Unlocking the Oxygen Evolving Activity of Molybdenum Nickel Bifunctional Electrocatalyst for Efficient Water Splitting

Abstract

Earth-abundant transition metal-based catalysts with exceptional bifunctionality for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are greatly desired. Alloyed catalysts, such as molybdenum-nickel (MoNi), are known to demonstrate enhanced HER activity, yet suffer from low OER performance. To realize improved functionality, elemental doping can be an effective approach, giving rise to synergistic interactions between incorporated metal species, optimizing surface adsorption of target intermediates, and promoting reaction. Herein, the enhanced OER performance of the MoNi catalyst while simultaneously boosting HER activity via incorporating a small amount of iron and chromium into MoNi (Mo-Ni(FeCr)) is demonstrated. For an optimized Mo-Ni(FeCr) catalyst, in 1.0 m potassium hydroxide electrolyte, an overpotential of only 11 and 179 mV for HER and OER, respectively, are required to afford a current density of 10 mA cm⁻². For the overall water splitting, a current density of 20 mA cm⁻² is reached at 1.489 V. The DFT calculations demonstrated that the inclusion of Fe and Cr in a molybdenum-nickel catalyst reduced the limiting potentials for both OER and HER, unlocking efficient bifunctionality activity for water splitting. These findings signify the improved electrocatalytic performance of, amongst the most active bifunctional electrocatalysts.