Sunday, 29 May 2022: 14:00
West Meeting Room 211 (Vancouver Convention Center)
Redox flow batteries are one of the prominent electrochemical energy storage devices with large-scale storage and high energy density.1 The highly reversible Zn/Zn2+ (-0.76 V vs. RHE) and Br-/Br2 (1.08 V vs. RHE) redox couple have been employed in Zn-Br2 flow batteries (1.84 V vs. RHE). However, the dendritic growth of Zn electrodeposits during the repetitive discharge process triggers an internal short-circuit between the anode and the cathode.1 Besides this, cross-diffusion of the highly soluble Br- (Br3-) ion causes a severe self-discharge of the system and reduced cycle life.2 Additives and ion-selective membranes have been employed to mitigate these challenges for improved cycle life and coulombic efficiency in Zn-Br2 batteries.3 Here, we fabricate an aqueous Zn-Br2 static battery with internally contained and moderate magnetic fields, (~ 30, 40, 50 and 60 mT) at the anode and cathode by incorporating 1 mm thick Nd permanent magnets. A solid complex of tetrapropylammonium tribromide was supported on activated carbon and employed as the positive electrode. Introducing a magnetic field can generate the Lorentz force (acting on Br- and Zn2+ ions), and create a controllable magnetohydrodynamic mass transport during the charge-discharge processes. Among the various magnetic fields, ~50 mT resulted in the highest coulombic efficiency (99 % for 100 cycles) and suppressed Zn dendritic growth. To rationalize the effect of magnetic fields on the efficiency and cycle life, Raman analysis, X-ray diffraction, scanning electron microscopy, electrochemical impedance spectroscopy, and cyclic voltammetry (for the calculation of diffusion coefficient of Br- ion) are performed on the positive and negative electrodes of Zn-Br2 battery.
References:
(1) Z. Yuan, X. Liu, W. Xu, Y. Duan, H. Zhang, X. Li, Nat. Commun., 9, 3731 (2018).
(2) L. Gao, Z. Li, Y. Zou, S. Yin, P. Peng, Y. Shao, X. Liang, iScience, 23, 101348 (2020).
(3) E. Sánchez-Díez, E. Ventosa, M. Guarnieri, A. Trovò, C. Flox, R. Marcilla, F. Soavi, P. Mazur, E. Aranzabe, R. Ferret, J. Power Sources, 481, 228804 (2021).