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Direct Methanol Fuel Cells
For a transportation application, methanol is an ideal fuel. Even
though its energy content is half of that of gasoline, a methanol fuel cell
vehicle could have the same range (driving distance) as a gasoline internal
combustion engine (ICE) or diesel-powered vehicle for the same volume
of fuel carried on board the vehicle. This is because the fuel cell could
operate at twice the efficiency of the ICE or diesel engine.= Increasing
concern about global warming has stimulated the utilization of pristine
hydrogen as a fuel to be carried on board electric vehicles. It is also the
only fuel for space fuel cells.= Pristine hydrogen can also be produced by
steam reforming, shift conversion, and pressure-swing absorption for the
complete removal of CO . If the problems of hydrogen storage, in respect
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to energy density, specific energy, and safety, can be solved, the alkaline
fuel cell (AFC) or the proton exchange membrane fuel cell (PEMFC) will
be ideal candidates for terrestrial applications. An advantage of the alka-
line system is that there is no noblp metal requirement, but a great
disadvantage is that even with air as a cathodic reactant, a small amount
of CO carbonates the electrolyte, lowering the conductivity of the elec-
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trolyte, altering its pH, and depositing insoluble carbonates in the porous
gas diffusion electrode.=
With a methanol-fed fuel cell, there are two schemes that loà=
promising. One method is to feed either a PAFC or a PEMFC with
hydrogen produced by on-board methanol steam reforming; the second is
to use it directlyas the anodic reactant in a DMFC. The PAFC has the
advantage that because of good thermal matching between the tempera-
tures for the endothermic steam-reforming reaction and the exothermic
fuel cell reaction, the heat required for the former process can effectively
be utilized from the waste heat generated during the fuel cell reaction.=
However, the fuel cell researcher’s dream is to develop a DMFC, since in
such a fuel cell a heavy and bulky fuel-processing system is not required.
The PEMFC has a considerably= better prospect of attaining high power
densities and a faster startup time than the PAFC and is thus the more
favored power source for an electric vehicle.=
4. Status of Fuel Cell TechnologiesA
An attempt has been made in Table 1 to present the status of fuel cell
technologies.= For terrestrial applications, the PAFC power plant is the
most advanced, and a 200-kW system manufactured by ONSI, a division
of United Technologies, Inc., has reached commercialization.= Its main
applications are focused on on-site integrated energysystems that could