Activation of Water‐Splitting Photocatalysts by Loading with Ultrafine Rh–Cr Mixed‐Oxide Cocatalyst Nanoparticles

The activity of many water‐splitting photocatalysts could be improved by the use of Rh(III)–Cr(III) mixed oxide (Rh(2−x)Cr(x)O(3)) particles as cocatalysts. Although further improvement of water‐splitting activity could be achieved if the size of the Rh(2−x)Cr(x)O(3) particles was decreased further, it is difficult to load ultrafine (<2 nm) Rh(2−x)Cr(x)O(3) particles onto a photocatalyst by using conventional loading methods. In this study, a new loading method was successfully established and was used to load Rh(2−x)Cr(x)O(3) particles with a size of approximately 1.3 nm and a narrow size distribution onto a BaLa(4)Ti(4)O(15) photocatalyst. The obtained photocatalyst exhibited an apparent quantum yield of 16 %, which is the highest achieved for BaLa(4)Ti(4)O(15) to date. Thus, the developed loading technique of Rh(2−x)Cr(x)O(3) particles is extremely effective at improving the activity of the water‐splitting photocatalyst BaLa(4)Ti(4)O(15). This method is expected to be extended to other advanced water‐splitting photocatalysts to achieve higher quantum yields.