WO2015102479A1

WO2015102479A1 - A water electrolyzer

Info

Publication number: WO2015102479A1
Application number: PCT/MY2014/050013
Authority: WO
Inventors: Mahidzal DAHARI
Original assignee: Universiti Malaya
Priority date: 2013-12-30
Filing date: 2014-12-12
Publication date: 2015-07-09
Also published as: MY175986A

Abstract

A water electrolyzer (100) for producing hydrogen gas comprising a stack of electrode plates (101) arranged in alternate polarities separated by dividers (104) and sandwiched between two end plates (107, 108), in which one of the end plates is an anode terminal (107) and the other is a cathode terminal (108), wherein the stack of plates (101) has a hollow centre for electricity connection and apertures (113, 114) around the hollow centre forming channels for distribution of electrolyte and collection of electrolytic products.

Description

A WATER ELECTROLYZER

FIELD OF INVENTION

This invention relates to an apparatus for producing hydrogen gas. More particularly, the present invention relates to an apparatus which electrolyzes water to produce hydrogen gas for hydrogen refueling system.

BACKGROUND OF INVENTION

Hydrogen is considered as one of the best sources of energy as the only by-product of combustion for energy production is water. Hydrogen-fueled or fuel cell vehicles are one of the latest researches that are powered by hydrogen. However, such technologies are still not mature enough to be commercialized due to the limited source of hydrogen as hydrogen in the atmosphere of Earth is less than 1%. Hence, obtaining hydrogen from air is impossible and not cost effective.

Conventional processes of producing hydrogen include coal extraction, oil pyrolysis, and catalytic steam reforming. However, these processes release high amount of greenhouse gas, such as carbon dioxide, to the atmosphere as they are fossil fuel dependent. Though carbon sequestration can be applied to eliminate or reduce emission of carbon dioxide, the efficiency of this approach is not satisfying.

There are upcoming technologies which involve production of hydrogen biologically in order to avoid the consequences of using the convention processes. For example, direct biophotolysis, indirect biophotolysis, photo-fermentation, dark fermentation, and water-gas shift reaction of photoheterotrophic bacteria. In these biological processes, photosynthetic bacteria are used to produce hydrogen from water in their metabolic activities in the presence of light energy. However, these technologies have limitations in oxygen sensitivity of the hydrogen evolving enzyme and mass transfer of bacteria in the bioreactor which greatly influence the production efficiency and hydrogen purity. Due to the drawbacks from the above technologies, electrolysis becomes an alternative method of producing hydrogen gas which is eco-friendly and cost effective. Electrolysis is a process of separating chemically bonded elements using a direct electric current. Electrolysis of water refers to the decomposition of water into oxygen and hydrogen gas due to an electric current being passed through the water. Different types of electrolyzer can be used to perform the electrolysis of water. The most common type of electrolyzer is alkaline water electrolyzer.

There are few patented technologies over the prior art relating to electrolyzer or an electrochemical fuel cell stack. However, there is a wide variation in the apparatus designs and qualities.

One of the inventions relates to an electrochemical fuel cell stack is U. S. Patent No. 6057053. The invention relates to a compression assembly for an electrochemical fuel cell stack which applies internal compressive force to the fuel cell assemblies as the internal fluid pressure or fuel cell thickness changes. The cell stack comprises at least one fuel cell assembly interposed between two end plates with a compression mechanism and a restraining mechanism. The retraining mechanism prevents the deflection of the compression mechanism which may cause the end plates to urge apart.

Another invention which relates to a laminated fluid flow field assembly for electrochemical fuel cells is U. S. Patent No. 5300370. The assembly comprises a separator layer and a stencil layer cooperating to form open-faced channel for conducting pressurized fluid introduced at the fluid inlet. The assembly has reduced weight and volume, and is simpler and less expensive to manufacture than conventional fluid flow field plates.

One of the drawbacks of the above prior art is the short lifetime of the electrolyzer due to the use of highly corrosive electrolyte and the requirement of high temperature working condition. The assembly also has poor electrical contact which results in low electrochemical efficiency. To overcome the drawbacks of the prior art, it is desirable for the invention to develop an improved electrolyzer for hydrogen refueling system which is simple, low in cost, and high efficiency, with appropriate lifetime.

SUMMARY OF INVENTION

One of the objects of the invention is to provide an apparatus for producing hydrogen gas through alkaline water electrolysis.

Another object of the invention is to develop a water electrolyzer in which the assembly has a good electrical contact.

Still another object of the invention is to develop a water electrolyzer which has good chemical resistance towards the corrosive liquid electrolyte. Yet another object of the invention is to develop a simple and efficient water electrolyzer which is low in cost.

Again another object of the invention is to develop an apparatus for producing hydrogen gas with high purity through water electrolysis.

Also another object of the invention is to develop a water electrolyzer in which the hydrogen gas produced can be used in hydrogen fueled vehicles.

