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Understanding the Effects of Cations on the Selectivity Modulation of the Conversion of Electrochemical Acetylene to
Jiajun Wang1, Chuanqi Cheng1, Jie Deng1
1Institute of Molecular Plus, Department of Chemistry, School of Science, Tianjin University, Tianjin300072, China.
Abstract:
Unraveling the not-yet-definitive mechanism of the extensively studied cation effects in the electrocatalytic hydrogenation (ECH) process would provide methods to suppress competitive side reactions and address selectivity issues, which have impeded the development of the electrosynthesis strategy. Here, taking electrochemical acetylene (C2H2) to ethylene (C2H4) hydrogenation (EAH) as a model case, the C2H4 selectivity over commercial polycrystalline copper (p-Cu) exhibits a volcano-type trend with increasing cation radius (Li+ < Na+ ≈ K+ > Cs+). The observed cation-dependent selectivity modulation results are attributed to the opposite trend in the hydrogen evolution reaction (HER) (inhibited) and C2H2 dimerization (boosted) with increasing cation size. Further mechanistic studies reveal that the increased electronic interaction, asymmetric charge distribution, and increased discontinuity of the hydrogen bond network with increasing cation size result in easier activation and adsorption of C2H2 feedstocks, accounting for the suppressed HER and enhanced coupling, respectively. Notably, the mechanism mentioned is also appropriate for explaining the highest C2+ selectivity of CO2 electroreduction with Cs+-containing electrolytes.
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