Insights into Interfacial Changes and Photoelectrochemical Stability of InxGa1–xN (0001) Photoanode Surfaces in Liquid Environments

The long-term stability of InGaN photoanodes in liquid environments is an essential requirement for their use in photoelectrochemistry. In this paper, we investigate the relationships between the compositional changes at the surface of n-type InxGa1–xN (x ∼ 0.10) and its photoelectrochemical stability in phosphate buffer solutions with pH 7.4 and 11.3. Surface analyses reveal that InGaN undergoes oxidation under photoelectrochemical operation conditions (i.e., under solar light illumination and constant bias of 0.5 VRHE), forming a thin amorphous oxide layer having a pH-dependent chemical composition. We found that the formed oxide is mainly composed of Ga–O bonds at pH 7.4, whereas at pH 11.3 the In–O bonds are dominant. The photoelectrical properties of InGaN photoanodes are intimately related to the chemical composition of their surface oxides. For instance, after the formation of the oxide layer (mainly Ga–O bonds) at pH 7.4, no photocurrent flow was observed, whereas the oxide layer (mainly In–O bond...