All Polythiophene Redox Flow Battery

Surge in demand for electrical energy has been a common phenomenon around world. In addition, greenhouse gas emission is another challenge. As a solution to these problems, large-capacity energy storage system have been proposed. This energy storage system can manage the increasing energy demand more efficiently in conjunction with renewable energy and smart grid.

Among various large energy storage systems, the redox flow battery (RFB) is one of the most viable alternatives. In particular, RFB in the range of 10 kW-10 MW is the most competitive in terms of cost, flexibility, rapid response and safety over other secondary batteries such as lithium ion and sodium sulfur batteries [1].

RFB can be simply classified into aqueous and organic redox flow batteries. Of the aqueous RFBs, all vanadium RFB and zinc/bromine RFB are the most representative ones. Many companies have been considering the commercialization of those flow batteries based on their high energy density and low cost. However, the aqueous redox flow battery is limited by water electrolysis which prevents from increasing the cell potential out of the hydrogen or oxygen evolution voltage.

Organic redox flow battery, which is free from the water electrolysis problem, has been studied extensively. Organic molecules can be synthesized from low-cost, lightweight, widely available materials. In addition, their electrochemical properties can be easily adjusted using the well-established knowledge of organic chemistry [2]. By taking these attributes of organic materials, it may be possible to make a redox flow battery with very high energy densities and power densities.

Polythiophene is a representative conjugated polymer.  It has received a lot of attention due to its various availability as nonlinear optics and electronic device [3].

In this study, we investigated the possibility of polythiophene as a redox couple in organic redox flow battery. Polythiophene shows electrochemical redox activities at two different potentials of about -2.0 V and +0.5 V versus Ag/Ag⁺ (figure 1). The polythiophene is reduced at -2.0 V (n-doping) and oxidized at +0.5 V (p-doping). To investigate the charge-discharge characteristics, a single cell with the active electrode area of 7.0 cm úI 5.0 cm was used.

References

1. P. Leung, X. Li, C.P. de León, L. Berlouis, C.T. John, and F.C. Walsh, RCS Advances, 2, 10125 (2012).

2. S.E. Burkhardt, M.A. Lowe, S. Conte, W. Zhou, H. Qian, G.G. Rodriguez-Calero, J. Gao, R.G. Hennig, and H.D. Abruna, Energy Environ. Sci., 5, 7176 (2012).

3. S. Jin, S. Cong, G. Xue, H. Xiong, B. Mansdorf, and S.Z.D. Cheng, Adv. Mater. 14, 1492 (2002).