At least one of the preceding aspects is met, in whole or in part, by the present invention, in which the embodiment of the present invention describes a water electrolyzer for producing hydrogen gas comprising a stack of electrode plates arranged in alternate polarities separated by dividers and sandwiched between two end plates, in which one of the end plates is an anode terminal and the is a cathode terminal, wherein the stack of plates has a hollow centre for electricity connection and apertures around the hollow centre forming channels for distribution of electrolyte and collection of electrolytic products. In a preferred embodiment of the invention, the electrode connections are positioned centrally at the end plates.

In another preferred embodiment of the invention, the end plates further comprise channels for distribution of electrolyte and collection of electrolytic products.

Still in another preferred embodiment of the invention, the two end plates are equi-potential.

A further embodiment of the invention is the stack of plates is annular in shape.

In another further embodiment of the invention, the electrode plates and the end plates are composed of material selected from the group consisting of nickel, cobalt, platinum, molybdenum, zirconium, an oxide thereof, or any combination thereof. The preferred embodiment of the invention consists of novel features and a combination of parts hereinafter fully described and illustrated in the accompanying drawings and particularly pointed out in the appended claims; it being understood that various changes in the details may be effected by those skilled in the arts but without departing from the scope of the invention or sacrificing any of the advantages of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of facilitating an understanding of the invention, there is illustrated in the accompanying drawing the preferred embodiments from an inspection of which when considered in connection with the following description, the invention, its construction and operation and many of its advantages would be readily understood and appreciated.

FIGURE 1 is an exploded isometric view of the water electrolyzer as embodied by one of the preferred embodiments of the invention. FIGURE 2 is a side view of the water electrolyzer as embodied by one of the preferred embodiments of the invention.

FIGURE 3 is a front view of the electrode plates of the water electrolyzer as embodied by one of the preferred embodiments of the invention.

FIGURE 4 is a front view of the two end plates of the water electrolyzer as embodied by one of the preferred embodiments of the invention.

FIGURE 5 is an exploded view of the bipolar cells of the water electrolyzer as embodied by one of the preferred embodiments of the invention.

FIGURE 6 is a schematic flow diagram of the method of producing hydrogen gas using the water electrolyzer as embodied by one of the preferred embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to an apparatus for producing hydrogen gas. More particularly, the present invention relates to an apparatus which can electrolyze water to produce hydrogen gas for hydrogen refueling system.

Hereinafter, the invention shall be described according to the preferred embodiments of the present invention and by referring to the accompanying description and drawings. However, it is to be understood that limiting the description to the preferred embodiments of the invention and to the drawings is merely to facilitate discussion of the present invention and it is envisioned that those skilled in the art may devise various modifications without departing from the scope of the appended claim.

The invention discloses a water electrolyzer (100) for producing hydrogen gas comprising a stack of electrode plates (101) arranged in alternate polarities separated by dividers (104) and sandwiched between two end plates (107, 108), in which one of the end plates is an anode terminal (107) and the other a cathode terminal (108), wherein the stack of plates (101) has a hollow centre for electricity connection and apertures (113, 114) around the hollow centre forming channels for distribution of electrolyte and collection of electrolytic products.

As illustrated in FIGURE 2, the water electrolyzer (100) comprises a stack of electrode plates (101). Each stack of electrode plates (101) is formed by a plurality of bipolar cells; each bipolar cell comprises an anode plate (102) and a cathode plate (103) separated by a diaphragm or a membrane (104). The bipolar cells are sandwiched between two end plates (107, 108), in which one of the end plates is an anode terminal (107) and the other a cathode terminal (108). The bipolar cells are arranged in side-by-side manner, with the anode plate (102) and the cathode plate (103) arranged in alternating fashion.

According to the preferred embodiment of the invention, the end plates (107, 108) and the electrode plates (102, 103) have a predetermined dimension and can be made of any material providing the required catalytic properties and corrosion resistance towards high pH value of electrolyte. Preferably, the material is selected from the group, but is not limited to, consisting of nickel, cobalt, platinum, molybdenum, zirconium, an oxide thereof, or any combination thereof. The anodic end plate (107) and the anode plate (102) are preferred to be made of plain nickel. Platinum alone or an alloy of platinum with nickel can also be used. However, the overall unit cost may be increased. The cathode end plate (108) and the cathode plate (103) are preferred to be made of raney-nickel. The plates (102, 103, 107, 108) are configured to have a large electroactive area to produce high density current and hydrogen production rate. As described by the preferred embodiment of the invention, the divider (104) is able to keep a good ionic conductivity while effectively separating hydrogen and oxygen gases generated at the cathode (103) and the anode (102) respectively. Typically it consists of matrix porous material which has a high resistance towards corrosive environment and a high temperature. At the same time, the diaphragm (104) possesses sufficient mechanical strength to withstand changes in dimension due to stress associated to the structural design and temperature change. In accordance with the preferred embodiment of the invention, the electrolyzer (100) is configured to be used for water alkaline electrolysis, in which alkaline electrolyte is used. Potassium hydroxide (KOH) is commonly used as the alkaline electrolyte. However, any alkaline electrolyte providing the required ionic conductivity can be used. The electrolyte is enclosed in a closed circuit to avoid contact with carbon dioxide from the atmosphere which may impose technical challenge due to precipitation of carbonates formed. KOH concentration is one of the important factors determining the ionic conductivity. The ionic conductivity is remained high to reduce the use of higher voltage from ohmic losses. In the apparatus disclosed in the invention, the diameter of the end plates (107, 108) is 30cm to 40cm, preferably 37.5cm, while the diameter of the electrode plates (102, 103) is 25cm to 35cm, preferably 29.5cm. The thickness of the end plates (107, 108) is 20cm to 30cm, preferably 24cm, while the thickness of the electrode plates (102, 103) is 5cm to 10cm, preferably 7.5cm. The number of bipolar cells sandwiched between the two end plates (107, 108) is between 10 to 30, depends on the required productivity of the electrolyzer. A typical number of bipolar cells are 12, or 24 electrode plates (102, 103). However, increasing cell numbers in series may result in larger pressure drop within the stack (101). Additional hardware such as high pressure pumps may be required. In another preferred embodiment of the invention, the electrode plates (102, 103) are substantially an annular pate having a hollow centre with apertures (113, 114) around the hollow centre as illustrated in FIGURE 3. When the bipolar cells are stacked together, the apertures (113, 114) form hollow channels for distribution of electrolyte and collection of electrolysis products. The end plates (107, 108) also comprise apertures (113, 114) positioned correspond to the axis of the apertures (113, 114) of the bipolar cells.

