Products Cited in Publications Worldwide Utilization of substituted 2,5-dicyanoterephthalates in combination with green solvents for commercialization of non-aqueous redox flow batteries

Utilization of substituted 2,5-dicyanoterephthalates in combination with green solvents for commercialization of non-aqueous redox flow batteries

Horbalová, Julia

Abstract

In this report, terephthalonitriles substituted with nitrile groups are explored as anolyte compounds for their applications in non-aqueous redox flow batteries. Green solvents such as propylene carbonate (PC), γ-butyrolactone (GBR) and γ-valerolactone (GVL) are explored as possible alternatives for acetonitrile (ACN) to achieve lower toxicity and price of the electrolyte solutions utilized in the flow batteries. Three derivatives of terephthalonitriles, dimethyl 2,5-dicyanoterephthalate (C1), diethyl 2,5-dicyanoterephthalate (C2) and bis(2-methoxyethyl) 2,5-dicyanoterephthalate (C3) are investigated as anolytes. Their electrochemical properties and longterm stability are explored using cyclic voltammetry, symmetric H-cell cycling coupled with UV-Vis spectroscopy. Coin cell cycling and symmetric mixed flow battery cycling are completed to investigate the behavior of the active compounds under static and flow conditions, respectively. Experimental results obtained reveal a positive effect of the nitrile group on the redox potential achieving less deep reduction. Furthermore, diffusion coefficients alongside the electron-transfer rate constant are determined presenting values in the range of 1.0x10-5 cm2 /s to 1.0x10-7 cm/s. Additionally, electrontransfer rate constants indicate the systems to be of a quasi-reversible nature the lowest value being in an order of 1.1x10-3 cm/s. Improved diffusivity and electron-transfer rate is further explored in γ-GVL at 54°C and 74°C achieving diffusivity of 2.2x10-4 for C2 making it faster than in ACN. Exploring the compatibility of the anolyte compounds with a catholyte is obtained through coin cell cycling achieving retained capacity of 84% of 50 mM C2 and N-[2-(2-methoxyethoxy)ethyl]phenothiazine (MEEPT) in γ-GVL over 1000 cycles. This particular combination is further investigated under dynamic conditions in flow battery cycling observing the importance of incorporating ACN as a co-solvent to obtain feasible cycling. Various of performing parameters and components of the flow cell were explored and require further optimization to obtain reasonable cyclability limiting the capacity fade of the flow battery. Last, but not least, flow batteries of 10 mM C2 with 10 mM MEEPT in TBAPF6 and one-to-one solution of GVL:ACN achieving retained capacity of 65% and the same flow battery was carried out with C3 as an anolyte obtaining 85% capacity retention, making C3 a good candidate as an anolyte in GVL:CAN flow battery system. Finally, long-term stability measurements of C2 were performed and have presented no indication of decomposition or presence of newly formed species for the length of over one month, indicating a good stability of C2 for long-term measurements.

Purchased from AmBeed

A13194113731-82-398%

2,5-Dibromoterephtalic acid

12.0/5g

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