Tuning Intermediate Adsorption and Interfacial Water Networks via Lattice Strain of NiFe Alloys Boosts Low-Concentration Nitrate Electroreduction.

Abstract

The electrochemical nitrate-to-ammonia reduction (NO₃ ^-RR) in low-concentration neutral media is often hindered by sluggish mass transfer and competitive hydrogen evolution reaction (HER). Herein, we propose a strategy to introduce lattice strain into a Ni catalyst through the co-evaporation of a small proportion of Fe heteroatoms. According to in situ spectroscopy and theoretical calculations, the strain effect can optimize the d-band center of the Ni active sites, thereby modulating the adsorption strength of key intermediates (^*NO₃ ^-, ^*NO₂, ^*NO) and enhancing the intrinsic activity for NO₃ ^-RR. Furthermore, the strained surface can reorganize the interfacial hydrogen-bond network and modulate the proportion of free water, thereby balancing the supply of active hydrogen (^*H) with the suppression of HER. Consequently, NiFe-T1.4 achieves remarkable NH₃ Faradaic efficiencies (FE) up to 95.5% and yield rates up to 8.57 mg h^-1 cm^-2 in neutral low-concentration (5-50 mm) nitrate solutions. Furthermore, NiFe-T1.4 can also be employed as a cathode in a Zn-NO₃ ^- battery, delivering a high open-circuit voltage of 1.53 V and a peak power density of 8.10 mW cm^-2. This work presents a feasible approach to engineering high-performance catalysts for nitrate-to-ammonia conversion by combining lattice strain and interfacial water management.