Pd Nanoparticle Size‐Dependent H* Coverage for Cu‐Catalyzed Nitrate Electro‐Reduction to Ammonia in Neutral Electrolyte

Electrochemical conversion of nitrate (NO 3 − ) to ammonia (NH 3 ) is an effective approach to reduce nitrate pollutants in the environment and also a promising low‐temperature, low‐pressure method for ammonia synthesis. However, adequate H * intermediates are highly expected for NO 3 − hydrogenation, while suppressing competitive hydrogen evolution. Herein, the effect of H * coverage on the NO 3 RR for ammonia synthesis by Cu electrocatalysts is investigated. The H * coverage can be adjusted by changing Pd nanoparticle sizes. The optimized Pd@Cu with an average Pd size of 2.88 nm shows the best activity for NO 3 RR, achieving a maximum Faradaic efficiency of 97% (at −0.8 V vs RHE) and an NH 3 yield of 21 mg h −1 cm − 2 , from an industrial wastewater level of 500 ppm NO 3 – . In situ electrochemical experiments indicate that Pd particles with 2.88 nm can promote NO 3 − hydrogenation to NH 3 via well‐modulated coverage of adsorbed H * species. Coupling the anodic glycerol oxidation reaction, ammonium and formate are successfully obtained as value‐added products in a membrane electrode assembly electrolyzer. This work provides a feasible strategy for obtaining size‐dependent H * intermediates for hydrogenation.