Cho, Hyeongrae7; Hur, Eun4; Henkensmeier, Dirk7; Jeong, Gisu7; Cho, Eunae7; Kim, Hyoung Juhn7; Jang, Jong Hyun7; Lee, Kwan Young8; Hjuler, Hans Aage6; Li, Qingfeng1; Jensen, Jens Oluf1; Cleemann, Lars Nilausen1
1 Department of Energy Conversion and Storage, Technical University of Denmark2 Proton conductors, Department of Energy Conversion and Storage, Technical University of Denmark3 Korea Institute of Science and Technology4 Korea University of Science and Technology5 Korea University6 Danish Power Systems ApS7 Korea Institute of Science and Technology8 Korea University
Methylation of polybenzimidazole leads to positively charged polymer backbones, and moveable anions. Ion exchange of methylated PBI-OO in phosphoric acid (PA) shows that the resulting polymers dissolve. meta-PBI, however, absorbs about 400wt% PA while remaining a self supported membrane. We investigate the properties of blend membranes, employing meta-PBI for mechanical integrity and methylated PBI-OO for high PA uptake and resulting proton conductivity. While small additions of PBI-OO decrease the tensile strength of blend membranes (58MPa for 10% PBI-OO), further addition leads to an increase, and 50% blend membranes show again a tensile strength of 74MPa, just 3MPa lower than pure meta-PBI membranes. Thermal stability of iodide exchanged blend membranes appears to be remarkably high, probably because cleaved iodomethane does not evaporate but methylates meta-PBI. PA concentration in doped membranes of 60–63% is reached by doping in 60% PA (blend; 6.3PA/repeat unit) and 70% PA (meta-PBI; 4.6PA/r.u.). This suggests that blends absorb PA more strongly. Both membranes show similar conductivity between rt and 140°C, indicating that PA concentration describes these membranes better than PA/r.u. In the fuel cell, blend membranes show similar or better performance than meta-PBI. In the TGA, blends doped in 20% PA showed a stable plateau between 115 and 180°C, while meta-PBI lost weight continuously.
European Polymer Journal, 2014, Vol 58, p. 135-143
Polybenzimidazole; Blend membranes; Methylated PBI-OO; Polybenzimidazolium; Phosphoric acid doping; High temperature polymer electrolyte fuel cell