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

Abstract

In this study, SiO 2 @TiO 2 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 TiO 2 (HTiO 2 ) is significantly affected by the pH. Below a pH of 7.0, the particle size of TiO 2 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 SiO 2 and HTiO 2 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-HTiO 2 for the water formation were determined to be 19.1, 13.8, and 25.0 m 2 /g, with the increase in pH. The cell performance is similar under high relative humidity. However, under zero humidity, a significant enhancement is observed at pH 9.0 (0.8 W/cm 2 ) compared with 0.67 W/cm 2 for pH 5.0 and 0.59 W/cm 2 for pH 7.0, indicating an excellent self-humidifying ability.