Hurdles to organic quinone flow cells. Electrode passivation by quinone reduction in acetonitrile Li electrolytes

Abstract

Hurdles to organic quinone flow cells. Electrode passivation by quinone reduction in acetonitrile Li electrolytes. Journal of Power Sources, (2017). 350.

A π‐Conjugation Extended Viologen as a Two‐Electron Storage Anolyte for Total Organic Aqueous Redox Flow Batteries

“…In our previous research, the N,N′‐dimethylated 4,4′‐bipyridinium (MV 2+ ) showed reliable performance in AORFBs application ,. So we first synthesized the N,N′‐dimethylated dipyridinium thiazolo[5,4‐d]thiazole dichloride ( (Me 2 TTz)Cl 2 ) as shown in Scheme .…”

“…As shown in Figure S8, at higher concentrations of electrolytes, that is, 0.25 m [(NPr) 2 TTz]Cl 4 and 0.5 m N Me ‐TEMPO as catholyte (equivalent to 0.5 m electrons), the AORFB (13.4 Ah L −1 and 9.65 Wh L −1 ) delivered similar rate performance and slightly lower energy efficiency (68.6 % EE at 40 mA cm −2 ) than the 0.1 m [(NPr) 2 TTz]Cl 4 and 0.2 m N Me ‐TEMPO battery. Same as the previously reported viologen‐based RFBs,,,, the [(NPr) 2 TTz]Cl 4 /N Me ‐TEMPO AORFB displayed concentration dependent long‐term cycling stability. Specifically, the 0.5 m electron RFB delivered 99.94 % capacity retention per cycle.…”

“…Organic compounds have been used as electrolytes in AORFBs and non‐aqueous organic redox flow batteries (NAORFBs) . We and others have utilized water‐soluble viologen (anolyte),,–, ferrocene (catholyte),,, and TEMPO (catholyte), compounds to demonstrate high performance neutral AORFBs. Among the reported organic compounds, only quinone or alloxazine based (anolyte) compounds are capable of storing two electrons in AORFBs, however, they have been applied in strong acidic or basic AORFBs ,.…”

“…There is not a two‐electron storage compound that is applied in a neutral aqueous system. In addition, very few total organic aqueous redox flow batteries with redox active organic electrolytes in both anode and cathode sides have been reported ,,,…”

“…Unfortunately, due to the high rigidity and hydrophobicity of the Py 2 TTz skeleton, (Me 2 TTz)Cl 2 is poorly water‐soluble (<10 m m in water). Incoporation of highly hydrophilic groups such as ammonium, sulfonate, and phosphate, has been suggested as an efficient strategy to improve the water solubility of redox active organic compounds for AORFB applications . Herein, a highly hydrophilic ammonium functional group was applied to functionalize the N atoms of the pyridine to overcome the solubility issue of the TTz 2+ .…”