Solid‐State or Flux‐Assisted Doping of Hydrogen‐Evolving Y 2 Ti 2 O 5 S 2 Photocatalyst With Lower‐Valence Cations

The doping of Y 2 Ti 2 O 5 S 2 (YTOS) photocatalyst particles with lower‐valence Al 3+ or Mg 2+ cations at Ti 4+ sites was investigated using either solid‐state reaction (SSR) or flux‐mediated crystal growth techniques. Adding Al 2 O 3 or MgO as a dopant source to the precursor mixture slightly decreased the size of the YTOS particles obtained by the SSR method. At relatively low doping levels, Al 3+ cations were incorporated into YTOS via the SSR process. However, overly high Al 3+ additions caused particulate Al 2 O 3 to deposit on the YTOS surface. Mg 2+ cations were only minimally incorporated into the photocatalyst crystals when using the SSR process, resulting in the formation of a separate MgTiO x impurity. The flux method drastically altered the size and morphology of the resulting crystalline photocatalyst particles. Interestingly, either Al 3+ or Mg 2+ cations could be incorporated into the photocatalyst crystals through this method without generating impurities, meaning that the flux technique promoted doping. The incorporation of Al 3+ cations via either the SSR or flux processes improved the photocatalytic activity of YTOS during the hydrogen evolution half‐reaction compared with the undoped material. This effect resulted in a maximum hydrogen evolution rate of 113 μmol h −1 under visible light irradiation.