| A direct methanol fuel cell（DMFC） has the advantages of high energy density, low cost, simple assembly, and as a renewable power source it can be widely used in daily life, e.g. a portable power source, vehicles（cars and boats）, and even power plants. The proton exchange membrane is the core part of direct methanol fuel cell and, at present, Du Pont`s Nafion is the main material used for a DMFC membrane. There are some problems with Nafion such as high methanol permeability and the proton conductivity is too low at high temperature and or low water content so it is necessary to modify it.This report is an extension of previous work that used different sized particles of Na-X and NH4-X type zeolites as a filler in Nafion. A hydrothermal method was used to make three size ranges; 30-50nm（nano）, 500-700nm（sub-micron）, and 1-1.5μm（micron） of Na-X zeolite which were then converted into NH4-X and H-X zeolite. After converting to NH4-X and H-X these were dispersed into Nafion solution at 2.5wt%, 5wt% loadings and then solution cast to make composite membranes. The zeolites were characterized by XRD, TGA/DSC, SEM/EDS, FTIR, and the composite membranes were characterized by FTIR, SEM, TGA, and water uptake, IEC, conductivity, permeability, and then assembled into a single cell to test the membranes’ performance in a DMFC using 2mol/L methanol.The test results show that NH4-X/Nafion composite membranes` have higher water uptake and lower permeability than H-X/Nafion composite membranes` but the ion exchange capacity and proton conductivity are higher for H-X/Nafion. Compared with pure Nafion membranes, the permeability of the composite membranes is decreased by over 50%, and the selectivity has improved eight times more than that of pure Nafion membranes. The results from DMFC single cell tests show that 2.5wt% loading tends to give better results than 5wt% loading. The single cell DMFC test results show the maximum value of power density for pure Nafion occurs at 80 ℃ but for 2.5wt% NH4-X/Nafion and 2.5wt% H-X/Nafion composite membranes the maximum power density values occur at 80℃（the maximum temperature available） and are more than twice that of pure Nafion at 80℃.The results obtained here show the optimum zeolite size is submicron（500-700nm） and when loaded at 2.5wt%; NH4-X/Nafion and H-X/Nafion composite membranes have the best single cell performance with a power density of 127 m W/cm2 and 114 m W/cm2 respectively. These results confirm an enhanced performance of the proton exchange membrane in a DMFC single cell when compared to pure Nafion. |
PDF Full Text Request