Direct methanol fuel cell operation with pre-stretched recast Nafion ®

Abstract

Direct methanol fuel cell operation with uniaxially pre-stretched recast Nafion ® membranes (draw ratio of 4) was investigated and compared to that with commercial (un-stretched) Nafion ®. The effects of membrane thickness (60–250 μm) and methanol feed concentration (0.5–10.0 M) on fuel cell power output were quantified for a cell temperature of 60 °C, ambient pressure air, and anode/cathode catalyst loadings of 4.0 mg cm −2. Pre-stretched recast Nafion ® in the 130–180 μm thickness range produced the highest power at 0.4 V (84 mW cm −2), as compared to 58 mW cm −2 for Nafion ® 117. MEAs with pre-stretched recast Nafion ® consistently out-performed Nafion ® 117 at all methanol feed concentrations, with 33–48% higher power densities at 0.4 V, due to a combination of low area-specific resistance (the use of a thinner pre-stretched membrane, where the conductivity was the same as that for commercial Nafion ®) and low methanol crossover (due to low methanol solubility in the membrane). Very high power was generated with a 180-μm thick pre-stretched recast Nafion ® membrane by increasing the cell temperature to 80 °C, increasing the anode/cathode catalyst loading to 8.0 mg cm −2, and increasing the cathode air pressure to 25 psig. Under these conditions the power density at 0.4 V for a 1.0-M methanol feed solution was 240 mW cm −2 and the maximum power density was 252 mW cm −2.