Selective Electrocatalytic Oxidation of Ethylene Glycol into Glycolic Acid at Coin-Group Electrodes: An Investigation on Catalytic Activity and Selectivity

Ethylene glycol (EG) is an important platform molecule that can be produced from biomass and waste plastics. The electrochemical upgrading of EG is essential to approach the goal of low-carbon sustainable development. Coin-group metals (CGMs) including Au, Ag, and Cu have recently emerged as promising alternatives to platinum-group metals on selective electrooxidation of EG (EGOR) to value-added C2 chemicals, especially glycolic acid/glycolate. Nevertheless, the corresponding electrocatalytic processes are still indistinct, which is essential to be clarified. Specifically, it shows that the Au and Cu electrodes can exhibit considerable EGOR activity, but not Ag. Product analysis results show that the Faradaic efficiency (FE) of the EG-to-glycolate pathway on Au surface is over 95% at 1.0 V vs reversible hydrogen electrode (RHE). It is also around 90% on Cu surface, but Cu electrodes suffer from electrochemical dissolution within the potential range of EGOR, which is urgent to be addressed. Importantly, the different reaction mechanisms of EGOR at Au and Cu are found at the molecular level. In detail, the adsorbed 2-hydroxyacetyl and glyoxal could be the key reaction intermediates for the generation of glycolate at Au and Cu, respectively. This work might provide theoretical guidance for the electrocatalytic conversion of EG into value-added chemicals, which is further conducive to promoting the upgrading of biomass and waste plastics.