Crystal phase determined Fe active sites on Fe2O3 (γ- and α-Fe2O3) yolk-shell microspheres and their phase dependent electrocatalytic oxygen evolution reaction

Transition metal oxide nanomaterials have been extensively applied to the field of oxygen evolution reaction (OER), but few works have been studied to demonstrate the relationship between their crystal phases and OER performance. Herein, we compare the OER performance of the two different crystal phase iron oxide (alpha-Fe2O3 and gamma-Fe2O3). The iron oxide yolk-shell microspheres were facile realized via one-step solvothermal method and the subsequent annealing treatment. An interesting phenomenon is present that alpha-Fe2O3 yolk-shell microspheres with a smaller specific surface area have better OER performance than that of gamma-Fe2O3 yolk-shell microspheres. The crystal structure and X-ray photoelectron spectroscopy (XPS) results show that alpha-Fe2O3 yolk-shell microspheres have better electrocatalytic activity, which is due to the presence of more Fe active sites (Fe3+) exposured on the surface. These Fe active sites are beneficial to enhance the adsorption of hydroxyl groups in water molecules, leading to a higher OER performance. As an application example, the Fe2O3 yolk-shell microspheres are employed as an efficient OER electrocatalyst, showing the interdependence between phase and OER behavior.