Dependence of activity and stability of germanium nitride powder for photocatalytic overall water splitting on structural properties

Germanium nitride (Ge3N4) powder prepared by thermal ammonolysis of GeO2 is examined as a photocatalyst for overall water splitting. Nitridation of GeO2 under a flow of NH3 at temperatures higher than 1123 K for 10 h results in production of either a single phase of beta-Ge3N4 or a mixture of elemental Ge, alpha-Ge3N4, and beta-Ge3N4, depending on the nitridation conditions. beta-Ge3N4 exhibits activity for the stoichiometric decomposition of pure water into H-2 and O-2 under ultraviolet (UV) irradiation (lambda > 200 nm) when loaded with nanoparticulate RuO2 as a cocatalyst. Improving the crystallinity of the beta-Ge3N4 catalyst results in greater activity for overall water splitting and markedly reduced N-2 release due to self-decomposition by photogenerated holes.