Built-in electric field Synergizes tandem catalysis boosting Co2B@MXene heterostructure for electrochemical nitrate reduction

Abstract

Electrochemical nitrate reduction reaction (NO₃RR) to ammonia (NH₃) receives widespread attention for its mild reaction conditions and environmental friendliness. However, due to the complex multi-electron reactions in NO₃RR, there is an urgent need to develop efficient electrocatalysts. Herein, Co₂B@MXene heterostructure with spontaneous built-in electric field (BIEF) was designed by combining molten salt etching with boron thermal reduction strategy. BIEF redistributed interfacial charge, accelerating electron transfer at the hetero-interface. Meanwhile, the tandem catalysis maintained the balance between nitrogenous intermediates and active hydrogen (H_ads), the B site absorbed and activated NO₃⁻, the Co site accelerated H₂O dissociation to provided abundant H_ads for the subsequent hydrogenation reaction. The Co₂B@MXene catalyst exhibited NH₃ yield rate of 7.34 mg h⁻¹ mg_cat⁻¹ and Faradaic efficiency (FE) of 92.13 % at − 0.7 V versus reversible hydrogen electrode (RHE). The Zn-NO₃⁻ battery with Co₂B@MXene showed a power density of up to 6.86 mW cm⁻² and a FE of 91.74 % for NH₃, which enabled the simultaneous elimination of nitrate pollutants, ammonia production, and energy supply. Moreover, the pathway and mechanism of NO₃RR were clarified through validation experiments and density functional theory calculation. This work provided a new inspiration for designing high-performance MXene-based tandem catalysts for NO₃RR.