School Papers

There be obtained,(iv) The strength of fuel cell

There is a growing demand for highly efficient, zero pollution fuel cell power sources for a wide variety of applications including automotive, portable systems, stationary, emergency back-up, and telecommunications systems, high temperature polymer electrolyte fuel cells (HT-PEMS),
which operate at significantly higher temperatures (120-200°C) than conventional PEM fuel cells. Cell
contain polymer electrolyte membrane is basically of polybenzimidazole.  Polybenzimidazole (PBI) fiber is a synthetic
fiber with a very high melting
point. It has exceptional thermochemical
stability and does not readily ignite. PBI doped with phosphoric
acid was utilized as a high temperature fuel
cell electrolyte. Doping of phosphoric acid is done
because PBI has low tensile stress to overcome
this issue we doped phosphoric acid to increase thermochemical stability,
proton conductivity and to enhance the membrane efficiency.

PBI-based HT-PEM, the water that is generated by reaction plays a major role in the degradation of these systems due to the fact that it limits obtaining of high current density, to overcome this issue by using the Microporous Layer (MPL) at the electrode (cathode) for more removal of excessive
liquid water. Gas diffusion layer help to remove water from
outside of catalyst layer and prevent water flooding . MPL contain pore that absorber the water, if pours diameter size
small is size it may causes water flooding(cathode catalytic layer) due to this
low voltage is gain but if pore diameter size is large(150nm) it show higher
cell voltage. By using MPL several things are observed (i) The ohmic losses can be reduced by using the MPL
(ii) Mass transport of protons and electrons can be enhanced by using MPL,(iii)
With MPL,more uniform water distribution profiles can be obtained,(iv) The
strength of fuel cell can be enhanced with MPL since it acts as a buffer layer
between the catalyst layer and diffusion layer.As microporous layer thickness increases, water content in MEA decreases. Ionic transport in
PBI membrane
depends on strongly phosphoric acid
level and cell temperature. Since high water content in MEA causes phosphoric acid leakage from here, ionic conductivity of membrane decreases with the cell operating time. Therefore, the water content should be kept at a certain level.

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In the case of with MPL, water content in MEA decreases with the increase of microporous layer thickness. In the gas diffusion layer, the distribution of water concentration declines by using an MPL.If water content in MEA is low, phosphoric acid leakage can be prevented and so the ionic conductivity of phosphoric acid doped PBI membrane can
be made stable. There is no remarkable effect of MPL on the cell performance. Polymer electrolyte membrane fuel cell are
suitable for small stationary application in power range is 1MW. Polymer
electrolyte membrane fuel cell are the electrochemical converted with
efficiency of more than 60% and no gaseous environmental pollutants are
produces.

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