The development of sustainable materials capable of capturing and transforming solar energy into green chemical fuels has become of great interest in the last decade, following the increased risk of global warming. Hydrogen is an environmentally friendly fuel, which can be obtained by photoelectrochemical water splitting, where a water molecule is split into H2 and O2 in presence of a semiconductor and sunlight. Recently developed materials are not practical for mass industrial use due to their low efficiencies, thus the combination of different compounds is an interesting point towards the design of better performant systems.
Titanium dioxide (TiO2) is a stable, non-toxic and abundant semiconductor, which has a suitable band gap to conduct the water splitting reaction.[1] However, improvements are still needed in terms of efficiencies, such as enhancing light absorption into the visible range and increasing the rate of redox reactions at the interface. In this work we present the synthesis of mesoporous TiO2 thin films prepared via a sol-gel approach. These films can be easily modified either with photosensitizer or cocatalysts, which makes them an ideal support for the formation of nanocomposites.
We studied the effect of the crystallinity in the photoelectrochemical efficiency. We then modified the films with different cobalt catalysts (CoPi, Co-PBA) [2,3] and we studied the efficiency of the composite photoelectrodes. The materials were characterized by means of photoelectrochemical techniques, scanning electron microscopy, X-ray diffraction and reflectometry, and UV-visible spectroscopy. The films have high surface areas, which improves the photoelectrochemical efficiency when compared to non-porous films. Also, crystalline (anatase) films show much higher photocurrents than amorphous ones. In terms of the catalyst, we have seen that only Co-PBA gives an increase in photocurrent, while the presence of CoPi is only beneficial at high overpotentials.

[1]: Ahmad, H., et al. Renewable and Sustainable Energy Reviews, 2015, 43, 599-610, 10.1016/j.rser.2014.10.101
[2]: Kanan M., Nocera D., Science,2008, 321, 1072-1075, 10.1126/science.1162018
[3]: Pintado S., Goberna-Ferrón S., Escudero-Adán E. C., Galán-Mascarós J.R., Journal of the American Chemical Society, 2013, 135, 13270-13272, 10.1021/ja406242y