Maximized specific activity for the methanol electrooxidation by the optimized PtRu-TiO2-carbon nano-composite structure

Abstract

The kinetics of the methanol electrooxidation needs to be improved to increase the power density using a lower amount of noble metal catalysts (i.e., Pt and Ru) in direct methanol fuel cells (DMFC). PtRu nanoparticles (∼5 nm) supported on TiO2-nanoparticle (∼4 nm)-coated carbon nanofibers were proposed as an alternative active catalyst for the DMFC. The nano-sized TiO2 can provide a short distance of electron transport from PtRu (reaction site) to the carbon (current collector). At the composite catalyst, the activity enhancement by the PtRu-TiO2 interaction suggested the sufficient electron conductivity at the electrode. The maximized specific activity of the proposed catalyst was 3 times higher compared to that of the commercial PtRu/C. The pore structure of the catalyst was changed by the oxidation conditions due to gasification of the carbon, and the higher activity was obtained by the catalyst with the higher surface area of the micropores (>800 m2 g−1). However, the contribution of micropore would be a secondary effect to the activity. The maximized specific activity was obtained when the volumes of PtRu and TiO2 were similar for the almost same size (around 5 nm) of these particles suggesting that the number of contact points between the PtRu and TiO2 were optimized and the interaction between them was maximized. The PtRu-TiO2-carbon nano-composite catalyst has a high potential as an alternative catalyst as the anode of DMFC.