Studies On The Reinforced And Self-humidifying Membranes For PEMFCs Applications

The proton exchange membrane (PEM), a key component of proton exchange membrane fuel cells (PEMFC), has dual functions of proton conduction and separation of the anode from the cathode. So far, only perfluorinated sulfonic acid ionomer membranes have been used in practical fuel cells, and their costs are the highest among different components of a fuel cell. The high cost of the perfluorinated membrane is one of the most important factors for retarding the commercialization of PEMFC. It is obvious that the PEMFC steadily working at an elevated temperature can resolve the poisoning problem of CO on the catalyst surface. Operating of PEMFC at the mode of non-humidification of the reactant gases is advantageous for simplifying the PEMFC system.Firstly, SiO₂/Nafion 115 composite membranes were produced via the in situ acid-catalyzed sol-gel reaction of tetraethylorthosilicate (TEOS) in Nafion 115 perfluorosulfonic acid films. The results show that the performance and the stability of a MEA using the composite membrane were higher than that of a commercial Nafion 115 membrane at 130℃.Secondly, a carbon nanotubes reinforced Nafion composite membrane for PEMFCs was developed. Compared with the commercial Nafion? membrane, CNTs/Nafion composite membrane could decrease the dimensional change and improve the mechanical strength of the membrane markedly. At the same time, on account of the low content of the CNTs, the continuous electron transfer channelwas not formed in the membrane and the short circuit did not occur. The proton conductivity of CNTs/Nafion membrane was similar to that of commercial Nafion membrane.Thirdly, a novel three-layer reinforced and self-humidifying composite membrane has been developed based on the CNTs reinforced Nafion membrane. The membrane has two outer layers of plain Nafion and a middle layer of Pt/CNTs dispersed Nafion. The Pt/CNTs present in the membrane provide the sites for the catalytic recombination of H₂ and O₂ permeating through the membrane from the anode and cathode to produce water and improve the mechanical properties of the composite membrane at the same time. The water produced directly humidifies the membrane and allows the operation of PEMFCs with dry reactants.Finally, a Pt/SiO₂-CNTs-Nafion membrane has been developed. The membrane has two outer layers of plain Nafion and a middle layer of CNTs dispersed Nafion seperately. The Pt/SiO₂ present in the membranes provide the sites for the catalytic recombination of H₂ and O₂ permeating through the membrane from the anode and cathode to produce water. The water produced directly humidifies the membrane and allows the operation of PEMFCs with dry reactants. The self-humidifying composite membrane could minimize membrane conductivity loss under dry conditions and improve mechanical strength due to the presence of CNTs.