Heteropolyacids as Co-Catalysts with Platinum on the Anode of a Direct Methanol Fuel Cell

In this work, polarization and electrochemical impedance spectroscopy experiments were performed on a direct methanol fuel cell (DMFC). Two heteropoly acids, phosphomolybdic acid (PMA) and phosphotungstic acid (PTA), were incorporated into the anode catalyst layer in combination with Pt/C. Both PTA-Pt and PMA-Pt showed higher performance than the Pt control at 30 psig of backpressure. Anodic polarizations were also performed, and Tafel slopes were extracted from the data. An equivalent circuit model which incorporated constant phase elements (CPEs) was used to model the impedance data. From the impedance model it was found that the incorporation of HPAs into the catalyst layer resulted in a reduction in the resistance to charge transfer, Rct. This shows that these two heteropoly acids do act as co-catalysts with platinum for methanol electrooxidation. However, the performance seen here is below that of PtRu catalysts.