Achieving efficient and inexpensive vanadium flow battery by combining CexZr1-xO2 electrocatalyst and hydrocarbon membrane

Vanadium flow battery (VFB) is one of the most promising technologies for grid scale energy storage because of its unlimited capacity and ultralong lifespan. Improving energy efficiency (EE) and reducing cost are critical to the practical application of VFB. The efficiency and cost of VFB mainly depend on its key materials such as electrode and proton-conducting membrane. Herein, we report the use of highly active ceria-zirconia mixed oxide decorated graphite felt (CexZr1-xO2/GF) electrodes in combination with a high proton-selective sulfonated poly(ether ether ketone) (SPEEK) membrane to achieve efficient and inexpensive VFB. CexZr1-xO2 electro-catalysts can improve the electrolyte wettability and electrochemical activity of the GF electrode towards VO2+/VO2+ and V2+/V3+ redox couples, leading to remarkably enhanced voltage efficiency (VE) of VFB. On the other hand, SPEEK membrane can effectively suppress the crossover of vanadium ions, resulting in greatly improved coulombic efficiency (CE) of VFB. As a result, the CexZr1-xO2/GF-SPEEK combination demonstrates superior battery efficiencies (CE, VE and EE) and cycling stability to the traditional GF-Nafion combination. Meanwhile, since hydrocarbon-based SPEEK membrane is much cheaper than commercial Nafion membrane, the cost of VFB is also significantly reduced.