Regulation of Active Hydrogen and Nitrate Concentration: Pulsed Potential Strategies in Nitrate Electroreduction Microenvironments

The electrochemical reduction of nitrate (eNO₃RR) plays a significant role in the nitrogen cycle and environmental remediation. The dynamics of active hydrogen in the eNO₃RR were studied in depth by varying the nitrate concentration and applying a pulsed-potential approach. The effect of both factors on regulation of the degree of hydrogenation of the intermediates and the product distribution was evaluated. Density functional theory (DFT) calculations indicated that elevated nitrate levels decrease the energy barrier for *NO to *ONNO conversion, enhancing the adsorption of *NO₃. The experimental results indicate that under high nitrate concentrations, copper-palladium (CuPd) catalysts exhibit faster reaction kinetics and higher nitrogen selectivity. In situ characterizations illuminated the critical role of active hydrogen on reaction intermediates. The CuPd catalyst achieved 95% NO₃-N conversion and 99% N₂ selectivity at 1 M nitrate by pulse potential modulation of the active hydrogen concentration on the catalyst surface. Finite element analysis (FEA) and molecular dynamics (MD) simulations verified that pulsed potentials modulate the local nitrate and hydrogen ion concentrations. The present work brings the eNO₃RR closer to practical applications, aiding in environmental protection and the balance of the nitrogen cycle.