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 membrane electrode assembly (MEA), hindering further improvements 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 and forming cation vacancy defects. Results demonstrated that the leaching of Mo ions facilitated the bulk transformation of NiFe to NiFeO_xH_y with an optimized electronic state, while Mo cation vacancies accelerated the deprotonation of hydroxyl (*OH) species, significantly lowering the free energy barrier required for *OOH formation. The resulting V_Mo-NiFe catalyst achieved an overpotential of 222 mV during rotating disk electrode (RDE) testing. After rapid in situ activation, the AEMWE equipped with a V_Mo-NiFe catalyst layer delivered 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 MEA performance and reduces the risk of activity loss during MEA preparation.