Evaluation of thermal stability assessment for flow batteries and deeper investigation of the ferrocene co-polymer
The stability of reported organic materials for redox flow batteries (RFB) continues to improve. Consequently, the relevance of analytical techniques to assess degradation rates also grows. To contribute to the development of in operando thermal stability assessment techniques, we evaluated the comm...
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| Published in | Journal of materials chemistry. A, Materials for energy and sustainability Vol. 12; no. 8; pp. 486 - 4825 |
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| Main Authors | , , , , , , , , , , , |
| Format | Journal Article |
| Published |
20.02.2024
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| Online Access | Get full text |
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| Summary: | The stability of reported organic materials for redox flow batteries (RFB) continues to improve. Consequently, the relevance of analytical techniques to assess degradation rates also grows. To contribute to the development of
in operando
thermal stability assessment techniques, we evaluated the commonly-reported heating setups using the ferrocene-based FPMAm-
co
-METAC polymer (PFc) in a Zn-based hybrid RFB with a size-exclusion membrane. In the first stage, the conditions for RFB cycling were selected and evaluated. The amperometric SOC measurement technique revealed oxygen intolerance of the PFc. While no polymer cross-over was detected, cross-over of its hydrolysis products occurred and facilitated the capacity fade. Adjustment of membrane pore size and electrolyte composition helped to mitigate the hydrolyzed products' cross-over. In the second stage, different heating setups for the thermal stability evaluation of PFc were compared. Eventually, a thermostatic setup established the desired temperature most accurately and homogeneously, while the popular oil/sand bath setup exhibited a deviation of 22 °C down from the expected 60 °C. The PFc stability was further evaluated from ambient conditions (28 °C) to 60 °C. At temperatures above 50 °C a facilitated capacity fade was observed. The volumetrically unbalanced, compositionally symmetric flow cell cycling has unraveled that the degradation was caused by catholyte self-reduction and following half-cell imbalances. A mechanism involving the ferrocene complex decomposition is proposed as the origin of the catholyte self-reduction. Finally, the properties and thermal stability of the PFc material as well as the reliability of the studied heating setups are discussed.
Reliability of common heating setups for RFBs was evaluated. The ferrocene polymer exhibited highest thermal stability among all currently studied organic materials; still, further improvements are needed to approach practical applications. |
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| Bibliography: | CV; electrospray ionisation mass spectrometry; cyclic voltammetry of the PFc in the newly applied tetramethylammonium-based electrolyte; cross-over evaluation in TMACl-based electrolytes; estimation of RFB technical parameters under the finalized testing conditions; photographs depicting precipitate formation on RFB tank walls in setup 3; validation of the SOC assessment by the OCV measurement technique; GS-MS results; evaluation of the apparent rate constants for PFc catholyte fade in full RFBs using different heating setups; capacity fade rates estimated from the digitized results from the study by Quinn Cl-based electrolyte; comparison of RFB performances, utilizing OS-NF-8800 membrane and cycling in different regimes; dendrite formation evaluation and studies; exemplary curves from the RFB tests in lower current cycling regime; UV-vis calibration for PFc containing solutions; cross-over evaluation in the NH mechanism of the diphenylacetate oxidation redox mediated by ferrocene. See DOI Electronic supplementary information (ESI) available: Evaluation and mitigation of the zinc dendrite growth; a brief review of temperatures applied during in situ https://doi.org/10.1039/d3ta05809c via in operando 4 thermal stability assessment in RFBs; chemical characterization of the PFc; full RFB practical voltage; potentiometric titration; atomic absorption spectroscopy; exemplary curves from the RFB tests in higher current cycling regime; validation of the calibration-free amperometric SOC measurement technique; photographs on the post mortem RFB electrolytes; capacity fade during the UCSFCC test in, utilizing NH Cl-based electrolytes; qualitative analysis of PFc capacity fade in RFB anolyte thermal stability assessment in redox flow batteries (RFBs); reasoning of the choice of the heating setups for the investigation; heating setups applied for et al. |
| ISSN: | 2050-7488 2050-7496 |
| DOI: | 10.1039/d3ta05809c |