POLYMER ZEOLITE NANOCOMPOSITE MEMBRANES FOR PEM FUEL CELLS AND GAS SEPARATIONS

摘要

Polymer-zeolite nanocomposite membrane exploits the unique size of zeolite nanocrystals (e.g., adjustable diameter from 15-80 nm), and has the potential to combine synergistically the advantages of polymers and zeolites while overcoming the shortcomings of both. In this presentation, I will focus on two technologically important applications: proton-exchange-membranes (PEM) for fuel cells and air separation membranes. PEM fuel cells have been identified as a promising power source for transportation, residential power generation, and portable electronics. Here I will discuss the potential of using polymer-zeolite nanocomposite membrane to solve major problems with the current PEM fuel cells, such as water management at electrodes, CO poisoning of anode catalyst, and slow cathode kinetics by allowing the fuel cell to operate at higher temperatures (e.g., 110°C to 150°C vs. the current 80°C). Air separation by polymer membranes is a promising alternative to the conventional energy-intensive cryogenic distillation. Polymer membranes are inexpensive and can be fabricated and assembled into very compact modules such as hollow fibers. One major limitation of the current polymer membranes is their low O_2/N_2 selectivity (～6). Zeolites are known for their high permselectivity (i.e., molecular sieving) and zeolite particles have recently been incorporated into polymer membranes to increase their permselectivity. However, the zeolite particles used so far are fairly large (e.g., μm), and this has led to interfacial defects. As a result, selectivity improvement has been limited even though O_2/_2 selectivity as high as 32 has been predicted. Here I will discuss the potential of using nanometer-sized zeolite crystals to modify the polymer matrix to offer molecular sieving characteristics (e.g., O_2/N_2=32) while maintaining the flexibility of polymers.