Electrochemical Flow Capacitor Research Articles

Charge Transfer and Storage in the Electrochemical Flow Capacitor – A New Concept for Grid-Scale Energy Storage

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Optimization of Flowable Electrode for Electrochemical Flow Capacitors

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Effects of flow cell design on charge percolation and storage in the carbon slurry electrodes of electrochemical flow capacitors

The electrochemical flow capacitor (EFC) is an electrical energy storage concept recently introduced for grid-scale energy storage applications. The EFC utilizes flowable carbon-based electrodes as the active material in a flow battery type architecture for capacitive storage and recovery of energy. Charged slurry can be stored in external reservoirs until it is needed, enabling scalable energy storage to satisfy a variety of large-scale applications. Here, the capacitance and conductivity of EFC slurry electrodes were measured as a function of flow rate (from 0 to 10 ml min−1) and flow cell channel depth (electrode ‘thickness’, ranging from 0.5 to 3 mm). The effect of salt concentration in the electrolyte was also explored. The interfacial resistance associated with the current collector|slurry interface was found to constitute a large portion of the total cell resistance. Bulk slurry conductivity was found to vary significantly with changes in electrolyte concentration, flow rate and channel depth. Very respectable capacitance values of up to ∼30 F ml−1 (150 F g−1) were obtained during intermittent flow operation. However, significant underutilization of the slurry due to increased ohmic losses at larger channel depths was observed, as evidenced by a rapid decay in capacitance with increasing channel depth.

A high performance pseudocapacitive suspension electrode for the electrochemical flow capacitor

The electrochemical flow capacitor (EFC) is a new technology for grid energy storage that is based on the fundamental principles of supercapacitors. The EFC benefits from the advantages of both supercapacitors and flow batteries in that it is capable of rapid charging/discharging, has a long cycle lifetime, and enables energy storage and power to be decoupled and optimized for the desired application. The unique aspect of the EFC is that it utilizes a flowable carbon-electrolyte suspension (slurry) for capacitive energy storage. Similar to traditional supercapacitor electrodes, this aqueous slurry is limited in terms of energy density, when compared to batteries. To address this limitation, in this study a pseudocapacitive additive has been explored to increase capacitance. A carbon-electrolyte slurry prepared with p-phenylenediamine (PPD), a redox mediator, shows an increased capacitance on the order of 86% when compared with KOH electrolytes, and a 130% increase when compared to previously reported neutral electrolyte based slurries. The redox-mediated slurry also appears to benefit from a decrease in ohmic resistance with increasing concentrations of PPD, most likely a result of an increase in the ionic diffusion coefficient. Among the tested slurries, a concentration of 0.139M of PPD in 2M KOH electrolyte yields the largest capacitance and rate handling performance in both cyclic voltammetry and galvanostatic cycling experiments. The improved performance is attributed to the addition of quick faradaic reactions at the electrolyte-electrode interface as PPD undergoes a two-proton/two-electron reduction and oxidation reaction during cycling.

Investigation of carbon materials for use as a flowable electrode in electrochemical flow capacitors

A recently introduced, novel electrical energy storage concept, the electrochemical flow capacitor (EFC), holds much promise for grid-scale energy storage applications. The EFC combines the principles behind the operation of flow batteries and supercapacitors, and enables rapid charging/discharging and decoupled energy/power ratings. Electrical charge is stored in a flowable carbon slurry composed of low-cost and abundantly available carbon particles in pH-neutral, aqueous electrolyte. Charge storage and transfer is analogous to solid carbon electrodes in conventional supercapacitors. Here, the effects of carbon particle solid fraction, shape, and size on the electrochemical and rheological properties of slurry electrodes are investigated. A static cell configuration is utilized for studying the electrochemical properties of the flowable electrodes. The electrochemical properties of the slurry electrodes tested in a static cell are found to be similar to that of solid electrodes in conventional supercapacitors for both, large spherical and anisometric activated carbons. Flow properties of the slurry electrodes are obtained for shear rates corresponding to pumping shear rates by rheometry. Results indicate that electrochemical and rheological properties of slurries depend on their concentration, shape and size of the carbon particles used in the slurries. For a range of concentrations, slurries based on spherical carbon particles show lower viscosities compared to anisometric activated carbon based slurries while performing similar electrochemically.

Electrochemical Flow Cells: The Electrochemical Flow Capacitor: A New Concept for Rapid Energy Storage and Recovery (Adv. Energy Mater. 7/2012)

The electrochemical flow capacitor (EFC) described by E. C. Kumbur, Y. Gogotsi, and co-workers utilizes a flowable slurry of capacitive carbon particles in an aqueous or organic electrolyte. The proposed concept combines the scalability of flow batteries with the high power density and long lifetime of electrochemical capacitors. EFC technology also decouples energy and power ratings, which is important for storage and use of energy from highly fluctuating sources. The proof-of-concept study on page 895 presents promising initial performance data and discusses further development steps for this technology. Flow cell design by the Materials Research Center (Ukraine) and cover design by Kristy Jost (USA).

Electrochemical Flow Capacitors: A New Concept for High-Power Scalable Energy Storage

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The Electrochemical Flow Capacitor: A New Concept for Rapid Energy Storage and Recovery

AbstractAvailability of grid‐scale electric energy storage systems with response rates on the order of seconds plays a key role in wide implementation of renewable energy sources. Here, a new concept called the electrochemical flow capacitor (EFC) is presented. This new concept shares the major advantages of both supercapacitors and flow batteries, providing rapid charging/discharging while enabling the decoupling of the power and energy ratings. Like in supercapacitors, energy is stored in the electric double layer of charged carbon particles. A flowable carbon‐electrolyte mixture is employed as the active material for capacitive energy storage, and is handled in a similar fashion to flow or semi‐solid batteries (i.e., for charging/discharging, it is pumped into an electrochemical cell, and for storage, it is pumped into reservoirs). This study presents the proof‐of‐concept of this technology and reports initial EFC performance data obtained under static and intermittent flow operations.