Carbon flow electrodes for continuous operation of capacitive deionization and capacitive mixing energy generation

Abstract

Capacitive technologies, such as capacitive deionization and energy harvesting based on mixing energy ("capmix" and "CO 2 energy"), are characterized by intermittent operation: phases of ion electrosorption from the water are followed by system regeneration. From a system application point of view, continuous operation has many advantages, to optimize performance, to simplify system operation, and ultimately to lower costs. In our study, we investigate as a step towards second generation capacitive technologies the potential of continuous operation of capacitive deionization and energy harvesting devices, enabled by carbon flow electrodes using a suspension based on conventional activated carbon powders. We show how the water residence time and mass loading of carbon in the suspension influence system performance. The efficiency and kinetics of the continuous salt removal process can be improved by optimizing device operation, without using less common or highly elaborate novel materials. We demonstrate, for the first time, continuous energy generation via capacitive mixing technology using differences in water salinity, and differences in gas phase CO 2 concentration. Using a novel design of cylindrical ion exchange membranes serving as flow channels, we continuously extract energy from available concentration differences that otherwise would remain unused. These results may contribute to establishing a sustainable energy strategy when implementing energy extraction for sources such as CO 2-emissions from power plants based on fossil fuels.

Energy Consumption and Recovery in Capacitive Deionization Using Nanoporous Activated Carbon Electrodes

“…Therefore, the electrosorption capacity is determined by the volume (porosity) of the micropores and the energy barrier. The microporosity-based electrosorption theory is critical in analyzing energy consumption during CDI.z E-mail: kkarthikeyan@wisc.edu Although significant progress has been made recently in the development of diverse electrode materials, 13,[19][20][21][22][23][24][25][26][27] theoretical models, [16][17][18] water treatment and desalination devices, 28-30 only very few studies address the issue of energy consumption during CDI. The role of electrode materials in electrosorption and energy consumption is not completely understood and, more importantly, the impact of operational conditions on energy consumption has not been rigorously evaluated when nanoscale porous electrode is applied.…”

Flowable Conducting Particle Networks in Redox-Active Electrolytes for Grid Energy Storage

“…Capacitive suspension electrodes are also strong candidates for low-energy, low-concentration ion removal in applications such as capacitive deionization (desalination) and capacitive mixing (energy generation) and benefit from fast ion adsorption processes. [24][25][26][27][28][29] Nevertheless, for success in energy storage applications, self-discharge and energy density issues need to be addressed. Previously, this energy density issue has been addressed by hybridizing the EFC with either redox-active organic molecules, 23 or pseudocapacitive metal-oxides, 21 e.g.…”

Review Article: Flow battery systems with solid electroactive materials

“…This intermittent operation limits the productivity and causes extra energy consumption during the regeneration procedure. 106 Solid carbon dispersions have also been applied to capacitive deionization applications [see Fig. 4(b)].…”

“…Once flowing carbon electrodes are integrated into the system, the device can run continuously with high capacity because the active carbon can be regenerated without interfering with the deionization process by simply mixing the two carbon suspensions, filtering the carbon suspensions to separate the liquid with concentrated ions, and reinjecting the carbon into the fresh water flow. 106,109,110 The system can be adjusted to fit particular working loads by changing channel size and/or flow rate. More details and discussions on capacitive water deionization and electrochemical flow electrodes can be found in recent reviews.…”

“…29,40,45,46,103,104 Capacitive water deionization is another application where solid suspensions have been coupled into a system with electrodes and electrical potential driving forces. [104][105][106][107] In a conventional capacitive deionization system, a potential is applied between the two electrodes which forms electric double layers and drives ions toward the two electrode surfaces [shown in Fig. 4(a)].…”