Sulfonated poly(ether ether ketone)/amine-functionalized graphene oxide hybrid membrane with various chain lengths for vanadium redox flow battery: A comparative study

In this paper, a series of sulfonated poly(ether ether ketone) (SPEEK) hybrid membranes containing aliphatic amine-functionalized graphene oxide nanofillers as the interface modifiers, reacted with primary amine (NH2-GO), ethylenediamine (EDA-GO) and 1,6-hexanediamine (HMD-GO), respectively, have been fabricated via a simple solution-casting method. Three hybrid membranes (S/NH2-GO, S/EDA-GO, and S/HMD-GO) demonstrate much higher physicochemical property than that of pristine SPEEK and Nafion 117, which is originated from the varied interfacial interaction and the surface architecture behavior. A superior ion selectivity of S/EDA-GO-1 (24.8 10(3) S min cm(-3)), S/HMD-GO-2 (24.6 x 10(3) S min cm(-3)) and S/NH2-GO-2 (20.4 x 10(3) S min cm(-3)) to pristine SPEEK (4.3 x 10(3) S min cm(-3)) and Nafion 117 membrane (4.0 x 10(3) S min cm(-3)) is shown. At the current density of 50 mA cm(-2), S/EDA-GO-1 hybrid membrane gives the highest energy efficiency than that of S/NH2-GO-2 and S/HMD-GO-2, endowing an excellent charge capacity retention during 100 cycles. The varied interfacial structure state originated from the introduced EDA-GO and HMD-GO nanofillers provide the different proton conductivity and vanadium ion permeability. This present work provides a guidance for developing high-performance PEMs through the regulated interfacial structure via the moderate chain length.