Selective Glycine Electrosynthesis via C-N Coupling Enabled by Synergistic Mott-Schottky Heterojunction and Oxygen...

Glycine, an indispensable amino acid essential for diverse biological processes, remains challenging to synthesize directly via electrosynthesis from simple carbon and nitrogen precursors. Herein, we report a highly efficient electrochemical route for glycine production through the reductive coupling of oxalic acid (H₂C₂O₄) with hydroxylamine (NH₂OH) or nitrate (NO₃ ^-) over a Mott-Schottky Sn/SnO₂ heterojunction catalyst enriched with oxygen vacancies. When employing H₂C₂O₄ and NH₂OH as feedstocks, a remarkable Faradaic efficiency (FE) of 91.6% for glycine is achieved at -0.7 V versus RHE, alongside a high yield of 135 mmol g_cat. ^-1 h^-1. To the best of our knowledge, this represents one of the best performances ever reported in this system. The catalyst also shows strong substrate versatility, enabling efficient glycine formation when NO₃ ^- (in situ reduced to NH₂OH) couples with glyoxylic acid or H₂C₂O₄. Mechanistic studies indicate that the Mott-Schottky heterojunction significantly promotes the co-adsorption of H₂C₂O₄ and NH₂OH, while oxygen vacancies facilitate the hydrogenation of oxime intermediates to glycine. This study highlights the profound synergistic interplay between Mott-Schottky heterojunctions and oxygen vacancy defects in precisely modulating active sites and accelerating reaction kinetics, thereby offering a sustainable strategy for the green electrosynthesis of amino acids.