PEM hydrogen production is a variety of good, unique and costly, of which the plate cost accounts for a large proportion, and this paper shows a simple and cost-effective manufacturing method to produceOne-piece titanium-based bipolar plate。An innovative diffusion welding process is used to efficiently join together low-cost, commercially available raw materials (titanium plates, expanded metals, and nonwovens) that reduce the contact resistance of multi-component bipolar platesleft and right, reducing the number of components, thus greatly simplifying stacking assembly. The in-situ test of the contact pressure distribution on the surface of the active battery shows that the contact pressure distribution shows a uniform pattern with a value of about 375 mpa(±1.25 mpa)。The solid groove is assembled100cm2The PEM heap of the effective cell area, in2acm/2The average battery voltage is1.71v
BPP Development Goals:
The development of the new bipolar plates (hereinafter referred to as BPP) focused on cost-effectiveness and efficient assembly and operation. The specific objectives are as follows:1Simple and fault-tolerant stacking assembly: Stacked components should be as few as possible. For the stack assembly itself, the BPP should be made from a single piece of material. 2.Alternative flow field structure: The traditional flow field structure is composed of macroscopic channel rib structure, which has a negative impact on the mechanical compression and flow distribution uniformity in the active region. The BPP should be constructed in a structure that supports improved compression distribution. 3.Use of low-cost, market-oriented components: Particularly for the flow field of BPP, various types of porous media, such as metal structures, metal flannel or expanded metals, are readily available and widely used in many applications. For the optimization function of the flow field structure, a combination of different types of porous media or a combination of porous media of the same type but with different porosities is advantageous. Fig. 1 is the ** diagram of the designed BPP, which is composed of ten individual elements (the flow channels on both sides of the plate are sandwich structures, and each sandwich is actually composed of 3 layers of expanded metal mesh of different specifications), passing throughDiffusion weldingcombined into a single unit (BPP). The middle of the BPP consists of a flat titanium plate to ensure complete isolation of hydrogen and oxygen, and other elements of the BPP include a frame and an expanded metal mesh located on either side of the central plate. The anode side is also includedTi feltto ensure that the pressure is even. 
Figure 1** view of the new bipolar plate unit, where all the displayed elements will be combined into a single whole by diffusion welding.
Figure 2 shows the design of the PEM hydrogen cell fluid distribution and gas collection, where the cathode and anode of the electrolyzer are designed to have circulating water through them (although the hydrogen side does not consume water, the introduction of circulating water can better control heat dissipation). There is a row of holes on the opposite side of both groups of BPP and is interconnected with the manifold of the tank fluid distributor collector (manifold: connecting the hole and the groove inside the tank, which plays the role of fluid distribution), and the left figure of Figure 2 shows the main flow direction on the cathode side of the plate, the water inlet hole is located in the upper row of holes, and the hydrogen outlet hole is located in the lower row of holes. The frame frame overlaps only a portion of the channel, where the anode side in this case water flows in from the left side and out from the right, so the cathode and anode are designed for transverse flow.
Figure 2Media distribution, collection and direction of cathode and anode two-phase flow.
The expanded titanium mesh used is a diamond-shaped hole based on a thin sheet of metal of Ti1 grade, and the geometric parameters are shown in the table below.
Fig.3. Geometry of expanded metal. Left: Isometric view, right: Cross-section along the line. Table 1Geometric parameters of a single expanded metal used in the BPP test.
In the following diffusion welding technology, the use of TA1 substrate needs to meet the sealing requirements of the plates and frames, and in addition, the expanded titanium mesh and titanium felt need to have the maximum contact area possible to maximize the conductivity. Both sides of the titanium felt need to be opened to prevent the uniformity of the distribution of the incoming and outgoing liquid. These requirements preclude ordinary welding or bonding schemes, which can cause binders or solder to clog the mesh holes, common fusion welding processes that do not provide a full-surface connection of the component, and can cause considerable deformation due to localized melting or the presence of stress zones. Therefore, diffusion welding solves this problem as an effective way. Due to the high affinity of titanium for nitrogen and oxygen, it must be welded under vacuum or in an atmosphere using a pure inert gas. Since the diffusion welding process is carried out in a vacuum, it is particularly suitable for the joining of titanium. The related equipment of diffusion welding ZEA-1 is shown in Figure 4. (Note: Diffusion welding can make all the titanium materials in contact with the effective connection and maximize the contact area).
Figure 4Zea-1 diffusion welder when the door is opened. In addition to the heating element, the base plate and slide connected to the bipolar plate can also be seen.
In order to verify the feasibility of diffusion welding, 5 pieces of sheet metal titanium frames were superimposed together (as shown in Fig. 5), and more than 885 (suitable for pure titanium) were used for diffusion welding, and the leakage rate of multi-piece joints was less than 5*10-9 mbar l s. The compression amount is set to 01mm layer, pressure 10MPa.
