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

该项目的主要目的是通过制造优化电解液流分布和氧化还原过程的电极来提高有机水溶液氧化还原液流电池（OARFB）的性能。通过新的制造工艺优化的主要性能指标是：-增加电极上电解质分布的均匀性。这增加了局部电流/电压分布的均匀性，增加了电池性能的寿命，因此增加了OARFB成本。它还可以增加可用的反应位点的总数，因为电解质被供应到先前未充分利用的区域。- 减少电极上的压降。这减少了泵送能量损失。- 改进电化学性能为了实现这一目标，次要目标包括：-开发新的制造工艺，以使碳毡和碳纸（目前最流行的电极材料）图案化，并在电极中引入流动通道，例如使用激光加工。- 测试流通式OARFB中的通道和非通道电极，以确定压降和电化学性能的任何差异。- 模拟电解质通过通道电极和非通道电极的流量分布，以支持电池测试的结果。- 使用MRI对电极中的电解质流动进行原位成像。- 综合从电池测试、建模和MRI测试中收集的信息，以提高电极中电解质流动行为的清晰度。作为这项工作的一部分，进一步探索的领域包括通过将纳米颗粒和碳纳米管添加到碳毡或纸中来制造混合电极，以及使用分层结构作为电极设计的灵感。理由和文献：RFBs的电化学性能与电极中电解质的分布密切相关。由于电极两端的压降而由RFB引起的泵送损失也取决于流量分布。因此，通过电极的流动的优化有可能使这两个性能指标受益，降低氧化还原液流电池的成本，从而支持它们的部署，这是电网规模可再生能源存储所需的。电极的仔细结构改性具有改善电极中电解质的流动分布的潜力。结构改性还避免了对潜在有毒、稀有或昂贵材料的需求，因此该项目的最初重点将是结构改性，而不是化学改性。虽然通过电极结构的流动优化可以应用于许多电池化学，但该项目将专注于优化有机水性RFBs的流动。这是由于与市场领先的全钒RFB（VRFBS）相比，它们的潜在成本更低，有机材料丰富，毒性更低。目前对OARFB电极结构的改性研究普遍缺乏。虽然已经对VRFB的结构改性进行了一些研究，但通常与添加钒化学特定的催化剂有关，例如在碳纤维上生长的Ti纳米线。向电极添加通道是电极改性的相当简单的处理步骤。文献中有一项研究使用不同的设计模拟了电极中通道的潜在效应，另一项研究以简单的形式将通道物理添加到电极中。两者都表明该方法是有前途的，但缺乏广泛的调查，这种方法，或开发的优化设计。此外，尽管近年来已经探索了一些用于电极的原位流动成像方法（即热成像和荧光显微镜），但是没有方法能够实现理解碳毡中的流动所需的3D成像。

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.