X-ray Photoelectron Spectroscopy and Resonant X-ray Spectroscopy Investigations of Interactions between Thin Metal Catalyst Films and Amorphous Titanium Dioxide Photoelectrode Protection Layers

The use of electrochemistry, X-ray photoelectron spectroscopy, and resonant X-ray spectroscopy has unlocked the paradox of interfacial hole conduction through amorphous TiO2 (a-TiO2) to deposited Ni, Ir, and Au metal catalysts. Although electrocatalysts for the oxygen-evolution reaction derived from metallic Ir and Ni have mutually similar overpotentials in alkaline media, Si/a-TiO2/Ir interfaces exhibit higher overpotentials than Si/a-TiO2/Ni interfaces. The data allow formulation of full band energy diagrams for n-Si/a-TiO2/metal interfaces for M = Ni, Ir, or Au. Although both Ni and Ir produce band bending in a-TiO2 favoring hole conduction, only Ni creates multiple states within the a-TiO2 band gap at the a-TiO2/Ni interface, which produces a quasi-metallic interface at the a-TiO2/Ni junction. Au, however, produces a flat-band interface that limits hole conduction without any new band gap states.

Automated summary

The use of electrochemistry, X-ray photoelectron spectroscopy, and resonant X-ray spectroscopy has revealed that while iridium (Ir) and nickel (Ni) electrocatalysts for the oxygen-evolution reaction have similar overpotentials in alkaline media, the interfaces with a-TiO2 exhibit different behaviors. Nickel (Ni) and iridium (Ir) both cause band bending in a-TiO2 for hole conduction, while gold (Au) produces a flat-band interface that limits hole conduction without introducing new band gap states.