Chemistry: electrical current producing apparatus – product – and – Having earth feature
Patent
1990-01-26
1991-07-02
Walton, Donald L.
Chemistry: electrical current producing apparatus, product, and
Having earth feature
H01M 492
Patent
active
050284983
DESCRIPTION:
BRIEF SUMMARY
A fuel cell which directly converts the chemical energy in a liquid fuel to electricity in the cold combustion process taking place in a fuel cell has for a long time been considered the final goal for the fuel cell researchers. Several very large development projects have been concerned with this task. Methanol has been the fuel of choice but other fuels like diesel oil or organic compounds with high energy density like ethylene diglycol have also been tested. These efforts have not been entirely unsuccessful. By means of heavy load of noble metal catalysts corresponding to about 300 mg platina/W it has been possible to demonstrate a performance corresponding to the level 20-30 mW/cm.sup.2 electrode area. This performance level is satisfactory in special applications like cordless chargers. Such generators, however, become very expensive because of the noble metal content.
This kind of fuel cells uses PTFE bonded carbon electrodes with the active catalytic material disposed on the carbon support. The air electrode is a conventional gas diffusion electrode with 0.5-1 mg platinum/cm.sup.2 The methanol electrode is using PTFE only as a binder not as a hydrophobic agent. The catalytic material is frequently a 50/50 mixture of platinum and ruthenium. It has also been found that small additions of lead, tin and bismuth as an alloy component or as so called adatoms improves the catalytic action somewhat. The electrolyte is typically 4-M sulphuric acid and the operating temperature 50.degree.-60.degree. C. Methanol is added to the electrolyte from a tank by means of a pump. Carbon dioxide which is formed in the cold corbustion process evaporates from the acid electrolyte.
The air electrode is frequently sensitive to the presence of methanol and may be protected by means of an ion exchange membrane. Fuel cells of this kind are described in U.S. Pat. No. 4,262,063. The state of art is described in B.D. McNicol and D.A.J. Rand: "Power Sources for Electric Vehicles", Elsevier, Amsterdam 1984, p. 807-836. The reason for the high quantities of noble metal required in state of art methanol electrodes is considered to be poisoning by intermediates or by-products of the electrode reaction. A methanol electrode shows initially a very high activity. This high initial activity is lost already within 50 milliseconds. Several studies have been carried out to clarify the poisoning effect but the results are not entirely conclusive. Many researchers, however, maintain that the poisoning can be attributed to absorption of carbon monoxide which also is in harmony with experiences from other types of fuel cells with acid electrolyte and noble metal catalyst.
The present invention is the result of an unconditional evaluation of fairly large quantities of different chemical compounds which have been chosen by intuition with no regard to any views regarding reaction mechanism. This search has been successful and resulted in a methanol electrode with very much better performance and therefore very much lower material costs than the methanol electrodes which have been briefly described above. In this way the most important obstacle for the use of the direct methanol air cell in practice has been eliminated. It has also been shown that the new electrode is useful also with other fuel cells and fuel cell types which utilize acid electrolytes in a temperature region up to about 250.degree. C.
The invention is characterized in that it refers to a fuel cell anode with noble metal catalyst for fuel cells with acid electrolyte characterized in that the anode contains a separate addition of lead or lead compounds in a concentration above about 5 mg Pb/cm.sup.2.
The voltage current curve for a methanol electrode with lead addition is improved with more than 200 mV compared to a corresponding electrode without lead addition. No explanation to this can be offered at the present stage. As mentioned above lead in the form of adatom or alloying component has a certain positive effect on the performance of the methanol electrode but this effect is sma
REFERENCES:
patent: 3428544 (1969-02-01), Bianchi et al.
patent: 3444003 (1969-05-01), Moser
patent: 3650838 (1972-03-01), Giner et al.
patent: 4828941 (1989-05-01), Sterzel
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