A deep eutectic solvent (DES) electrolyte-based vanadium-iron redox flow battery enabling higher specific capacity and improved thermal stability. (10th January 2019)

• Record Type: Journal Article
• Authors: Xu, Q.; Qin, L.Y.; Ji, Y.N.; Leung, P.K.; Su, H.N.; Qiao, F.; Yang, W.W.; Shah, A.A.; Li, H.M.
• Is Part Of: Electrochimica acta. Volume 293(2019)
• Page Start: 426
• Page End: 431
• Publication Date: 2019-01-10
• Subjects: Deep eutectic solvent (DES) -- Redox flow battery -- Electrochemical characteristics -- Cell performance; Electrochemistry -- Periodicals; Electrochemistry, Industrial -- Periodicals; 541.37
• DOI: 10.1016/j.electacta.2018.10.063
• Languages: English
• ISSNs: 0013-4686

Abstract

Abstract: Compared with conventional aqueous electrolyte, due to unique merits of deep eutectic solvents including a wide electrochemical window, ease in preparation, low vapor pressure and low cost, they have been used as electrolyte in the non-aqueous flow battery. This work reports a reline deep eutectic solvent, which is prepared as the anolyte and catholyte of a vanadium-iron redox flow battery. Since the solubility of the vanadium and iron species in deep eutectic solvent has been improved, an increased specific capacity can be obtained, up to 54.6% compared with the aqueous electrolyte one. However, the viscosity of this electrolyte is much larger than that of aqueous electrolyte, which causes more pumping losses. With the increase of operating temperature, the viscosity experiences a huge drop. The open-circuit voltage of such an non-aqueous system begins near 0.9 V with a decrease rate of 0.005 V h −1, suggesting a better capacity retention ability than does the aqueous flow battery. The cycling performance of this redox flow battery is evaluated at a current density of 2.0 mA cm −2 under the temperature of 30 °C. The coulombic efficiency is up to 94.8%, while voltage efficiency and energy efficiency are just 68.3% and 64.7%, respectively. The low voltage efficiency stems from the sluggish redox kinetics of the vanadium ions, and large internal ohmic resistance. With an improved thermal stability, this vanadium-iron redox flow battery is preferred to be operated at elevated temperature, which helps to greatly reduce the ohmic loss and pumping loss, such that to increase the system energy efficiency. Graphical abstract: A vanadium-iron redox flow battery works with deep eutectic solvent electrolyte. Image 1 Highlights: A V-Fe redox flow battery (RFB) with DES electrolyte is set up and tested. Enhanced solubility of ions results in an increased capacity up to 54.6% compared with the aqueous electrolyte. This DES-based RFB has a better capacity retention ability than aqueous one. Low voltage efficiency stems from both sluggish kinetics and large ohmic resistance. Improved stability helps to operate at elevated temperature with higher energy efficiency.