A novel Fe (II/0) redox couple with key components for the V/Fe redox flow battery

Abstract

In this study, ammonium iron (II) sulfate hexahydrate [(NH4)2Fe (SO4)2·6H2O] was used as a negative electrolyte and vanadium sulfate oxide hydrate (VOSO4) as a positive electrolyte to develop a vanadium/iron redox flow battery (V/Fe RFB). To promote the battery's efficiency, its key components (i.e., separation membrane, electrode, and flow channel) were modified through various methods. The carbon paper (C) electrode was modified through electroless plating and sol–gel method to form a C–TiO2–CoP composite electrode, which showed a high electrocatalytic activity for the hydrogen evolution reaction (HER) in acid medium. In purely capacitive model, we can obtain the internal and external capacities, Cd,i and Cd,e from the C–TiO2–CoP electrode; however, other composite electrodes can't be measured because no faradaic reactions occurred. The results showed that the C–TiO2–CoP electrode combined with staggered flow channels could greatly improve the voltage efficiency from 64% to 84% compared with the C electrode. Using the N–117/SiO2–SO3H membrane as the separation membrane, the C–TiO2–CoP as the negative electrode, and staggered flow channels in a single V/Fe RFB, excellent cyclic performances in a charge–discharge durability test of 50 cycles could be achieved. The coulombic efficiency is still kept to 97% at a current density of 60 mA/cm2, and the attenuated percentage is less than 3% for the discharge capacity.