As global energy demand increases, environmentally friendly and sustainable energy system is necessary to reduce the pollution and greenhouse gases (GHGs) which would also increase in result of more energy production. Utilizing hydrogen as a fuel in energy system is a promising candidate to deal with such problem with advantages of only water generated after reaction in fuel cell and high gravimetric energy density of hydrogen. Currently, hydrogen is mainly produced by gas reforming which simultaneously emit CO₂, which is one of the GHGs, during industrial process. On the contrary, hydrogen production through water electrolysis only produces H₂ and O₂. However, if the electric power for water electrolysis is from energy produced by fossil fuel, it is quite doubtful whether the system is suitable for sustainable and carbon neutral energy system. These are reasons for combining hydrogen production with renewable energy sources like solar, wind, biomass, and ocean that hydrogen could be produced without environmentally harmful byproducts in a broad perspective.

For production of clean fuel hydrogen, photocatalytic hydrogen evolution is one of promising way to handle environmental problems utilizing solar energy. Among various photocatalysts, TiO₂ has been widely researched as photocatalyst for water splitting, CO₂ reduction, wastewater treatment and nitrogen fixation with advantages of low toxicity, stability against photocorrosion, and low cost. In photocatalytic system using TiO₂ for hydrogen evolution reaction, there are strategies to overcome TiO₂ properties of rapid photo-generated charge recombination and lack of absorption ability in the visual light which takes most part of sunlight due to large band gap. Various strategies like surface defect engineering, doping with heteroatom, forming heterojunction with other semiconductors, and co-catalyst loading have been applied to tune the band gap and optical property, enhance the charge separation efficiency, and facilitate the desired reaction at interface.

In the case of catalyst for hydrogen evolution, Pt is known as the best catalyst for hydrogen evolution reaction, but scarce amount and high cost make it difficult to accomplish large application. Therefore, research for reducing the loading amount of Pt but maintaining enough catalytic performance has been conducted. The self-terminating growth of Pt films by electrodeposition has drawn much attention to fabrication of ultrathin Pt monolayer film on electrode with extremely low noble metal catalyst loading amount. The concept of this promising method is the passivation of electrodeposited Pt surface by hydrogen adsorption in appropriate overpotential region which results in formation of Pt monolayer on the electrode. Additionally, Pt layer thickness could be easily controlled by repeated pulse electrodeposition. On the other hand, loading single atom catalysts (SACs) as a co-catalyst on photocatalyst are considered as promising method because it presents better performance with much lower catalyst content than bulk co-catalyst loaded one and can fully utilize the co-catalyst atoms in interfacial reaction.

Motivated by these works, we modified experimental conditions of this self-terminating growth of Pt film to apply the concept in photodeposition method targeting Pt SACs on TiO₂. we chose TiO₂ as semiconductor because it is widely used as photocatalyst and has suitable band position which can reduce Pt ion species in solution and evolve hydrogen. In this research, we present facile photodeposition method that can achieve highly dispersed Pt clusters on TiO₂ for hydrogen evolution. By adjusting photodeposition parameters like pH and concentration of precursors in solution, we successfully fabricated well dispersed and uniform size Pt clusters loaded TiO₂ photocatalyst. The optimized Pt/TiO₂ showed comparable performance to reported Pt cluster or Pt single atom loaded TiO₂. This study suggests new photodeposition method which is different from the photodeposition with defect engineering or utilizing organic materials on the surface of semiconductor. This study will be continued to achieve smaller Pt co-catalyst in size of single atom to further lowering Pt loading amount but maintaining or enhancing the hydrogen evolution performance.