Effect of silicotungstic acid (STA) on the performance of a polymer electrolyte fuel cell (PEMFC) based on Nafion® cast in dimethylformamide

A casting process for composite Nafion (R)/STA membranes was achieved. The membrane casting was based on the evaporation of 5% Nafion (R) solution in N,N '-dimethylformamide (DMF) with and without silicotungstic acid (STA) as an additive. Optimized parameters for the casting process were determined. The water uptake and the ionic conductivity of the cast membranes were measured. The variation of the volume of Nafion (R) and the STA concentrations on the water uptake and conductivity of the cast membranes were investigated under various conditions. The sulphuric acid uptake was also determined. The effect of the membrane soaking conditions, on water uptake and conductivity, were determined. The contribution of the (-SO3H) groups, the STA species, and/or the sulphuric acid to the membrane properties was discussed. The performance of hydrogen/oxygen (H-2/O-2) PEM Fuel Cells based on the membranes cast with STA was compared to those based on membranes cast without STA. It was shown that the water uptake of the cast membrane increased from 18% to 50% when the STA concentration used in the casting bath increased from 0 to 5 x 10(-3) M. For the membrane fabricated without STA, the water uptake and the conductivity do not change with membrane thickness, whereas for the membranes cast with STA, the water uptake and the conductivity increase with membrane thickness. A performance improvement of 0.3 A cm(-2) at 0.6 V was obtained with the H-2/O-2 PEM fuel cell based on membranes cast with STA, compared to the performance of the cell based on membranes cast without STA. On the other hand, this performance improvement, for the cells based on the membranes cast in DMF (0.3 A cm(-2) at 0.6 V), is higher than that for the cells based on membranes cast in aqueous electrolyte (0.15 A cm(-2) at 0.6 V) was anticipated that soaking the membranes in sulphuric acid might improve their performance for H-2/O-2 PEMFC applications.