Hydroxyl Adsorption as a Selectivity Descriptor for Electrocatalytic Nitrate Reduction over Cu Catalysts

The electrocatalytic nitrate reduction reaction (NO3–RR) driven by renewable electricity has recently emerged as a promising route for ammonia (NH3) synthesis under mild conditions. Yet, the energy-efficient NH3 electrosynthesis from NO3– is hindered by high overpotential and competing nitrite (NO2–) formation. Here, we demonstrate potential- and concentration-dependent NO3–RR product selectivity over a size- and shape-selected Cu nanocube model catalyst. More negative potentials and lower NO3– concentrations are favorable for improving selectivity toward NH3 over NO2–. Such apparent dependence is closely associated with weakened hydroxyl (*OH) adsorption. In combination with operando spectroscopic characterization and density functional theory calculation results, *OH adsorption has been proposed as a descriptor that determines product selectivity by affecting the availability of surface adsorbed hydrogen (*H) produced through water dissociation. Our work underscores the importance of the *OH adsorption as a selectivity descriptor for designing more efficient systems toward NO3–RR to NH3.