Electrochemical cell stacks

Details Electrochemical cell stacks Electrochemical cell stacks

2001-03-22

2003-03-04

Valentine, Donald R. (Department: 1741)

Chemistry: electrical and wave energy

Apparatus

Electrolytic

C204S256000, C204S257000, C204S258000, C204S265000, C204S266000, C204S282000

Reexamination Certificate

active

06527921

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to electrochemical cell stacks, particularly, to monopolar filter press cell stacks, and more particularly to internally pressurized monopolar water electrolytic cells for the production of hydrogen and oxygen.
BACKGROUND TO THE INVENTION
Electrosynthesis is one example of an electrochemical process comprising a method for the production of chemical reaction(s) that is electrically driven by passage of an electric current, typically a direct current (DC), in an electrochemical cell through an electrolyte between an anode electrode and a cathode electrode from an external power source. The rate of production is proportional to the current flow in the absence of parasitic reactions. For example, in a liquid alkaline water electrolysis cell, the DC current is passed between the two electrodes in an aqueous electrolyte to split water, the reactant, into component product gases, namely, hydrogen and oxygen where the product gases evolve at the surfaces of the respective electrodes.
Water electrolysers have typically relied on membranes or separators between the two halves of an electrolysis cell to ensure that the two gases, namely, oxygen and hydrogen produced in the electrolytic reaction are kept separate and do not mix. Each of the separated gases must be discharged from the cell at essentially the same pressure since membranes and separators fail with pressure differential. Simple pressure control systems, such as a small water column of several centimeters in height for each gas and discharge to atmospheric pressure are used to control the pressure within this pressure differential.
In the conventional monopolar cell design in wide commercial use today, one cell or an array of cells in parallel is contained within one functional electrolyser, cell compartment, or individual tank. Each cell is made up of an assembly of electrode pairs in a separate tank where each assembly of electrode pairs connected in parallel acts as a single electrode pair. The connection to the cell is through a limited area contact using an interconnecting bus bar such as that disclosed in Canadian Patent No. 3,02,737, issued to A. T. Stuart (1930). The current in the form of a flow of electrons is taken from the cathode bus bar via an electrical connection to a portion of a cathode in one cell, then through the electrolyte in the form of ions to the anode of that cell and then to the anode bus bar using a similar electrical connection. The current is usually taken off one electrode at several points and the connection made by means of clamps, soldered joints, mechanical screw connections and the like.
Electrolysis apparatus having pressurized external cell structures are known for producing hydrogen. For example, U.S. Pat. No. 5,665,211, issued 1997, describes a pressurized container within which is an electrolytic cell. There is no integration of the cell itself as the pressure containment device, and, thus, the apparatus is bulky and heavy. U.S. Pat. No. 3,652,431, issued 1972, describes an electrolysis cell where external pressure from a liquid such as water is used to support a container in which pressurized electrolysis is conducted. U.S. Pat. No. 4,042,481, issued 1977, describes a pressurized tank containing cylindrical porous anode and cathode tubes which allow escape of the oxygen and hydrogen produced. However, the apparatus requires the need for a tank to house cells and, thus, this does not represent efficient use of overall space or footprint. There is also the potential for mixing of oxygen and hydrogen produced if gas does not diffuse through the porous electrode tubes. The cylindrical configuration of the anodes and cathodes present fabrication challenges and the spacing of these electrodes will require substantial room to prevent non-uniform currents if multiple cells are used. U.S. Pat. No. 5,733,422, issued 1998, describes a tank with a header box wherein the top is screwed onto the side wall plates. Again, this is clearly not a design suitable for lightweight and inexpensive polymeric materials.
There is, therefore, a need for electrolytic cells, particularly, water electrolysers, which do not suffer from the aforesaid disadvantages.
SUMMARY OF THE INVENTION
The present invention provides an electrolytic cell stack having a beneficial novel relationship of cell components involving the inverse structural role of some components, through the use of a single electrolyte circulation and membrane frame within each cell. There is no need for end-boxes and compressible elastomeric materials which, however, may be optional. The circulation and membrane frame preferably, is formed of a structural plastics material, which can provide support to thin foil electrodes if the latter are used. In the absence of gaskets and compressible elastomeric frames, advantageous higher operating temperatures can be readily attained. This is particularly so when the cell stack is pressurized as hereinafter described.
In one aspect, the invention provides an electrochemical cell stack comprising stack walls and a plurality of electrolytic cells within the stack walls, each cell comprising cell members selected from an anode; a cathode; a membrane separator frame formed of a non-conductive material and having a first side and a second side opposite to said first side;
(a) a frame first planar peripheral surface on said first side;
(b) a frame second planar peripheral surface on said second side; and
(c) a central portion defining a membrane-receiving aperture;
a membrane within the aperture which provides an anolyte circulation chamber and a catholyte circulation chamber distinct one from the other within said frame; an impermeable cell end wall formed of a non-conductive material between said anode and said cathodes and the anodes and cathodes of adjacent cells of the stack; wherein each of said anode, said cathode, said separator frame and said end wall has a portion defining an anolyte flow inlet channel, a catholyte flow inlet channel, a spent anolyte channel and a spent catholyte channel; and wherein said anolyte flow inlet channel and said spent anolyte channel are in communication with said anolyte circulation chamber, and said catholyte flow inlet channel and said spent catholyte channel are in communication with said catholyte circulation chamber.
In one preferred embodiment, the invention provides a cell stack as hereinabove defined wherein said anode has an anode first planar surface which abuts said frame first planar peripheral surface as to define with said member said anolyte circulation chamber within the confines of said frame, and said cathode has an cathode second planar surface which abuts said frame second planar peripheral surface as to define with said member said catholyte circulation chamber within the confines of said frame.
In another preferred embodiment, the invention provides a cell stack as hereinabove defined wherein said anode in whole or in part is disposed within said anolyte circulation chamber and said cathode in whole or in part is disposed within said catholyte circulation chamber. In this later defined cell stack, one or both of the anode and the cathode are in contact with the membrane, on opposite sides thereof, within the respective electrolyte circulation chamber, as for example, a laminate with or coating on the membrane.
The production of a bilayer or trilayer porous assembly offers the distinct advantages of minimal electrode/membrane thickness and, hence, inter-electrode cell resistance, as well as ease of processing on a continuous basis by the integration of separate parts, namely, current carrier+activation+membrane, using known, suitable processing methods.
The production of such a bi or trilayer composite structure can be carried out, for example, by utilizing a core membrane material and metallizing this externally, wherein the membrane may be either polymeric or ceramic in nature, formed by, for example, weaving, felting, tape casting, sintering and the like. The metallizing process can be selected, b

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