Glycine electrosynthesis by the co-reduction of oxalic and nitric acids on rutile TiO2

Glycine is an important amino acid for daily life, but its conventional synthesis often involves the use of toxic chemicals or catalysts. The electrochemical co-reduction of oxalic acid and nitric acid under mild conditions offers a greener alternative but is challenging over a single catalyst. Herein, we have realized this glycine electrosynthesis on a single low-cost and nontoxic rutile TiO₂/CNT (CNT = carbon nanotube). The high glycine yield of 57% was made possible by the uniqueness of rutile TiO₂ in the appropriate proton environment. Oxalic acid and nitric acid were competitively adsorbed on rutile TiO₂ and selectively converted into glyoxylic acid and NH₂OH at identical potentials. Further solution-phase C–N coupling and oxime reduction on rutile TiO₂ produced glycine in high yields. Density functional theory calculations revealed that the appropriate Ti–Ti distance on the reduced rutile TiO₂ fadvored the desorption of glyoxylic acid and NH₂OH, as well as the stabilization of N-containing species at early-stage nitrate reduction.