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

Electrochemical nitrate reduction reaction (NORR) has received considerable attention due to its potential for the denitrification of wastewater and sustainable NH production. Among various catalysts for NORR, 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 NORR 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 NH production in the NORR across acidic, neutral, and alkaline electrolytes, while the hydrogen evolution reaction (HER) exhibits the strongest competition with NORR in alkaline electrolyte. DFT calculations identify the NHO*-mediated pathway as the most favorable for NORR on Fe-N-C and further reveal the pH dependence of the potential-determining steps for both NORR and HER, elucidating the origin of the pH-dependent selectivity. Our studies provide new mechanistic insights into the NORR on single-atom catalysts and guide the design of broad pH-range electrocatalysts for efficient and versatile nitrate recycling.