Anionic Oxidation\nActivity/Stability Regulated by\nTransition Metals in Multimetallic (Oxy)hydroxides for Alkaline Water\nOxidation

Transition metal (oxy)hydroxides are currently the benchmark\nmaterials\nfor the oxygen evolution reaction (OER) in alkaline media. Superior\nactivity can be achieved due to the anionic redox mechanism of transition\nmetal (oxy)hydroxides, which enables the OER to proceed with the lattice\noxygen pathway beyond the conventional adsorbate evolution mechanism.\nAlthough it is widely accepted that lattice oxygen oxidation stems\nfrom the high energy nonbonding oxygen states, which is mainly determined\nby the π-type hybridization between metal and oxygen orbitals,\nhow to regulate the lattice oxygen oxidation mechanism remains a challenge.\nHere, the lattice oxygen oxidation in the benchmark NiFe (oxy)hydroxides\nis investigated by introducing 3<i>d</i> transition-metal\ndopants. We discover that the hybridization between metal <i>t</i><sub><i>2g</i></sub> orbitals and oxygen <i>p</i> orbitals is essential for the energy level of oxygen states\nby density functional theory and is regulated by the number and energy\nlevel of transition metal <i>d</i> electrons. We propose\nthat constratedly strong or weak hybridization between transition\nmetal <i>t</i><sub><i>2g</i></sub> and oxygen <i>p</i> orbitals is key to activating lattice oxygen oxidation.\nSupported by electrochemical tests and spectroscopic characterizations,\nthe regulation of the anionic oxidation in transition metal (oxy)hydroxides\nwill enable the control of cumulative lattice oxygen reactions for\ndeveloping efficient and robust oxygen evolution electrocatalysts.