Activation of lattice oxygen in a medium-entropy oxide to facilitate an enhanced oxygen evolution reaction

Aiming to overcome the low efficiency of the oxygen evolution reaction (OER) at photoanodes, this study developed a novel medium-entropy oxide catalyst for photoelectrochemical water splitting. By <i>in situ</i> growing medium-entropy oxides on a BiVO₄ substrate to optimize the electronic structure of the catalyst, the prepared CoFeMnMoO_<i>x</i>/BiVO₄ composite photoanode exhibits excellent catalytic performance under alkaline conditions, including a remarkable photocurrent density of 5.58 mA cm^-2 at 1.23 V <i>vs.</i> RHE, low overpotential and good stability. Additionally, the results from photoelectrochemical catalytic water splitting performance tests and DFT calculations reveal that Fe, Co and Mo sites act as active centers for the OER, the introduction of Mn increases active sites and promotes electron transfer, and the multimetallic synergistic effect enhances the d-p orbital hybridization of Mo-O bonds. After the water oxidation reaction, the lattice oxygen content in CoFeMnMoO_<i>x</i>/BiVO₄ decreases while the oxygen vacancy content increases, indicating that the lattice oxygen-mediated mechanism dominates the OER reaction pathway. This study not only improves the efficiency of PEC water splitting for hydrogen production but also demonstrates the broad application prospects of medium-entropy oxides in the field of photoelectrochemical water splitting.