Toyota Mirai fuel cell stack parameters

　　The volume and mass of the Toyota Mirai fuel cell stack are 37L and 56kg respectively. The maximum output power of the stack is 114kW. It is composed of 370 single cells connected in series, and the thickness of the single cell is 1.34mm. According to the SAI report, the total reaction area of a Toyota Mirai fuel cell stack is 9.91㎡, so the area power density is 1.15W/c㎡. The aspect ratio of the battery reaction area (activearea) is 1:2. The reaction area and the total reaction area are The area ratio is 0.4:1 (0.4:1 is the ratio of the electrochemical reaction area to the total area, in which the MEA area under the ridge is not included in the reaction area).

　　Detailed calculation of Toyota Mirai fuel cell stack cost from materials and processes is $14,545

　　Mirai stack structure

　　Detailed calculation of Toyota Mirai fuel cell stack cost from materials and processes is $14,545

　　Mirai battery size (announced by SAI)

　　The parts of the fuel cell stack include bipolar plates, sealing rings, gas diffusion layers, catalytic layers, proton exchange membranes, etc. The picture below is a list of Toyota Mirai fuel cell stack parts suppliers. Note that the materials and preparation technologies for catalysts and sealing rings are included in the cost calculation; although the Toyota Mirai fuel cell uses the GORE-SELECT proton exchange membrane produced by the American Gore Company, its cost is not directly included in SAI's cost. In the computational study, the costs were calculated using conventional proton exchange membrane preparation techniques.

　　Detailed calculation of Toyota Mirai fuel cell stack cost from materials and processes is $14,545

　　Toyota Mirai fuel cell stack parts supplier list

　　Catalyst preparation

　　It can be seen from the above Toyota Mirai fuel cell stack parts supplier list that the catalyst for the Mirai stack is prepared by CATALER. SAI's cost study used two catalyst synthesis patents from Kotla. Kotla's catalyst processing steps are very similar to the dealloyed PtNiO3/C synthesis method, except for the additional processing step of graphitizing the carbon powder for improved durability.

　　It has been reported that cerium oxide can be added to catalysts using radical scavenging methods to improve durability. According to relevant information, it is assumed that the Pt load capacity is 0.3mgPt/c㎡, so each stack is about 30gPt. Note that since there is currently no reference directly from Toyota to verify this catalyst Pt loading, this value still needs to be verified through sensitivity analysis.

　　Detailed calculation of Toyota Mirai fuel cell stack cost from materials and processes is $14,545

　　Mirai stack PtCo catalyst graphitization synthesis and preparation process

　　In the method of preparing the PtCo catalyst, it is assumed that the platinum donor material (hexahydroxyplatinate) costs twice as much as the platinum donor material (chloroplatinic acid). The breakdown of materials, preparation and pricing during the catalyst synthesis process is shown in the figure below. In the case of an annual output of 1,000 sets (pile), related materials (excluding Pt), catalyst synthesis and related processing will all have a markup of 25%.

　　Detailed calculation of Toyota Mirai fuel cell stack cost from materials and processes is $14,545

　　Synthesis cost of PtCo catalyst when annual output is 1,000 sets and 3,000 sets

　　Mirai catalysts are prepared by a batch slot die coating method. SAI's cost study mentioned that the approximate cost of the catalytic layer preparation process through intermittent slot die coating is $800 per stack. The intermittent slot die coating method can reduce material waste caused by partial coating of inactive areas. The figure below shows the intermittent slot die coating system used by Toyota.

　　Detailed calculation of Toyota Mirai fuel cell stack cost from materials and processes is $14,545

　　Toyota intermittent slot die coating equipment diagram

　　Preparation of amorphous carbon coating on titanium metal plate surface

　　Relevant documents released by Toyota show that Mirai bipolar plates are stamped titanium plates with a π-conjugated amorphous carbon coating on the surface. The carbon coating on the surface of the titanium metal plate is prepared by an argon plasma cleaning step and a plasma chemical vapor deposition method. The cost model is based on Toyota's patent, which identifies the precursor gas formulations used in the process of preparing amorphous carbon and forming a certain coating thickness.

　　Detailed calculation of Toyota Mirai fuel cell stack cost from materials and processes is $14,545

　　Preparation process of amorphous carbon coating on titanium metal plate surface

　　First, each thin plate was manually loaded into the PECVD vacuum chamber (45cm diameter × 30cm high chamber). After the chamber was evacuated, argon plasma was used to clean the surface for 5 seconds. A 50 nm thick amorphous carbon coating was formed from a pyridine precursor in a nitrogen carrier gas environment. Note that plasma is formed by electric field ionization and controlled using magnetic fields. After 10 seconds of deposition, the plate was manually unloaded. Immediately afterwards, the coating was completed after a 2-minute nitric acid etching process and a 1-minute rinsing process.

