Regulating the d-Band Center of Metal–Organic Frameworks for Efficient Nitrate Reduction Reaction and Zinc-Nitrate Battery

Abstract

The electrochemical reduction of nitrate ions to valuable ammonia enables the recovery of nitrate pollutants from industrial wastewater, thereby synchronously balancing the nitrogen cycle and achieving NH₃ production. However, the currently reported electrocatalysts still suffer from the low NH₃ yield rate, NH₃ Faradaic inefficiency, and NH₃ partial current density. Herein, a strategy based on the regulation of the d-band center by Ru doping is presented to boost ammonia production. Theoretical calculations unravel that the Ru dopant in Ni metal–organic framework shifts the d-band center of the neighboring Ni sites upward, optimizing the adsorption strength of the N-intermediates, resulting in greatly enhanced nitrate reduction reaction performance. The synthesized Ru-doped Ni metal–organic framework rod array electrode delivers a NH₃ yield rate of 1.31 mmol h^–1 cm^–2 and NH₃ Faradaic efficiency of 91.5% at −0.6 V versus reversible hydrogen electrode, as well as good cycling stability. In view of the multielectron transfer in nitrate reduction and electrocatalytic activity, the Zn-NO₃^– battery is assembled by this electrode and Zn anode, which delivers a high open-circuit voltage of 1.421 V and the maximum output power density of 4.99 mW cm^–2, demonstrating potential application value.