Computational Insights for Electrocatalytic Synthesis of Glycine

Amino acids, e.g. glycine, are vital for lives and the biomedical field, whereas conventional synthesis methods usually have limitations. The electrochemical synthesis of glycine is an emerging route. However, the reaction mechanism and network of glycine electrosynthesis are intricate due to the coexistence of multiple competing (thermochemical and electrochemical) reactions toward different products. Herein, we employed density functional theory calculations to explore the electrosynthesis mechanism of glycine, derived from nitrate and oxalic acid. We initially established a (quasi) activity trend based on global energy optimization and found that Cu-supported Hg-rich sites exhibit great activity toward glycine. The C-N bond of glycine is constructed through the coupling of an amino group (NH2*) and glyoxylic acid (GX) in a local GX-rich environment, independent of oxime production and reduction. We further verified the mechanism using an electric field controlling constant potential method and microkinetic modeling. The computational results aligned well with experimental findings on the potential-dependent selectivity of glycine production. These findings can provide comprehensive insights and potential improvements for glycine electrosynthesis, which is the basis for the development of mercury-free alternative catalysts.