PFAS-free cellulose-based membranes for green applications

Introduction. Cellfion is a company developing PFAS-free membranes based on chemically functionalized nanocellulose. The membranes are highly tuneable and exhibit favourable properties such as high selectivity, low resistance and low swelling. Cellfion’s membranes have shown potential for use in different applications such as electrodialysis, fuel cells, electrolyzers, humidification systems and flow batteries. Cellfion’s membranes are a sustainable, completely PFAS-free alternative to traditional selective membranes. Experimental/methodology. Cellfion’s membranes are based on nanocellulose extracted from bleached softwood fibres, and are produced in a process similar to papermaking, which we have developed in our labs in Stockholm. The chemical modifications are done on the cellulose fibres, which are thereafter processed via high-pressure homogenization to liberate the cellulose nanofibrils. The nanofibrils contain functional groups on their surface, the type and amount of functionalization is controlled by the initial chemical process step. The nanofibril dispersion is converted into membrane form. The membrane properties can also be enhanced via additives and/or post-modifications. Membranes are characterized by electrochemical impedance spectroscopy to determine their resistivity, and their selectivity is determined via membrane potential measurements. Membranes have been tested for electrodialysis for desalination of water, for both organic and inorganic flow batteries as well as for fuel cells and electrolyzers. Results and discussion. Cellfion’s membranes have been characterized by several methods including electrochemical measurements to determine resistivity and selectivity. Membranes show low resistivity and high selectivity towards sodium, potassium, ammonium and lithium ions as well as protons. Crosslinked membranes exhibit low swelling in the Z-direction. Afterwards, membranes have been evaluated for use in different electrochemical applications. Tuning the membrane properties to make them suitable for a variety of applications can be done via the type and degree of chemical modification of the starting material or by post-modifications of the membranes. Using these strategies Cellfion has developed membranes that show promise for use in systems such as electrodialysis, proton exchange membrane fuel cells, redox flow batteries, and electrolyzers. Specifically, membranes tested for desalination of salt water have shown similar rates of desalination to standard commercial membranes. Work is ongoing to further develop and optimize the membranes into products for the applications listed above. Acknowledgments We thank our collaborators, financial partners and investors: Lund University, EIC Accelerator, Swedish Energy Agency, Vinnova, Almi Greentech Invest, Voima Ventures, Klimatet Invest, and KTH Innovation, LiU Invest.