Vanadium Redox Flow Batteries Using meta-Polybenzimidazole-Based Membranes of Different Thicknesses

Chanho Noh; Mina Jung; Dirk Henkensmeier; Suk Woo Nam; Yongchai Kwon

doi:10.1021/acsami.7b10598

Vanadium Redox Flow Batteries Using meta-Polybenzimidazole-Based Membranes of Different Thicknesses

ACS Appl Mater Interfaces. 2017 Oct 25;9(42):36799-36809. doi: 10.1021/acsami.7b10598. Epub 2017 Oct 10.

Authors

Chanho Noh¹, Mina Jung^{1

2}, Dirk Henkensmeier^{2

3

4}, Suk Woo Nam^{2

4}, Yongchai Kwon¹

Affiliations

¹ Graduate School of Energy and Environment, Seoul National University of Science and Technology , Nowon-gu, Seoul 01811, Republic of Korea.
² Fuel Cell Research Center, Korea Institute of Science and Technology , Hwgrangno 14-gil 5, Seongbukgu, Seoul 02792, Republic of Korea.
³ ET-GT Convergence, University of Science and Technology , Hwarangno 14-gil 5, Seongbukgu, Seoul 02792, Republic of Korea.
⁴ Green School, Korea University , Seoul 136-713, Republic of Korea.

PMID: 29016108
DOI: 10.1021/acsami.7b10598

Abstract

15, 25, and 35 μm thick meta-polybenzimidazole (PBI) membranes are doped with H₂SO₄ and tested in a vanadium redox flow battery (VRFB). Their performances are compared with those of Nafion membranes. Immersed in 2 M H₂SO₄, PBI absorbs about 2 mol of H₂SO₄ per mole of repeat unit. This results in low conductivity and low voltage efficiency (VE). In ex-situ tests, meta-PBI shows a negligible crossover of V³⁺ and V⁴⁺ ions, much lower than that of Nafion. This is due to electrostatic repulsive forces between vanadium cations and positively charged protonated PBI backbones, and the molecular sieving effect of PBI's nanosized pores. It turns out that charge efficiency (CE) of VRFBs using meta-PBI-based membranes is unaffected by or slightly increases with decreasing membrane thickness. Thick meta-PBI membranes require about 100 mV larger potentials to achieve the same charging current as thin meta-PBI membranes. This additional potential may increase side reactions or enable more vanadium ions to overcome the electrostatic energy barrier and to enter the membrane. On this basis, H₂SO₄-doped meta-PBI membranes should be thin to achieve high VE and CE. The energy efficiency of 15 μm thick PBI reaches 92%, exceeding that of Nafion 212 and 117 (N212 and N117) at 40 mA cm^-2.

Keywords: coulombic efficiency; electrostatic energy barrier; meta-polybenzimidazole-based membranes; vanadium crossover; vanadium redox flow batteries.