Improved performance of direct methanol fuel cells with the porous catalyst layer using highly-active nanofiber catalyst

Abstract

PtRu supported on TiO2-embedded carbon nanofibers (PtRu/TECNF), which was recently reported as a highly-active catalyst for methanol oxidation, was applied to a direct methanol fuel cell (DMFC), and the power generation performance was compared to that using the commercial PtRu/C. Before the comparison, the effect of the catalyst loading on the power density of the DMFC was investigated using PtRu(18 wt%)/TECNF. The DMFC power density showed a maximum at about a 1.5 mg cm−2 PtRu loading that corresponds to about an 80 µm layer thickness. A catalyst layer thicker than this value reduced the power density probably due to the concentration overvoltage. The PtRu content in the PtRu/TECNF was then increased to 30 wt% or more to reduce the layer thickness and to increase the power density. The DMFC performance was compared to that of different anode catalysts at a 1 mg cm−2 PtRu loading. The power density was maximized using the PtRu30 wt%/TECNF, which showed a 173 mW cm−2 at 353 K and had 66 µm layer thick, that was 26% higher than that of commercial PtRu/C. The current–voltage curve of the DMFC with the PtRu/TECNF suggested an improved mass transport overvoltage, but a little improvement in the activation one despite using the catalyst with about a 2 times higher activity compared to that of the commercial PtRu/C. This was attributed to the lower Pt utilization of the nanofiber catalyst layer.