Gas diffusion electrodes for polymer electrolyte fuel cells using novel organic/inorganic hybrid electrolytes

We have prepared gas diffusion electrodes for polymer electrolyte fuel cells (PEFC) using new organic/inorganic hybrid electrolytes. The catalyst layers were prepared by mixing 3-(trihydroxysilyl)-1-propanesulfonic acid [(THS)Pro-SO₃H], 1,8-bis(triethoxysilyl) octane (TES-Oct), Pt loaded carbon black (Pt-CB) and water, followed by a sol-gel reaction. The polarization properties and the microstructure of the catalyst layer were investigated as a function of the composition. The catalyst layer exhibited higher catalyst utilization than that with conventional Nafion® ionomer. The maximum cathode performance was obtained at (THS)Pro-SO₃H/CB = 1 (by weight). It was found by a mercury porosimetry that the volume of both primary and secondary pores decreased with increasing the acidic ionomer content. The high catalyst utilization with increasing the acid content is ascribed to an enhanced proton conduction, because the hybrid ionomer could penetrate both in the primary and secondary pores. However, an excess ionomer loading showed a detrimental effect due to disturbance of the gas diffusion. The novel organic/inorganic hybrid materials have proved to be a potential material as the ionomer in the electrodes for high temperature PEFCs.