WO2013012343A2

WO2013012343A2 - Pressure element

Info

Publication number: WO2013012343A2
Application number: PCT/NO2012/050142
Authority: WO
Inventors: Oddmund Wallevik; Hans Jörg FELL; Petr CHLADEK
Original assignee: Nel Hydrogen As
Priority date: 2011-07-20
Filing date: 2012-07-20
Publication date: 2013-01-24
Also published as: NO20111046A1; WO2013012343A3

Abstract

The present invention comprises a pressure element for an electrolysis cell comprising a fluid-permeable pressure element applied between an electrode and a bipolar plate in said electrolysis cell, in which said pressure element is resilient. Further use of a resilient fluid-permeable pressure element is also comprised in the present invention.

Description

PRESSURE ELEMENT

Introduction

The present invention relates to a pressure element for an electrolysis cell comprising a fluid-permeable pressure element applied between an electrode and a bipolar plate in said electrolysis cell and use thereof.

Background of the invention

Electrolysers of filter press type are commonly used for the production of hydrogen and oxygen from brines or lyes, usually aqueous alkali hydroxide solutions. Cell stacks in such configurations are formed by electrochemical cells which commonly consist of a sequence of a bipolar plate, first current distributor, first electrode (anode or cathode), a diaphragm element, said diaphragm element separating the cell into anode and cathode compartments, a second electrode, second current distributor and a new bipolar plate. Gaskets are commonly used for sealing purposes.

Traditionally electrodes are mounted by solid spacer, serving as a current collector, to the bipolar plate and there is a gap between electrode and diaphragm where gas bubbles are formed and escape into the gas collecting chambers.

According to prior art mounting of electrodes on bipolar plate is time-consuming and expensive. The gas-tightness of bipolar plate is compromised by drilling-through, which may lead to gas leakages especially during the pressurized operation. In addition current is concentrated in fewer spots which lead to non-uniform current distribution across the electrodes. Further, rigid fixing of electrode prevents intimate and adjustable contact of electrode with membrane as in a zero gap design, thus increasing the ohmic resistance and decreasing the efficiency of the electrolysis.

Summary of the invention

The object of the present invention is to provide a pressure element with one or more of the following advantages: efficient stacking in an electrolysis cell stack and suitable for automated stacking, enabling zero-gap when stacked in an electrolysis cell leading to lower ohmic resistance and thus higher energy efficiency in an electrolysis cell,

effective gas transport when used in an electrolysis cell and thereby higher efficiency for the production of preferred gases, i.e., higher production capacity, enhanced current distribution and in addition higher efficiency and better local temperature control in an electrolysis cell,

inherent gas-impermeable bipolar plate and further improved safety,

steady tension between electrode and diaphragm in pressurized operation.

The present invention is conceived to solve or at least alleviate the problems identified above.

The present invention comprises a pressure element for an electrolysis cell comprising a fluid-permeable pressure element applied between an electrode and a bipolar plate in said electrolysis cell, in which said pressure element is resilient. The pressure element of the present invention possesses an inherent conductivity. Further, said pressure element tolerates current density from 0 to 5 A/cm .

In addition said pressure element tolerates a compression pressure in at least one of the following ranges: 0.001 to 100 bar, 0.01 to 50 bar, 0.1 to 1.0 bar.

The pressure element of the present invention is fluid permeable in at least two dimensions. Furthermore, the said pressure element comprises at least a two

dimensional structure. In this regard it should be understood that said pressure element can also comprise a three-dimensional structure the strength and permeability of which can be such that fluid flow is unrestricted in three dimensions. The pressure element is resistant to corrosion. The pressure element comprises at least one of the following components: stretched material or perforated foil. Furthermore the pressure element comprises at least one of the following components: mesh or felt fiber mat. At least one component material according to the present invention is chosen among at least one of the following: metal, polymer or carbon. The metal is chosen among at least one of the following: nickel, nickel coated steel, nickel containing alloys. With regard to the present pressure element said at least one component material is prepared in one of the following manners: knitted, woven, interwoven, perforated and stretched, rolled and/or pressed. In addition at least one component material is further prepared in at least one of following manners: pleating, embossing, corrugating, or rolling. The fluid permeable pressure element comprises openings in one of the following ranges: 0.05-20 mm, 0.5 - 5 mm, 1-2 mm. The pressure element according to the present invention comprises at least one component material such as mesh or felt fibre mat in the form of at least a wire, in which a predetermined wire thickness is a function of the opening as follows:

* A = wire thickness (mm) where parameter A is chosen from one of the following ranges: 0.01 -10, 0.1-1, 0.1- 0.3. A is a parameter which relates mesh opening to the wire thickness, without limitation to only 1 wire dimension for any given opening. The values of parameter A originate from the experimental data and outside of the given ranges, the element will not have sufficient mechanical strength.

The pressure element according to the present invention is in the corrugated form comprising a wave height in the range of at least one of the following: 3-50 mm, 5-20 mm, 6-15 mm. Further the ratio wave length: wave height is in at least one of the following ranges: 0.1-10, 0.5-5, 1-3.

