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Degradation Phenomena of Bismuth-Modified Felt Electrodes in VRFB Studied by Electrochemical Impedance Spectroscopy

1
Institute for Chemistry and Biochemistry, Freie Universität Berlin, Takustr. 3, D-14195 Berlin, Germany
2
Chemistry Department, Faculty of Science, Cairo University, Cairo 12613, Egypt
3
Department of Physics, Freie Universität Berlin, Arnimallee 14, D-14195 Berlin, Germany
*
Author to whom correspondence should be addressed.
Batteries 2019, 5(1), 16; https://doi.org/10.3390/batteries5010016
Received: 13 November 2018 / Revised: 9 December 2018 / Accepted: 17 January 2019 / Published: 23 January 2019
(This article belongs to the Special Issue Vanadium Redox Flow Battery and Its Applications)
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Abstract

The performance of all-V redox flow batteries (VRFB) will decrease when they are exposed to dynamic electrochemical cycling, but also when they are in prolonged contact with the acidic electrolyte. These phenomena are especially severe at the negative side, where the parasitic hydrogen evolution reaction (HER) will be increasingly favored over the reduction of V(III) with ongoing degradation of the carbon felt electrode. Bismuth, either added to the electrolyte or deposited onto the felt, has been reported to suppress the HER and therefore to enhance the kinetics of the V(II)/V(III) redox reaction. This study is the first to investigate degradation effects on bismuth-modified electrodes in the negative half-cell of a VRFB. By means of a simple impregnation method, a commercially available carbon felt was decorated with Bi 2 O 3 , which is supposedly present as Bi(0) under the working conditions at the negative side. Modified and unmodified felts were characterized electrochemically using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in a three-electrode setup. Surface morphology of the electrodes and composition of the negative half-cell electrolyte were probed using scanning electron microscopy (SEM) and X-ray fluorescence spectroscopy (TXRF), respectively. This was done before and after the electrodes were subjected to 50 charge-discharge cycles in a battery test bench. Our results suggest that not only the bismuth catalyst is dissolved from the electrode during battery operation, but also that the presence of bismuth in the system has a strong accelerating effect on electrode degradation. View Full-Text
Keywords: vanadium; redox flow battery; degradation; bismuth; electrochemical impedance spectroscopy vanadium; redox flow battery; degradation; bismuth; electrochemical impedance spectroscopy
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Schneider, J.; Bulczak, E.; El-Nagar, G.A.; Gebhard, M.; Kubella, P.; Schnucklake, M.; Fetyan, A.; Derr, I.; Roth, C. Degradation Phenomena of Bismuth-Modified Felt Electrodes in VRFB Studied by Electrochemical Impedance Spectroscopy. Batteries 2019, 5, 16.

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