(Invited) Understanding the Electrocatalytic Mechanisms of Oxygen and Carbon Dioxide Reduction Reactions

Abstract

Oxygen reduction reaction (ORR) is one of the most important reactions in the field of electrocatalysis today. ORR represents a key cathodic reaction in hydrogen fuel cell, which typically needs to be promoted by the platinum group metals (PGMs), particularly Pt. The high cost of Pt adds significant barrier to the widespread implementation of the fuel cell technology. During the last two decades, substantially amount of effort has been invested in searching for low-cost replacements, or PGM-free catalysts for ORR. Although significant progress has been made, such catalysts still face major challenge in durability. By adding small amount of Pt over PGM-free catalytic substrate, we have found that both activity and stability will be significantly improved through synergistic interaction. [1] To better define synergistic effect in ORR catalysis, however, requires a carefully designed experiment that can separates multiple factors during the catalyst synthesis that can potentially influence the overall activity. In this report, we will discuss our recent study in understanding of the ORR catalysis synergy between Pt/PGM-free components in rationally designed catalyst systems.Another fast developing area of electrocatalysis is CO2 reduction reaction (CO2RR), which promises to electrochemically convert CO2 to fuels and chemicals using renewable electricity. While CO2RR via 2-electron transfer, such as the conversion to CO or formate, has been proven high selective with fast kinetics, conversions to C2+ chemicals require significantly stronger binding between the catalytic site and CO2 to complete multiple electron transfers (8 to 16) and C-C bond coupling steps, therefore are more challenging. More recently, we develop a new amalgamated lithium metal (ALM) synthesis method to preparing highly selective and active CO2RR catalyst for C2+ chemicals such as ethanol production. [2] In this presentation, we will discuss the hypothesis driven CO2RR catalyst design, combined with the mechanistic study for preparing effective catalysts. We will also share some critical insight on CO2RR mechanism through advanced structural characterization and computational modelling. Acknowledgement: This work is supported by U. S. Department of Energy, Hydrogen and Fuel Cell Technologies Office through Office of Energy Efficiency and Renewable Energy and by Office of Science, U.S. Department of Energy under Contract DE-AC02-06CH11357.[1] L. Chong, J. Wen, J. Kubal, F. G. Sen, J. Zou, J. Greeley, M. Chan, H. Barkholtz, W. Ding, and D.-J. Liu, “Ultralow-loading Platinum-Cobalt Fuel Cell Catalysts Derived from Imidazolate Frameworks,” Science (2018) 362, 1276[2] “Highly selective electrocatalytic CO2 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