Engineering a ZnO@(NiFe)OOH Heterointerface for Enhanced Electrocatalytic Nitrate Reduction to Ammonia at Neutral pH

This study successfully fabricated a freestanding ZnO@(NiFe)OOH nano-heterostructure array electrocatalyst with high hydrophilicity for efficient electrocatalytic nitrate reduction to ammonia (NO 3 RR) in neutral media. The material integrates the large specific surface area of one-dimensional ZnO nanoarrays with the electronic modulation capability of heterogeneous interfaces, which significantly enhances nitrate adsorption and activation, promotes proton supply, and effectively suppresses the hydrogen evolution side reaction. The highly hydrophilic surface further accelerates electrolyte diffusion, nitrate ion transport, and product desorption. In a neutral electrolyte of 0.1 M PBS containing 0.15 M KNO 3 at a potential of −1.0 V (vs. RHE), the catalyst achieves an ammonia production rate of 4.86 mg·h −1 ·cm −2 with a Faradaic efficiency of 85.58%, while generating minimal byproducts, demonstrating excellent catalytic selectivity and stability. This work provides a new strategy for the structural design and performance enhancement of NO 3 RR electrocatalysts, which holds significance for advancing green ammonia synthesis and enabling efficient conversion of nitrate in water pollution control. Graphical A self-supported ZnO@(NiFe)OOH core-shell array enables efficient nitrate-to-ammonia conversion. The ZnO core accelerates NO 3 -diffusion and prevents active site coverage while enhancing conductivity and stability. The (NiFe)OOH shell facilitates intermediate conversion and suppresses hydrogen evolution by weakening H+ adsorption. Its surface hydroxyl groups promote water dissociation, ensuring a local proton supply. In neutral media, this design achieves superior performance: at −1.0 V vs RHE in 0.15 M KNO 3 , it delivers an NH3 yield of 4.86 mg h −1 cm −2 and a faradaic efficiency of 85.58%.