A Rapid and Universal Construction of 2D Amorphous Metal Boride Nanosheets toward Electrocatalytic Nitrate-to-Ammonia Conversion and Zinc–Nitrate Batteries

Abstract Two-dimensional (2D) metal borides have attracted increasing attention in electrocatalysis owing to their high surface areas and tunable electronic structures. However, their controllable synthesis remains challenging due to rapid nucleation and isotropic growth commonly associated with borohydride reduction. Herein, a series of 2D amorphous metal boride nanosheets (MBX, M = Co, Cu, Fe, and Mn) were synthesized via a facile chemical reduction route. The results indicate that NO3– directs nanosheet formation by modulating the local reaction environment, accumulating at the metal boride interface, and altering BH4– consumption to suppress excessive nucleation. Among the as-prepared MBX materials, CoBX exhibits optimal performance in electrocatalytic nitrate reduction reaction, achieving an NH3 yield rate of 4.34 mol gcat–1 h–1, a Faradaic efficiency of 91.9% at –0.6 V vs RHE. In situ characterizations reveal that CoBX facilitates a deoxygenation and stepwise hydrogenation pathway, underpinned by its large electrochemically active surface area and effective stabilization of key reaction intermediates. Furthermore, a Zinc–nitrate battery assembled with CoBX cathode enables simultaneous electricity generation, nitrate removal, and NH3 production, delivering an open-circuit voltage of 1.42 V, a maximum power density of 14.05 mW cm–2, and good long-term stability. This work provides a promising strategy for morphology-controlled synthesis of 2D metal borides, as well as for nitrate wastewater valorization and self-powered green ammonia production.