Modification Of Montmorillonite And Intercalated Proton Exchange Membrane

Proton exchange membrane (PEM) is the key part of direct methanol fuel cell (DMFC), which not only separates the fuel to avoid direct contact, but also transfers a proton from anode to cathode. Non-fluorosulfonic acid PEM has low methanol permeability, but the higher proton conductivity, the higher swelling ratio. In order to resolve the contradiction of conductivity and swelling ratio, montmorillonite (MMT) has been chosen to limit the swelling of membrane because of layer structure of MMT, the limit of swelling can improve the range of sulfonation degree of membrane, thus the conductivity of membrane can be improved. Based on this analysis, the polymer/OMMT PEM system and polymer/water soluble polymer/Na+-MMT PEM system have been designed, which can improve the dispersion of OMMT and Na+-MMT in polymer. The sulfonated poly (phthalazione ether sulfone ketone)(SPPESK), sulfonated polyetheretherketones (SPEEK), polyvinyl alcohol (PVA) and MMT have been used to prepare SPPESK/OMMT, SPEEK/PVA and SPEEK/PVA/MMT composite PEM, and the PEM has been characterized.Firstly, in order to improve the compatibility of MMT and polymer, surfactant with different alkyl chain length and different species ion have been used to modify MMT. In this paper, the arrangement of vertical paraffin-type bilayer has been proposed and confirmed, which improve the arrangement model of alkyl chain in MMT layer. With increasing of surfactant adding content, the alkyl chain take arrangement of1) lateral monolayer,2) lateral bilayer,2) tilt paraffin-type monolayer,4) vertical paraffin-type bilayer,5) tilt paraffin-type bilayer. The biggest d-spacing of STAB-MMT is6.44nm. Increasing the alkyl chain length and branch chain scale are of benefit to improve the d-spacing of OMMT.Secondly, in order to improve the dispersion of OMMT in solvent, the swelling behaviors of OMMT at the micrometer scale and macroscopic scale have been studied in this paper, effect of hansen solubility parameters on the arrangement alkyl chain has also studied. The results show that, the hansen solubility parameters of solvent is very important to the arrangement of alkyl chain,δp of solvent is the primary factor determining whether the solvent intercalated into MMT layer, δd of solvent is the factor determining the d-spacing of MMT, the effect of δh of solvent is lower δp and δd. Based on the properties of solvent, the arrangements of alkyl chain in swelling MMT layer have four forms:1) tilt paraffin-type monolayer,2) vertical paraffin-type monolayer,3) Staggered vertical paraffin-type bilayer,4) exfoliation. With increasing of surfactant adding content, the arrangement developments of alkyl chain in different solvent show the different form. The results of swelling at macroscopic scale show that the hansen solubility parameters of solvent and surfactant adding content are very important to improve the swelling ratio of OMMT.The OMMT have been chosen to prepare the polymer/MMT PEM, which can improve the range of sulfonation degree of membrane. In order to improve the conductivity of SPPESK membrane, higher DS (101%) SPPESK membrane and OMMT have been chosen to prepare SPPESK/OMMT PEM. The results show that the swelling of SPPESK membrane has been limited when the OMMT was added, the water uptake and swelling of membrane are decreased with increasing of OMMT content. The conductivity of SPPESK/OMMT membrane with2%OMMT is0.143S·cm-1, which is80%higher than SPPESK (82%) membrane with the same selling ratio and close to Nafion115membrane (0.186S-cm-1). The methanol permeability of PEM is8.7x10-8cm2·s-1, which is about1/26of the Nafion115.In order to improve the conductivity of PEM, the polymer/water soluble polymer/Na+-MMT PEM system has been designed in this paper. The conductivity of SPEEK/PVA composite membrane, which is prepared by SPEEK (81%) and30%PVA, is0.163S·cm-1(80℃) which is104%higher than SPEEK (51%) membrane with the same selling ratio and close to Nafion115membrane (0.186S·cm-1). The conductivity of SPEEK/PVAMMT composite membrane with20%PVA content and1%MMT is0.185S·cm-1(80℃), which is131%higher than SPEEK (51%) membrane and very close to Nafion115membrane (0.186S·cm-1). The methanol permeability of SPEEK/PVAMMT composite membrane is1.50×10-7cm2·s-1, which is about1/15of the Nafion115.