Alberto Gasparotto and colleagues, Padova University, Italy, have made p-type Co₃O₄ nanostructured films for the photocatalytic production of H₂. The team applied fluoride anion doping to the semiconducting Co₃O₄ films. Anion doping is common in n-type semiconductors, but rare in p-type and has never been reported for photoassisted H₂ production.

The films were tested in water/ethanol solutions under both near-UV and solar irradiation. F-doped Co₃O₄ showed a five-fold H₂ yield increase with respect to the corresponding undoped oxide upon near-UV irradiation. The H₂ yields per gram of catalyst are among the best reported so far for semiconductor-based photocatalytic processes. The high activity was predominately attributed to replacement of surface −OH groups by F, leading to more free OH• radicals in the liquid-phase. This results in faster ethanol oxidation and concomitant enhancement of the H⁺ to H₂ reduction.

Under simulated solar light, doped Co₃O₄ showed no decrease in H₂ evolution after 20 h of irradiation. This time stability makes this material a very attractive photocatalyst.

• F-Doped Co₃O₄ Photocatalysts for Sustainable H₂ Generation from Water/Ethanol
  A. Gasparotto, D. Barreca, D. Bekermann, A. Devi, R. A. Fischer, P. Fornasiero, V. Gombac, O. I. Lebedev, C. Maccato, T. Montini, G. Van Tendeloo, E. Tondello,
  J. Am. Chem. Soc. 2011.
  DOI: 10.1021/ja210078d