Photocatalysis offers a promising route for the scalable conversion of sunlight to hydrogen or other solar fuels . Various particulate photocatalysts for water splitting, largely based on semiconductors such as TiO2 , SrTiO3 or C3N4 have been developed, but the methods for their activity evaluation vary widely within the literature. To move towards a trajectory of continuous improvement (of activity, stability and efficiency), it is crucial that consistent and reproducible protocols for photocatalyst testing are developed and deployed. These protocols should allow for control of all relevant reaction parameters (such as temperature, light intensity, catalyst dispersion, among others) and provide accurate insight into the formed products.