Blending polybenzimidazole with an anion exchange polymer increases the efficiency of Vanadium Redox Flow Batteries
- Blending polybenzimidazole with an anion exchange polymer increases the efficiency of Vanadium Redox Flow Batteries
- 헨켄스마이어디억; 이규성; 아나스타시아; Mina Jung; Wonmi Lee; Chanho Noh; Sangwon Kim; Yongchai Kwon
- VRFB; Polybenzimidazole; FAA3; Blend membranes
- Issue Date
- Journal of membrane science
- VOL 580-116
- PBI membranes are recently discussed as stable, well performing membranes for vanadium redox flow batteries (VRFB). Blending meta-PBI with an anion exchange polymer (FAA3i) slightly reduces the coulomb efficiency from 99.7 to 97.8%, but strongly increases the voltage efficiency from 82.5 to 88.2%, leading to an increased energy efficiency (86.2% at 80  mA  cm− 2), exceeding that of meta-PBI (82.2%) and N212 (83%). Apparently, since the conductivity of sulfuric acid has a maximum around a concentration of 3.8  M, the concentration of the absorbed acid has a dominant influence on the conductivity. Addition of FAA3i decreases the concentration of the acid absorbed by PBI membranes. Furthermore, an ex-situ stability test in 1.5  M V5+ solutions in 2  M sulfuric acid for 87 days showed a very high stability for meta-PBI and Nafion 212, while the commercial FAA3 membrane disintegrated into pieces. Blending of meta-PBI and FAA3 decreased the stability, as proven by formation of V4+, but all tested blend membranes retained their membrane shape and could still be handled. Blending with FAA3 reduces the tensile strength and Young's modulus of meta-PBI, and doping with sulfuric acid leads to a further decrease in the mechanical strength. However, an acid doped PF-21 still showed a tensile strength of 37  MPa and a Young's modulus of 0.7  GPa.
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