Anionic Oxidation Activity/Stability Regulated by Transition Metals in Multimetallic (Oxy)hydroxides for Alkaline Water Oxidation

Transition metal (oxy)hydroxides are currently the benchmark materials for the oxygen evolution reaction (OER) in alkaline media. Superior activity can be achieved due to the anionic redox mechanism of transition metal (oxy)hydroxides, which enables the OER to proceed with the lattice oxygen pathway beyond the conventional adsorbate evolution mechanism. Although it is widely accepted that lattice oxygen oxidation stems from the high energy nonbonding oxygen states, which is mainly determined by the π-type hybridization between metal and oxygen orbitals, how to regulate the lattice oxygen oxidation mechanism remains a challenge. Here, the lattice oxygen oxidation in the benchmark NiFe (oxy)hydroxides is investigated by introducing 3d transition-metal dopants. We discover that the hybridization between metal t2g orbitals and oxygen p orbitals is essential for the energy level of oxygen states by density functional theory and is regulated by the number and energy level of transition metal d electrons. We propose that constratedly strong or weak hybridization between transition metal t2g and oxygen p orbitals is key to activating lattice oxygen oxidation. Supported by electrochemical tests and spectroscopic characterizations, the regulation of the anionic oxidation in transition metal (oxy)hydroxides will enable the control of cumulative lattice oxygen reactions for developing efficient and robust oxygen evolution electrocatalysts.