Bi-doped Co3O4 nanosheets for nitrate to ammonia with near 100% faradaic efficiency†

The electrocatalytic nitrate reduction reaction (NO₃⁻RR) represents a feasible approach for carbon-free synthesis of NH₃ at room temperature. Nevertheless, the NO₃⁻RR encounters considerable challenges attributed to the multi-proton and electron transfer processes. Herein, Bi-doped Co₃O₄ nanosheets (0.25-Bi–Co₃O₄ NS) were synthesized to overcome these challenges. The catalyst exhibited high activity and selectivity, achieving an NH₃ production rate of 2.38 mmol h⁻¹ cm⁻² and a faradaic efficiency (FE) of approximately 100%. Additionally, the catalyst maintained over 93.2% FE across a broad potential range, even in low-concentration nitrate electrolytes. The excellent performance of the catalyst originated from the dual roles of Bi. The incorporation of Bi realized the transfer of electrons from Bi to Co₃O₄, facilitating the adsorption and conversion of intermediates (*NO_x) in the NO₃⁻RR. In addition, Bi effectively suppressed the hydrogen evolution reaction (HER), thereby improving the selectivity of NO₃⁻RR. The dual roles collectively optimize the NO₃⁻RR kinetics, resulting in high NH₃ yield and FE. The 10-cycle test highlighted the excellent stability and durability of 0.25-Bi–Co₃O₄ NS. This work provides a reliable catalyst design strategy for achieving high selectivity of NH₃.