Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
1999-04-27
2001-06-26
Valentine, Donald R. (Department: 1741)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S266000
Reexamination Certificate
active
06251239
ABSTRACT:
The use of gas diffusion electrodes in pressure-equalised electrochemical cells of large overall height necessitates the partitioning of the gas space into segments situated one above another, which are termed gas compartments, and which in the respective edge region have to be in contact with the electrode and sealed so that they are gas-tight. A half cell which has a basic construction such as this is described in DE 44 44 114 Al. A disadvantage of the mode of construction disclosed in DE 44 44 114 is the comparatively elaborate manner of making contact with and sealing the gas diffusion electrode. It is desirable for the electrode to be placed in electrical contact with the gas compartment and sealed in the smallest possible space, in order to keep the area of the electrode which is inactive as regards the electrode reaction as small as possible.
The object of the present invention is to provide an electrochemical gas diffusion half cell which makes it possible to utilise the active electrode area as extensively as possible, wherein the electrode together with the gas compartment is optionally fashioned as a module so that it is removable, thus permitting prior electrode installation in the gas compartment so that the edge contact is gas-tight, and so that making electrical contact for the operation of the gas diffusion electrode in the half cell is simplified.
A further object of the invention is to fashion the half cell and the electrode- and gas compartment module in particular so that modules of the half cell can also be replaced in a simple manner by a conventional electrode, for example a nickel electrode which produces hydrogen.
This object is achieved according to the invention by providing compartments fitted with gas diffusion electrodes such that said compartments can be removed from the half cell, optionally even individually, and can be detached from their gas supply or pressure equalisation means and from the electrical connections. In this respect, the gas compartments are manufactured as compact shallow elements, the front face of which is blanked off by the gas diffusion electrode so that when the electrode is installed in the half cell no electrolyte emerges into the gas space and no gas emerges in the opposite direction from the gas compartment.
The present invention relates to an electrochemical half cell based on a gas diffusion electrode as cathode or anode, having a gas space, which is formed from one or more gas compartments, for the gas diffusion electrode, having an ion exchange membrane, a holding structure for the installation of the electrode, electrical connections for the electrode, a gas inlet to the gas compartment and a pressure-equalised gas outlet to the gas compartment, a electrolyte feed line and an electrolyte discharge line, and having a housing for receiving the cell constituents, which is characterised in that the gas diffusion electrode is joined to the gas compartment to form a module which is detachably fastened to the holding structure, wherein the gas inlet and the gas outlet form a detachable connection to the gas compartment.
In one preferred embodiment, the gas space is partitioned into a plurality of gas compartments which are optionally supplied with electrode gas independently of each other, and which are optionally pressure-equalised in relation to the electrolyte space located in front of the gas diffusion electrode.
A half cell is particularly preferred in which, when there is a plurality of individual gas compartment modules, the individual modules are detachably fastened to the holding structure independently of each other.
Embodiments are also particularly preferred in which the gas diffusion electrodes are fastened to the gas compartment in an easily detachable manner so as to permit their replacement by modified electrodes.
The gas inlet and gas outlet are preferably designed as a flexible hose connection to which the gas compartment is attached, and which makes it easier to remove the gas compartments after the ion exchange membrane has been removed.
Alternatively, it is also possible in particular to employ gas inlets manufactured as a coupling seal and designed as bubble channels, and correspondingly pressure-equalising immersed elements.
In another preferred form of the half cell according to the invention the gas compartment modules are positioned in the half cell with the aid of structural elements, are electrically connected to the external power supply and are optionally sealed to such an extent that electrolyte from the electrolyte gap through which flow occurs cannot overflow in an uncontrolled manner into the rear, pressure-equalised space of the gas compartment, wherein the structural elements position the gas compartment modules so that the gas diffusion electrodes can serve simultaneously as an electrolyte gap for the passage of the electrolyte into the electrolyte space between the gas diffusion electrode and the ion exchange membrane.
The electrical contact between the gas compartment modules and an external source of electric current, e.g a source connected to the half cell housing, can be improved in that, in addition to the press contacts in the edge region, the modules are brought into electrical contact with the aid of an auxiliary structure, which is in pressed contact with the half cell housing for example, from the rear face thereof, namely the face remote from the gas diffusion electrode, via flexible, electrically conducting contact elements (e.g. spring contacts).
A low resistance supply of electric current to the electrode is made possible due to the electrical contact in the edge region and due to the contact of the electrode, which is distributed over the area of the electrode.
In another preferred variant of the half cell according to the invention, the gas diffusion electrode is brought into electrical contact on its side facing the gas space of the gas compartment with the aid of a support grid on its face. The support grid is thereby in electrical contact with the gas compartment rear wall.
A possible additional channel which is formed at the lower edge between the gas diffusion electrode and the gas compartment can serve to receive condensate which may possibly arise. The condensate can be discharged into the rear electrolyte space, together with the excess gas, via the gas outlet situated at the lowest point.
In one preferred variant, any heterogeneity in the supply of fresh electrolyte to the electrolyte space situated in front of the gas diffusion electrode can be prevented by providing the half cell behind the electrolyte feed line with an additional electrolyte distributor which homogenises the flow of electrolyte over the width of the half cell. In this embodiment, there is optionally no flow through the pressure-equalising rear space. The rear space only communicates with the flow of electrolyte at the top end of the half cell.
One particular advantage of the mode of construction of the half cell according to the invention is the possibility of easily operating the half cell also, when the gas compartment module is replaced, using conventional electrodes, particularly electrodes which produce hydrogen, e.g. nickel electrodes. In one preferred variant, the gas compartment modules are therefore fashioned so that they can be replaced by conventional electrodes, wherein the gas feed line to the gas compartment can optionally be blanked off or removed.
The present invention also relates to the use of the electrochemical half cell according to the invention in an electrochemical cell particularly an electrolysis cell, for operation according to choice with gas compartment modules or with conventional electrodes, particularly with electrodes which produce hydrogen, especially activated nickel electrodes.
REFERENCES:
patent: 4436608 (1984-03-01), Bennett et al.
patent: 4657651 (1987-04-01), Wainerdi
patent: 4705614 (1987-11-01), Morris
patent: 4732660 (1988-03-01), Plowman et al.
patent: 4744873 (1988-05-01), Sorenson
patent: 5693202 (1997-12-01), Gestermann et al.
patent: 4444
Camphausen Jens
Gestermann Fritz
Pinter Hans-Dieter
Bayer Aktiengesellschaft
Norris & McLaughlin & Marcus
Valentine Donald R.
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