Jung Ock Park

Durable cross-linked copolymer membranes based on poly(benzoxazine) and poly(2,5-benzimidazole) for use in fuel cells at elevated temperatures

Cross-linked benzoxazine–benzimidazole copolymer membranes with interpenetrating network structures containing a large amount of phosphoric acid (PA) were prepared by a direct casting method for polymer electrolyte membrane fuel cells at elevated temperatures. The direct casting solution was prepared by adding 6-fluoro-3-(pyridin-2-yl)-3,4-dihydro-2H-benzoxazine into the polymerization solution of 3,4-diaminobenzoic acid in poly(phosphoric acid) (PPA). Once the PPA in the membranes has been hydrolyzed to PA, the membranes can contain large amounts of PA and showed high proton conductivity, ca. 0.14 S cm−1, at 150 °C under anhydrous conditions. Membrane–electrode assemblies (MEAs) prepared using the copolymers showed high operating voltages of 0.69 V at 0.2 A cm−2, long-term durability for up to 1584 cycles, with much slower performance decay than those prepared using poly(benzimidazole) homopolymers, such as poly[2,2′-(m-phenylene)-5,5′-bibenzimidazole] and poly(2,5-benzimidazole), from the in situ accelerated lifetime test.

Poly[2,2′-( m-phenylene )-5,5′-bibenzimidazole] and poly[6-fluoro-3-(pyridin-2-yl)-3,4-dihydro-2H-benzoxazine] based polymer electrolyte membranes for fuel cells at elevated temperature

AbstractCross-linked copolymer membranes were prepared by casting poly[2,2′-(m-phenylene)-5,5′-bibenzimidazole] (PBI) solutions containing 6-fluoro-3-(pyridin-2-yl)-3,4-dihydro-2H-benzoxazine (pF) in N,N-dimethylacetamide, with subsequent step-wise heating to 220 °C. The phosphoric acid (PA) content, proton conductivity, and cell performance were found to increase with the increase in benzoxazine content in these membranes. The proton conductivities of the cross-linked copolymer membranes reached 0.09 S cm−1 at 150 °C under anhydrous conditions. Membrane-electrode assemblies (MEAs), prepared using the cross-linked copolymer membranes, showed larger operating voltage, 0.71 V at 0.2 A cm−2, than those from commercially available PBI membranes. Additionally, the MEAs were durable until 1,077 cycles, with slow lifetime loss rate, −0.14 mV h−1 on in situ accelerated lifetime mode (load cycling test).

Design and Optimization of HT-PEMFC MEAs

The HT-PEMFC systems are mostly developed for the combined heat and power (CHP) and auxiliary power unit (APU) generation applications because of their relatively simple system configuration and tolerance to a wide choice of fuels. To achieve the cost and durability targets that are needed for the commercialization of the HT-PEMFC systems, many developments have been made to enhance the performance of the HT-PEMFC MEAs. The efforts to enhance the cell voltage include using catalysts with high ORR activity, controlling properties of binders and optimizing amount of acid to increase the electrochemically active surface area in the catalyst layer. The lifetime of the MEA is reported to depend on the catalyst degradation and acid loss, and notable improvements on the durability of MEAs were achieved by using oxidation-resistant catalysts. In this chapter, the factors that determine the cell voltage and durability of MEAs for HT-PEMFC are discussed, and the design of low-cost durable MEAs for HT-PEMFC is suggested.