An electrolyser is a device that splits water to produce hydrogen. However, there are different types of electrolysers, and therefore different systems to split water into hydrogen and oxygen. At ANEMEL, we specialise in anion exchange membrane (AEM) electrolysers. At their core lies, of course, a membrane.
Not all electrolysers need membranes, but ours do. They are central to our devices, not only because they literally occupy the central position, separating the anode and cathode, but because they are essential for the electrochemical reactions. But let’s start from the beginning.
An AEM is actually a very thin plastic film. It is typically based on a polymer backbone with cationic functional groups. This positively charged polymer interacts with anions, negatively charged ions, allowing them to flow freely and quickly across the membrane.
This is a crucial feature for a membrane, as one of its main roles is to effectively transport hydroxide anions (OH–) —and water— between the two electrodes. Such property is related with the efficiency of the electrolyser, as it’s this free flow of hydroxide ions that eventually enables the electrochemical reaction. Alongside this “carrier” role, the membrane also plays a “barrier” role as it separates the hydrogen (H₂) and oxygen (O₂) gases formed in the electrodes during electrolysis. If both were to mix, the result could be… extremely explosive!
AEM electrolysis is particularly interesting as it operates under alkaline conditions, which are less corrosive than other electrolytic technologies. This opens the door to using materials such as nickel, iron, or steel, avoiding the need for precious and scarce metals in both the catalysts and the hardware. As a result, the technology is more cost-effective and scalable.
Another advantage is that membrane-based technologies typically exhibit a lower resistance, leading to higher current densities. This means the amount of energy required to produce hydrogen is smaller, which means a smaller carbon footprint. Plus, AEM is compatible with intermittent energy sources, including renewable energies such as solar, wind, and hydrothermal.
Despite these advantages, AEM water electrolysis is still in a premature position compared to current alternatives in hydrogen production. It is indeed the least developed compared to proton exchange membrane (PEM) electrolysis and alkaline water electrolysis. Why, you wonder? It’s because for many years, the technology stayed behind —it was extremely challenging to make membranes work reliably.
Achieving a high-performance membrane presents several challenges. First, it must provide sufficient ionic conductivity, which is a critical requirement for the electrochemical reactions to work. Secondly, the chemical stability is a major concern, due to the side reactions that occur in the presence of hydroxide ions, which lead to wear and tear
The third challenge is related to the membranes’ mechanical stability, key to the integration into cells and stacks. The difficulty with mechanical stability is a complex paradox: while high conductivity usually requires a high concentration of ionic functional groups. this increases instability. More moieties in the membrane, i.e. cationic groups, increase the ion exchange capacity and conductivity, but make the membrane highly hydrophilic. As a result, it absorbs large amounts of water, becomes gel-like, which is weaker and wobblier.
With all these three challenges together, it is no wonder why membranes remained a mystery for many years. Over the past few years, however, researchers have begun to explore new generations of membranes, as explained by ANEMEL researcher Xile Hu in this ANEMEL webinar.
This means, of course, we are still struggling too to build our membranes. But we are certainly going in the right direction. To make matters worse, at ANEMEL we decided to take a step further, building our membranes with fluorine-free “functional groups” and polymers, to avoid the reliance on polluting PFAS —the infamous “forever chemicals”. Over the past year, we have continued working on some promising polymers, as well as on scaffolding to provides polymers with extra mechanical stability. However, we have encountered some plot twists along the way…
At the beginning of the project, we worked with commercial polymers, improving them with key chemical modifications. Since the project has a limited timeframe, it made sense to build on something that already worked well. Later on, we explored designing polymers from scratch. ANEMEL considers sustainability and scalability from the start, and, in an industrial perspective, materials built “brick by brick” may be better. We achieved very promising results, but when it came to scaling up, this approach was less successful. The polymers were not mechanically strong enough, which eventually made ANEMEL researchers return to commercially available alternatives.
We have not only achieved excellent results with this option, it also works well at a larger scale. This required identifying a suitable commercial scaffold that we could use. Our WP2 is now focusing on scaling up the membranes, not yet to an industrial level, but large enough to allow WP3 and WP4 develop our stacks. For more up-to-date information on the latest developments, check out our latest annual report!