The synthesis conditions of the semiconductor BiVO4have markedinfluence on its physicochemical and photocatalytic properties. In this work,a pH-controlled co-precipitation route was systematically investigated. Specialattention was paid to the pH value during co-precipitation and co-precipitate post-treatment. In a sacrificial photocatalytic water oxidation test, the highest activitywas observed for a sample precipitated at pH=1 and 70°C, which was posttreated at 600°C in air for 3 h after washing and drying. The activity was furtherimproved by another 90% by the addition of the Co3O4-based co-catalyst. Goodsynergy between semiconductor and co-catalyst was obtained for the depositionof pre-formed nanoparticles at a loading of 0.1 w% (physical impregnation). Theeffects of different synthesis conditions of the semiconductor and impregnationmethod for the co-catalyst on the structure, morphology and optical propertiesof the catalysts were investigated by PXRD, SEM, UV-vis spectroscopy, and TEM,while the water oxidation activity was compared in the dark and with the aid ofvisible light using cerium (IV) or silver (I) as sacrificial agents, respectively, withthe aim of establishing structure-activity correlations. The roles of semiconductorparticle anisotropy and co-catalyst particle distribution for optimal photo-activityin the oxygen evolution reaction are discussed.