Composite membranes to reduce crossover in PEM fuel cells

Nafion has long been the standard polymer for use in polymer electrolyte membrane (PEM) fuel cells. The main purpose for the electrolyte is to allow protons to pass through freely while being a barrier to electrons and reactants. Nafion fails as a barrier to methanol solutions, and thus much research has been carried out to find a replacement for Nafion in liquid feed direct methanol fuel cells. In the present work, the authors present a method to modify both polybenzimidazole (PBI) and Nafion to make an improved methanol barrier while maintaining suitable proton conductivity. PBI was chemically modified, by sulfonation, ((s)-PBI) to make it an intrinsic proton conductor and deposited as an additional layer on a Nafion membrane. The addition of (s)-PBI to Nafion creates a composite polymer electrolyte that is a reasonable proton conductor while reducing the crossover of methanol.