Regulating intermediate adsorption and H2O dissociation on a diatomic catalyst to promote electrocatalytic nitrate reduction to ammonia

Abstract

Electrochemical conversion of nitrate (NO₃⁻) is an efficient approach to reduce NO₃⁻ pollutants and it offers a promising alternative for sustainable NH₃ synthesis. However, this process is limited by the mismatched reaction kinetics of NO₃⁻ discharge, active hydrogen (H*) formation via water dissociation, and stepwise hydrogenation processes. Herein, using density functional theory (DFT) calculations, we screened a library of Cu–M diatomic catalysts coordinated with a N doped carbon matrix (Cu–M–N–C, M = Fe, Co, Ni, Mn, Zn) by balancing N-containing intermediate adsorption and H₂O dissociation barriers. Among these catalysts, Cu–Fe–N–C demonstrates the best performance with a NH₃ yield rate of 1.22 mmol h⁻¹ cm⁻² and a high Faradaic efficiency (FE) for NH₃ synthesis of 95.08% at −0.8 V vs. the reversible hydrogen electrode, in which diatomic sites facilitate the first NO₃⁻ discharge step to generate adsorbed *NO₃ and lower the energy barriers of the following hydrogenation/dehydration steps. More importantly, the incorporated Fe sites could promote the H₂O dissociation, providing a large supply of H* for the deep hydrogenation of N-containing intermediates. This work reveals the tunable bonding interactions of diatomic sites with multiple reactant/intermediates, offering a new avenue for rational design of highly efficient atomic-level dispersed catalysts for both NO₃⁻ abatement and NH₃ synthesis.