Fe₂PO₅-Encapsulated Reverse Energetic ZnO/Fe₂O₃ Heterojunction Nanowire for Enhanced Photoelectrochemical Oxidation of Water

Zinc oxide is regarded as a promising candidate for application in photoelectrochemical water oxidation due to its higher electron mobility. However, its instability under alkaline conditions limits its application in a practical setting. Herein, we demonstrate an easily achieved wet-chemical route to chemically stabilize ZnO nanowires (NWs) by protecting them with a thin layer Fe₂O₃ shell. This shell, in which the thickness can be tuned by varying reaction times, forms an intact interface with ZnO NWs, thus protecting ZnO from corrosion in a basic solution. The reverse energetic heterojunction nanowires are subsequently activated by introducing an amorphous iron phosphate, which substantially suppressed surface recombination as a passivation layer and improved photoelectrochemical performance as a potential catalyst. Compared with pure ZnO NWs (0.4 mA cm⁻²), a maximal photocurrent of 1.0 mA cm⁻² is achieved with ZnO/Fe₂O₃ core–shell NWs and 2.3 mA cm⁻² was achieved for the PH₃-treated NWs at 1.23 V versus RHE. The PH₃ low-temperature treatment creates a dual function, passivation and catalyst layer (Fe₂PO₅), examined by X-ray photoelectron spectroscopy, TEM, photoelectrochemical characterization, and impedance measurements. Such a nano-composition design offers great promise to improve the overall performance of the photoanode material.