ABSTRACT
Vanadium Redox flow Battery (VRB) is a promising technology as an efficient Energy Storage System (ESS) for a wide range of applications such as large-scale, renewable and grid energy storage (Fabjan et al. 2001, Joerissen et al. 2004, Tokuda et al. 2000, Chakrabarti et al. 2007, Skyllas-Kazacos et al. 2011). By employing V (II)/V (III) and V (IV)/V (V) redox couples as negative and positive electrolytes, respectively, with sulfuric acid as the supporting electrolyte, the output power and capacity of the VRB are dependent on the volume and concentration of the electrolytes (Wu 2012). During the charging and discharging of the VRB, electrochemical reactions within the battery change the balance of the vanadium ions, respectively, (Faizur & Skyllas-Kazacos 2009) at the positive electrode:
VO H e VO H OE V2 2
2 1 0 + +2 ++
discharge
charge
(1)
at the negative electrode:
V e V E3 2 0 26+ = − charge
discharge . (2)
However, to date, the VRB cannot be used in the widespread environment because several problems have restricted its industrialization. For example, the positive electrolyte tends to generate V2O5 precipitation, which deposits on the carbon felt electrode and blocks the separator surface (Chang et al. 2012). Especially, the V (V) electrolyte suffers from thermal precipitation above 40°C, which leads to the limited specific energy density of the VRB (Rahman & Skyllas-Kazacos 1998). This situation causes the decline in the battery performance and may even cause battery malfunction (Lu 2001).
