Direct dimethyl-ether proton exchange membrane fuel cells and the use of heteropolyacids in the anode catalyst layer for enhanced dimethyl ether oxidation

Abstract

In this study, polarization and impedance experiments were performed on a direct dimethyl ether fuel cell (DMEFC). The experimental setup allowed for independent control of water and DME flow rates. The DME flow rate, backpressure, and water flow rate were optimized. Three heteropolyacids, phosphomolybdic acid, H 3PMo 12O 40. (HPMo), phosphotungstic acid, H 3PW 12O 40, (HPW), and silicotungstic acid, H 4SiW 12O 40, (HSiW) were incorporated into the anode catalyst layer in combination with Pt/C. Both HPW-Pt and HSiW-Pt showed higher overall performance than the Pt control. Anodic polarizations were also performed, at 30 psig, Tafel slopes of 67 mV dec −1, 72 mV dec −1, and 79 mV dec −1 were found for HPW-Pt, HSiW-Pt and the Pt control, respectively. At 0 psig, the Tafel slopes were 56 mV dec −1, 58 mV dec −1, and 65 mV dec −1 for HPW-Pt, HSiW-Pt and the Pt control. The trends in the Tafel slope values are in agreement with the polarization data and the electrochemical impedance spectroscopy results. The addition of phosphotungstic acid more than doubled the power density of the fuel cell, compared to the Pt control. When the maximum power density obtained using the HPW-Pt MEA is normalized by the mass of Pt used, the optimal result, 78 mW mg −1 Pt, the highest observed at 30 psig and 100 °C to date.