Effect of catalyst loading in direct methanol fuel cell using sulfonated-poly-ether-ether-ketone/charged surface modifying macromolecules membranes

Abstract

Direct methanol fuel cell (DMFC) for portable power applications requires high power density and high-energy conversion efficiency which largely depends on membrane and electrocatalyst to achieve high performance. In improving these factors, the first objective of this study was to synthesize and characterize sulfonatedpoly- ether-ether-ketone (SPEEK) and SPEEK/ charged surface modifying macromolecules (cSMM). The second objective was to synthesize and characterize Platinum/Ruthenium (Pt/Ru) catalyst for anode and Palladium (Pd) catalyst for cathode. Consequently, the third objective was to test the performance of SPEEK/cSMM using single cell DMFC under different catalyst loadings. In this work, 20 wt %, 30 wt % and 40 wt % Pt/Ru were used as the catalyst for anode while 5 wt % and 10 wt % Pd were used on the cathode, with three different loadings of 2, 4 and 6 mg/cm2, respectively for each 4 cm2-electrode. The electrodes were prepared using catalyzed diffusion media (CDM) method, while the membrane electrode assembly (MEAs) was prepared by hot pressing method. The single cell DMFC tests were run at constant condition of 100 ml min-1 air flowrate, 1M methanol concentration, 1 ml min-1 methanol flowrate and 60°C operating temperature, respectively. In finding the suitable catalyst loading in anode, commercial 40 wt % Pt electrode was used as the cathode. On the anode, it was found that the best result of catalyst loading was 30 wt % Pt/Ru with 4 mg/cm2, which then was used to get the suitable catalyst loading in cathode for 5 wt % and 10 wt % of Pd/Carbon. On the cathode, the best catalyst loading was 10 wt % Pd with 4 mg/cm2 loading. By applying the best loading of catalysts, the highest power density of 123 mW/cm2 was achieved, eventhough its open circuit voltage (OCV) and ohmic voltage yielded the lowest values. This shows that a combination of the best anode and cathode loading were able to generate the highest power density for SPEEK/cSMM electrolyte membrane for DMFC application.