In harmony: Nanoparticles of Mn3O4 and core/shell-structured Rh/Cr2O3 as cocatalysts on the surface of a solid solution of GaN and ZnO as catalyst promote O2 and H2 evolution, respectively, under visible light (λ>420 nm), thereby achieving enhanced water-splitting activity compared to analogues modified with either Mn3O4 or Rh/Cr2O3. Detailed facts of importance to specialist readers are published as "Supporting Information". Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.