WO2014075741A1

WO2014075741A1 - Pem-type electrolyzer stack for operation at high pressure

Info

Publication number: WO2014075741A1
Application number: PCT/EP2012/072982
Authority: WO
Inventors: Pedro Blach Servera
Original assignee: TINA ENERGY SYSTEMS SL
Current assignee: TINA ENERGY SYSTEMS SL
Priority date: 2012-11-19
Filing date: 2012-11-19
Publication date: 2014-05-22
Anticipated expiration: 2015-05-19
Also published as: US20150329977A1

Abstract

Electrolyzer module comprising a front plate, end plate enclosing an anode cavity, and a cathode cavity.

Description

PEM-TYPE ELECTROLYZER STACK FOR OPERATION AT HIGH PRESSURE

FIELD OF THE INVENTION A PEM Electrolysis module is a filter- pressure design (STACK) collected from the cells, sandwiched between the end plates with bolts. An Electrolyzer has an internal communication system associated with the external system of water regime providing and gas separators. Internal communication is facilitated by channels that are formed by the connections of individual parts by doing in these parts a number of coaxial holes. Elements of the cells are sealed with gaskets from made of fluorine rubber.

STATE OF THE ART The improvement and optimization of a PEM electrolyzer efficiency and operative life operating at high pressures is linked to the following:

• Membranes with low ion-exchange capacity

• The technology of the MEA manufacturing with structural improvements in order to increase contact with the current collectors.

• Optimization of the mesh elements design, gaskets, bipolar plates, as well as system of supply and distribution of reagents to the cell contours.

• Providing a more uniform distribution of water on the active surface of the electrolyzer cells

• Providing rapid removal of electrolysis gases from the cathode and anode spaces.

• Providing a minimum electrical contact resistance of electrolysis cell elements and minimum degradation

Hydrogen occurrence in oxygen may in some cases accompanied by decreasing of a current efficiency (up to 50% at smaller currents) relative to theoretical value, which is obtained at the assumption of losses from a crossover. Hence, processes, which lead to hydrogen formation in anode area, may be electrochemical character and directly accompany anode processes of water decomposition. Hydrogen concentration in electrolytic oxygen cannot be caused only membranes gas permeability; It is possible that the hydrogen in electrolyzer anode space is formed as a result of electrochemical processes directly in anode catalyst layer or corrosion processes on electrolyzer design elements. It should be noted that the specific reasons for such processes to the end and not yet clarified the issue continues to be relevant.

Uniform distribution of water on the active surface of the cell provides a uniform release rate of electrolysis gases formation. This eliminates the possibility of the formation of stagnant zones, and increases efficiency and life of work, improves the purity of electrolysis gases and prevents accidents related to local heat, causing destruction of the elements of MEA.

Quickly remove of electrolysis gases from the cathode and anode spaces provides increased water content in the cathode and the anode space of the electrolyzer, which contributes to improving the efficiency of electrolysis.

The minimum contact resistance of electrolysis cell design elements at operating conditions provides the best electrical characteristics of the cell and, consequently, increases its efficiency as a whole.

For obtain of pure electrolytic gases it is necessary to improve MEA manufacturing techniques (improve the homogeneity of the catalytic layers structure, clarification of requirements for the degree of

Dependence of membrane gas permeability from temperature has exponential increase and increases approximately by 5 times at increase temperature from 40°C to 80°C while hydrogen concentration in anode area almost does not depend from temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

To complete the description and in order to provide for a better understanding of the invention, a set of drawings is provided. Said drawings illustrate a preferred embodiment of the invention, which should not be interpreted as restricting the scope of the invention, but just as an example of how the invention can be embodied.

Fig.1 Shows the electrolysis module in the backpressure case where the

electrolyzer stack, is located.

Fig. 2 Shows the end plate with a handing out channels to be implemented in the present invention

Fig. 3. Shows a gasket with the holes and channels with conical to be implemented in the present invention

Fig. 4. Is a representation of a mesh insert to be implemented in the present invention

Fig. 5. Show the mesh insert with dividing walls to be implemented in the present invention.

Fig .6. Show the water and gases flows in the electrolisis stack with the components of the present invention

DESCRIPTION OF THE INVENTION The invention is related to several improvements in the design and construction of components and manufacture techniques of the PEM electrolyzer stack components that solve the majority of the technical issues that have influence in the gas production at high pressures up to 500 bars. The invention provides a PEM electrolyzer working at high pressure, placed in a backpressure case (fig.1). The case is filled by an inert gas (or hydrogen) at pressure, which corresponds to the pressure inside the electrolyzer. This design and operating mode has been described in our Patent P200900163.

Because the distribution and collection of reagents in the electrolysis module is made from the front side, there is a need to direct flows towards the rear of the electrolysis module. To do this, the invention presents an end plate with milled grooves, (fig. 2) with this end plate design, distribution and collection of reagents is performed from the two sides of the plate. In order to obtain a more uniform distribution of water on the active surface of the cell and more efficient removal of electrolysis gases from the cathode and anode space by optimization of sizes, amount and configuration of the input and output of gases and water, the invention presents in a particular embodiment, a configuration of the gaskets with conical windows for inserts of a conical shape, (fig. 3). The configuration of distributing holes in gaskets, depends on the amount of generated gas (ie, the number of cells in the electrolysis module and pressure) can be made from two to eight over-sized holes. The size of the slot channels of the upper and lower inserts made different: in the upper groove gasket are installed inserts with E = 1 .00 mm tp 2,8 mm, in the lower grooves are installed inserts with E = 0,70 mm to 1 .50 mm. This allows to provide the necessary backpressure to improve the uniformity of reagents and flow distribution on the cross sections of electrolysis cells.

