Direct splitting of water using a particulate photocatalyst would be a good way to produce clean and recyclable hydrogen on a large scale, and in the past 30 years various photocatalysts have been found that function under visible light. Here we describe an advance in the catalysis of the overall splitting of water under visible light: the new catalyst is a solid solution of gallium and zinc nitrogen oxide, (Ga(1-x)Zn(x))(N(1-x)O(x)), modified with nanoparticles of a mixed oxide of rhodium and chromium. The mixture functions as a promising and efficient photocatalyst in promoting the evolution of hydrogen gas.