Activating Lattice Oxygen in Spinel Oxides via Engineering Octahedral Sites for Oxygen Evolution

Spinel oxides, representing an emerging class of highly active catalysts for oxygen evolution (OER), suffer from weak covalency of metal d and oxygen p orbitals from their typical crystal structure, which generally proceeds the OER with an adsorbate evolution mechanism (AEM) pathway. For activating the lattice oxygen in spinel oxides to bypass the scaling relationship limitation of AEM, we herein grow the sulfate salts on the octahedral sites of spinel NiFe2O4 to introduce the Ni4+ cations and Ni vacancies in octahedral sites, which exhibit remarkable OER performance with an overpotential of 293 mV at 500 mA cm–2. Experiments and theoretical calculations reveal that the formation Ni4+ cations and Ni vacancies jointly enhance the metal–oxygen hybridization and strengthen the metal–oxygen bond covalency in both NiFe2O4 and NiFeOOH phases, activating the lattice oxygen and successfully triggering the lattice oxygen mechanism (LOM) pathway on spinel oxides.