Introduction to Proton Exchange Membranes
Introduction to Proton Exchange Membranes – PEM, Electrolyzer Coatings – Cheersonic
At present, the proton transfer mechanism recognized by the academic community is mainly divided into two types: the Vehicle mechanism and the Grotthuss mechanism. Vehicle mechanism believes that protons are combined with carriers and diffuse and transfer in the form of hydronium ions under the action of electroosmosis, concentration difference and pressure difference. The amount of proton transfer is affected by the diffusion rate of carriers, and there is no proton exchange between carriers. The Grotthuss mechanism believes that protons are transferred between carrier molecules in the form of hopping or structural diffusion along hydrogen bonds.
Proton exchange membranes are classified according to their fluorine content and can be divided into four main categories: perfluorinated proton exchange membranes, partially fluorinated polymer membranes, new non-fluorinated polymer membranes, and composite membranes.
1. Perfluorosulfonic acid membrane
The perfluorosulfonic acid ion exchange membrane is composed of a fluorocarbon main chain and an ether branched chain with a sulfonic acid group. It has extremely high chemical stability and is currently the most widely used fuel cell membrane material. Its proton conductivity can reach above 0.10S·cm-1 at 80℃ and under fully wet conditions. Since the main chain of the perfluorosulfonic acid resin (PFSA) molecule has a polytetrafluoroethylene structure, it has excellent thermal stability, chemical stability and high mechanical strength, and the service life of the polymer film is long; at the same time, the molecular branched chain The hydrophilic sulfonic acid groups on it can adsorb water molecules and have excellent ion conduction properties.
2. Non-perfluorinated proton exchange membrane
Non-perfluorination is mainly reflected in the replacement of fluororesins with substituted fluorides, or the use of fluorides in blends with inorganic or other non-fluorinated compounds.
3. Non-fluorinated proton exchange membrane
The non-fluorinated membrane is essentially a hydrocarbon polymer membrane, which is not only low in cost but also has relatively little environmental pollution, which is a major trend in the development of proton exchange membranes. The main problem of non-fluorinated hydrocarbon polymer membrane used in fuel cells is its chemical stability. At present, there are many polymers with excellent thermal and chemical stability, such as polyphenylene ether, aromatic polyester, polybenzimidazole. , polyimide, polysulfone, polyketone, etc., the key lies in how to use them for proton exchange membrane fuel membrane cells through protonation.
4. Composite film
The perfluorosulfonic acid membrane has the disadvantages of low electrical conductivity and poor alcohol resistance due to lack of water under low humidity or high temperature conditions. research reports. Enhanced perfluorinated proton exchange membranes mainly include PTFE/perfluorosulfonic acid composite membranes and glass fiber/perfluorosulfonic acid composite membranes. High temperature composite proton exchange membrane mainly includes heteropolyacid/perfluorosulfonic acid composite membrane and inorganic oxide/perfluorosulfonic acid composite membrane.
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