Oxygen-Deficient Zirconia (ZrO(2−x)): A New Material for Solar Light Absorption

Here, we present oxygen-deficient black ZrO(2−x) as a new material for sunlight absorption with a low band gap around ~1.5 eV, via a controlled magnesiothermic reduction in 5% H(2)/Ar from white ZrO(2), a wide bandgap(~5 eV) semiconductor, usually not considered for solar light absorption. It shows for the first time a dramatic increase in solar light absorbance and significant activity for solar light-induced H(2) production from methanol-water with excellent stability up to 30 days while white ZrO(2) fails. Generation of large amounts of oxygen vacancies or surface defects clearly visualized by the HR-TEM and HR-SEM images is the main reason for the drastic alteration of the optical properties through the formation of new energy states near valence band and conduction band towards Fermi level in black ZrO(2−x) as indicated by XPS and DFT calculations of black ZrO(2−x). Current reduction method using Mg and H(2) is mild, but highly efficient to produce solar light-assisted photocatalytically active black ZrO(2−x).