Page 76 - MODERN ASPECTS OF ELECTROCHEMISTRY

Direct Methanol Fuel Cells
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in Italy; and Fuji, Mitsubishi, and Sanyo in Japan] to develop and manu-
facture high-performance PEMFCs.=
As stated earlier, the fuel cell researcher’s dream is to develop
DMFCs.= Until recently (i.e.,= the early 1990s), most of the efforts to
develop DMFCs had used sulfuric acid as the electrolyte.= Recent success
with a proton-conducting membrane (perfluorosulfonic acid membrane)
in PEMFCs has steered DMFC research toward the use of this electrolyte.=
The positive feature of a liquid feed to a DMFC is that it eliminates the
humidification subsystem, which is required for a PEMFC with gaseous
reactants.= Another advantage is that the DMFC does not require a heavy
and bulky fuel processor.= Two problems continue to be challenging in the
projects to develop DMFCs: (1) The exchange current density for metha-
5
nol oxidation, even on the best electrocatalyst to date (Pt-Ru), is 10 –10 6
times lower than that for the electrooxidation of hydrogen.= (2) The
transport of methanol through the membrane, from the anode to the
cathode side, reduces the Coulombic efficiency for methanol utilization
byabout 30%. However, a compensating feature of DMFCs compared
with PEMFCs is that they eliminate the fuel processor, and a lower
performance of the electrochemical cell stack maystill be acceptablp for
some applications, e.g.,= portable power sources.=
The DMFC projects are still at an infant stage, but the progress made
toward their development by fuel cell companies (IFC, Sanyo, Fuji,
Siemens, Giner, Inc.), government laboratories [Jet Propulsion Laboratory
(JPL), Los Alamos National Laboratory(LANL), Os¸€ National Re -
search Institute, Consiglio Nazionale delle Richerche (CNR) Messina]
and universities (Université de Poitiers, University of Newcastle, Univer-
sity of Bonn, Case Western Reserve University, University of Southern
California, Yamanashi University) gives some food for thought. Accord-
ing to some projections, the energy densities of DMFCs could be consid-
erably= higher than those of even lithium ion batteries, so that DMFCs
could find low-power applications (laptop computers, backpack power
sources for soldiers). International Fuel Cells and Siemens have designed,
constructed, and tested kilowatt-sized DMFC power plants.= Research
studies in the above-mentioned government laboratories, universities, and
industries have shown prospects of attaining a current density of 400
2
mA/cm at a cell potential of 0.5 V.