This article reports a rapid and low-cost method to fabricate FeOOH nanofilms decorated on GaN epitaxial films to carry out photoelectrochemical (PEC) reactions. In reality, n-GaN epitaxial films grown on a sapphire substrate contain dense surface defects due to lattice mismatch. Consequently, n-GaN photoelectrodes suffer from corrosion during PEC reactions. An active photocatalyst, FeOOH nanofilm, was synthesized via a facile hydrothermal technique and decorated on n-GaN to passivate surface defects and suppress the recombination of photogenerated carriers. The deposited FeOOH nanofilm on the n-GaN surface can enhance the carrier transfer efficiency and kinetics of PEC reactions, as confirmed through the findings of electrochemical impedance spectroscopy and linear sweep voltammetry. Moreover, band bending between the GaN photoelectrode and the electrolyte can be affected by decoration of the FeOOH nanofilm, which was evidenced by the Mott–Schottky plot. As a result, the photocurrent of FeOOH-decorated GaN photoelectrodes was approximately four times higher than the bare GaN photoelectrodes. In addition to the improved photocurrent, the FeOOH-decorated GaN photoelectrodes exhibited a corrosion-free surface feature after a stability test. Overall, the FeOOH nanofilm is an excellent photoelectrocatalyst to strengthen the performance of n-GaN in conducting PEC reactions while protecting it from photocorrosion in PEC experiment.

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