Modulation of Surface Bonding Topology: Oxygen Bridges on OH-Terminated InP (001)

An understanding and control of complex physiochemical processes at the photoelectrode/electrolyte interface in photoelectrochemical cells (PECs) are essential for developing advanced solar-driven water-splitting technology. Here, we integrate ambient pressure X-ray photoelectron spectroscopy (APXPS) and high-level first-principles calculations to elucidate the evolution of the H₂O/InP (001) interfacial chemistry under in situ and ambient conditions. In addition to molecular H₂O, OH and H are the only two species found on InP (001) at room temperature. Under elevated temperatures, although the formation of In-O-P is thermodynamically more favorable over In-O-In, the latter can be preferentially generated in a kinetically driven and nonequilibrated environment such as ultrahigh vacuum (UHV); however, when InP is exposed to H₂O at both elevated pressures and temperatures, its surface chemistry becomes thermodynamically driven and only In-O-P (or PO_x) oxygen bridges form. Our simulations suggest that In-O-In, rather than In-O-P, constitutes a charge carrier (hole) trap that causes photocorrosion in PEC devices. Therefore, understanding and modulating the chemical nature of oxygen bridges at the H₂O/InP (001) interface will shed light on the fabrication of InP-based photoelectrodes with simultaneously enhanced stability and efficiency.