Rational Design and Synthesis of CO2 Reduction Reaction Catalysts of High Faradaic Efficiency Toward C2 + Chemical Conversions

Carbon dioxide emission from fossil fuel combustion poses a major threat to global environment and ecological systems.Carbon capture, sequestration and conversion technologies are widely pursued as possible solutions to mitigate negative impact by CO 2 . The electrochemical CO 2 reduction reaction (CO 2 RR) to fuels and chemicals using renewable electricity offers attractive “carbon-neutral” and “carbon-negative” mitigation strategies. Various catalysts have been investigated as the electrocatalysts for CO 2 RR. Key challenges facing the current catalyst and electrolyzer designs include insufficient energy efficiency and low single product selectivity. CO 2 RR to C 2 + chemicals represent a highly important area for CO 2 reduction and utilization. For example, ethanol, ethylene, propanol, etc. are among the most produced chemicals by the industry and are widely used for various applications. Using CO 2 as raw material for chemical production through electrocatalysis not only improves the carbon cycling, but also reduces the overall emissions from chemical production. While CO 2 RR via two proton-electron pairs (PEPs), such as the conversion of CO 2 to CO or formate, have been proven high selective with fast kinetics, conversions to C 2 + chemicals are significantly more difficult due to the rapid escalation of required PEPs to much higher numbers (for example, 12 for ethanol and 18 for propanol), in addition to C-C bond coupling. The increased PEPs substantially complicate the conversion by required multiple steps along the electrochemical coordinate, leading to a high probability of branching reactions and low single product Faradaic efficiency (FE). To address these challenges, the design criteria for CO2RR to C 2 + chemicals should be based on high uniformity of active center for directing identical catalytic path and suppressing competing reactions, strong catalyst-reactant binding in capturing the transient species through multiple PEP transfers, and microenvironment with nanoconfinement for retaining reaction intermediates during extended catalytic processes. Recently, we developed a new amalgamated lithium metal (ALM) synthesis method of preparing highly selective and active CO 2 RR catalyst and achieved > 90% FE for conversion of CO 2 to ethanol 1. Our have since expanded the approach to other C 2 + chemicals including acetate, acetone, glycerol, isopropanol, etc., all with FE at or higher than 80%. To better formulate our catalyst design strategy, we not only measured the CO 2 RR performance over a variety of electrocatalysts, but also investigated their activity-structure relationship through advanced material characterizations, combined with the first-principle computation. We found many interesting properties uniquely associated to CO 2 RR mechanism and kinetics, such as catalyst-size and electro-potential modulated single selectivity. In this presentation, we will share our recent discoveries and future perspective on the development of highly selective CO 2 RR catalysts for C 2 + chemical conversions. Acknowledgement : This work is supported by U. S. Department of Energy, Office of Energy Efficiency and Renewable Energy - Industrial Efficiency & Decarbonization Office and by Office of Science, U.S. Department of Energy under Contract DE-AC02-06CH11357. 1 “Highly selective electrocatalytic CO 2 reduction to ethanol by metallic clusters dynamically formed from atomically dispersed copper” Haiping Xu, Dominic Rebollar, Haiying He, Lina Chong, Yuzi Liu, Cong Liu, Cheng-Jun Sun, Tao Li, John V. Muntean, Randall E. Winans, Di-Jia Liu and Tao Xu, ( 2020 ) Nature Energy , 5 , 623–632