Cationic Covalent Organic Frameworks as Anion Exchange Membranes for Electrochemical Energy Applications – COFFEE

The COFFEE project is a fundamental research project that seeks to combine research expertise from different European research institutes and universities, across multiple areas of materials chemistry to develop innovative anion exchange membrane (AEM) solutions for electrochemical energy conversion and storage technologies. This innovative project employs a bottom-up approach to membrane design that aims overhaul the traditional AEM designs that rely on linear cationic polymers and instead develop an entirely new class of membranes based on covalent organic frameworks (COFs). By functionalizing the inside of the cyclic COF structures with cationic groups, we can provide hydroxide conductivity properties to the synthesized COFs. The functionalized COFs then undergo self-assembly to form highly ordered nanochannels, enabling ultrafast hydroxide ion transport through the COF structure. These highly ordered COF structures will then be embedded in a polymer matrix to form membranes with an optimal balance of ionic conductivity and mechanical stability.

A key feature of the COFFEE project is the highly tuneable nature of the final membrane properties through the careful selection of the molecular building blocks used in the COF synthesis. By building up a library of molecular building blocks and understanding their influence on the structure-property-performance relationship of the final membranes, we will be able to successfully predict membrane properties and provide tailor-made membranes for a range of ion exchange membrane-based technologies.

The versatility of our membrane design strategies will be demonstrated by producing membranes optimized for two separate electrochemical energy applications that require significantly differently properties to achieve optimal performance (aside from the universal requirement for high ionic conductivity and stability). As AEMs have gained significant research attention in the areas of electrolysis and solid-state batteries, we will focus our demonstration efforts on anion exchange membrane water electrolysis (AEMWE) and zinc-air battery (ZAB) technologies. This will elevate the COF-based AEMs from a formulated concept, i.e., a TRL of 2, to a validated technology at the lab-scale, i.e., a TRL of 4.

These emerging energy technologies have been touted by the European Commission's Hydrogen Strategy for a Climate Neutral Europe and the European Strategic Energy Technology Plan as key research directions for meeting Europe's ambitious climate goals. The COFFEE project is therefore aligned with the aim of the M-era.Net call of supporting the European Green Deal and the United Nations Sustainable Development Goals. More specifically, the COFFEE project will contribute to obtaining the following expected impacts outlined in the M-rea.Net 2021 call:

- Support the European strategic policy targets in terms of greenhouse gas emission reduction and developing affordable sustainable energy sources and usage.
- Strengthened innovation excellence of the European academia and research institutes.
- Breakthrough outcomes in energy storage, conversion, and harvesting.
- Developing next-generation materials for batteries.
- Developing advanced functional materials for electrochemical energy conversion technologies, such as electrolysers.

The innovative COFFEE solutions are expected to result in scientific breakthroughs, high visibility, and a competitive advantage for the involved partners. The project will contribute to the education of material scientists who might be involved in the implementation of technology in the future. The COFFEE consortium brings together highly skilled scientists with complementary expertise in a range of disciplines, e.g., organic synthesis, COF materials, membranes, electrochemical devices, and creates the opportunity for long term collaboration in research dedicated to excellence in science and innovative industrial applications.