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...

The renewable electricity-powered electrolysis of CO 2 could be a viable carbon-neutral method for producing carbon-based value-added chemicals like carbon monoxide, formic acid, ethylene, and ethanol. A typical CO 2 electrolyzer suffers, however, from the high power requirements, mainly due to the energy-intense anode reaction. In this work, we decrease the anode overpotential and thus reduce the overall cell energy consumption by using a NiFe-based bimetallic catalyst at the anode and applying a magnetic field. For a CO 2 electrolysis process producing CO in a gas diffusion electrode-based flow electrolyzer, we demonstrate that power savings in the range from 7% to 64% can be achieved at CO partial current densities exceeding −300 mA/cm 2 using a NiFe catalyst at the anode and/or by using a magnetic field at the anode. We achieve a maximum CO partial current density of −565 mA/cm 2 at a full cell energy efficiency of 45% with 2 M KOH as the electrolyte.

No abstract

The electrochemical reduction of CO2 (CO2RR) holds promise for the reduction of environmentally taxing CO2 emissions, for the carbon-neutral production of valuable fuels and chemicals, and for storage of excess renewable energy from intermittent sources such as wind and solar in chemical products. Durability of cathodes used in high-throughput CO2RR systems is of paramount importance for the commercial readiness of the CO2RR technology. In this study, we investigate the durability of silver-coated gas diffusion electrode cathodes under potential cycling conditions to simulate the impact of repeated cycles of startup and shutdown as might be experienced in connection with a variable renewable power source. We determine that cycling can impact the cathode via two distinct degradation mechanisms: (1) carbonate formation at negative potentials and (2) catalyst layer restructuring and loss in the relatively positive “oxide formation” potential range. We also explore tailored potential cycling as a mechanism for inhibiting carbonate formation by interrupting the high concentration of OH– at the catalyst layer. The findings from this work lend insight into the types of variable potential operating conditions under which CO2RR systems can deliver continuous, robust performance.