Mechanistic Understanding of Capacitive Deionisation (MU-CDI)

水系统中离子的捕获和管理对社会具有广泛的重要性。最突出的应用之一是海水淡化，由于人口增长和气候变化对淡水资源造成压力，海水淡化正成为一项日益重要的技术。近年来，电容式去离子（CDI）作为一种潜在的低能耗替代方法（如反渗透）越来越受到关注。CDI通过使盐溶液通过电化学电池来工作，其中正盐离子和负盐离子固定在带相反电荷的多孔碳电极的表面上。CDI优于其他脱盐方法的优点之一是，在初始离子捕获步骤之后，电极可以通过排放到单独的流出液中而再生。在该步骤中，回收了用于离子捕获的一些能量，此外，电极的有效再生减少了结垢。尽管CDI有希望，但它的效率在高盐浓度下会降低。在这方面，它不会与其他方法竞争，例如反渗透处理海水。近年来，人们进行了大量的研究工作，以扩大CDI有效的浓度范围。大多数发展都集中在材料和电池设计的优化上，取得了相当大的成功，然而，令人惊讶的是，很少考虑到离子行为或在每个电极上发生的基本过程的细节。主要考虑因素之一是确保离子电荷由电极捕获的离子存储，而不是与进料电解质中的离子交换（这不会降低盐浓度）。该建议旨在发展对CDI的机械理解，并应用这些知识来控制离子存储机制以优化盐去除效率。这将通过使用详细的电化学分析和使用核磁共振（NMR）来完成，这使我们能够“看到”和计数电极中捕获的离子，并将其与电化学响应和除盐效率相关联。我们将研究电极孔径和电解质性质，如浓度和存在的离子的性质，如何影响它们如何被捕获。然后，该信息将用于通知和优化电池设计和操作条件（例如，流速和电池电压）。我们提出的工作本质上是基础性的，主要目的是提高对CDI基础科学的理解，而不是制造原型CDI堆栈。然而，通过与学术和工业合作伙伴的合作，我们的目标是使用和识别可扩展和商业相关的电极材料。

The capture and management of ions in water systems are of widespread importance to society. One of the most prominent applications is water desalination, which is becoming an increasingly important technology due to population growth and climate change putting pressure on freshwater resources. In recent years, capacitive de-ionisation (CDI) has gained increasing attention as a potentially low-energy alternative to more common desalination methods such as reverse osmosis. CDI works by passing a saline solution through an electrochemical cell where the positive and negative salt ions are immobilized on the surfaces of oppositely-charged porous carbon electrodes. One of the advantages of CDI over other desalination methods is that following the initial ion capture step, the electrode can be regenerated by discharging into a separate effluent stock. In this step, some of the energy used for the ion capture is recovered, and furthermore, the efficient regeneration of the electrode reduces fouling. Despite the promise of CDI, its efficiency reduces at high salt concentrations. In this respect, it does not compete with other methods such as reverse osmosis for treatment of seawater. In recent years there have been considerable research efforts to extend the concentration range in which CDI is effective. Most development has focused on optimisation of materials and cell designs with considerable success, yet, surprisingly little consideration has been given to details of the the ion behaviour or the elementary processes taking place at each electrode. One of the primary considerations is to ensure that ionic charge is stored by ions being captured by the electrode, rather than being exchanged with those in the feed electrolyte (which does not reduce the salt concentration). This proposal seeks to develop a mechanistic understanding of CDI and apply this knowledge to control the ion storage mechanism to optimize the salt removal efficiency. This will be done through the use of detailed electrochemical analysis and the use of nuclear magnetic resonance (NMR), which allows us to "see" and count ions that are captured in the electrode, and correlate this with the electrochemical response and salt removal efficiency. We will investigate how the electrode pore size and electrolyte properties, such as concentration and the nature of the ions present, affect how they are captured. This information will then be used to inform and optimise the cell design and operational conditions (e.g., flow rate and cell voltage). Our proposed work is necessarily fundamental in nature with the key aim of improving the understanding of the underlying science of CDI, rather than fabrication of prototype CDI stacks. However, through our collaborations with academic and industrial partners, we aim to work with, and identify, scalable and commercially-relevant electrode materials.