Figure 5Five sheet metal titanium frames before diffusion welding (left) and after diffusion welding (right).
All bipolar plates can achieve the required internal and external tightness. The leak rate of less than 10 -8 mbar L S-1 was determined by helium leak test. Metal mesh and titanium felt are able to be fully bonded together. The gap between the metal mesh, titanium felt, and frame can be reduced to a certain extent to keep the membrane electrode assembly undamaged during assembly and avoid displacement of the membrane. Two tests were performed to quantify the gain of the one-component method in terms of contact resistance. According to Figure 1, the first group stacks the individual elements of the bipolar plates on top of each other and places them between two gold-plated contact plates (45 mm * 45 mm). A hydraulic press is used to continuously increase the contact pressure between the elements. At the same time, a current of about 10 A is fed through the contact plate and the intermediate components, and the voltage is measured. The second set simply replaces individual elements with soldered bipolar plates. At a contact pressure of 1 MPa, the resistance of the individual elements is 1539 m ·cm2, welded bipolar plate is 214 mω·cm2。In 2At 5 MPa, the resistance is 503 m · cm2 and 128 mω·cm2。This means that the contact pressure on the surface of the target active unit is 2At 5 MPa, the resistance of the welded bipolar plate is reduced by about 75% compared to the unwelded version.
The 100cm2 bpp is verified below, and the 100cm2 bpp welding is completed by diffusion welding, and the effect is shown in the figure below.
Fig.6 Renderings of 100cm2 bpp.
Prior to the electrochemical cell pack test, an external test was performed to evaluate the uniformity of the pressure distribution of the bipolar plates over the active cell area. Figure 10 shows a schematic diagram of the test setup and test results. It can be seen that the pressure distribution of the entire plate can be divided into three zonesin the active area, the pressure is mainly at 2Varying between 5 and 5 MPa, the overall uniformity of the pressure distribution is very high, and the characteristic pattern of the pressure distribution shows that the structure of the metal mesh is at a microscale (2-25 mm) on the local pressure (fine streaks of the active area). The second areaIt is the junction of the active area and the frame. Due to the overlap of rigid frames and porous materials, mechanical support is not optimal. This phenomenon results in relatively low pressure in the junction area, below 1 MPa and up to 2 MPa. The third areaIt is the outer frame area. Here, the contact pressure is mostly higher than 10 MPa, which ensures a tight connection to the outside.
Figure 7Test the pressure distribution in situ in situ. Left: Schematic diagram of the installation;Right: Local pressure on the frame and active area.
The diffusion-welded BPP was assembled for a stack test, which consisted of 5 cells with an active cell area of 100 cm. (The basic configuration of the attached part: gas-liquid separator, conductive gold-plated copper bolts, MEA composed of 212 film, TORAY 120 2-layer carbon paper, and diffusion welded titanium felt, 0..)25 mg cm2 PT cathode, 1 mg cm2 iridium oxide anode, Viton 65 Shore A stack seal plate gasket with a thickness of 500 μm). Polarization performance is shown from 03 A cm2 to the maximum current, mainly ohmic resistance predominates, and the transport loss is not significant, indicating that the liquid is delivered adequately. As the current density increases, the voltage deviation between the five cells increases. Cell No. 3 is slightly worse (up to 18 mV at the highest current density), with an average voltage of 1 measured at 2 A cm2 for the overall electrolyzer71 v。
Figure 8PEM electrolyzer is a polarization performance test.
*: Hydrogen fuel cell technology sharing platform.
China Hydrogen Energy Alliance, National Energy Group, Zhongguancun China Electricity Council and other units will hold the "China Hydrogen Energy Exhibition" in Beijing from March 26 to 28, 2024, and the 2024 China Hydrogen Energy Exhibition will be held in the form of exhibition + forum with the theme of "Promoting the Deep Integration of Hydrogen Energy Innovation Chain and Industrial Chain". During the meeting, the China Hydrogen Energy Alliance held the "International Hydrogen Energy Industry Summit".Zhongguancun Hydrogen Energy Industry Alliance held a number of forums such as the "Beijing Hydrogen Energy Industry Conference and the Beijing-Tianjin-Hebei Hydrogen Energy Industry Development Summit Forum". It aims to build a diversified international exchange platform between the entire hydrogen energy industry chain. At present, the recruitment has begun, welcome to book a booth!
Electrolyzer equipment companies that have participated in the exhibition: Kunhua Technology, Sichuan Yalian, Sunshine Hydrogen Energy, Trina Hydrogen, Beijing CLP Fengye, Shanghai Hydrogen Era (Shanghai Electric), Perry Hydrogen Energy, LONGi Hydrogen Energy, Cockrell Competition, Suzhou Xibeiyou, Solar, EVE Hydrogen Energy, Hewang Electric Hydrogen Energy, Shuangliang Hydrogen Energy, Hydrogen Hui Energy.