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In order to increase the chemical stability of polybenzimidazole (PBI) membrane against the highly oxidizing environment of a vanadium redox flow battery (VRFB), PBI/Nafion hybrid membrane was developed by spray coating a Nafion ionomer onto one surface of the PBI membrane. The acid-base interaction between the sulfonic acid of the Nafion and the benzimidazole of the PBI created a stable interfacial adhesion between the Nafion layer and the PBI layer. The hybrid membrane showed an area resistance of 0.269 U cm 2 and a very low vanadium permeability of 1.95 Â 10 À9 cm 2 min À1 . The Nafion layer protected the PBI from chemical degradation under accelerated oxidizing conditions of 1 M VO 2 + /5 M H 2 SO 4 , and this was subsequently examined in spectroscopic analysis. In the VRFB single cell performance test, the cell with the hybrid membrane showed better energy efficiency than the Nafion cell with 92.66% at 40 mA cm À2 and 78.1% at 100 mA cm À2 with no delamination observed between the Nafion layer and the PBI layer after the test was completed.