Fabrication and impedance studies of DMFC anode incorporated with CNT-supported high-metal-content electrocatalyst

Abstract

In this study, the fabrication of a direct methanol fuel cell (DMFC) anode with the incorporation of a multiwalled carbon nanotube (CNT)-supported high-metal-content Pt/Ru electrocatalyst, i.e., 40 wt%Pt-20 wt%Ru/CNT, using a novel approach and the resultant DMFC performances were investigated. Employing a vacuum filtration method, we were able to successfully fabricate the DMFC anode with a good electrode structure using an in-house prepared Pt-Ru/CNT electrocatalyst. The catalyst layer was formed directly on a Teflon-treated carbon cloth having a buckypaper texture with a catalyst loading of 4.0 mg cm −2. From single-cell tests, excellent cell performances were obtained. At 80 °C, the power density was found to be as high as >100 mW cm −2. This can be attributed to a thinner catalyst layer formed with a more efficient utilization of the catalyst than that using a low-metal-content counterpart, i.e., 20 wt%Pt-10 wt%Ru/CNT, as reported in an earlier study. However, the Nafion ® ionomer content in the catalyst layer played a key role in the anode fabrication to obtain a good cell performance. In addition, the electrochemical impedance spectroscopy (EIS) with a constant phase element (CPE)-based equivalent-circuit model was employed to analyze the fabricated anode. It distinctively revealed some specific characteristics in the resistances and the interface properties. Overall, the obtained impedance results are somewhat different from those of a conventional DMFC anode with the catalyst layer coated onto a porous gas diffusion layer (GDL) on a carbon backing material. Based on the experimental results and the impedance analyses, the high-metal-content Pt-Ru/CNT catalyst was found to be much more favorable and suitable for use as a DMFC anode catalyst.