Crossover of formic acid through Nafion® membranes

Formic acid has been proposed as a possible fuel for miniature fuel cells, because formic acid is expected to show low crossover and easy water management. In this paper, the permeation of formic acid through Nafion® membranes is investigated at room temperature. It is found that the permeation of formic acid through Nafion® 112 and 117 is much lower than that of methanol. For example, at a 1 M concentration, the steady state flux of formic acid through Nafion® 117 is only 2.03±0.07×10−8 mol/cm2 s. By comparison, previous workers have observed a methanol flux of 3 to 6×10−6 mol/cm2 s through Nafion® 117 under similar conditions. The flux through Nafion® 117 increases with increasing formic acid concentration, reaching a maximum of 1.86±0.11×10−7 mol/cm2 s at a formic acid concentration of 10 M. The flux of formic acid is about a factor of two higher through Nafion® 112 than through Nafion® 117 but still low. These results show that the permeation of formic acid through Nafion® is much slower than the permeation of methanol through the same membrane. Consequently, formic acid is an attractive alternative fuel for small polymer electrolyte membrane (PEM) fuel cells.