Bi-Doped Co3O4 Nanosheets for Nitrate to Ammonia with Near 100% Faradaic Efficiency

Abstract

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 (*NOx) 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.