Interactions of hydrogen with the interface formed between ZrO2 and zirconium suboxide (ZrOx, x < 2) were studied on a 10 Å zirconium oxide film prepared on gold foil for X-ray photoelectron spectroscopy (XPS) analysis. This film was subject to a set of sequential treatments. Reaction with H2 gas at 2 mbar pressure and room temperature indicates that the ZrO2ZrOx interface appeared to undergo a redox-type reaction and convert to a new ZrO2ZrOy (x