Dynamic dissolution and re-adsorption of molybdate ion in iron incorporated nickel-molybdenum oxyhydroxide for promoting oxygen evolution reaction

Transition metal-based pre-catalysts undergo drastic reconstruction to form the active catalysts during the alkaline oxygen evolution reaction (OER). However, the effect of escaped inactive ion from pre-catalysts themselves is usually ignored during reconstruction processes. Here, we investigate the effect of inactive MoO42- escaped from a pre-catalyst of Fe incorporated nickel-molybdenum oxyhydroxide (NiMo-Fe) on OER performance. The results of in-situ Raman and X-ray photoelectron spectroscopy reveal that MoO42- can be easily dissolved into KOH electrolyte and re-adsorbed on surface of catalyst during OER processes, which delivers a promoting effect on OER performance. The dissolution of MoO42- is beneficial for increasing the reconstruction degree of NiMo-Fe to form the active phase of NiFeOOH. Theoretical calculations demonstrate that the re-adsorbed MoO42- is favorable for the adsorption of the OOH* intermediate, thus boosts the OER activity. As expected, the NiMo-Fe shows a superior electrocatalytic performance for OER, outperforming the pre-catalyst without Mo species. This finding enriches the knowledge of inactive-ion effect on alkaline OER performance and offers a path for developing efficient electrocatalysts.