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

Electrochemical conversion of nitrate (NO ) to ammonia (NH) 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 hydrogenation, while suppressing competitive hydrogen evolution. Herein, the effect of H coverage on the NORR 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 NORR, achieving a maximum Faradaic efficiency of 97% (at -0.8 V vs RHE) and an NH yield of 21 mg h cm , from an industrial wastewater level of 500 ppm NO . In situ electrochemical experiments indicate that Pd particles with 2.88 nm can promote NO hydrogenation to NH 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.