Magnetic field enhancement of the FeCoSe2 photoanode for the oxygen evolution reaction by adjusting the hole density to reduce competitive adsorption between Fe and Co in a photoelectrochemical water-splitting system

Abstract

An efficient photochemical reaction is crucial to solar-to-chemical energy conversion though water splitting to produce hydrogen. Herein, we report FeCoSe₂, a ferromagnetic material with tunable spin states, as a photoanode in a photoelectrocatalytic water splitting system under an applied magnetic field. Owing to the spin polarization of the electrons, FeCoSe₂ acquires a more reasonable d-band center. The introduction of a magnetic field can increase the material polarization potential, decrease the charge transfer resistance, and reduce the recombination of the photogenerated electron–hole. Hence, the bulk electron separation efficiency and the surface electron injection efficiency are increased, which accelerate the charge transfer to the surface of the material for OER. DFT calculations, operando Raman and XPS verified that the hole density at the Fe position decreases while it increases at the Co position, which leads to the formation of trilinear oxygen at the Co-site to improve the OER performance. Moreover, the Gibbs free energy for the OER process is reduced due to spin-polarization. The catalysts show a maximum photocurrent density of 3.98 mA cm⁻² at 1.23 V vs. RHE with η_sep and η_inj of 55.40% and 43.22%, respectively, under the magnetic field.