Preparation And Evaluation Of Novel Bacterial Cellulose-Based Methanol-Resistant Proton Exchange Membrane Composites

Bacterial cellulose (BC) is a kind of natural macromolecular nano-material obtained via fermentation of some microorganisms. Compared to plant cellulose (PC), BC is chemically same but distinguished by its special3D nanostructure morphology, high tensile strength, high crystallinity, high chemical purity, high water binding capacity, low gas permeation and good biocompatibility. Hence, BC has been studying in various fields. Most recently, the applications of BC in key devices of proton exchange membrane fuel cell (PEMFC) including carbon support catalysts, gas diffusion layer (GDL) and proton exchange membranes have been investigated. However, researches on fabricating the proton exchange membrane from BC are not systematic and in-depth. Therefore, in this paper, BC films from two microbial sources were comparatively investigated by scanning electron microscopy (SEM), FTIR spectra, TG profiles, contact angle, methanol uptake. A gas chromatographic method for determining methanol permeability of pure BC membranes was established. The methanol permeability of BC membranes was studied in detail from four aspects including film thickness, methanol concentration, testing temperature and sources of BC membranes. Experimental results showed that the BC films from two microbial cultures had good three-dimensional network structure, and good thermal stability, especially, the BC films produced by Kombucha had better performance of alcohol resistance.In this study, BC/Nafion/BC sandwich composite membrane was prepared as a model for proton exchange membrane by using gel attachment. The sandwich membranes were investigated by SEM, TG profiles, water uptake, size stability, proton conductivity, methanol permeability properties. Some selected samples were sandwiched with catalysts and GDLs and hot-pressed into membrane electrode assemblies (MEAs) in order to evaluate power performances in a real direct methanol fuel cell. The results showed that the sandwich membrane had good structure stability and thermal stability, excellent mechanical strength and flexibility, appropriate water uptake, high proton conductivity, very low methanol permeability. BC/Nafion212/BC sandwich composite membrane and Nafion212membrane were selected for power performance testing and got7.2mW cm-2(room temperature) and223.8mW cm-2(room temperature) of the maximum power density, respectively.Additionally, a series of doped hybrid membranes with different proportion of Nafion were made by using doping method based on freeze-dried BC membranes. The doped hybrid membranes were investigated by evaluating microscopic structure, TG profiles, water uptake, size stability, proton conductivity, and methanol permeability properties. The results proved that BC and Nafion between hydrogen bonding interactions. The higher Nafion proportion, the larger absorption peak intensity. The doped hybrid membranes showed two glass transition process, good thermal stability (less than120℃), high water uptake, good proton conductivity and low methanol permeability. Thus toughened hybrid membrane had the advantages of high selectivity, which is more suitable for DMFC.