Water dissociation interfaces for high current density bipolar membrane electrolysers

预计氢气将成为重要的工业燃料、储能介质和替代供热燃料。因此，迫切需要开发从非化石资源中产生氢的方法，避免产生二氧化碳作为副产品。零碳氢可以通过使用可再生能源电解水产生，氧气是唯一的其他产品。这是一个很有前途的方法，通过提供长期的能源储存，克服了与供应间歇性有关的问题，提供了一种增加可再生能源市场渗透率的方法。目前领先的水电解技术是在酸性环境下进行的。析氢反应在酸中是有效的，而析氧反应则不然。对于酸电解来说，唯一用于制氧的活性催化剂的可用性很低，不足以满足预测的需求。另一种选择是在碱中进行电解，虽然存在一系列可用的析氧催化剂，但析氢催化剂的效率降低。为了在全球范围内提供电解，需要替代技术。从电催化剂的角度看，理想的电解槽应在酸中进行析氢反应，在碱中进行析氧反应。这将利用现有的可伸缩电催化剂。双极膜电解槽实现了这一点。当双极膜充分反向偏压时，其中的水解离，质子被输送到析氢电极，产生酸性环境，氢氧化物被输送到析氧位点，产生碱性环境。双极膜电解槽代表了第三种通过电解产生零碳H2的方法，但研究还远远不够，重要的是，它们可以按要求的规模交付。但要使双极膜成为一种可行的技术，还需要在效率和稳定性方面有很大的改进。从历史上看，水在膜上的运输会导致脱水和脱层，这导致了不稳定性，但最近的研究表明，这些问题可以通过仔细控制聚合物膜的厚度来解决。尚未解决的问题是双极膜内水解离效率低所造成的巨大损失。在双极膜中添加催化剂层是一种很有前途的方法，但还需要进一步的研究。在这里，我们将利用金属氧化物催化剂在膜结构中开发新的水解离界面，这些催化剂针对当地的pH环境进行了优化，以赋予高水平的活性和稳定性。我们提出的创新界面设计将探索如何最大化局部电场和水解离的催化增强，同时最大限度地减少膜中的阻力损失，以实现水解离活性的阶跃变化，并通过双极膜电解证明零碳氢的可行性。

Hydrogen gas is predicted to become an important fuel for industry, energy storage medium and an alternative heating fuel. Therefore an urgent need exists to develop ways to generate hydrogen from non-fossil resources, avoiding the generation of carbon dioxide as a by-product. Zero carbon hydrogen can be generated by the electrolysis of water using renewable power with oxygen being the only other product. This is a promising approach, providing a way to increase market penetration of renewable power by providing a long-term energy store which overcomes issues relating to intermittency of supply. The current leading water electrolysis technology operate in acid. Whilst the hydrogen evolution reaction is efficient in acid the oxygen evolution reaction is not. For acid electrolysis the only active catalysts for oxygen production have a very low availability and there is insufficient to meet predicted demand. An alternative is to carry out electrolysis in base, whilst a range of available oxygen evolution catalysts exist, the efficiency of the hydrogen evolution catalyst is decreased. To deliver electrolysis at a global scale alternative technologies are needed.From an electrocatalyst perspective the ideal electrolyser would run the hydrogen evolution reaction in acid and the oxygen evolution reaction in base. This would make use of the existing, scalable electrocatalysts. Bipolar membrane electrolysers achieve this. When the bipolar membrane is reverse biased sufficiently water within it dissociates and protons are transported towards the hydrogen evolution electrode, generating an acid environment and hydroxide to the oxygen evolution site, generating a basic environment. Bipolar membrane electrolysers represent a third, but massively under-researched, way to generate zero-carbon H2 by electrolysis and importantly they can be delivered at the scale required. But to be a viable technology large improvements in efficiency and stability of the bipolar membrane are needed. Historically issues relating to water transport across the membrane, which lead to dehydration, and also delamination have caused instabilities but recent studies have shown that these can be largely addressed by careful control of the polymer membrane thickness. What has not been solved is the large losses associated with the low efficiency of water dissociation within the bipolar membrane. Addition of catalyst layers into the bipolar membrane is a promising approach but more research is urgently needed. Here we will develop new water dissociation interfaces within the membrane structure with metal oxide catalysts that are optimised for the local pH environment to impart both high levels of activity and stability. Our proposed innovative interface design will explore how to maximise the local electric field and the catalytic enhancement of water dissociation whilst minimising resistance losses in the membrane, to deliver a step change in water dissociation activity and demonstrate the viability of zero carbon hydrogen by bipolar membrane electrolysis.