Enhancing Electrochemical CO Reduction to Methane by Modulating the Interfacial Water Structure with Glycerol

Abstract

Interfacial water serves as the proton source in both the electrochemical CO reduction reaction (CORR) and the competing hydrogen evolution reaction (HER). Engineering the interfacial water structure to enhance the CORR and suppress the HER is an effective strategy but remains underexplored. In this study, we demonstrate that adding low amounts of glycerol to the electrolyte can effectively modulate the interfacial water structure and influence the CORR product distribution. Glycerol addition suppressed the HER and promoted the CORR conversion to CH₄, with its Faradaic efficiency increasing from 5.4 ± 3.3 to 23.9 ± 2.7%. Electrochemical in-situ Raman spectroscopy combined with ab initio molecular dynamics (AIMD) simulations reveals that the glycerol additive reduces the interfacial water content and strengthens the interfacial hydrogen bonding network, thus inhibiting water dissociation and promoting *CO protonation to produce CH₄. These findings shed light on the significance of the interfacial water structure in dictating CORR selectivity.