Abstract
Both cation-exchange membranes and anion-exchange membranes are used as ion conducting membranes in vanadium redox flow batteries (VRFBs). Anion-exchange membranes (AEMs) are applied in vanadium redox flow batteries due to the high blocking property of vanadium ions via the Donnan exclusion effect. In this study, novel anion-exchange blend membranes (AEBMs) were prepared, characterized, and applied in VRFBs. Bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide), poly[(1-(4,4′-diphenylether)-5-oxybenzimidazole)-benzimidazole] (PBI-OO) and sulfonated polyether sulfone polymer were combined to prepare 3-component AEBMs with 1,2,4,5-tetramethylimidazole (TMIm) for quaternization. 3-component AEBMs showed significantly enhanced chemical and mechanical properties compared with those of 2-component AEBMs, resulting in an improved performance in VRFBs. The compositions of the anion-exchange polymers in 3-component AEBMs were systematically varied to optimize the AEBMs for the redox-flow battery application. While the 3-component AEBMs showed comparable efficiencies with Nafion® 212 membranes, they displayed improved vanadium ions cross-over as was confirmed by open circuit voltage tests and capacity fade tests conducted in VRFBs. In addition, one of the synthesized 3-component AEBM had a superior coulombic efficiency and capacity retention in a charging–discharging test over 300 cycles at a current density of 40 mA/cm2. It can thus be concluded that 3-component AEBMs are promising candidates for long-term operation in VRFBs.
Highlights
Vanadium redox flow batteries (VRFBs) provide a promising technology for large-scale energy storage
Since ion conducting membranes are used in redox flow batteries (RFBs) as a separator between the two electrolytes, they are an integral component of VRFBs
VRFB performance regarding showed significantly improved vanadiumcontaining ion cross-over when vanadium ion cross-over when compared to 2-component blend membranes only PPO-Br compared to
Summary
Vanadium redox flow batteries (VRFBs) provide a promising technology for large-scale energy storage. Vanadium redox flow batteries can be described as electrochemical devices that store energy in two separated solutions containing different redox couples. In VRFBs, vanadium ions, which are stored separately (V2+ /V3+ and V4+ /V5+ ) in electrolyte reservoirs, undergo electrochemical redox reactions on the surface of electrodes [1,2]. Since ion conducting membranes are used in redox flow batteries (RFBs) as a separator between the two electrolytes, they are an integral component of VRFBs. Since ion conducting membranes are used in redox flow batteries (RFBs) as a separator between the two electrolytes, they are an integral component of VRFBs Their role is to conduct semi-permeable ions such as H+ for cation-conducting membranes or SO4 2− and HSO4 − for anion-conducting membranes thereby maintaining charge balance, and to prevent the cross-mixing of the two electrolytes (V2+ /V3+ and V4+ /V5+ ).
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