Aluminium-doped strontium titanate (Al:SrTiO3) was selected as a UV-active PC material due to its high activity toward overall water splitting, simple synthesis, and low cost. The Al:SrTiO3 powder was synthesized following a previously reported flux method (see Methods section). The absorption edge of ~380 nm corresponds to a bandgap energy of 3.2 eV (Fig. ). Fig. shows the scanning electron microscopy (SEM) image of Al:SrTiO3. Powder X-ray diffraction (PXRD) pattern confirms the crystal structure of Al:SrTiO 3 (Supplementary Fig. ). The RhCrO x hydrogen evolution co-catalyst was loaded onto Al:SrTiO3 (RhCrOx-Al:SrTiO3) by impregnation method. The role of the Cr component is to prevent the water-forming backward-reaction of O2 and H2 by blocking O2 from reaching the embedded Rh species. Transmission electron microscopy energy-dispersive X-ray elemental mapping (TEM-EDX) and inductively coupled plasma-optical emission spectrometry (ICP-OES) analysis confirmed the conformal deposition of the RhCrOx on Al:SrTiO3 (Fig. , Supplementary Fig. , Supplementary Table ).