Study On The Structure And Performances Of Miniaturized Polymer Electrolyte Fuel Cells

Miniature polymer electrolyte fuel cells (PEMFCs) are greatly promising in application to fields of portable electronics power. In this study, the basic structure, fundamental materials and manufacture techniques have been explored in ways different from the conventional fuel cells, so as to achieve the miniaturization of fuel cells and promote the commercialization.Firstly, the key component of fuel cells—Membrane Electrode Assembly was studied. A simple catalyst coated membrane (CCM) fabrication technique was developed which showed high performances. A high mechanical strength and thin titanium substrate has been applied to micro fuel cells. We initially took microfabrication and surface coating techniques to fabricate and treat the titanium substrate which acted as a multi-functional component as flow field plate and gas diffusion layer in fuel cells, in place of the conventional thick graphite and fragile carbon paper. A micro fuel cell was fabricated by hot-pressing a CCM and treated titanium substrates. The maximum power density of 220 mW cm-2 and 450 mW cm-2 have been achieved with air and O2 as oxidant under normal temperature and pressure, respectively.A novel concept of Integrated Membrane Electrode Assembly (I-MEA) structure has been proposed in this study. This I-MEA integrates the layered and separated components of membrane, catalyst layer, gas diffusion layer, and flow field plate as a monolithic chip. This new concept has many advantages over conventional structure: the structure of fuel cells was simplified and the weight and volume was reduced; The I-MEA showed high mechanical strength and good dimensional stability; The CCM fabrication processes could be simplified and be made more suitable for streamline production; some sub-systems to supply pressure on fuel cell stack could be eliminated; in addition, almost all the components in I-MEA can be fabricated by domestic materials, and hence the cost can be greatly reduced. Only a 200 μm thick integrated composite membrane was fabricated by impregnating domestic-produced ionomer dispersion into a sandwiched structure composed of porous metal sheets and ePTFE. The I-MEA showed the maximum power density of above 100 mW cm-2 under normal temperature and pressure in self-breathing H2/air fuel cells. While in a DMFC under normal temperature and pressure, the maximum power density obtained was about 19 mW cm-2, higher than a home-made Nafion 115 MEA under the same conditions. The I-MEA was successfully assembled into all passively feed DMFCs and planar banded stacks, which were compact and lightweight and showed acceptable power output.TiO2-RuO2 non-carbon catalyst support was investigated. The results showed that the new catalyst support had higher oxidant resistance and stability than XC-72 carbon. TiO2-RuO2 supported Pt gave acceptable performances when acting as DMFC anode catalyst and PEMFC anode and cathode catalyst.