Manipulating key intermediates and suppressing the hydrogen evolution reaction <i>via</i> dual roles of Bi for high-efficiency nitrate to ammonia and energy conversion

The nitrate reduction reaction (NO₃RR) is a promising technology for simultaneous treatment of NO₃^- wastewater and synthetic ammonia. However, the NO₃RR involves multiple electron and proton transfer processes, and the ammonia selectivity and yield are highly susceptible to the evolution of key intermediate (*NO₂) 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 CoS₂ (Bi-CoS₂) can refine the d-band center of CoS₂, which optimizes the adsorption of *NO₂, reduces the accumulation of NO₂^- on the surface of the catalyst and then releases more active sites, thereby enhancing the NO₃RR activity. This viewpoint is verified by experimental results, density functional theory (DFT) calculations and <i>in situ</i> Raman. Benefitting from the dual roles of Bi, Bi-CoS₂ exhibits a highest NH₃ Faraday Faradaic efficiency (FE) of 87.18%, an ammonia yield rate of 944.64 μg h^-1 cm^-1 and long-term stability at -0.2 V <i>versus</i> the reversible hydrogen electrode (RHE). Furthermore, an assembled Zn-NO₃^- battery can reach a maximum power density of 16.3 mW cm^-2 and high FE_NH₃ of 95.76%, providing a high-efficiency multifunctional system for nitrate to ammonia and energy conversion.