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.