Electronically Coupled Uranium and Iron Oxide Heterojunctions as Efficient Water Oxidation Catalysts

Abstract

The most critical challenge faced in realizing a high efficiency photoelectrochemical water splitting process is the lack of suitable photoanodes enabling the transfer of four electrons involved in the complex oxygen evolution reaction (OER). Uranium oxides are efficient catalysts due to their wide range optical absorption (E-g approximate to 1.8-3.2 eV), high photoconductivity, and multiple valence switching among uranium centers that improves the charge propagation kinetics. Herein, thin films of depleted uranium oxide (U3O8) are demonstrated grown via chemical vapor deposition effectively accelerate the OER in conjunction with hematite (alpha-Fe2O3) overlayers through a built-in potential at the interface. Density functional theory simulations demonstrate that the multivalence of U and Fe ions induce the adjustment of the band alignment subject to the concentration of interfacial Fe ions. In general, the equilibrium state depicts a type II band edge as the favored alignment, which improves charge-transfer processes as observed in transient and X-ray absorption (TAS and XAS) spectroscopy. The enhanced water splitting photocurrent density of the heterostructures (J = 2.42 mA cm(-2)) demonstrates the unexplored potential of uranium oxide in artificial photosynthesis.