A poly(2-ethylaniline) blend membrane for vanadium redox flow batteries

Polyaniline (PANI), being one of the best chemically stable conducting polymers endowed with coupled electron and proton transport, has been poorly evaluated in vanadium redox flow batteries (VRFBs) due to its poor processability. Here, we have reported the synthesis of processable poly(2-ethylaniline) (E-PANI) and its blend with sulphonated poly(ether sulfone) (SPES) with proposed applications in VRFBs. The synthesis of E-PANI was confirmed by 1H-NMR, FT-IR, and powder XRD. Membranes EP1, EP2, and EP3 were prepared by solution blending of 5, 10, and 15 wt% E-PANI with 95, 90, and 85 wt% of SPES, respectively, in N-methyl-2-pyrrolidone. The membrane with the highest loading of E-PANI, i.e., EP3, delivered the best VRFB performance of 99.5, 53.0, and 52.7% of CE, VE, and EE, respectively, at 140 mA cm−2 current density for 300 charge/discharge cycles with 65% capacity retention for the initial 100 cycles. This performance is far better than that of Nafion 117 in identical experimental conditions, which exhibits merely 15% capacity retention in the initial 100 cycles at the same current density. The EP3 membrane delivered a peak power density of 266 mW cm−2. The membrane analysis revealed no E-PANI leaching or fouling, indicating its potential utility in VRFB applications.