Embroidered electrodes for fundamentals of redox flow cells

Wind and solar technologies only produce energy when the wind is blowing or the sun is shining and alone they cannot be used as effective renewable energy systems. They require the support of a system that can store the energy when it is produced, and release electricity when necessary. Redox Flow Batteries (RFBs) are a promising solution for the energy storage on a large scale. The principle is the following. The electrical energy from wind turbines or solar power is converted into chemical energy through electrochemical reactions. These chemical reactions are called reduction or oxidation reactions (redox reactions) and create energy rich solutions, which are then stored in external tanks. Porous electrodes are required to pump the storage solution through the flow fell. Many RFBs use electrodes made from carbon-based porous materials, which are complex structures and hence it becomes difficult the detailed analysis of the chemical and physical processes occurring inside the batteries. In this project, we will utilise technical embroidery to manufacture innovative electrodes with customized geometries, from very simple structures (only one wire) to more complex shapes. This technology will also enable us to combine conductive elements (copper, aluminium, among others) with non-conductive yarns, such as polyester or polyethylene yarns. As a result of this new ground breaking approach, it will be possible to thoroughly investigate the electrochemistry in 3D-electrodes. This will allow for the first time a systematic analysis of 3D-electrodes in RFBs leading towards the following benefits: A new experimental approach with embroidered electrodes with a desired geometry. Systematic variation in electrode parameters will form the experimental basis for a deepened understanding of the electrochemistry in RFBs. The direct integration of electrodes as sensors for monitoring processes. The experiments will support the development of improved theoretical models for RFBs. This project will provide a substantial contribution towards an improved scientific understanding of Redox Flow Batteries, which will be of high relevance for energy storage from renewable sources, as well as for the design of smart electrical grids.

Renewable energy sources, such as wind and solar energy, are not always available and require the support of a system that can store the energy when it is produced, and release electricity when necessary. Redox Flow Batteries (RFBs) are a promising solution as a stationary energy storage system on a large scale. The principle is the following. The electrical energy from wind turbines or solar power is converted into chemical energy through electrochemical reactions. These chemical reactions are called reduction or oxidation reactions (redox reactions), and create energy rich solutions, which are then stored in external tanks. Porous electrodes are required to pump the storage solution through the flow cell. Many RFBs use electrodes made from carbon-based fiber materials with a complex morphology (random fiber networks), which makes difficult a systematic evaluation of the impact of the electrode structure on the chemical and physical processes occurring inside the batteries. In this project, a textile manufacturing technique called embroidery was employed to create customized electrode structures, from very simple (single wires) to more complex shapes (three-dimensional fiber structures). This allowed for the first time a systematic investigation of three-dimensional porous electrodes in RFBs. As a result, it was possible to determine the impact of electrode structure parameters, such as the number of fibers, the fiber orientation and distribution with respect to the electrolyte flow, on the performance of RFBs. The results allowed for the identification of electrode structure parameters contributing to voltage losses in RFBs, as well as the identification of the main mechanisms responsible for electron transfer and reactant transport related voltage losses. The project provided a substantial contribution towards advances in porous media research, in particular in porous electrodes for redox flow batteries, which is of high relevance for the development of decarbonisation technologies.