Two-step tandem electrochemical conversion of oxalic acid and nitrate to glycine

Abstract

This study presents a facile tandem strategy for improving the efficiency of glycine electrosynthesis from oxalic acid and nitrate. In this tandem electrocatalytic process, oxalic acid is first reduced to glyoxylic acid, while nitrate is reduced to hydroxylamine. Subsequent coupling of these two precursors results in the formation of a C–N bond, producing the intermediate glyoxylic acid oxime, which is further reduced in situ to glycine. Here we show, using only a simple Pb foil electrode, which maximizes the yield of the first step of the transformation (i.e. the reduction of oxalic acid to glyoxylic acid) prior to the coupling step allows for an unprecedented selectivity and conversion for glycine electrosynthesis to be achieved. Overall, a maximum glycine faradaic efficiency (FE) of 59% is achieved at −300 mA cm⁻² and a high glycine partial current density of −232 mA cm⁻² and a glycine production rate of 0.82 mmol h⁻¹ cm⁻² are attained at −400 mA cm⁻², thereby paving the way for an energy and economically efficient electrochemical synthesis of glycine.