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

Abstract

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.

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