Abstract

A transparently hydrated manganese phosphate (“Mn–Pi”) catalyst is coated onto a Ti-doped hematite (Ti:Fe2O3) photoanode by the photo-assisted electrochemical deposition. Under a visible light illumination of 100 mW cm–2, the photocurrent density of Ti:Fe2O3/Mn–Pi reaches 0.28 mA cm–2 at 1.2 VRHE, which is around two times higher than that obtained with the pristine Ti:Fe2O3 electrode in a neutral electrolyte, and the “onset” potential reduces by 100 mV. The passivating role of the Mn–Pi catalyst is revealed experimentally. The surface states of hematite are significantly passivated after Mn–Pi deposition, which relieves the degree of Fermi level pinning of hematite and enhances the surface band bending of hematite. Therefore, the photovoltage and the charge separation are improved. Moreover, due to the valence change of the Mn element in Mn–Pi, the charge transfer through the Mn–Pi layer is favorable, which has a low charge transfer resistance for photogenerated holes. The suitability of this transparently passivating catalyst for concentrating light is also identified. This work demonstrates that Mn–Pi can be applied for photoelectrochemical water splitting as a transparently passivating catalyst.

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