Exploring amino acid-based electrolytes for enhanced carbon dioxide electroreduction efficiency using a copper oxide catalyst

Abstract

This study investigates the CO2 electroreduction ( CO2ER) using a Copper / Copper (I) Oxide (Cu/Cu2 O) catalyst adapted from a previous study, focusing on the impact of electrolyte composition on product selectivity and efficiency. The catalyst, featuring a porous aerogel network with Cu^0/Cu^+ interfaces, promotes carbon-carbon (C-C) coupling and ethanol synthesis with high current density. Potassium chloride, used in the original study as a non-buffering reference electrolyte, was reproduced in our experiment to serve as a benchmark. It maintains a high local pH, which enhances *CO intermediate accumulation, yielding formate and ethanol with faradaic efficiency (FE) of ~6% and ~0.44% at -1.7V vs. Ag/AgCl, respectively. FE for ethanol and formate was determined via nuclear magnetic resonance (NMR) spectroscopy. Amino acid electrolytes (arginine, histidine, glycinate, L-lysine hydrate) were tested at an adjusted applied voltage of -1.3V vs. Ag/AgCl to account for lower conductivity. NMR analysis revealed electrolyte-dependent chemical shift variations, with histidine showing the highest formate FE (0.67%), followed by arginine (0.35%) and glycinate (0.12%). L-lysine hydrate uniquely produced acetate, likely due to high local pH promoting *CO retention and C-C coupling. However, overestimated FE (>100%) suggests NMR integration errors due to peak broadening. These findings underscore the influence of electrolyte hydration, pH, and composition on CO_2 ER selectivity, with NMR offering a valuable, though pH -sensitive, method for CO2 reduction products quantification.