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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