Water dissociation interfaces for high current density bipolar membrane electrolysers

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.