Electrolytic cell with bipolar electrode including diamond

Details Electrolytic cell with bipolar electrode including diamond Electrolytic cell with bipolar electrode including diamond

2000-02-25

2001-10-23

Valentine, Donald R. (Department: 1741)

Chemistry: electrical and wave energy

Apparatus

Electrolytic

C204S290010

Reexamination Certificate

active

06306270

ABSTRACT:

The present invention concerns an electrolytic cell with a bipolar electrode, i.e. a cell wherein the anode and the cathode are separated by at least a third electrode, called a bipolar electrode, itself forming both an anode and a cathode. It will easily be understood that the presence of such an electrode allows the electrochemical reaction surface and, consequently, the efficiency of the cell, to be increased.
For more details regarding electrolytic cells with a bipolar electrode or electrodes, reference could be made, for example, to the publication by Ch. Comninellis et al. in the Journal of Applied Electrochemistry, 21 (1991) 415-418.
For a bipolar electrode to be able to fulfil its function, it is imperative that it is made of a material which is compatible both with the anode function and the cathode function. In the present state of the art, nickel, copper and lead are generally used.
An advantageous application of bipolar electrodes is the integration thereof in electrolytic cells intended for the pollution abatement of waste water by oxidising the contaminating elements contained therein. Certain non-biodegradable organic constituents can thus be decomposed. Such an approach has however two drawbacks. On the one hand, the electrodes used to date tend to wear out quickly. On the other hand, they release metals, particularly heavy metals, which are pollutants.
Making bipolar electrodes from platinum has also been proposed, but they have the drawback of wearing out quite quickly. Moreover, this metal is very expensive.
Bipolar electrodes can either take the form of plates, or the form of a plurality of balls, typically having a diameter comprised between 0.5 and 10 mm, suspended in the electrolyte in movement, as proposed, for example, by M. Fleischmann et al. in the Journal of Electrochemical Society, Vol. 116, No. 11, November 1969.
Unfortunately the lifetime of these conductive balls, which are generally made of copper or graphite, is quite short because of mechanical effects due to their agitation in the electrolyte and the dissolution, or respectively oxidisation of the material itself. Electrolytic cells including such electrodes thus require almost permanent monitoring. Consequently, they cannot easily be used in applications such as water pollution abatement.
The main object of the present invention is to propose an electrolytic cell with a bipolar electrode having the double peculiarity of having a long lifetime and not releasing any pollutants into the electrolyte.
More precisely, the invention concerns an electrolytic cell including an anode, a cathode and at least one bipolar electrode arranged between the anode and the cathode, characterised in that said bipolar electrode includes a substrate and a compact diamond film which is made conductive by a doping agent and which coats the substrate.
Advantageously, the anode and the cathode also include a substrate and a compact diamond film which is made conductive by a doping agent and which coats the substrate.
The material forming the substrate can be selected from among silicon, silicon carbide, both made conductive by doping, quartz and glass. It may also be a refractory transition metal preferably selected from among zirconium, molybdenum, tantalum, niobium, titanium and silicides thereof.
Preferably the doping agent used to make the diamond conductive is boron, nitrogen or a mixing of both. The diamond film has, moreover, a thickness of 0.1 to 1 &mgr;m.
The cell according to the invention can either include a bipolar electrode in the form of a plate or a plurality of bipolar electrodes in the form of balls.


REFERENCES:
patent: 5399247 (1995-03-01), Carey et al.
patent: 5894077 (1999-04-01), Jones et al.

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