How electrolyte properties and applied potential impact pathways and performance in electrochemical nitrate reduction

Electrochemical nitrate reduction reaction (NO 3 RR) is a promising route for the valorization of nitrate pollutants into ammonia; however, while extensive efforts have focused on catalyst development, the influence of electrolyte properties on NO 3 RR performance has been largely overlooked and remains poorly understood. Here, we show that the electrolyte alone contributes significantly and systematically to the reaction, independent of catalyst identity. To identify the electrocatalytic trends driven by the electrolyte, key parameters —including pH, nitrate concentration, and co-existing cations— were investigated through rationally designed electrochemical experiments performed across multiple metals (Cu, Ag, Pd, Au, Bi, Mo, and Ti), enabling differentiation of catalyst-specific behavior from electrolyte-driven effects. We find that pH and co-existing cations are critical, as they modulate interfacial proton availability, nitrate adsorption, intermediate stabilization, and controlled protonation toward ammonia formation. The effect of nitrate concentration depends on these two parameters as well as the applied potential. Importantly, our study highlights a commonly neglected aspect: alkali metal cations are not simple spectators but act as critical electrostatic field mediators in NO 3 RR. This work provides guidance for engineering electrolytes for nitrate-to-ammonia electrocatalytic systems and calls for redefining alkali metal cations as a key tuning parameter.