APPLICATION OF ZIRCONIA AND ION EXCHANGED HETEROPOLYACID NANOCOMPOSITE MODIFIED PFSA IONOMERS FOR PROTON EXCHANGE MEMBRANE FUEL CELLS

摘要

Proton exchange membrane fuel cells (PEMFCs) remain a potential alternative energy source for a wide range of applications such as transportation, stationary power and electronics. The current PFSA ionomer, Nafion, suffers from various disadvantages. Hence, continuous efforts are being made in the field of proton exchange membranes in order to improve the performance of the fuel cell. At high temperatures, the membrane faces severe problems such as dehydration, reduction of proton conductivity, poor water retention and loss of mechanical strength. In order to overcome these disadvantages, the PFSA ionomers are suitably modified with some functional materials. Incorporation of inorganic additives into PFSA ionomers would enhance the proton conductivity by improving the water retention capacity. Inclusion of metal oxides such as heteropolyacids, zirconia, silica, tungsten oxides in PFSA ionomers are more promising as they have tendency to hold more water. Inspite of their high water retention capacity, many inorganic additives suffer from solubility in water which can ultimately lead to their removal from membrane. Immobilization of an inorganic additive on various inorganic solid supports such as silica, zirconia, titania and tungsten oxides is a possible way to increase its stability with long lasting proton conductivity at high RH. In addition to increased proton conductivity, they also possess other desired properties such as low fuel crossover, good thermal stability and high water uptake. It was shown that the presence of inorganic additive in nafion membrane has increased the water retention which in turn improved the fuel cell performance. In the current work, membranes have been synthesized by using an inorganic composite. Zirconia and ion exchanged heteropolyacid composites were prepared by a sol-gel followed by hydrothermal method. The sol-gel method allows easy introduction of pure inorganic phase into polymer matrix. The gel formed will have a rigid and continuous network with pores under micrometer size and polymer chains which have the average length greater than micron too.