Dynamic Ionization Equilibrium-Induced "Oxygen Exchange" in CO Electroreduction

HN Zhang and Y Cui and CJ Ren and Q Li and CY Ling and JL Wang, ACS CATALYSIS, 14, 10737-10745 (2024).

DOI: 10.1021/acscatal.4c01773

The oxygen source of oxygenates is the fundamental issue for CO2/CO electroreduction, which was firmly believed to originate from the gas feed (O-gas) for a long time. However, recent experiments have confirmed that most O atoms of the generated alcohols via CO reduction arise from the solvent (O-aq), indicating the existence of a rather mysterious "oxygen exchange" process. In this work, we solved this mechanistic puzzle using comprehensive computations. Our results revealed that high CO pressure enables COgas oxidation by surface *OaqH, which opens a pathway for oxygenate production. The generated *COgasOaqH can react with another *CO to form *COCOgasOaqH, which leads to the formation of a series of carboxyl-containing intermediates (RCOgasOaqH) in subsequent steps. Due to the dynamic ionization equilibrium, H+ moves rapidly between O-gas and O-aq via reversible "inner" proton transfer (*RCOgasOaqH (sic) *R-COgasOaq- + H+ (sic) *RCOaqOgasH). The oxygen exchange completes when *RCOaq forms via the dehydroxylation of a certain *RCOaqOgasH. The completed reaction pathways were further explored by using COgas reduction into C2H5OaqH as an example, which explains related experiments. Therefore, these results refresh the insights into CO2/CO electroreduction and give specific guidelines for the optimization of catalytic performance.

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