Photocatalytic Water Splitting Using Modified GaN:ZnO Solid Solution under Visible Light: Long-Time Operation and Regeneration of Activity

Overall water splitting using GaN:ZnO solid solution photocatalyst modified with Rh2-yCryO3 nanoparticles as H-2 evolution cocatalysts under visible light (400 < lambda < 500 nm) was examined with respect to long-term durability and regeneration of photocatalytic activity. The rate of visible light water splitting remained unchanged for 3 months (2160 h), producing H-2 and O-2 continuously at a stoichiometric amount. After 6 months of operation, a 50% loss of the initial activity occurred. Regeneration treatment of deactivated catalysts was attempted by reloading the Rh2-yCryO3 cocatalyst. The degree of activity regeneration depended on the reloading amount. Up to 80% of the initial activity for H-2 evolution could be recovered under optimal treatment conditions. It was also found that deactivation of GaN:ZnO was suppressed to some extent by prior coloading of an O-2 evolution cocatalyst, which helped to suppress oxidative decomposition of GaN:ZnO by valence band holes, thereby improving the durability.