PtRu Catalysts on Nitrogen-Doped Carbon Nanotubes with Conformal Hydrogenated TiO₂ Shells for Methanol Oxidation

The methanol oxidation reaction (MOR) is the limiting factor in direct methanol fuel cells (DMFC). There is an urgent need to improve the catalytic activity and stability of MOR catalysts. This study reports a highly active PtRu catalyst for MOR based on a hybrid multifunctional catalyst support consisting of a conformal amorphous hydrogenated TiO2 shell wrapped around the oxygenated N-doped carbon nanotube core, denoted as PtRu/TiO2/ONCNT-400. Both the TiO2 shell and the subsequent PtRu nanoparticles are deposited by a rapid microwave-assisted synthesis processes. The hydrogenated TiO2 shell is found to exhibit a strong interaction with the deposited PtRu catalyst nanoparticles and effectively prevent them from agglomeration during the postdeposition thermal annealing to form more active crystalline PtRu alloy catalysts. In addition, the defective hydrogenated TiO2 shell enhances the PtRu catalyst activity by the synergistic effects of partial charge transfer from TiO2 to PtRu and high oxophilicity, which improves the kinetics of oxidation of poisonous CO intermediate to CO2. The mass activity for MOR and long-cycling stability of the PtRu/TiO2/ONCNT-400 catalyst surpass the two benchmark commercial PtRu/C catalysts from Johnson Matthey (JM) and Tanaka KiKinzoku (TKK), respectively. The results demonstrate that PtRu/TiO2/ONCNT-400 can serve as an efficient catalyst for MOR in DMFC.