Rapid in situ bulk transformation of NiFe particle for highly efficient oxygen evolution in anion exchange membrane water electrolyzers

Abstract

The limited surface reconstruction of NiFe alloy-based catalysts in an anion exchange membrane water electrolysis (AEMWE) restricts the utilization of active sites in the MEA (membrane electrode assembly), which hinders further improve in mass activity and AEMWE performance. Additionally, during MEA preparation using highly active powder-based catalysts, challenges such as contamination and coverage of the active sites may arise, impacting performance. This work presents an in situ anodic oxidation method to selectively leach Mo ions from pre-designed NiFe alloy particles, achieving bulk transformation with the formation of cation vacancy defects. Results demonstrate that the leaching of Mo ions facilitates the bulk transformation of NiFe to NiFeO_xH_y with optimized electronic state, while Mo cation vacancies accelerate the deprotonation of hydroxyl (*OH) species, significantly lowering the free energy barrier required for *OOH formation. The resulting VMo-NiFe catalyst achieves an overpotential of 222 mV during rotating disk electrode (RDE) testing. After the rapid in situ activation, AEMWE equipped with a VMo-NiFe catalyst layer delivers 1.0 A cm⁻² at 1.71 V, exhibiting high stability in galvanostatic and fluctuation tests. The in situ bulk transformation method developed in this work effectively enhances the MEA performance and reduces the risk of activity loss during MEA preparation.