Significance of Site Proximity in Cu Single-Atomic Site Catalysts for Electrocatalytic Synthesis of Alanine

Synthesis of amino acids via electrocatalytic C−N coupling is considered a promising and green approach. Whether C−N coupling relies on cooperative sites (bonded or nonbonded) is an open question and is crucial for the development of highly efficient catalysts. Here, Cu single-atomic site (SAS) catalysts with different site densities were synthesized via an ion exchange approach, and the impact of site proximity on Faradaic efficiency of alanine (FEalanine) was probed. The FEalanine is positively correlated with Cu SAS loadings. An FEalanine of 42% can be achieved at 15 wt % loading. Remarkably, it is revealed that fully isolated Cu SASs (at 1 wt % loading) do not result in alanine. This suggests that the presence of adjacent-site configurations is probably essential for the C−N coupling. It is speculated that fully isolated Cu SASs prefer to adsorb pyruvic acid rather than nitrate, thus failing to form the key intermediate hydroxylamine.