Recently, Professor Huamin ZHANG’s group achieved a major breakthrough in the R&D of non-fluorinated ion exchange membrane for VRB application. This work was published on Energy & Environmental Science (http://x.rsc.org/?doi=C1EE01117K) and was commented as “New story” by the Chemical World, a journal affiliated to the Royal Society of Chemistry. (http://www.rsc.org/chemistryworld/News/2011/April/13041101.asp) Quoted from clean energy pundit, Dr. John Varcoe from University of Surrey, “using nanofiltration membranes in redox flow batteries is an exciting new development in the field. The simplicity of the system does not lead to a sacrifice in performance and efficiency.”

As the key component of VRB, ion exchange membranes (IEMs) are employed to separate the positive and negative electrolyte and complete the current circuit by transferring ions. The membranes traditionally used in VRB are prepared from perfluorosulfonic polymers, of which the extremely high cost and low ion selectivity have hampered the commercialization of VRB. Meanwhile, low-cost non-fluorinated ionomers suffer from low stability under battery operating condition. Hence, developing alternative membranes with high ion selectivity, high stability and low cost materials is of significant importance.

The concept of nano-filtration membrane was creatively adopted in VRB membrane, due to the similar mechanism of molecule sieving between nano-filtration and VRB membrane separator. Owing to this brand-new idea, vanadium ions, which share larger stokes radius than proton, were “cut off” by pores of nano-scale, while protons could selectively transport through the membrane. Without using ionomer, NF membranes allow much wider range of options in polymer materials, illuminating a possible way to acquire membranes with high performance and low cost for VRB. The progress in membrane R&D is expected to promote the commercialization of VRB, which is regarded as a solution to the bottleneck of on-grid renewable energy.

2011.4.14