Proton-Regulated C-N Coupling for Efficient Amino Acid Electrosynthesis

Electrosynthesis of amino acids from abundant nitrogen sources and α-keto acids represents a sustainable route. Enhancing the reaction efficiency and exploring the mechanisms influencing the reaction are of great significance. Herein, we studied the effect of protons in the electrolyte on amino acid synthesis, which has been overlooked to date. Using the coreduction of oxalic acid and nitrate (NO₃^-) to glycine (Gly) on dendritic Bi as a model system, we found that optimal proton concentrations specifically enhance two key steps of the four-step reactions, governing Gly selectivity and production rate. One is that protons directly coordinate with key intermediates in NO₃^- reduction. Suitable proton concentration induces the desorption of *NH₂OH (where * denotes an adsorption site) as protonated NH₃OH⁺ from the catalyst surface. This desorption effectively prevents *NH₂OH from further reduction to NH₃, securing the essential intermediate (NH₃OH⁺) for Gly synthesis. The other is that suitable proton concentration favors the proton-coupled electron transfer hydrogenation of glyoxylic acid oxime to Gly, which finally enhances the Gly selectivity and production rate. Guided by this mechanistic insight, we optimized the reaction conditions to precisely control each critical step, achieving excellent Gly electrosynthesis performance with an FE_Gly of 78.9% and a partial current density of 108.2 mA cm^-2. The versatility of this approach was further demonstrated through efficient synthesis of diverse amino acids, including alanine, aspartic acid, and phenylglycine, delivering very high FEs and yield rates.