　　Detailed calculation of Toyota Mirai fuel cell stack cost from materials and processes is $14,545

　　Schematic of plasma chemical vapor deposition method equipment (announced by Toyota)

　　As shown in the figure below, when producing 1,000 systems (stacks) per year, the plasma chemical vapor deposition process accounts for 58% of the total coating cost (0.63/1.08), and the etching step accounts for the remaining cost. Among etching costs, etching tooling is the main expense. Since the detailed details of the etching process are not yet known, it is simply assumed that the etching tool cost is $5,000 per 1,000 etches for etching materials or filtration. There is no information on the amount or type of material used in the etching process, so estimated etching tool costs may vary.

　　Detailed calculation of Toyota Mirai fuel cell stack cost from materials and processes is $14,545

　　Cost composition of amorphous carbon coating on titanium plate surface

　　Seal preparation

　　Toyota Mirai fuel cell stack seals are designed and developed by Sumitomo Riko, a company controlled by Toyota Motor Corporation. The sealing ring design of the Mirai fuel cell stack consists of two parts, namely the injection molded structural seal ring around the MEA (injectionmolededframe gasket around the MEA) and the injection molded bipolar plate gasket (injectionmolededbipolar plate gasket).

　　Detailed calculation of Toyota Mirai fuel cell stack cost from materials and processes is $14,545

　　Sealing principle

　　The preparation and assembly process of Mirai fuel cell stack sealing rings can be seen from Sumitomo Riko's two sealing ring design patents. As shown in the figure below, the patent mentions a method of using EPDM rubber material and preparing fuel cell sealing rings. . The injection molding process of EPDM material preforming is divided into two steps: bipolar plate sealing ring preforming and MEA structural sealing ring preforming. Put combination #1 and combination #2 into a single mold and apply the coating to the cathode bipolar plate, then clamp and heat at 150°C for 10 minutes to form cross-linked EPDM, forming a single seal and composition after completion Battery.

　　Detailed calculation of Toyota Mirai fuel cell stack cost from materials and processes is $14,545

　　Sumitomo Riko seal ring preparation process (paint is used to increase adhesion)

　　Cost studies show that due to the long processing time and the limited number of parts that can be heated simultaneously in one mold (corresponding to the three steps of "EPDM heating to 150°C for 10 minutes" in the figure above), the battery assembly cost exceeds 60% of the total cost of the sealing ring process. % (The total cost of the three steps in the picture above is $939 per Mirai stack). Correspondingly, the cost related to the bipolar plate in the above steps only accounts for 10%, and injection molding in steps one and two accounts for about 30%. As a supplier of Toyota Motor Corporation, Sumitomo Riko provides injection molded sealing rings. Assume that the price of the injection molded sealing rings is only increased by 30%, and the single cells are finally handed over to Toyota Motor Corporation for assembly.

　　gas distribution manifold

　　The Toyota Mirai fuel cell stack contains an aluminum gas distribution manifold and Kuraray GENESTAR resin, which serves as the stack end plate, inlet and outlet ducts, and insulator.

　　Detailed calculation of Toyota Mirai fuel cell stack cost from materials and processes is $14,545

　　Mirai intake manifold real thing

　　Among them, the resin component is molded on the aluminum plate. The resin is a proprietary polyamide material that insulates the aluminum plate from the stack. In addition, the resin contains additives that reduce electrical conductivity and has low water absorption (high water absorption at high temperatures will reduce the electrical insulation of the resin material). The in-mold injection molding process accounts for 67% of the total manifold cost (approximately $277/piece).

　　Detailed calculation of Toyota Mirai fuel cell stack cost from materials and processes is $14,545

　　Mirai intake manifold diagram

　　Detailed calculation of Toyota Mirai fuel cell stack cost from materials and processes is $14,545

　　Stack Manifold Cost Estimate

　　Mirai stack cost

　　Let’s compare the costs of Toyota Mirai stacks and SAI’s baseline stack with a net power of 88.5kW with an annual production volume of 1k and 3k sets, item by item. When the annual production volume is 1k sets, the cost of a single Mirai stack is about $14,545, and the single cost of SAI's 88.5kW net power benchmark stack is about $9,700.

　　Detailed calculation of Toyota Mirai fuel cell stack cost from materials and processes is $14,545

　　Mirai stack cost breakdown under annual production volume of 1k and 3k

　　The cost comparison of the two stacks is shown in the table below. The cost difference is mainly caused by the following factors:

　　1. The titanium bipolar plates in the Mirai fuel cell stack are more expensive than the stainless steel bipolar plates in the benchmark stack.

　　2. Mirai has a higher Pt loading of 0.4 mg/c㎡, which is higher than the Pt loading of the benchmark stack (the Pt loading in the benchmark stack is 0.125 mg/c㎡). The reason may be that large Pt loading improves durability.

　　3. Since the Mirai stack has more accessory parts (such as manifolds), the cost is higher than that of the baseline stack.

　　4. Although some Mirai stack components use the same preparation process and method as the reference stack, the effective reaction area of the Mirai stack (9.91㎡) is larger than the reference stack (8.88㎡).

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