Developing energy-efficient nitrate-to-ammonia flow cells with bifunctional NiFeW-oxide thin-film electrodes made by magnetron sputtering technique

Abstract

Herein, we develop a sputtered NiFeW-oxide thin-film bifunctional electrocatalyst with the incorporated oxygen vacancies and multivalent cations of Ni2+/3+, Fe2+/3+, and W6+ to enhance the economic viability of electrocatalytic nitrate reduction for commercial applications. Our NFW-0.5 achieves a notable 54.6 mg/h.cm2 ammonia yield rate at a modest applied potential of −0.2 V vs. RHE, coupled with an outstanding Faradaic efficiency of 93.7%. Furthermore, our NFW-0.5(+)‖NFW-0.5(−) flow-cell electrolyzer with a larger electrode of 2×2 cm2 reveals an impressive ammonia productivity of 143.5 mg/h.cm2 at a cell voltage of 2.0 V, accompanied by a superior Faradaic efficiency of 96.1%, an energy efficiency of 26%, and a low energy consumption of 26.3 kWh/kg.NH3. An oxygen vacancy-based NO3-pinned mechanism is proposed to explain our excellent nitrate reduction. Our work introduces a new paradigm to design efficient and bifunctional electrocatalysts for potential industrial-scale ammonia production.