Characterisation of the ferrocene/ferrocenium ion redox couple as a model chemistry for non-aqueous redox flow battery research

Abstract

The simple ferrocene/ferrocenium ion (Fc/FcBF4) redox couple was examined as a model chemistry for non-aqueous redox flow battery research. Its properties were fully characterised using voltammetry, flow-cell battery cycling, and UV-vis spectroscopy to validate flow-cell performance. Fc demonstrates facile kinetics and high stability of its oxidation states, making the Fc/FcBF4 redox couple a useful low-cost model chemistry, despite its limited 0.16 M solubility in acetonitrile. By use of 'single redox couple cycling', in which only the Fc/FcBF4 redox couple is battery cycled, the high capacity retention of Fc at 2 10 mM concentration was demonstrated; 80 % capacity retention after 200 cycles (7.8 days). The mechanism for the capacity loss was investigated and diagnosed to occur via FcBF4 decomposition in the electrolyte, which proceeds irrespective of battery cycling.

Organic–Inorganic Hybrid Polyoxotungstates As Configurable Charge Carriers for High Energy Redox Flow Batteries

“…Several studies have offered experimental methodologies to determine the source of capacity fade in novel RFB systems. 37,38 No electrolyte leakage or charge carrier precipitation was observed during the cycling experiment. In order to investigate the cause of capacity fade, discharged electrolytes were removed from the cell after 21 cycles and were analyzed using cyclic voltammetry.…”

“…There are several physical and chemical factors that could contribute to the observed capacity loss, including degradation, precipitation or oxidation of TBA 3 W 11 SiPh , asymmetric membrane crossover (preferential in one direction), electrolyte leakage, or unwanted side reactions. Several studies have offered experimental methodologies to determine the source of capacity fade in novel RFB systems. , No electrolyte leakage or charge carrier precipitation was observed during the cycling experiment. In order to investigate the cause of capacity fade, discharged electrolytes were removed from the cell after 21 cycles and were analyzed using cyclic voltammetry.…”

Imide-Based Multielectron Anolytes as High-Performance Materials in Nonaqueous Redox Flow Batteries

“…The use of 2i as a prime candidate was then evaluated in a proof-of-concept RFB to investigate the performance at higher concentrations as well as in a full system with a catholyte present. As the cycling performance of the anolyte is of interest within this study, a stable and known catholyte, N -(ferrocenylmethyl)- N , N -dimethylethanaminium bis­(trifluoromethanesulfonyl)­imide Fc1N112-TFSI, was chosen and used in slight excess. − Fc1N112-TFSI exhibits a chemically reversible oxidation at E 1/2 = 0.23 V vs Fc/Fc+. A mixed system was used with anolyte and catholyte present in both reservoirs to minimize capacity loss due to crossover of active species.…”

Redox Flow Batteries: Materials, Design and Prospects

“…The main difference between aqueous and NA-RFBs is in the electrolyte solvent and supporting ions. In NA-RFBs, organic solvents, such as acetonitrile (ACN) [165,[171][172][173][174][175][176][177][178][179], propylene carbonate (PC) [172,176,[180][181][182], and ethylene carbonate (EC) [180,181,183], are used to dissolve metal-ligand complexes as reactive species. To improve conductivity, an ionic liquid is added as a supporting electrolyte such as tetraethylammonium tetrafluoroborate (TEABF4) due to its compatibility with organic solvents [82].…”

“…Their main focus is on developing MCC-based anolytes with lower molecular weight per mole of electron transferred [168]. Other groups are studying about compounds such as Fc/FcBF 4 [174] and cobalt and vanadium trimetaphosphate polyanions promising good potential to the future of NA-RFB [199].…”