Use of a resilient fluid-permeable pressure element applied between an electrode and a bipolar plate in an electrolysis cell is also comprised by the present invention.

Summary of the drawings

Figure 1 illustrates compression curves for pressure element according to example 1 of the present application

Figure 2 illustrates a test of compression and reversibility according to example 2 of the present application.

Figure 3 illustrates one embodiments of the present pressure element. Detailed description

In one embodiment of the present invention a metal mesh of well-defined geometry is described to have following functions: reducing ohmic resistance by keeping the electrode in intimate contact with the diaphragm, conducting electrical current from bipolar plate to electrode and permitting gas to escape from the electrode surface.

The pressure element of the present invention is resilient, by resilient it should be understood, that the mechanical and geometrical properties of the said pressure element, e.g., a metal mesh, are balanced with regard to flexibility and stiffness in order to press the electrode to the diaphragm at all operational temperatures and not deform during cell assembly. The metal mesh has sufficient mesh opening to allow for non-hindered passing of fluid in both horizontal and vertical directions while maintaining the mechanical function.

In one embodiment of the pressure element the pressure element is in the corrugated form. The wording corrugated form should be understood as any wave form such as i.a. sinus wave or square wave.

In one embodiment the mesh or felt fibre mat can be described by the following properties:

Wire thickness is function of mesh opening and is defined by this function:

* A = wire thickness (mm) with parameter A being chosen from one of the following ranges: 0.01 -10, 0.1-1, 0.1-0.3. A is a parameter which relates mesh opening to the wire thickness, without limitation to only 1 wire dimension for any given opening. The values of parameter A originate from the experimental data and allow the person skilled in the art to reproduce the results. Outside of the given ranges, the element will not have sufficient mechanical strength.

Height of the mesh - height is a function of maximum production capacity of the electrolyser.

Angle of the wave walls (limited by desired mechanical strength: sharp = stiff + deforming, dull = too weak + flattening): 10-120 °, preferably 20- 100°, most preferably 30-50°.

Distance between the waves maxima: given by angle and height.

Diameter of circle at top of the wave: given by angle and height.

The present pressure element comprises a combination of mechanical strength, current conductivity, chemical resistance and minimum gas diffusion resistance due to the different optimized geometries as described in more detail in the following. The pressure element is supplied in one piece, which can be manually or automatically inserted between a bipolar plate and an electrode in an electrolysis cell thus simplifying the stacking. When a pressure element according to the present invention is inserted on each side of a bipolar plate, conduction of current is ensured between the bipolar plate and the electrodes, without compromising the mechanical integrity of said bipolar plate. In the present invention, large numbers of points of electrical contact are established leading to uniform current distribution by pressing the pressure element to the electrode surface. The obtained optimized wave function of the present pressure element provides required spring force to keep electrode in intimate contact with a diaphragm regardless of distance variation due to temperature/pressure variation, thus maintaining the zero gap and low ohmic resistance. Further, free transport of the produced gas in both vertical and horizontal direction, thus ensuring an efficient removal of gas from inner electrode-bipolar plate area is achieved according to the present invention.

In an electrolyser of filter-press design, the compression force (force needed to compress the cell stack) is the sum of the force required to seal the stack and the force needed to compress the pressure elements. The compression force is decisive for the design of the end lids of the electrolyser. In case of pressurized systems the design of the end lid would need to take into account the operation pressure.

From our co-pending patent application comprising an inventive rubber frame design, we have invented frames which are self- sealing, which means that that there is virtually no extra compression force from the rubber frames acting on the end lids of the electrolyser.

The compression of the pressure elements, however, acts in concert with the internal pressure and if the compression force of the pressure elements becomes substantial, this will have direct impact on the design of lids and tie rods of an electrolyser. According to the present invention a pressure element comprising specific features and properties has been invented. The present pressure element tolerates a compression pressure in the range 0.001 to 100 bar. In one embodiment the present pressure element withstands a maximum compression pressure of roughly 1 bar, and the typical pressure exerted by the pressure elements is in the range of 0.2-0.5 bar, which constitute about 1-2 % of the design pressure of an electrolyser . The impact of the present pressure elements on the design of the end lids of the electrolyser is thus insignificant. Even used under atmospheric conditions, the current pressure elements would have minor impact on the lid design.

In one embodiment of the present invention the pressure element can be stacked in an electrolyser as follows: a closed frame defining at least one first opening in which one first element is chosen as a diaphragm, in which said frame is partly covered with a sealing and electric insulating material;

a first electrode;

a first pressure element;

a bipolar plate;

a second pressure element;

a second electrode;

a closed frame defining at least one first opening in which one first element is chosen as a diaphragm, in which said frame is partly covered with a sealing and electric insulating material.

