Suppression of the water splitting back reaction on GaN:ZnO photocatalysts loaded with core/shell cocatalysts, investigated using a [mu]-reactor

Graphical abstract Water splitting back reaction (stoichiometric H2 oxidation). The water formation rate for Cr2 O3 /Rh is strongly suppressed and negligible compared to the one for Rh. Display Omitted Highlights Gas-phase photocatalytic water splitting using GaN:ZnO loaded with cocatalysts. H2 /O2 back reaction on photocatalysts for water splitting. Direct evidence of suppression of the back reaction by Cr2 O3 shell on Rh and Pt. Suppression of the back reaction enhances the net photocatalytic activity. Stronger suppression of the back reaction with Cr2 O3 /Rh than with Cr2 O3 /Pt. Using silicon-based μ-reactors, we have studied the photocatalytic water splitting reaction and the catalytic back reaction on the same catalysts. GaN:ZnO without cocatalyst and loaded with Rh, Pt, Cr2 O3 /Rh, Cr2 O3 /Pt, and Rh-Cr mixed oxide has been tested for gas-phase photocatalytic water splitting. The results confirm the high activity observed in liquid-phase experiments with Cr2 O3 /Rh and Rh-Cr mixed oxide as cocatalysts. To investigate the reason of this enhanced activity, the back reaction was studied by reacting stoichiometric H2 /O2 and monitoring the water molecules produced. The comparison of the two experiments shows that the suppression of the back reaction with the core/shell cocatalysts and the Rh-Cr mixed oxide corresponds to an increase in the net photocatalytic water splitting activity. The fact that the back reaction is not completely suppressed with Cr2 O3 /Pt compared to Cr2 O3 /Rh may be the cause of the higher net activity of the Cr2 O3 /Rh. [PUBLICATION ABSTRACT]