Molybdate ion leaching and re-adsorption facilitate structural and electronic modulation of nickel–iron catalysts for seawater electrolysis

Abstract

Developing active and robust NiFe-based catalysts as alternatives to noble metals remains a significant challenge for low-cost hydrogen generation. Generally, the original catalysts will undergo self-reconstruction to derive into oxyhydroxides (MOOH) under the operation situation. Herein, we propose a Mo oxidative leaching strategy to promote the self-reconstruction of NiFe-based pre-catalysts. Operando Raman and time-dependent X-ray photoelectron spectra revealed that, during the OER operation, Mo dopants are oxidized to soluble molybdate ions (MoO₄²⁻) and leach into the electrolyte, facilitating the reconstruction of pre-catalysts to active MOOH sites. Then, various electrochemical measurements and density functional theory calculations demonstrated that the re-adsorbed MoO₄²⁻ ions modify the electronic environment of the Ni and Fe sites and enhance the adsorption of oxygenated intermediates, boosting the OER kinetics. The optimized catalysts achieve long-term stability of 150 h at 1000 mA cm⁻² in simulated seawater and 200 h for overall seawater splitting. This work provides a design path for OER catalysts and enriches the understanding of the role of adsorbed oxyanions.