Direct Electroreduction of Carbonate to Formate

Abstract

A cause of losses in energy and carbon conversion efficiencies during the electrochemical CO2 reduction reaction (eCO2RR) can be attributed to the formation of carbonates (CO3 2–), which is generally considered to be an electrochemically-inert species. Herein, we employ in-situ electrochemical Raman spectroscopy, liquid chromatography, nuclear magnetic resonance spectroscopy, 13C isotope-labelling and density functional theory (DFT) simulations to understand the role of carbonate species formed on copper catalysts during eCO2RR, and its ability to reduce to formate. Direct carbonate-to-formate conversion was confirmed by the the direct reduction of CuCO3, and by pulse reduction of N2-saturated K2CO3 electrolyte on Cu,. DFT simulations elucidated the nature of the active sites generating the Cu-CO3 2– species and revealed the mechanism for the pulse-enabled carbonate reduction to formate. Combining both experimental and computational results, we proposed that a dynamic carbonate intermediate was constantly formed on Cu during eCO2RR, that further evolves to formate between –0.4 to –1.2 VRHE on Cu. Control systems using Pb, Ag and Au electrodes were also studied.