Proton Concentration Tunes the Double-Layer Characteristics of Lead Catalysts to Boost the Electrosynthesis of Glyoxylic Acid

Abstract

Glyoxylic acid (C₂H₂O₃) is an important platform molecule. Oxalic acid (H₂C₂O₄) electroreduction into C₂H₂O₃ offers a sustainable alternative to conventional multistep synthesis while limited by insufficient activity (>-200 mA cm^-2). Herein, we presented a convenient strategy that created a counterintuitive interfacial structure to decouple the proton supply from surface proton activation on the Pb catalyst via tuning the acidity of the electrolyte. During H₂C₂O₄ electroreduction, the activity for C₂H₂O₃ reached -420.1 mA cm^-2 in the mixed solution containing saturated H₂C₂O₄ and 1.0 M HCl, 2.8 times higher than that (-111.5 mA cm^-2) in the saturated H₂C₂O₄ solution. Based on mechanistic investigation, the adsorption of protons was suppressed, whereas the rate-determining protonation of the adsorbed H₂C₂O₄ was facilitated under high acidity conditions. By adopting urea and C₂H₂O₃ solution with residual acid as reactants, we further validated commercial feasibility for the downstream separation and transformation of C₂H₂O₃ into high-value-added allantoin products.

Keywords: C2H2O3 electrosynthesis; H2C2O4 electroreduction; electrochemical double layer; microenvironment construction; proton coverage.