Core/shell p-BiOI/n-β-Bi2O3 heterojunction array with significantly enhanced photoelectrochemical water splitting efficiency

Core/shell p-BiOI/n-β-Bi2O3 heterojunction arrays were successfully fabricated with a simple solvothermal method followed by calcination. The p-n junction electrode was characterized with X-ray diffraction spectroscopy, field emission scanning electron microscope, high resolution transmission electron microscope, X-ray photoelectron spectroscopy, UV–visible diffuse reflectance spectra, and photocurrent responses. The photoelectrochemical water splitting efficiency of the plain BiOI array was significantly improved through in-situ formation of the β-Bi2O3 shell via a simple calcination treatment to form the core/shell p-BiOI/n-β-Bi2O3 heterojunction array. The success in boosting the efficiency was attributed to the much enhanced charge separation facilitated by the internal electric field established by the p-n junction, formation of the type-II band structure, and the excellent interfacial contact between the BiOI and β-Bi2O3 domains enabling smooth charge transport across the interface.