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Design Of Small Alkaline Electrolyzer

There are usually two basic cell configurations, namely unipolar cell and bipolar cell. Figures 1 and 2 illustrate unipolar and bipolar battery configurations, respectively. UM and IM are the voltage and current of the electrolytic module.

A note on some parts:
1.Intermediate Base Plate: Intermediate base plate (can be assembled or synthesized with pole frame).
2.Bipolar Plate
3.Electrodes (current collector plate) : electrodes, we usually refer to as electrodes, or current collector plate.
Hydrogen evolution reaction (HER) selects a larger space of materials, generally divided into the following three categories; High overpotential metals :Cd, Ti, Hg, Pb, Zn, Sn, etc. Medium overpotential metals :Fe, Co, Ni, Cu, Au, Ag, W, etc. Low overpotential metals: platinum, palladium, etc.
According to the oxygen evolution reaction (OER), the metal material of the anode should be nickel (Ni), nickel-plated steel or its alloy. Generally, the same material can also be used as a cathode.
*** Cathode HER, anode OER***

4.Separating Diaphragm or separating diaphragm A separator is used to separate the anode and cathode from each other. Originally, the separator (separation membrane) was made of asbestos, but now asbestos is no longer used due to safety and health regulations. Today, they are dominated by polybenzoimide, polybenzene sulfide, sulfonated polymers and composites. The composite materials are mainly ceramic materials or microporous materials, such as polyether sulfone (PES) a reinforced, microporous polymer film, glass reinforced polyphenylene sulfide (PPS) compounds, titanium oxide mesh on the nickel oxide layer, potassium titanate pores and mainly ceramic. Diaphragms must keep product gases separate to maintain efficiency and safety. In addition, the diaphragm must be permeable to water molecules and hydroxide ions.

5.Electrocatalyst (Previous articles have described electrocatalysts). In order to improve the efficiency of the electrolytic process, electrocatalyst was added to the electrolyte solution. Therefore, it is an important material for improving hydrogen production capacity. Electrocatalyst reduces the activation energy of electrochemical reaction. In this design, in order to improve the efficiency of electrolytic process, electrocatalyst is used. Generally need diffusion layer (nickel mesh or porous nickel, etc.) as the support body.
6. It's full of electrolytes. The alkalinity is usually 25%~30% (KOH) or (NaOH) aqueous solution.
7.Sealing Gasket: Sealing gasket Has the ability to minimize gas leakage to the external atmosphere; Minimize electrolyte leakage to the outside atmosphere; Avoid mixing product gases near the catalyst area. The general use of silicone rubber, EPDM, PTFE, PEEK, PPS and other materials.

8.End Plate: End plate. It is used to fix both ends.

I. Design of single-pole electrolytic cell
In the unipolar structure, each electrolytic cell is connected in parallel to form a large module of electrolytic reactor, as shown in Figure 1. Thus, the voltage between individual electrode pairs is directly equal to the total electrolytic pile voltage, and the sum of the electrolytic pile current is equal to the total battery current. Moreover, in this structure, the same electrochemical reaction occurs on both sides of each electrode. The reaction can be either hydrogen evolution or oxygen evolution, depending on the polarity of the electrodes involved.
1.1. Solidwork design of unipolar alkaline electrolytic reactor
The stack consists of three cells. In addition, in order to improve the electrolytic efficiency, the porous stainless steel collector plate is used instead of the ordinary collector plate, as shown in the figure.

Figure is the standard drawing of corresponding dimensions of unipolar alkaline electrolytic reactor. The size of each monomer is the same as that of the secondary designed monomer alkaline electrolytic cell.

1.2. Preparation of monopolar alkaline electrolytic stack

The fabrication of monopolar alkaline electrolytic reactor is an important link to analyze and observe the reactor performance. The bipolar plate and connecting rod are used to connect the battery. The basic components of SolidWorks for unipolar alkaline electrolytic reactor are shown in the figure below.

The finished product of monopolar alkaline electrolytic stack is shown in the figure below

2、 Bipolar alkaline electrolytic reactor
In the bipolar structure, each electrolytic cell is connected in series to form an electrolytic stack module, as shown in Figure 2. Therefore, the sum of all voltages between individual electrode pairs is equal to the total voltage of the battery, and the battery current is directly equal to the current passing through each battery. In addition, in this structure, two different electrochemical reactions, hydrogen evolution reaction and oxygen evolution reaction, occur on both sides of each electrode. Therefore, one side of the electrode acts as the cathode and the other side as the anode.
The bipolar configuration has low ohmic loss compared with the unipolar configuration. Because the gap between electrodes in bipolar configuration is smaller than that in unipolar configuration. The gap between the electrodes is the distance that the ions must move in the electrolyte. Therefore, the ohmic loss inside the electrolytic stack can be reduced by reducing the gap, and the smaller gap between the electrodes has a smaller resistance for ion transmission. However, if the clearance is too small, it may cause safety hazards (which can be overcome by design). Therefore, it is very important to maintain the best gap between electrodes to obtain better performance.

2.1 Solidwork design of bipolar alkaline electrolytic reactor
The design and manufacturing process of bipolar alkaline electrolytic reactor is more complex than that of monopolar electrolytic reactor. In order to improve the electrolysis efficiency and the product gas flow rate, a small amount of improvement has been made to the current collector plate, which is composed of three monopole units.
In a bipolar structure, the electrolyte should be kept between the anode and cathode. Therefore, the bipolar plate area must not be affected by the electrolyte. 1mm thick rubber gasket is used inside the stack to prevent leakage inside the stack. In addition, only one side of the anode and cathode should be in contact with the electrolyte. As discussed in monopolar stacking, stainless steel is used as the collector plate to avoid the corrosion of the collector plate in KOH solution. The maximum thickness of the collecting plate is 7mm, and the processing process of the collecting plate is industrial milling machine. In order to increase the contact area and the volume of intermediate electrolyte, a longitudinal groove with a width of 5mm and a depth of 2mm is designed on the collecting plate (other types of flow channels can be made), as shown in Figure 8 below.

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