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Dispersions (also called ionomers) are one of the critical components of fuel cell components. Catalyst layers require improved ionic conductivity for their optimal operation and hence, preparation of catalyst slurries with the correct dispersion materials will enable high performances. Dispersion (or ionomers) also act as binder agents such as securing the catalyst particles either on the surface of the gas diffusion layers or on the surface of the membranes. During the evaporation of the catalyst ink solvents, a microporous structure is left behind and this helps to bring gaseous or liquid reactants to the catalyst layer or it facilitates the removal of generated gaseous by-products away from the catalyst layer.
Dispersion (or ionomers) can also be used to prepare mechanically reinforced membranes of self-supported membranes. Most of the commercially available dispersions would usually be manufactured either in low molecular weight or high molecular weight forms. Low molecular weight dispersions (or ionomers) would naturally have higher ionic conductivity values (or high acid or ion exchange capacity) compared to high molecular weight dispersions (or ionomers). The molecular weight may sometimes be defined as equivalent weight (EW).
Dispersions can be categorized in terms of their functionality: (1) Functional dispersions or functional ionomers or (2) Non-functional (also called inert) dispersions. Cation or anion exchanging dispersions are the main examples of functional dispersions since they can exchange various cations or anions, respectively. On the other hand, non-functional dispersions have no ionic functionality and hence, it cannot exchange ions. Teflon dispersion is a good example to non-functional dispersion (inert dispersion) and its main functions are to provide binding sites for the catalyst particles, provide a hydrophobic nature to remove by-product water, and also adjust the porosity of the section it has been used for.
Nafion dispersions are in nature cationic and hence they will exchange various cations including protons and should be used in proton exchange membrane (PEM) fuel cells, PEM electrolyzers, or any other cation exchange based electrochemical devices. Fumion, Sustainion, and Orion Polymer dispersions are in nature anionic and hence they will exchange various anions including OH- and should be used in hydroxyl exchange fuel cells (also called alkaline fuel cells), or any other anion exchange based electrochemical devices.