Bipolar fuel cell (BPFC) is a new kind polymer electrolyte membrane fuel cell (PEMFC) with acidic-alkaline bipolar interface formed by acidic and alkaline polyelectrolyte both used in one cell. BPFC has shown some novel characterizations: (1) water generated at the bipolar interface would provide the possibility to devise self-humidification over the entire cell, which would simplify the water manager system; (2) alkaline cathode with facilitated electrokinetics allows for the use of lower catalyst loading or non-noble catalysts, such as silver and nickel. In our previous work, the effect of bipolar membrane electrode configuration on the cell output performance was evaluated and the optimal configuration was achieved. The BPFC with optimal membrane electrode configuration has been operated under completely self-humidifying conditions for prolonged periods successfully. However, there exists a big gap with the cell performance between BPFC and the state-of-art PEMFC. In order to improve the fuel cell performance, optimization of the membrane electrode configurations and further advances in fabricating bipolar interface had been conducted in our previous work. Another issue that affects the performance of the fuel cell is the structure and composition of the catalyst layer. Since the oxygen reduction reaction (ORR) at cathode influenced the fuel cell performance a lot, the improvement of electrode was mainly focused on the cathode catalyst layer. In the present work, thin hydrophilic electrode and thick hydrophobic electrode were used as cathode for BPFC. The influence of ionomer binder, quaternary ammonium polysulfone (QAPSF) in thin hydrophilic electrode and polytetrafluoroethylene (PTFE) in thick hydrophobic electrode, concentration on BPFC performance was studied. The results indicated that the optimal content of QAPSF in thin hydrophilic cathode was 20 wt%, and the peak power density of BPFC reached to 186.1 mW/cm² at 25 ℃ without humidification. While the PTFE in the thick hydrophobic cathode was also 20 wt% with a peak power density of 461.5 mW/cm² at 40 ℃ without humidification. Due to the high demand of alkaline cathode for drainage, the thick hydrophobic electrode behaved better than thin hydrophilic electrode in BPFC.

Key words: cathode catalyst layer, polytetrafluoroethylene, quaternized polysulfone, polyelectrolyte membrane, bipolar fuel cell