In one embodiment of the present invention the pressure element can be stacked in an electrolyser as follows:

a closed frame defining at least one first opening in which one first element is chosen as a bipolar plate, in which said frame is partly covered with a sealing and electric insulating material;

a first pressure element;

a first electrode;

a diaphragm;

a second electrode;

a second pressure element;

a closed frame defining at least one first opening in which one first element is chosen as a bipolar plate, in which said frame is partly covered with a sealing and electric insulating material.

a diaphragm;

a closed frame defining at least one first opening, in which said frame is partly covered with a sealing and electric insulating material;

a first electrode;

a first pressure element;

a bipolar plate,

a second pressure element;

a second electrode; a closed frame defining at least one first opening, in which said frame is partly covered with a sealing and electric insulating material;

a diaphragm.

a closed frame defining at least one first opening in which one first element is chosen as a pressure element, in which said frame is partly covered with a sealing and electric insulating material;

a first electrode;

a diaphragm

a second electrode;

a bipolar plate.

a first pressure element;

a closed frame defining at least one first opening in which one first element is chosen as a first electrode, in which said frame is partly covered with a sealing and electric insulating material;

a diaphragm;

a closed frame defining at least one first opening in which one first element is chosen as a second electrode, in which said frame is partly covered with a sealing and electric insulating material;

a second pressure element;

a bipolar plate;

Having described preferred embodiments of the invention it will be apparent to those skilled in the art that other embodiments incorporating the concepts may be used. These and other examples of the invention illustrated above are intended by way of example only and the actual scope of the invention is to be determined from the following claims. Examples:

Example 1: Compressibility testing

The compressibility was measured on an area of 4x27 cm², first on a sample cut to size, and subsequently on the same area in the middle of the element, two parallels. The results of the compression tests are shown in Fig. 1. It is readily seen from Fig.l that the element behaves "sinusoidically" up to a compression of about 0.6 mm, where after it behaves "trapezoidically". The results from the sample cut to size and those from the uncut sample are very similar, and demonstrate that reliable measurements can be made on small samples cut to size as well as on areas on uncut elements.

The sample cut to size was compressed to 1 mm and became permanently deformed. The two parallels on the uncut sample also decompressed as shown in Fig.2. The first sample was compressed about 0.7 mm and the second about 0.8 mm. As readily seen from Fig.2, the upper flat part of the curve was completely reversible, even up to 0.8 mm compression! This means that the compression element, behaves like a constant pressure element after compression in the cell stack! For the electrical contacts that the pressure element is designed to maintain, this is the perfect situation. Variations in temperature and compression will have only very minor effects on the pressure on the cell stack components and the electrical contacts will be stable.

Claims

P a t e n t c l a i m s

1.

Pressure element for an electrolysis cell comprising a fluid-permeable pressure element applied between an electrode and a bipolar plate in said electrolysis cell, in which said pressure element is resilient.

2.

Pressure element according to claim 1 , wherein said pressure element possess an inherent conductivity.

3.

Pressure element according to any of the preceding claims, wherein said pressure element tolerates current density from 0 to 5 A/cm .

4.

Pressure element according to any of the preceding claims, wherein said pressure element tolerates a compression pressure in at least one of of the following ranges: 0.001 to 100 bar, 0.01 to 50 bar, 0.1 to 1.0 bar.

5.

Pressure element according to any of the preceding claims, wherein said pressure element is fluid permeable in at least two dimensions.

6.

Pressure element according to any of the preceding claims, wherein said pressure element comprises at least a two dimensional structure.

7.

Pressure element according to any of the preceding claims, wherein said pressure element is resistant to corrosion.

8. Pressure element according to any of the preceding claims, wherein said pressure element comprises at least one of the following components: stretched material or perforated foil.

9.

Pressure element according to any of the preceding claims, wherein said pressure element comprises at least one of the following components: mesh or felt fibre mat.

10.

Pressure element according to claims 8-9, wherein at least one component material is chosen among at least one of the following: metal, polymer or carbon.

11.

Pressure element according to claim 10, wherein said metal is at least one of the following: nickel, nickel coated steel, nickel containing alloys.

12.

Pressure element according to the claims 8-10, wherein said at least one component material is prepared in one of the following manners: knitted, woven, interwoven, perforated and stretched, rolled and/or pressed.

13.

Pressure element according to claims 8-10, wherein said at least one component material is further prepared in at least one of following manners: pleating, embossing, corrugating, or rolling.

14.

Pressure element according to any of the preceding claims, wherein said fluid permeable pressure element comprises openings in one of the following ranges: 0.05-20 mm, 0.5 - 5 mm, 1-2 mm.

15.

Pressure element according to claims 9-14, wherein said pressure element comprises at least one component material in the form of at least one wire, in which a predetermined wire thickness is a function of the opening as follows: 2 * opening {mm) * A = wire thickness {mm)

where parameter A is chosen from one of the following ranges: 0.01 -10, 0.1-1, 0.1-0.3.

16.

Pressure element according to any of the preceding claims, wherein said pressure element is in the the corrugated form comprising a wave height in the range of at least one of the following: 3-50 mm, 5-20 mm, 6-15 mm.

17. Pressure element according to claims 8-16, wherein said pressure element is in the the corrugated form comprising a ratio wave length: wave height in at least one of the following ranges: 0.1-10, 0.5-5, 1-3.

18.

Use of a resilient fluid-permeable pressure element applied between an electrode and a bipolar plate in an electrolyser cell.