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Electrochemical Engineering 159

leads to high overpotential at operating current densities. reportedly in the pilot plant stage. The main attractions
The side reactions produce carbon monoxide, which is of electroorganic syntheses are high material and energy
a poison for the noble metal catalysts currently used. A efficiency, ease of control, and ability to effect difficult
second issue is the problem of methanol containment by oxidations or reductions. A general disadvantage is that a
the membrane at the negative electrode. The crossover of reaction at the counterelectrode must be performed, and
methanol leads to losses of fuel and reduced efficiency. unless a useful synthesis occurs there, cost benefits may
Many other battery and fuel-cell systems are under con- not be realized.
tinuing development. Fuel cells operating at high temper- Electrode materials must be capable of conducting
atures have the advantage of improved electrode kinet- electrons in the external circuit; therefore, metal and
ics, but significant technical challenges include materials graphite are natural choices for electrode materials. Re-
problems, especially corrosion and thermal management. cently, doped polyacetylene has been used as an electrode
Development of molten carbonate fuel cells (MCFCs) and material. Organic electrodes may be effective in reducing
solid oxide fuel cells (SOFCs) has been ongoing for sev- batteryweightandsignificantlyincreasingspecificenergy.
eral decades. The MCFC uses a eutectic mixture of lithium Semiconductor electrodes have been considered for use in
and potassium carbonates as the electrolyte. Because the the solar photolysis of water. Materials such as n-TiO 2 an-
◦
MCFC operates at 650 C, reforming of a hydrocarbon odes and p-GaP cathodes have been successfully used to
fuel directly at the electrode is feasible. Steam reforming split water, but the efficiencies have been low.
of methane followed by a shift-conversion reaction has The intrinsic performance advantages of hydrocarbon-
been demonstrated in the MCFC. The SOFC operates in based energy conversion systems are formidable. Cur-
◦
a range near 1000 C and is capable of internal reform- rently, electrochemically based energy converters have
ing without a catalyst; however, because the reforming found application in limited, niche markets. Electrochem-
reaction is highly endothermic, thermal management is ical processes are frequently advantageous in terms of
a problem. The yttria-stabilized zirconia electrolyte is an intrinsic efficiency, process control, and pollution reduc-
oxygen-anion–conducting electrolyte. Efforts are also un- tion. Many systems await advances in electrocatalysis and
der way to develop materials that are conductive at lower materials.
temperatures, at which materials problems are less severe.
In electrodeposition technology, damascene electro-
plating of copper was developed in the 1990s for chip in- SEE ALSO THE FOLLOWING ARTICLES
terconnects, and copper is now displacing the aluminum–
copper alloy for this purpose. This application of elec- ALUMINUM • BATTERIES • CHEMICAL THERMODYNAM-
troplating represents a major shift in the processing of ICS • ELECTROCHEMISTRY • FUEL CELLS,APPLICATIONS
on-chip wiring and has resulted in a 40% reduction in re- IN STATIONARY POWER SYSTEMS • KINETICS (CHEM-
sistance of the interconnects. Damascene plating involves ISTRY) • TRANSPORTATION APPLICATIONS FOR FUEL
the deposition of a seed layer over a patterned insulating CELLS
material. The electroplated material then covers the entire
surface but fills trenches that serve as interconnects. Ex-
cess surface material is then removed through a planariza- BIBLIOGRAPHY
tion step such as chemical–mechanical polishing (CMP).
Issues of metal distribution, plated copper voids, and cop- Appleby, A. J., and Foulkes, F. R., eds. (1993). “Fuel Cell Handbook,”
per diffusion into the insulator had to be overcome prior Krieger, Malabar, Fla.
to commercial implementation. Newman, J. (1991). “Electrochemical Systems,” 2nd ed, Prentice Hall,
Englewood Cliffs, N.J.
Currently, adiponitrile is the only organic chemical pro- Pletcher, D., and Walsh, F. C. (1990). “Industrial Electrochemistry,” 2nd
8
duced in large quantity (10 kg/yr) by an electrochemical ed., Chapman & Hall, London.
route. Other smaller-scale products include gluconic acid, Prentice, G. A. (1991). “Electrochemical Engineering Principles,” Pren-
piperidine, and p-aminophenol. Electroorganic syntheses tice Hall, Englewood Cliffs, N.J.
in supercritical organic electrolytes have been demon- Tobias, C. W., Delahay, P., and Gerischer, H., eds. (1961). “Advances
in Electrochemistry and Electrochemical Engineering,” Wiley (Inter-
strated in bench-scale reactors. Production of dimethyl
science), New York.
carbonate from the mixture-critical region was performed. Varma, R., and Selman, J. R., eds. (1990). “Techniques for Characteriza-
There are at least a dozen electroorganic processes that are tion of Electrodes and Electrochemical Processes,” Wiley, New York.