Accelerating C-C coupling in alkaline electrochemical CO2 reduction by optimized local water dissociation kinetics

Abstract

Electrochemical carbon dioxide reduction reaction (CO₂RR) produces valuable chemicals by consuming gaseous CO₂ as well as protons from the electrolyte. Protons, produced by water dissociation in alkaline electrolyte, are critical for the reaction kinetics which involves multiple proton coupled electron transfer steps. Herein, we demonstrate that the two key steps (CO₂-*COOH and *CO-*COH) efficiency can be precisely tuned by introducing proper amount of water dissociation center, i.e., Fe single atoms, locally surrounding the Cu catalysts. In alkaline electrolyte, the Faradaic efficiency (FE) of multi-carbon (C₂₊) products exhibited a volcano type plot depending on the density of water dissociation center. A maximum FE for C₂₊ products of 73.2% could be reached on Cu nanoparticles supported on N-doped Carbon nanofibers with moderate Fe single atom sites, at a current density of 300 mA cm^–2. Experimental and theoretical calculation results reveal that the Fe sites facilitate water dissociation kinetics, and the locally generated protons contribute significantly to the CO₂ activation and *CO protonation process. On the one hand, in-situ attenuated total reflection surface-enhanced infrared absorption spectroscopy (in-situ ATR-SEIRAS) clearly shows that the *COOH intermediate can be observed at a lower potential. This phenomenon fully demonstrates that the optimized local water dissociation kinetics has a unique advantage in guiding the hydrogenation reaction pathway of CO₂ molecules and can effectively reduce the reaction energy barrier. On the other hand, abundant *CO and *COH intermediates create favorable conditions for the asymmetric *CO-*COH coupling, significantly increasing the selectivity of the reaction for C₂₊ products and providing strong support for the efficient conversion of related reactions to the target products. This work provides a promising strategy for the design of a dual sites catalyst to achieve high FE of C₂₊ products through the optimized local water dissociation kinetics.