Improving oxygen reduction efficiency in direct methanol fuel cells through structured catalyst design

Abstract

We have adopted a rational approach to the design of fuel-tolerant oxygen reduction catalysts for direct methanol fuel cells (DMFCs). Our methodology is to use structured catalysts with different core and shell components. These catalysts may be prepared by simple galvanic replacement reactions which can be scaled up for volume production. Density functional theory (DFT) calculations of changes in the d-band centers of the surface catalytic metals; and the strengths of adsorbed species are used to gain some insights into the relationship between surface structure and catalytic activity of these heterogeneously structured catalysts. We found that carbon-supported core-shell PdM@PdPt catalysts (where M=Ni, Co, Fe and Cr) can provide us with the greatest latitude in activity and selectivity tuning. A volcano-curve was obtained where maximum ORR activities occur around the compositions PdCo@PdPt/C and PdFe@PdPt/C. It is believed that the Pt d-band centers in these catalysts are at values representing a good balance between O-O bond dissociation and the removal of adsorbed OH groups on the catalyst surface. Compared with commercial Pt/C catalysts, the PdM@PdPt catalysts utilize less platinum, and yet display favorable catalytic outcomes in terms of ORR activity and selectivity (methanol tolerance).