Hydroxyl group's effects on the activity and durability of supported carbon–TiO2 for proton exchange membrane fuel cells

Abstract

Pt catalysts used for the cathode in proton exchange membrane fuel cells (PEMFCs) are mostly supported on carbon materials. However, durability issues arise under operating conditions due to carbon corrosion, which is a critical degradation mechanism. To improve the support durability, metal oxide supports combined with carbon have been extensively investigated. In this study, oxygen vacancy and hydroxyl group modified TiO₂ particles supporting Pt nanoparticles were developed for applications in the oxygen reduction reaction (ORR) and the membrane electrode assemblies (MEAs). The Pt catalyst supports were prepared using a microwave-assisted method, and their performance was compared according to the degree of TiO₂ crystallinity with and without heat treatment. X-ray diffraction (XRD) measurements before and after heat treatment revealed differences in the crystallinity of TiO₂, showing the presence of anatase TiO₂ and Ti–OH species. In the uncalcined carbon–TiO₂ composite, the presence of titanium hydroxide (Ti–OH) species was confirmed by X-ray photoelectron spectroscopy (XPS) and attenuated total reflection (ATR) spectroscopy. The prepared Pt nanoparticle/TiO₂–carbon (TiO₂–Pt/SC) and Pt nanoparticle/heat-treated TiO₂–carbon (TiO₂–Pt/SC–H) catalysts exhibited superior ORR activity compared to that of the calcined catalyst. The effect of Pt loading on the ORR performance was also examined, revealing enhanced activity in the presence of anatase TiO₂, which is attributed to its strong metal–support interactions (SMSIs). In addition, MEA tests confirmed that these samples exhibited high activity and improved stability. The enhanced oxygen reduction kinetics are ascribed to water dissociation and the formation of surface-adsorbed hydroxyl moieties. We believe that the results described herein provide important implications for the development of durable TiO₂–carbon hybrid supports for MEA applications.