An interface-strengthened cross-linked graphene oxide/Nafion212 composite membrane for vanadium flow batteries

An interface-strengthened cross-linked graphene oxide/Nafion212 (CLGO/Nafion212) composite membrane was successfully fabricated and served as ion conducting membrane for vanadium flow batteries (VFBs). Firstly, the surface of Nafion212 was endowed with plenty of amino groups via in situ sol-gel chemistry approach of 3-aminopropyltriethoxysilane. Subsequently, a thin layer of m-xylylenediamino-crosslinked GO was formed using the spin-coating method. The composite membrane demonstrated much lower vanadium ion permeability (0.30 × 10−6 cm2 min−1) than pristine Nafion212 (1.88 × 10−6 cm2 min−1), mainly due to the presence of a cross-linked GO layer with angstrom-scale channels. The cell assembled with CLGO/Nafion212 exhibited enhanced coulombic efficiencies (CEs, 93.0–97.2% vs. 68.0–91.6%) and energy efficiencies (EEs, 88.9–85.2% vs. 65.7–82.2%) compared with the one with Nafion212 at 20–100 mA cm−2. At a constant current density of 80 mA cm−2, the long-term cycling tests showed that the discharge capacity fading of the flow cell equipped with CLGO/Nafion212 reached 0.25% per cycle, which was much smaller than that of Nafion212 (0.47% per cycle). The above findings proved that the cell equipped with CLGO/Nafion212 displayed superior electrochemical performances than that with Nafion212, therefore CLGO/Nafion212 composite membrane showed a great potential in VFBs.