3D electrodes for more power and longer shelf-life
In FLOW 3D researchers created porous carbon structure, which represent a completely new class of materials. This should lead to an improvement of power density and stability for both redox flow cells and other electrochemical systems.
|Project status||Project completed|
|Project duration||July 2012 until December 2015|
The aim of the consortium is the fabrication of a composite electrode, which is adapted to the requirements of an all-vanadium redox flow battery, using different carbon materials. For this purpose, a novel carbon material with defined pore structure is applied, which due to its specific preparation offers a high accessible surface area. Because of the significantly reduced fraction of inaccessible micro pores, the reaction can occur almost kinetically unhindered. Due to their particular processing, these carbon materials bind well to the pore hierarchy of the carbon felts, so that the active surface is increased and a higher fraction of the electrode volume is addressed electrochemically. Here we are aiming at enhanced activities with simultaneously increased stabilities of the 3D structured electrodes.
Our product represents a completely new class of material, which may be applied not only in redox flow batteries, but also in other electrochemical systems, which need high power density and stability.
A technical feasibility study will be conducted in order to find out whether the processing of the individual industrial partners can be transferred into one joint production step. This measure may have the potential to reduce the production costs considerably.
Paving the way into industry
In contrast to other projects, the consortium of two academic and two industrial partners will at the one hand help to develop a fundamental understanding of the underlying electrochemical and degradation processes, whereas at the other hand also the design of a marketable product will be our focus. For this purpose, the carbon material will be modified using different strategies to generate active functional groups in order to enhance its activity. Moreover, the durability of the modified carbons and carbon felts will be tested directly in the respective electrochemical application. Here, one key aspect will be the detailed characterization of the novel materials, but also the final product, using sophisticated (in-situ) methods.
Generating 3D network directly in fleece
Vanadium-based redox flow cells have been around for quite a while and have demonstrated their aptitude in first field tests. Comparable to fuel cells, also in redox flow batteries energy conversion and storage can be scaled independently. However, in redox flow batteries the energy is stored in a liquid electrolyte. Both the morphology and the surface characteristics of the electrode have a significant impact on the cell's power density. In close cooperation between the four partners (Heraeus Quarzglas, Freudenberg Forschungsdienste - industry; Martin-Luther-Universität Halle-Wittenberg, Karlsruher Institut für Technologie - academia) it is planned to synthesize a novel carbon-based 3D composite electrode by direct templating into the carbon felt. By this approach, the gap between micro and macro porous carbons will be bridged. Starting with the impregnation of commercially available felts with the defined porous carbon, later in the project specifically adapted felts will be utilized with the emphasis on the fabrication of robust and hierarchic electrodes. With this approach it shall be possible to yield a good compromise between a high fraction of electrochemically adressable material and good flow-through characteristics.
The project is divided into three sub-tasks: 3D structuring, modification and characterization:
- 3D structuring of the carbon-based electrode: The aim is to generate controlled porosity in the electrode and to check the technical feasibility for combining the two independent processing steps of the industrial partners.
- Suitable modification of the carbon surface: This approach should lead to higher activities of the applied materials and allow for a larger potential window in redox flow applications.
- Systematic characterization ex situ, in situ and spatially resolved: Using sophisticated characterization methods, the effect of the electrode structure on the performance of the battery will be analyzed as well as the degradation phenomena during operation revealed. The detailed insight will help to develop suggestions for improvement, e.g. how to address a higher fraction of the material electrochemically.
In a first step, hierarchically structured electrodes were obtained in close cooperation of the industrial partners using their commercially available materials in the fabrication of the composite electrode. Felt electrodes were tested in a redox flow test bench, partially functionalized and characterized structurally and electrochemically.