ABSTRACTHighly efficient Pt-TiO₂ composite photoelectrodes were synthesized by combining two novel deposition methods: ACVD and a room temperature RF (radio frequency) magnetron sputtering method. A room temperature RF magnetron sputtering method allowed uniform deposition of Pt nanoparticles (NPs) onto the as-synthesized nanostructured columnar TiO₂ films by ACVD. Pt NP sizes from 0.5 to 3 nm demonstrating a high particle density (>10¹² cm⁻²) could be achieved by varying deposition time with constant pressure and power intensity. As-synthesized Pt-TiO₂ films were used as photoanodes for water photolysis. Pt nanoparticles deposited onto the TiO₂ film for 20s produced the highest photocurrent (7.92 mA/cm² to 9.49 mA/cm²) and maximized the energy conversion efficiency (16.2 % to 21.2 %) under UV illumination. However, as the size of Pt particles increased, more trapping sites for photogenerated electron-hole pairs decreased photoreaction.