Manipulating key intermediates and suppressing the hydrogen evolution reaction dual roles of Bi for high-efficiency nitrate to ammonia and energy conversion.

The nitrate reduction reaction (NORR) is a promising technology for simultaneous treatment of NO wastewater and synthetic ammonia. However, the NORR involves multiple electron and proton transfer processes, and the ammonia selectivity and yield are highly susceptible to the evolution of key intermediate (*NO) and the competing hydrogen evolution reaction (HER). In this study, bismuth (Bi), with a high hydrogen overpotential, is used as an inhibitor of the HER. Meanwhile, the Bi doping CoS (Bi-CoS) can refine the d-band center of CoS, which optimizes the adsorption of *NO, reduces the accumulation of NO on the surface of the catalyst and then releases more active sites, thereby enhancing the NORR activity. This viewpoint is verified by experimental results, density functional theory (DFT) calculations and Raman. Benefitting from the dual roles of Bi, Bi-CoS exhibits a highest NH Faraday Faradaic efficiency (FE) of 87.18%, an ammonia yield rate of 944.64 μg h cm and long-term stability at -0.2 V the reversible hydrogen electrode (RHE). Furthermore, an assembled Zn-NO battery can reach a maximum power density of 16.3 mW cm and high FE of 95.76%, providing a high-efficiency multifunctional system for nitrate to ammonia and energy conversion.