Accordingly, the anodic end plate (107) is integral with the cathode end plate (108). Hence, the anodic end plate (107) forms a stationary head of the stack (101) while the opposing cathode end plate (108) forms a floating head of the stack (101). The stationary head (107) is equipped with the fluid connections (113, 114) for feeding electrolyte to the stack (101) and for collecting products of water electrolysis. The stationary head (107) is also equipped with anodic electric connections (120) with the stack (101).

Still in another preferred embodiment of the invention, the anode electric connection (120) is given by a rod passing through the anodic end plate (107), carrying the anodic current directly to the first anode plate (102) of the stack (101). The first anode plate (102) is electrically insulated from the anodic end plate (107) by an insulating plate. The rod is provided with adequate gaskets to ensure the connections are leak-tight with respect to the internal space under pressure. Again in another preferred embodiment of the invention, the cathode end plate (108) is electrically in contact with the end cathode plate (103) of the stack (101). The end cathode plate (103) is connected to the cathode end plate (108) via tie rods. Accordingly, the two end plates (107, 108) are equi-potential. In a further embodiment of the invention, the cathode electric connection (121) is located on the cathode end plate (108) in the form of a bolt. As part of the safety feature of the electrolyzer (100), the electrolyzer (100) is grounded by grounding the cathode electric connection (121) to protect the electrolyzer (100) from in contacting with operating personnel. In another further embodiment of the invention, the water electrolyzer (100) can be powered by an electrical supply regulated by a transformer and a rectifier. Water is treated with potassium hydroxide before supplying to the electrolyzer (100) in water treatment section and lye tank. Lye tank is a section rich in potassium carbonate. Still in another further embodiment of the invention, the electrolyzer (100) electrolyzed treated water at the present of potassium hydroxide into oxygen gas and hydrogen gas at their respective outlet. Oxygen gas is treated in an oxygen gas lye separator before being vented out. Hydrogen gas is treated in a hydrogen gas lye separator and water is further removed in a demister. The demister eliminates liquid vapor to obtain pure gas with approximately zero humidity. Subsequently, the remaining oxygen atom in the output gas is removed in a deoxidizer to ensure high purity of hydrogen gas. The output gas is then further treated in a dryer to ensure absolute zero humidity and high purity of hydrogen gas. The hydrogen gas is compressed to a desired pressure and stored in a container.

Although the invention has been described and illustrated in detail, it is to be understood that the same is by the way of illustration and example, and is not to be taken by way of limitation. The spirit and scope of the present invention are to be limited only by the terms of the appended claims.

Claims

1. A water electrolyzer (100) for producing hydrogen gas comprising

a stack of electrode plates (101) arranged in alternate polarities separated by dividers (104) and sandwiched between two end plates (107, 108), in which one of the end plates is an anode terminal (107) and the other is a cathode terminal (108), wherein the stack of plates (101) has a hollow centre for electricity connection and apertures (113, 114) around the hollow centre forming channels for distribution of electrolyte and collection of electrolytic products.

2. A water electrolyzer (100) according to claim 1, wherein the electrode connections (120, 121) are positioned centrally at the end plates (107, 108).

3. A water electrolyzer (100) according to claim 1, wherein the end plates (107, 108) further comprise channels (113, 114) for distribution of electrolyte and collection of electrolytic products.

4. A water electrolyzer (100) according to claim 1, wherein the two end plates (107, 108) are equi-potential.

5. A water electrolyzer (100) according to claim 1, wherein the stack of plates (101) is annular in shape.

6. A water electrolyzer (100) according to claim 1, wherein the electrode plates (102, 103) and the end plates (107, 108) are composed of material selected from the group consisting of nickel, cobalt, platinum, molybdenum, zirconium, an oxide thereof, or any combination thereof.