Polymer electrolyte fuel cells based on phosphoric acid doped polybenzimidazole (PBI) membranes

The development of high temperature polymer fuel cell systems has gained great interest among manufacturers of automotive and combined heat and power systems due to the carbon monoxide (CO) tolerance, enhanced heat management and better mass transfer. One of the promising high temperature polymer systems is based on polybenzimidazole polymer impregnated with phosphoric acid. In order to make fuel cells with high power density the structure and morphology for the three dimensional gas diffusion electrodes (GDE) are very important. In general the electrodes consist of three layers: i) backing material, ii) micro porous layer and iii) catalytic layer. Different preparation techniques yield GDEs with very different properties. Teflon treatment of the backing material is found to be beneficial for the performance of the electrodes. In general the open circuit voltage (OCV) with PBI-based cells is very low. The performance of the fuel cells is found to increase with increasing temperature, with a typical power output of 0.3-0.4 W cm^-2 at 0.6 V and 175 °C.