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Physical and Electrochemical Properties of Pt-Hollow-Structured TiO2 Prepared at Different pH’s and Its Self-Humidifying Ability in PEMFC

In this study, SiO2@TiO2 core–shell nanoparticles were prepared under different pH’s such as 5.0, 7.0, and 9.0. Under acidic and neutral conditions, silica nanoparticles are more agglomerated, while less agglomeration occurs under alkaline conditions. The latter case is attributed to repulsive forces between negatively charged silica nanoparticles because of the lack of protons under alkaline conditions. It was also observed that the individual particle size of hollow-structured TiO2 (HTiO2) is significantly affected by the pH. Below a pH of 7.0, the particle size of TiO2 is larger than that at pH 9.0 because of the hydrolysis and condensation of titanium tetrabutoxide via the sol–gel process. The smaller the particle sizes of SiO2 and HTiO2 are, the larger is the Brunauer–Emmett–Teller (BET) surface area, and the higher are the water uptake and electrochemical active surface area (ECSA). The ECSAs of Pt-HTiO2 for the water formation were determined to be 19.1, 13.8, and 25.0 m2/g, with the increase in pH...