Optimisation of flow of electrolytes through electrodes in organic aqueous redox flow batteries

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The main aim of this project is to improve the performance of organic aqueous redox flow batteries (OARFBs) by manufacturing electrodes that optimise electrolyte flow distribution and redox processes. The main performance metrics to be optimised through new fabrication processes are: -Increased uniformity of electrolyte distribution across the electrode. This increases uniformity of local current/voltage distribution, increasing longevity of cell performance and hence OARFB cost. It may also increase the total number of reaction sites available, as the electrolyte is supplied to areas previously underutilized. -Reduction of pressure drop over electrodes. This reduces pumping energy losses. -Improvement of electrochemical performance To achieve this, secondary aims include: -The development of new manufacturing processes to pattern carbon felt and carbon paper (currently the most popular electrode materials) and introduce flow channels in the electrodes, for instance using laser processing. -To test channelled & non channelled electrodes in flow-through OARFBs, to determine any differences in pressure drop and electrochemical performance. -To model flow distribution of electrolyte through the channelled & non channelled electrodes, to support the results of the cell tests. -To use an MRI to image electrolyte flow in the electrode in situ. -To synthesize information gathered from cell testing, modelling and MRI testing, to provide increased clarity on the flow behaviour of the electrolyte in the electrode. Further areas to explore as part of this work includes the fabrication of hybrid electrodes by addition of nanoparticles and carbon nanotubes to carbon felt or paper, and the use of hierarchal structure as inspiration for electrode design.Justification & literature: The electrochemical performance of RFBs is strongly related to the distribution of the electrolyte in the electrode. The pumping losses incurred by an RFB due to pressure drop across the electrode are also dependent on the flow distribution. Therefore, optimization of flow through the electrode has the potential to benefit both these performance metrics, lowering the cost of redox flow batteries and hence supporting their deployment, which is required for the storage of grid scale renewable energy. Careful structural modification of the electrode has the potential to improve the flow distribution of the electrolyte in the electrode. Structural modification also avoids the need for potentially toxic, rare or expensive materials, and therefore the initial focus of this project will be on structural rather than chemical modification. Although flow optimization via electrode structuring could be applied to many cell chemistries, this project will focus on optimising flow for organic aqueous RFBs. This is due to their potential lower cost compared to the market leading all vanadium RFB (VRFBS), abundance of organic material and lower toxicity. There is a general lack of research into structural modification of electrodes for OARFB. Although there has been some investigation into structural modification for VRFBs, it is often related to addition of catalysts specific to the vanadium chemistry, e.g. Ti nanowires grown on carbon fibre. Adding channels to the electrode is a fairly simple processing step for electrode modification. There is one study in the literature that modelled the potential effect of channels in the electrode using different designs, and one other that physically added channels to the electrode, in a simple form. Both showed the method to be promising, but there lacks extensive investigation of this method, or development of optimised designs. Further to this, although a few in situ flow imaging method for the electrodes have been explored in recent years (namely thermal imaging and fluorescence microscopy) no method enables the 3D imaging required to understand flow in carbon felt.