Heteronanostructured photoelectrodes were fabricated by atomic layer deposition of WO3 and stabilized with an Mn-based oxygen-evolving catalyst. The resulting electrode absorbs photons to create electrons and holes, the separation of which is assisted by the built-in field within the semiconductor. Electrons are collected, and holes transferred to the catalyst to split H2O into oxygen and hydrogen (see schematic). 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.