Chemistry: electrical and wave energy – Apparatus – Electrolytic
Patent
1979-10-22
1984-01-17
Edmundson, F.
Chemistry: electrical and wave energy
Apparatus
Electrolytic
204290R, C25B 1104
Patent
active
044262698
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of stabilising the activity of electrodes coated with mixed oxide electrocatalysts during use in electrochemical cells.
An electrochemical cell is a device which has as basic components at least one anode and one cathode and an electrolyte. The cell may use electrical energy to carry out a chemical reaction such as the oxidation or reduction of a chemical compound as in an electrolytic cell. Alternatively, it can convert inherent chemical energy in a conventional fuel into low voltage direct current electrical energy as in a fuel cell. The electrodes, particularly the cathode, in such a cell may be of relatively inexpensive material such as massive iron. However, electrodes of such material tend to result in very low activity. These problems may be overcome to a degree by using electrodes activated with precious metals such as platinum. In such cases these precious metals are used as catalytic coatings on the surface of an elctrode core of inexpensive material. Such catalyst coatings are termed electrocatalysts. However, the use of precious metals in this manner results in high cost electrodes.
The above problems are particularly acute in electrochemical cells having a hydrogen electrode. Such electrochemical cells are used for several purposes, for example, the electrolysis of water to produce hydrogen and oxygen, in chlorine cells in which brine is electrolysed and in fuel cells which generate power by the oxidation of fuel. Of these processes, the electrolysis of water is used on an industrial scale for producing high purity hydrogen.
In the case of the production of hydrogen and oxygen by the electrolysis of water, water is decomposed into its elements when a current, eg a direct current, is passed between a pair of electrodes immersed in a suitable aqueous electrolyte. In order to obtain the gases evolved in a pure and safe condition, an ion-permeable membrane or diaphragm is placed between the electrodes to prevent the gases mixing. The basic elements of this cell are thus two electrodes, a diaphragm and a suitable electrolyte which is normally an alkaline electrolyte such as an aqueous solution of sodium hydroxide or potassium hydroxide due to their relatively low corrosivity.
In this case, the voltage, V, applied across the electrodes can be divided into three components, the decomposition voltage of water, E.sub.d, the overvoltage at the electrodes, E.sub.o, and the Ohmic loss in the inter-electrode gap which is the product of the cell current, I, and the electrical resistance (including the membrane resistance) of this gap, R.
Thus V=E.sub.d +E.sub.o +IR.
At 25.degree. C. and at a pressure of one atmosphere, the reversible decomposition voltage of water is 1.23 volts. However, in practice cells operate at voltages of 1.8 to 2.2 volts, as a result inter alia of activation overvoltage.
Activation overvoltage results from the slowness of the reactions at the electrode surface and varies with the metal of the electrode and its surface condition. It may be reduced by operating at elevated temperatures and/or by using improved electrocatalysts but increases with the current density of the electrode reaction. The use of cathodes containing precious metal electrocatalysts such as platinum, for example, does achieve a reduction in activation overvoltage. However, the technical advantage to be obtained by the use of such precious metal electrocatalysts is substantially offset by the expense. The use of mixed cobalt/molybdenum oxide as electrocatalyst has also been suggested. Such an electrode, made by painting a nickel gauze with a mixed cobalt/molybdenum oxide electrocatalyst and polytetrafluorethylene (PTFE) followed by curing under hydrogen at or below 300.degree. C. for 2 hours, initially had an electrode potential, versus a dynamic hydrogen electrode (DHE), of 142 mV at a current of 1000 mA/cm.sup.2 and 70.degree. C. The activity of this electrode decreased substantially when left immersed in solution on open circuit. The electrode potential rose to 260 mV ver
REFERENCES:
patent: 3336209 (1967-08-01), Hirschberg
patent: 3364072 (1968-01-01), Barber
patent: 3453314 (1969-07-01), Lewna et al.
patent: 3639647 (1972-02-01), Kehl et al.
patent: 3691100 (1972-09-01), Wright
patent: 3977958 (1976-08-01), Caldwell et al.
patent: 4035353 (1977-07-01), Kanetaka et al.
patent: 4061549 (1977-12-01), Hazelrigg et al.
patent: 4142005 (1979-02-01), Caldwell et al.
Spaziante, Ing. Chem. Ital., vol. 11, No. 10, pp. 155-160, Oct. 1975.
Jaksic et al., Elektrkhimiya. vol. 13, No. 9, 1355-1360, Sep. 1977.
Brown David E.
Mahmood Mahmood N.
Edmundson F.
The British Petroleum Company Limited
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