Fuel cell membranes and crossover prevention

A membrane electrode assembly for use with a direct organic fuel cell containing a formic acid fuel includes a solid polymer electrolyte having first and second surfaces, an anode on the first surface and a cathode on the second surface and electrically linked to the anode. The solid polymer electrolyte has a thickness t:where Cf is the formic acid fuel concentration over the anode, Df is the effective diffusivity of the fuel in the solid polymer electrolyte, Kf is the equilibrium constant for partition coefficient for the fuel into the solid polymer electrolyte membrane, ℑ is Faraday's constant nf is the number of electrons released when 1 molecule of the fuel is oxidized, and jfc is an empirically determined crossover rate of fuel above which the fuel cell does not operate.