Bipolar plates Micro

Mkaline Fuel Cell The electrolyte for NASA s space shnttle orbiter fuel cell is 35 percent potassinm hydroxide. The cell operates between 353 and 363 K (176 and I94°F) at 0.4 MPa (59 psia) on hydrogen and oxygen. The electrodes contain platinnm-palladinm and platinum-gold alloy powder catalysts bonded with polytetraflnoro-ethylene (PTFE) latex and snpported on gold-plated nickel screens for cnrrent collection and gas distribution. A variety of materials, inclnding asbestos and potassinm titanate, are used to form a micro-porous separator that retains the electrolyte between the electrodes. The cell structural materials, bipolar plates, and external housing are nsnally nickel-plated to resist corrosion. The complete orbiter fuel cell power plant is shown in Fig. 24-48. 

PEM fuel cells - continue work on components (electrolyte, electrodes, bipolar plates), systems (modelling and design) and phenomenology (thermohydraulics). Study and development of micro-cells for portable applications. 

Hawkes A, Leach M, (2005). Sohd oxide fuel cell systems for residential micro-combined heat and power in the UK Key economic drivers. Journal of Power Sources, 149 72-83 Hellmana H, van den Hoed R, (2007). Characterising fuel cell technology Challenges of the commercialisation process. International Journal of Hydrogen Energy 32 305 - 315 Hermann A, Chaudhuri T, Spagnol P, (2005). Bipolar plates for PEM fuel cells A review. 

In addition to the earlier described state of the art, nanotechnology plays a role in the development of micro fuel cells the realisation of special properties of surfaces and the enhancement of functionalities by nanostrnctnres, nanolayers as coatings and nanoparticles raise increasing interest. Nanostructnred electrolytes, carbon snp-ports or coatings for bipolar plates are examples. 

The diffusion model [5, 6] has been developed for mass transfer study within the system bipolar plate - gas diffusion layer (with micro-porous sublayer) - electrocatalytic layer . It was shown that the current density distribution is a complex function and depends mainly on the electrochemical parameters of the MEA (electrocatalytic layer activity) and... 

Lu and Wang [48] have reported that by using stainless steel plates as bipolar plates (electrodes) with the flow field machined with photochemical etching technology a micro-DMFC produce maximum power density of 62.5 mW cm" at 40°C and 100 mW cm at 60°C at atmospheric pressure. The active electrode area is only 1.625 cm. The power generated by the stainless steel DMFC is double to that of the Si-based DMFC which the authors had previously fabricated. 

Fig. 1 Schematic of a typical micro-fuel cell stracture with a sohd electrolyte membrane, catalysts, and gas diffusion layers on both sides. The structure is sandwiched by the two current collector bipolar plates acting also as the flow fields (After Morse 2007)...

Zeng, C. L. and Ren, Y. J. 2007. Corrosion protection of 304 stainless steel bipolar plates using TiC films produced by high-energy micro-arc alloying process. Journal of Power Sources 171 778-782. 

Peng, L., X. Lai, J. Ni and Z. Lin. Flow channel shape design of stamped bipolar plates for PEM fuel cell by micro-forming simulation. Proceedings of the 4th ASME International Conference on Fuel Cell Science, Engineering and Technology, Irvine, 2006. 

Conventional fuel cell stack mainly comprises of (a) membrane electrode assemblies (MEAs) for achieving the electrochemical energy conversion process, (b) bipolar plates for the supply of reactant (fuel and oxidant) gases to MEAs in addition to providing cell to cell electronic conduction path and removal of heat and (c) auxiliary components for the reactant supply and product removal. Table 1 provides some of the essential differences between DMFC and micro fuel cell. 

---