A proton exchange membrane is a membrane that only allows protons to permeate through. Therefore, a PEM is a selectively permeable membrane. In 99% of bio-fuel cells, a PEM is used to keep electron and proton charge equilibrium constant, which increases efficiency. What I want to know are are here any other people out there that have worked with microbial fuel cells and knows how to make one without a PEM.
A company called INI Power Systems (Cary, NC) makes a fuel cell with no membrane. It uses two fluids that flow next to each other. DUe to laminar flow, they don't mix significantly but still exchange ions as if there was a membrane there.
