Nafion/organic silica modified TiO₂ composite membrane for vanadium redox flow battery via in situ sol-gel reactions

To improve the selectivity of Nafion membrane, reduce the crossover of vanadium ions and decrease water transfer across the membranes used in VRB systems, the sol-gel method was employed to obtain a composite membrane of Nafion/organic silica modified TiO₂ (Nafion/Si/Ti hybrid membrane). The preparation technique and characteristics of the composite membrane were described. The water transfer and the permeability of vanadium ions were also measured. Results showed that crossover of vanadium ions and water transfer across the membrane for the composite membrane have a remarkable decrease comparing with the unmodified Nafion membrane. It has been confirmed by EDX and FT-IR analysis of the modified membrane that the Si and Ti elements distributed uniformly in the prepared membrane. As a result, the coulombic efficiency of the VRB single cell with modified Nafion membrane was higher than that of the VRB single cell with pristine Nafion membrane. The ion exchange capacity (IEC), the area resistance and the water uptake of the composite membrane were also evaluated. Furthermore, the open circuit voltage (OCV) of the VRB with modified and unmodified Nafion membrane has been carried out and cycle performance of the VRB with modified membrane proves that it has high stability in strong acid condition.