Development and optimization of flow electrode capacitor technology

Flowable slurry electrodes have recently received an increased interest for use in electrochemical energy storage and water treatment systems. Within this project we develop a model for efficient charging of flowable mixtures in circulating flow capacitor for large scale applications. The flow-capacitor (FC) is a novel all-liquid capacitor which working principle is based on the separation of ions from a fluid electrolyte by a low-voltage electric field. Such capacitor can be used in equipment where fluid flow or motion of liquid is essential for its operation. Target applications are hydraulic equipment (fork lifts, cranes, also geothermal heat pumps etc.). For breakthrough performance an improvement in self-discharge rate and optimisation in flow-process and in membrane architecture is needed. Thus, computer simulations, capable of accurate description of electrochemistry in the cell are needed. The finite element method (FEM) based simulations, combining the charge and mass transport, coupled to the charging of electrical double layer of carbon particles in liquid electrode slurry are used to conduct initial simulations of the FC cell. Such simulations assume that the convective movement of liquid electrolyte is negligible and will allow to characterize the basic properties of the system, such as the effect of cell geometry, material properties. Simulations allow to test combinations of electrolyte and membrane materials to pinpoint the most suitable ones and minimize the effects of self-discharge. The results of the simulations are coupled to the experimental studies by testing the proposed materials. Moreover, FEM simulations provide significant advantage of designing the FC geometry. Current FC applications rely on the use of millimetre scale equipment. Performance of such device is limited, since the utilization of liquid electrode material takes place only near the current collectors in diffusive layer. This effect can be countered, when convective mass transport in the FC electrodes is implemented and capacity to conduct the complete optimization of the device is reached. Application of mass and charge transport equations, coupled with convective flow simulations makes it possible to find suitable geometries and conduct optimization with maximum mixing of liquid electrolyte as final goal. By applying such approach, optimal utilization of the material is reached, leading to maximum charging/discharging rates optimal flow process of the electrode slurry.