Thin films composed of Zr-doped In2O3 grains rich in fracture surfaces and cracks for photoelectrochemical water oxidation

Abstract

Zr-doped In₂O₃ thin films are prepared on FTO substrates by a two-step method: firstly, Zr-doped In(OH)₃ thin films are hydrothermally deposited, and then converted to Zr-doped In₂O₃ films by heat treatment. It is found that during the phase transition from Zr-doped In(OH)₃ to Zr-doped In₂O₃, the cuboid-like crystal grains will fragment, resulting in a large number of new surfaces and cracks. Zr doping can introduce shallow impurity levels in the band gap of In₂O₃, which will enhance the absorption of incident light. The substitution of trivalent In³⁺ ions by tetravalent Zr⁴⁺ ions provides additional donors for In₂O₃, which reduces the charge transfer resistance of the photoelectrochemical water oxidation and thus improves the charge transfer kinetics. These factors synergistically improve the photoelectrochemical water oxidation performance of Zr-doped In₂O₃. For example, at a potential of 1.5 V versus reversible hydrogen electrode, the photocurrent density of the Zr-doped In₂O₃ electrode during photoelectrochemical water splitting can be as high as about 3.5 times that of the undoped In₂O₃. Furthermore, Zr doping will also cause changes in the nucleation of some In(OH)₃ grains, resulting in the formation of a small number of rod-bundle-shaped grains.