increased flooding and internal deposits within the GDE substrate. Electrolyte engineering-based solutions are suggested for improved GDE durability in future work.
While the use of flow electrolyzers has enabled high selectivity (>80%) and activity (>200 mA cm −2 ) in the reduction of CO 2 to value-added chemicals, the durability of these systems is still insufficient for feasibility at scale. A key component of flow electrolyzers, the gas diffusion electrode, must be hydrophobic and stable to maintain the triple phase boundary at the catalyst layer. The catalyst layer consists of an active catalyst and a binder to augment hydrophobicity and stability. Many CO 2 electrolysis systems utilize Nafion as the binder, yet, these cathodes are prone to carbonate formation and are often not stable beyond 20 h. Inspired by knowledge from other electrocatalysis applications, this paper explores alternatives to Nafion in the catalyst layer as well as different methods of catalyst layer preparation. Cathodes with a poly(tetrafluoroethylene) (PTFE) binder elude carbonate formation, although their performance still decreases over time. However, the addition of PTFE to Nafion (mixed binders) limited carbonate formation. Furthermore, we found that coating cathodes with a Sustainion ionomer over layer extends lifetimes, presumably by hindering carbonate formation. The characteristics of cathodes with these binders are further explored using surface-enhanced Raman spectroscopy to help explain their effect on the electroreduction of CO 2 .
In recent years, the electrochemical reduction of CO2 (ECO2RR) to value-added chemicals, fuels, and intermediates has been proposed as a promising option for utilizing excess CO2 emissions. ECO2RR could be...
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