To address the ongoing concerns about the global energy supply, scientists are trying to develop sustainable and renewable energy platforms. This includes the photocatalytic generation of hydrogen gas for use as a renewable energy source. In this process, solar light is applied to photochemically split water to generate hydrogen. Titania is commonly used as a semiconductor in such photoelectrochemical processes as the photoanode but the material still requires improvements for the electron transfer and kinetic profiles of optimal H₂ generation.

Patrick Schmuki, University of Erlangen-Nuremberg, Germany, and King Abdulaziz University, Jeddah, Saudi Arabia, and colleagues have investigated three approaches to titania “blackening” and the resulting influence on noble-metal-free H₂ generation. These three treatments are i) the previously reported high-pressure hydrogenation of TiO₂ [1], ii) a high temperature reduction in argon, and iii) an electrochemical (cathodic) reduction. The “black” TiO₂ nanotubes produced were tested for their electrochemical behavior and electrical conductivity.

Simply reducing TiO₂ leads to beneficial properties for use in dye-sensitized solar cells, lithium batteries, and photoelectrochemical processes. An interesting synergistic effect of cathodic reduction and high pressure hydrogenation was observed, providing a photocatalytic efficiency for H₂ generation that is three times higher than that of either method individually. The researchers believe this work could help to improve the “blackening” of titania nanotubes for photocatalytic applications.

• Noble-Metal-Free Photocatalytic H₂ Generation: Active and Inactive ‘Black’ TiO₂ Nanotubes and Synergistic Effects,
  Ning Liu, Christopher Schneider, Detlef Freitag, Eva M. Zolnhofer, Karsten Meyer, Patrik Schmuki,
  Chem. Eur. J. 2016.
  DOI: 10.1002/chem.201602714

[1] C. Schneider, D. Freitag, U. Venkatesan, V. R. Marthala, M. Hartmann, B. Winter, E. Spiecker, A. Osvet, E. M. Zolnhofer, K. Meyer, T. Nakajima, X. Zhou, P. Schmuki, Angew. Chem. Int. Ed. 2014, 53(51), 14201–14205. DOI: 10.1002/anie.201408493