Fuel cells use hydrogen, natural gas, coal gas, methanol and other non-petroleum fuels and pure oxygen or air to undergo oxidation-reduction reaction at the two poles of the cell, which can continually provide direct current electricity to the environment. According to the types of electrolytes, fuel cells can be divided into alkaline fuel cells, phosphoric acid fuel cells, molten carbonate fuel cells, solid oxide fuel cells, proton exchange membrane fuel cells and others. Membrane material is one of the most important components of fuel cell, which plays an important role in the performance of fuel cell. Material used as fuel cell membrane material need to have some special properties. First, the membrane material needs to have low gas permeability to ensure that the gas used as fuel does not leak. Second, membrane materials need to have high proton conductivity, which is related to the current density of the fuel cell. Moreover, the lower ohm resistance of the membrane can improve the efficiency of the battery. Third, membrane materials need to have good chemical and electrochemical stability, so that fuel cells can have a long working life. Fourth, the membrane material needs to have good thermal stability, which can withstand the uneven thermal impact in battery processing and operation. Fifth, the membrane material needs to have a certain mechanical strength, good machinability, which can meet the requirements of large-scale production. Sixth, considering the production cost, the price of membrane materials can not be too high.
- Sulfonated polyaryl ether ketone series membrane materials: Sulfonated polyaryl ether ketone thin films have good chemical stability, high temperature resistance and high electrical conductivity, so they are the candidates of fuel cell membrane materials. In practical application, in order to further improve the performance of sulfonated polyaryl ether ketone thin films, it is often necessary to modify them. At present, the common modification methods include blending method and organic/inorganic hybrid method. Blending modification can improve the stability of the film and improve the reliability of the modified film. Hybrid material technology is to compound two or more materials so as to synthesize the advantages of several materials to obtain new materials.
Figure 1. An example of sulfonated polyaryl ether ketone series membrane material used in full cell.
- Polybenzimidazole series membrane materials: The proton conductivity of pure polybenzimidazole membrane is low, which cannot meet the requirements of fuel cells. Most of the research focuses on improving proton conductivity by acid doping or base doping. Acid doping methods mainly include membrane immersion, mixed solution film formation, interfacial condensation, grafting reaction and copolymerization reaction. The methods of base doping mainly include membrane immersion and sulfonic acid grafted polybenzimidazole immersion.
Figure 2. An example of polybenzimidazole series membrane material used in full cell.
- Others: In addition to the above systems, materials that can be used as fuel cell membrane materials also include sulfonated polyimide system, polyquinoline system, sulfonated polysulfone system, polyphosphazenes, polysilamine, polyvinyl alcohol and others.
- Jiang J, Zhu X, Qian H, et al. Cross-linked sulfonated poly(ether ether ketone) electrolytes bearing pendent imidazole groups for high temperature proton exchange membrane fuel cells[J]. Sustainable Energy & Fuels, 2019.
- Li H Y, Liu Y L. Polyelectrolyte composite membranes of polybenzimidazole and crosslinked polybenzimidazole-polybenzoxazine electrospun nanofibers for proton exchange membrane fuel cells[J]. Journal of Materials Chemistry A, 2013.