Preparation Of Membrane Electrode Assembly For Micro-Tubular Proton Exchange Membrane Fuel Cell

Proton exchange membrane fuel cell (PEMFC) is a power package which could directly transform the chemical energy stored in the fuel and oxidizer into power by an efficient and pollution-free way. PEMFC is widely recognized as the most promising power supply used in the area of aerospace, military, electric vehicles and regional power stations because of its low working temperature, quick start-up and non-corrosion. More over, the cell stack system is simple and stable. Most PEMFC systems are currently designed as a plate structure, however, this structure has several flaws such as low power density, high cost and bulky volume etc., which made it hard to be used in small portable devices.In this work, a micro-tubular membrane electrode assembly (MEA) was prepared using porous hollow carbon fiber tube as a support. Different treatments of the PAN hollow fibers used to increase the reaction surface area of porous hollow carbon tube have been studied. Pt and Ru anode catalysts were deposited on the hollow carbon tubes and XC-72 Pt/C were used as the cathode catalysts. The micro-structures and the properties of the MEA have been investigated and the electrochemical properties of a single cell have also been tested.Based on the above work, we draw the conclusions as follows:(1) Etching the Polyacrylonitrile (PAN) hollow fibers by 50% DMSO can effectively increase the surface area of the hollow carbon tube products and make the holes in the tube wall internal and external linking. Acid washing method can remove the fractions and inorganic impurities on the hollow carbon tube products.(2) The result showed the Pt catalyst which was deposited by chemical reduction method on the hollow carbon tube has been well dispersed on both surface and inside holes of the hollow carbon tube. The loading of the Pt catalyst was 0.4 mg/cm² . The average size of Pt catalyst particles was 4.4nm and its electrochemical active area was calculated to be about 41.32 m²g_Pt^-1. Pt anode catalysts showed stable performance in 0.1mol/L H₂SO₄.(3) The nation was coated on the hollow carbon tube by impregnation method. The FTIR result showed the structure of the coated nafion film was similar to the commercial nafion(?) film. The thickness of the coated nafion film was about 1μm.(4) The electrochemical performance of a single micro-tubular fuel cell made of the above metioned membrane electrode assembly under passive and air breathing conditions at ambient temperature and pressure has been tested. When hydrogen was used as the fuel and air as the oxidizer, it showed a maximum power density of 0.23mW/cm² and a maximum current density of 2.1mA/ cm² . The open-circuit potential for hydrogen used as the fuel was 0.82V. However, when methanol was used as the fuel and air as the oxidizer, it exhibited a maximum power density of 1.75mW/cm²and a maximum current density of 14mA/cm² and with the open-circuit potential of 0.82V which was proved to be superior to the one using hydrogen as the fuel.