To provide uniform water distribution in the inner cavities of the electrolysis module cells and to reduce the "stagnant" zones in gasket construction in a particular embodiment, the invention is provided with slotted holes that form additional cross- cutting channels. To reduce dead zones, two to four channels , depending on the amount of generated gases, for distribution and collection reagents are provided, and the holes have a shape such as to direct the flow towards the gaskets corners. (fig.3)

To reduce corrosion at the center of the bipolar plates and the corners of porous current collectors, the inner corners of the gasket windows are rounded, with a predetermined curvature radius

Deposition of the catalytic layer directly on the membrane results in improvements in the homogeneity of the catalytic layer's structure, highly degree of purity of reagents and materials, specially when the process is carried on with a current density of 1 A/cm² and voltage lowered to 100mV for the cell, or at a current density of 2A/cm²- for 200mV. Hydrogen concentration in electrolytic oxygen falls under this conditions approximately a 10%.

In order to lower the electrical contact resistance of the mesh inserts of the electrolyzer (fig. 4) The first and third layer of the grids are immediately rolled "in size" and have a smooth surface, and the second layer, located between them, has a different thickness without smooth surfaces After welding of the grid layers "rolled on rollers to the desired size", which allows improving the contact resistance between the layers of grids and reduces the contact resistances. With the use of this technology object of the invention we reduce the contact electrical resistance of the electrolysis cell construction is reduced from 25 mQ/cm² to 15 mQ/cm², which corresponds to the decrease in cell voltage at a current of 1 A/ cm² at 10 mV.

Another variant of the mesh inserts construction described above (fig.5) may be with dividing walls for optimization of water distribution. The presence of walls directs the water flow to the right direction and eliminates the appearance of stagnant zones. This design is more effective in cells with a large work surface. In fig 6. is presented the scheme of water and gas flows inside the electrolysis stack manufactured with the elements of the present invention. Water is supplied to the anode channel through 3 lower front flange fittings,. After that, water is decomposed on the membrane and oxygen and part of remaining water passes to the rear end plate at its upper part, and through channels made in the end plate, turns to the side of the front flange and is expelled through two upper lateral connections. Water is supplied through 2 bottom side connections to the cathode cavity of the electrolysis stack ,then passes to the back plate where the flow turns in the opposite direction and is distributed over the cathode cavity. The resulting decomposition hydrogen input into the upper hole of the electrolyzer stack components and comes out through the top 3 fittings in the front flange.

Claims

1 . -PEM Electrolyzer stack in which the water is supplied to the anode cavity through 3 lower front flange fittings,. After that, water is decomposed on the membrane and oxygen and part of remaining water, passes to the rear end plate at its upper part, and through channels made in the end plate, turns to the side of the front flange and is expelled through two upper lateral connections. Water is supplied through 2 bottom side connections to the cathode cavity of the electrolysis stack, and then passes to the back plate where the flow turns in the opposite direction and is distributed over the cathode cavity. The resulting decomposition hydrogen flows into the upper hole of the electrolyzer stack components and comes out through the top 3 fittings in the front flange, (fig 6) .

2. - PEM Electrolyzer stack in accordance with claim 1. further comprising gaskets made of Fluor rubber or with Fluor rubber with a cover of Teflon film, the gaskets further comprising windows, slots and channels at their sides with conical windows for inserts of a conical shape, each channel having 3 distributing holes, the wholes being of a bigger size as the windows, the configuration of number of distributing holes, depends on the amount of generated gases and can be from two to eight. The size of the slot channels of the upper and lower inserts have different size: in the upper groove gasket inserts with E = 1 .00 mm tp 2,8 mm, in the lower grooves inserts with E = 0,70 mm to 1 .50 mm. (fig 3),

3. - PEM Electrolyzer Stack in accordance with any of the previous claims in which the end plates made with titanium with milled grooves.(fig 2) 4.- PEM Electrolyzer module in accordance with any of the previous Claims , Claim

1 . in which Gas Distribution layers made with Titanium or Composites of Titanium and Carbon in the cathode region, in which the first and third grids layer immediately rolled "in size" and have a smooth surface and a second layer, located between the two, has a margin thickness,

(fig 4)

5.- Electrolyzer module in accordance with Claim 4. in which Gas Distribution layers incorporated dividing walls (fig.5)

6- Electrolyzer module in accordance with any of the previous claims, further comprising current collectors and bipolar plates made with titanium or Composites of Titanium and Carbon which present a curvature radius on the inner corner.

7.- Electrolyzer module in accordance with any of the previous claims , in which the bipolar plates made with titanium or Composites of Titanium and Carbon have a curvature radius on the inner corner.