Phosphoric acid-doped electrodes for a PBI polymer membrane fuel cell

A study of a phosphoric acid (PA)-doped polybenzimidazole (PBI) membrane fuel cell is reported. The fuel cell used polytetrafluoroethylene (PTFE) in the catalyst layer of the membrane electrode assembly to act as a binder and did not use PBI. The PTFE provided an amorphous phase to hold the PA added to the catalyst layers. The study investigated several parameters of the fuel cell electrode, catalyst layer including: PA loading, PTFE content and catalyst loading and wt% of Pt in the carbon supported catalysts and doping of the PBI membrane. There was a minimum amount of acid doping that gave good cell performance for oxygen reduction in the cathode layer. Good performance of the fuel cell was achieved at 120°C with air of 0.27 W cm−2 using a 0.51 mgPt cm−2 loading of catalyst. Peak power of 0.4 W cm−2 was achieved with air at 150°C using a membrane doping of PA of 5.6 PRU (doped acid molecules per repeat polymer unit). Heat treatment of the PTFE-bonded electrodes to increase hydrophobicity did not improve the cell performance. The effect of a perfluorinated surfactant although reported to enhance oxygen solubility in the catalyst layer led to a poorer cell performance.