Template-assisted sol-gel route offers attractive possibilities of the controlled production of microporous and mesoporous oxide films. We recently prepared mesoporous tungsten oxide films through the sol-gel method involving ultrasonic stirring step as the main modification of the previously described procedure[1]. Investigation of solar-light-driven photo-electrolysis cell employing such a WO3 photoanode showed that the amount of the delivered steady-state photocurrent was improved by ca. 20%. This improvement is related to changes in the morphology of the nanostructured films shown in Fig. 1, consisting in a marked decrease in the particle size and, apparently, also in the film porosity.
Inspection of photocurrent-voltage curves, recorded under simulated AM 1.5 solar illumination, showed that stable photocurrents of the order of 3 mA/cm2 are attained in a 0.5 M NaCl(Fig.1). This solution, which resembles the sea water, does not require any preliminary acidification as the formation of chlorine sets locally the solution pH to ca. 2. It should be noted that, although in 0.5 M NaCl ca. 20% of chlorine is formed at the WO3 photoanode, oxygen remains the main photo-electrolysis product. Prolonged electrolysis experiments, demonstrated perfect stability of the WO3 photoanodes under conditions of mixed chlorine/oxygen evolution which allows anticipate its suitability for the sea-water photo-electrolysis [2]. The sea water is an abundant, non-toxic electrolyte suitable for massive hydrogen/ production via photo-electrolysis.

References:

1. C. Santato, M. Odziemkowski, M. Ulmann, J. Augustynski, J. Am. Chem. Soc., vol.123(2001), 10369 .
2. J. Augustynski, R. Solarska, H. Hagemann, C. Santato, Proc. SPIE, vol.6340(2006), 63400J/1.