pH-Dependent Electroreduction of Nitrate on Fe Single-Atom Catalyst

Electrochemical nitrate reduction reaction (NO₃RR) has received considerable attention due to its potential for the denitrification of wastewater and sustainable NH₃ production. Among various catalysts for NO₃RR, Fe-N-C single-atom catalyst has attracted significant interest due to its well-defined active sites and high stability across various media. Here, we investigate the pH dependence of NO₃RR on Fe-N-C by combining experiments and density functional theory (DFT) calculations. The Fe-N-C catalyst achieves high activity and >80% Faradaic efficiency for NH₃ production in the NO₃RR across acidic, neutral, and alkaline electrolytes, while the hydrogen evolution reaction (HER) exhibits the strongest competition with NO₃RR in alkaline electrolyte. DFT calculations identify the NHO*-mediated pathway as the most favorable for NO₃RR on Fe-N-C and further reveal the pH dependence of the potential-determining steps for both NO₃RR and HER, elucidating the origin of the pH-dependent selectivity. Our studies provide new mechanistic insights into the NO₃RR on single-atom catalysts and guide the design of broad pH-range electrocatalysts for efficient and versatile nitrate recycling.