Comparison of TiO2 and TiO2-CNT as Cathode Catalyst Supports for ORR

The aim of the present study is to compare the properties of Pt-TiO2, where TiO2 is utilized as a catalyst support, with those obtained from Pt-TiO2-CNT synthesized using MOCVD. The results showed that the Pt-TiO2-CNT composites displayed higher Pt activity than the Pt-TiO2 catalysts. X-ray diffraction studies revealed that both Pt-TiO2 and Pt-TiO2-CNT exhibited a body-centered tetragonal anatase TiO2 crystal structure. However, when fragmentation of the raw materials was vigorous, the particle size became smaller and the synthesized Pt-TiO2-CNT composites displayed an amorphous structure with lower intensity TiO2 reflections. STEM micrographs of the composites showed well-dispersed Pt nanoparticles deposited on anatase agglomerates and/or on CNT supports. Nevertheless, the Pt particles on TiO2 aggregates are electronically isolated, resulting in the performance of the electrodes being limited by insufficient local electronic conductivity and the low bulk electronic conductivity of TiO2. The carbon nanotubes in the Pt-TiO2-CNT composites create an electron-conducting network, resulting in an increase in macroscopic electronic conductivity. Comparisons of the Pt activity towards the O-2 reduction reaction (ORR) indicate that the Pt-TiO2-CNT catalysts possess better performance, regardless of CNT percentage, than the Pt-TiO2 composites. The overall ORR performance is enhanced with an increased percentage of CNT, mainly due to the relatively high conductivity of the CNT support. In contrast, the CNT-free Pt-TiO2 cathode had lower oxygen reduction activity due to the limited electronic conductivity of TiO2. This study demonstrates a stable Pt-TiO2-CNT composite material possessing a performance comparable to the conventional Pt-CNT material.