Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
2000-10-16
2002-04-16
Bell, Bruce F. (Department: 1741)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S252000
Reexamination Certificate
active
06372102
ABSTRACT:
TECHNICAL FIELD
This invention relates to a method for attaching a gas diffusion electrode used as an oxygen cathode in sodium chloride electrolysis using an ion-exchange membrane and for leading electricity therefrom and to a structure for leading electricity.
BACKGROUND ART
Systems of leading electricity from a gas diffusion electrode to a cathode current collecting frame that have conventionally been used are roughly divided into the following two methods.
1) In Case of Sheet-shaped Gas Diffusion Electrode
The outer perimeter of a gas diffusion electrode is adjusted so that the gas diffusion electrode may slightly overlap with the gasket seal surface of a cathode chamber frame or a plate-shaped cathode current collecting frame (also called a cathode current collecting pan). A whole electrolytic cell is assembled by bringing the outer peripheral portion of the gas diffusion electrode and the gasket seal surface of the cathode chamber frame or the cathode current collecting pan into contact, setting a gasket thereon, and clamping, whereby the contact area is also clamped, and electricity is led from the gas diffusion electrode to the cathode current collecting frame via the thus clamped contact area.
2) In Case of Cathode Current Collecting Frame/gas Diffusion Electrode Integrated Body
A sheet-shaped diffusion electrode is placed on a cathode current collecting frame having attached thereto a mesh (which has high electrical conductivity if made of a metal) for making a gas chamber in such a manner that the catalyst layer of the gas diffusion electrode may cover the surface of the mesh. The catalyst is sintered at a high temperature under a high pressure in a press to form a catalyst layer and, at the same time, to integrate the catalyst layer with the mesh for a gas chamber. Electricity is lead from the gas diffusion electrode directly to the cathode current collecting frame and the cathode chamber frame.
In either case, a flow of electricity from the cathode current collecting frame to the cathode chamber frame (cathode element) is secured by connecting the cathode current collecting frame and the cathode chamber frame by welding or by mechanically connecting using a volt or the like.
However, these conventional methods of attaching a gas diffusion electrode and of leading electricity involve the following problems attributed to the action and function.
1) Leading Electricity From the Outer Peripheral Portion of Gas Diffusion Electrode
In the case of a small-sized electrolytic cell, a suitable conducting contact area can be secured with respect to the reaction area so that the contact current density can be reduced, and the electrical contact resistance can be reduced. In the case of a practical electrolytic cell having a reaction area of about 3 m
2
, however, since a suitable conducting contact area cannot be secured with respect to that reaction area, the contact current density is increased, and the electrical contact resistance is increased. Further, in a large-sized electrolytic cell of which the side of the reaction area is 1 m or longer, the structural resistance of the conductor in the gas diffusion electrode becomes high. From these facts, operating economy is inferior. In addition, where the gas diffusion electrode has small strength, it may be fractured at the part pressed by the gasket, and oxygen and a caustic soda solution leak from the fractured part.
2) Integration of Gas Diffusion Electrode, Mesh Sheet and Cathode Current Collecting Frame
A practical electrolytic cell has a reaction area of about 3 m
2
. In order to integrate the gas diffusion electrode, the mesh sheet and the cathode current collecting frame, a huge pressing machine, a huge mold, and a huge heating apparatus are needed, which is not economical. The cathode current collecting frame is liable to thermal deformation upon pressing at a high temperature, meeting great difficulty in securing flatness precision. Supposing these members could be integrated with good precision, the integrated cathode current collecting frame whose reaction area is as large as 3 m
2
is mechanically weak, i.e., so flimsy that it is extremely hard to handle in transporting from a pressing factory to the place of installation of the electrolytic cell. This problem is common to the above-described case of “leading electricity from the outer peripheral portion of gas diffusion electrode”.
In renewing the gas diffusion electrode, it is difficult to detach the gas diffusion electrode from the cathode current collecting frame. Therefore, the cathode current collecting frame and the mesh sheet must be exchanged in the renewal of the gas diffusion electrode, which is uneconomical.
In the case of a practical electrolytic cell whose reaction area is as large as about 3 m
2
, a huge pressing machine and a huge pressing mold are required for integrating the gas diffusion electrode with the cathode current collecting frame.
DISCLOSURE OF THE INVENTION
The present invention has been made in the light of the above-mentioned problems in conventional techniques. It is an object of the invention to provide a method of attaching a gas diffusion electrode and of leading electricity and to provide a structure for leading electricity, which fulfill the following six requirements.
1. To reduce the sized of a unit gas diffusion electrode to make production and handling easier.
2. To diminish the resistance of a structure of the gas diffusion electrode itself by the size reduction of the gas diffusion electrode.
3. To make it easy to attach the gas diffusion electrode to the cathode current collecting frame while reducing the electrical resistance of the connecting part.
4. To make a structure allowing only the gas electrode to be detached in renewal of the electrode.
5. To make a structure for leading electricity which allows the cathode current collecting frame and the cathode chamber frame to easily be assembled together and separated apart and also which minimizes the electrical resistance of a structure at the cathode current collecting frame.
6. To make it possible, taking advantage of the separability, to carry out an integrating operation even in the production of a current collecting frame/gas diffusion electrode integrated body by using an exclusive tool which structurally withstands pressing, and yet to remove the gas diffusion electrode together with a conducting rib in renewing the gas diffusion electrode while leaving the cathode chamber frame re-useful.
The present inventors have conducted extensive studies in order to solve the above-described problems. As a result, they have found that the above problems can be overcome by interposing a conductor comprising a metallic mesh or spongy processed material between catalyst layers or attaching a catalyst layer onto the conductor to make a gas diffusion electrode allowing the conductor having excellent conductivity to be exposed only at the outer peripheral portion thereof, and fixing the exposed metallic conductor to a cathode current collecting frame, which functions as a medium for leading electricity from the gas diffusion electrode to a cathode chamber frame, either by welding (such as spot welding or laser welding) or by inserting a wedge into a groove made at a prescribed position of the cathode current collecting frame.
It has also been found that the above objects are accomplished by attaching a conducting rib to the back of the cathode current collecting frame of the gas diffusion electrode, attaching a conducting receptacle to the cathode chamber frame of the gas diffusion electrode of an electrolytic cell at the positions mating the conducting rib of the back of the current collecting frame, and fitting the conducting rib on the back into the receptacle. The present invention has been completed based on these findings.
That is, the present invention includes the following aspects.
The present invention relates to a method for leading electricity from a gas diffusion electrode, in which a part through which electricity is led to a cathode element is constructed by
provi
Aikawa Hiroaki
Katayama Shinji
Saiki Koji
Sakata Akihiro
Yamaguchi Kenzo
Bell Bruce F.
Toagosei Co. Ltd.
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