Advanced Automotive Technology: Visions of a Super-Efficient Family Car

Methanol Fuel Cells.

The direct methanol fuel cell (DMFC) uses methanol at the fuel cell anode, rather than

reforming it to hydrogen in a separate reactor. The DMFC is a different category of fuel cells and

can in principle, use an acid, alkaline or polymer electrode. Low temperature DMFCs are similar

to the PEM fuel cell, and current research work at the Jet Propulsion Laboratory uses a solid

acidic membrane similar to that used in the PEM fuel cell.

The DMFC suffers from two major problems. First, the methanol oxidation reaction is very

slow at the 60° to 80°C operating temperature of such cells, even with the best available catalyst.

Although there have been significant improvements in the reaction kinetics over the last three

years, the PEM cell operated on hydrogen still provides about seven times more power per unit

stack area than the DMFC, based on data from single cell testing.^109 Platinum loadings for the

electrodes are also much higher than for the hydrogen PEM fuel cell, although there have been

significant improvements recentlyll0 toward reduced loading requirements.

The second major problem is that methanol at the anode/membrane interface can diffuse and
vaporize into the passing air stream at the cathode or react directly with the oxygen at the cathode
catalytic surface. The vaporized methanol is a source of emissions and must be recaptured or
flared, while methanol that oxidizes at the cathode lowers cathode potential and exacerbates
waste heat removal problems. As a result, there are very large efficiency losses. Hence,
considerable research is required before a fuel cell stack of reasonable efficiency can be built even
as a prototype. DMFC researchers concur that it is too early to suggest whether and when it
could be commercialized.

The direct methanol solid oxide fuel cell is a high temperature cell that eliminates some of the

problems of the low temperature DMFCs. Although most solid oxide fuel cells operate at 800° to

1,000oC, Argonne National Laboratory is developing a novel design that could operate as low as

450°C.^111 Its advantages over the low temperature DMFC is elimination of methanol diffusion

through the membrane, and no water management problems. This type of solid oxide fuel cell is at

a very early stage of development, however, where only its technical potential has been

established, and has not been demonstrated even at the cell level. The solid oxide ceil is potentially

less expensive than other fuel cell types, but it is too early in the development phase to determine

commercialization

Ultracapacitors

Ultracapacitors

prospects.

and Flywheels

and flywheels provide additional means to store energy onboard vehicles.

Ultracapacitors are devices that store electrical energy directly, rather than in chemical form as do

energy fuels and batteries. They are double layer capacitors that store electrical energy in a

109 A.Hammet and G.L. Troughton, “Electro Catalysis and the Direct Methanol Fuel Cell,” Chemistry and lndustry, No. 13, July 1992, pp. 480-

483.

110 Springer et al., see footnote 106.

11l Argonne NationalLaboratory, “Direct Methanol Solid Oxide Fuel Cell for Transportation,” Electrochemical Technology Program Brochure,

1994.