Image adapted with permission from 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
In the EFC, a slurry of activated carbon spheres in a non-toxic electrolyte (water with dissolved sodium sulfate) is pumped from reservoirs into the electrode-contact cell (inset), where the spheres acquire surface charge. The charged spheres attract ions in the electrolyte to their surfaces, forming an electrochemical capacitor slurry. The charged slurries are then pumped into separate storage reservoirs. To discharge the cell and extract the stored electrical energy, the process is simply reversed.
A new discovery shows that carbon-electrolyte slurries can store electrical energy in electric double layers just like conventional supercapacitors.
Capacitive carbon slurries can flow, enabling a new type of electrochemical storage device called the electrochemical flow capacitor (EFC), which combines the high charge/discharge rates of supercapacitors with the scalable energy capacity of flow batteries. Because only activated carbon and an environmentally friendly electrolyte are used, this invention (patent pending) is suitable for large-scale storage of renewable energy.
Scientists at Drexel University studying the properties of carbon slurries have discovered that the electrochemical and physical flow characteristics of such slurries are favorable for a new grid-scale storage concept called the electrochemical flow capacitor (EFC). In work supported by the Fluid Interface Reactions, Structures, and Transport (FIRST) Center, a DOE Energy Frontier Research Center, researchers have discovered that, just like supercapacitors, energy is stored in the electric double layer of charged carbon particles in an electrolyte slurry. A flowable carbon-electrolyte slurry could serve as the active material for an EFC, in which the charged slurry is handled in a similar fashion to flow or semi-solid battery fluids (i.e., for charging/discharging, the slurry is pumped into an electrochemical cell; for energy storage, the charged slurry is pumped into reservoirs). This new concept shares the major advantages of supercapacitors and flow batteries, providing rapid charging/discharging and excellent cyclability, while enabling the decoupling of the power and energy ratings. The study reported promising initial EFC performance data for carbon slurries obtained under static and intermittent flow operations. This approach may reduce the use of polymer separators, metal current collectors and packaging materials; these passive elements increase the cost and weight in current devices without contributing to the charge storage.
Director of the Fluid Interface Reactions
Structures and Transport (FIRST) Center EFRC
DOE Office of Science, Basic Energy Sciences, Energy Frontier Research Centers (EFRC) Program (V.P. and Y.G.); Alexander von Humboldt Foundation (fellowship support for V.P.); National Science Foundation student fellowships - IGERT (C.R.D.), REU (K.W.K.) and Bridge to the Doctorate Fellowship (J.C.); and Southern Pennsylvania Ben Franklin Energy Commercialization Institute (E.C.K.)
Presser, V.; Dennison, C.R.; Campos, J.; Knehr, K.W.; Kumbur, E.C.; and Gogotsi, Y. “The Electrochemical Flow Capacitor: A New Concept for Rapid Energy Storage and Recovery” Advanced Energy Materials, 2, 895–902 (2012). [DOI: 10.1002/aenm.201100768]
Gogotsi, Y., Presser, V., Kumbur, C. “Electrochemical Flow Capacitors, Patent Application PCT/US2012/024960, February 14, 2012
Fluid Interface Reactions, Structures and Transport (FIRST) Center EFRC