Influence of Pt particle size and reaction phase on the photocatalytic performances of ultradispersed Pt/TiO2 catalysts for hydrogen evolution

•Investigation of photocatalytic HER over Pt/TiO2 from ethanol aqueous solution.•Activity increases as cluster size decreases from 1.7 to 0.9 nm.•Single Pt atoms less active and less stable than 1 nm Pt clusters.•0.2 wt% Pt/TiO2-P90 exhibits high HER performance.•Gas-phase and liquid-phase results are consistent with each other.