Development of Fuel Cell Vehicles (FCVs) and Expansion of Applications

FC system of the new Mirai (Source: Toyota)

  At the World Smart Energy Week 2021 Hydrogen & Fuel Cell Expo technical seminars held at the Tokyo Big Sight exhibition center in March 2021, there were presentations from Toyota and Honda in the session entitled "Trends in the Development and Popularization of Fuel Cell Vehicles (FCV) — from Passenger Cars to Expanded Applications." The following report introduces the content of the presentations.

  Mr. Kohei Yoshida, General Manager, FC Product Development Department, Toyota ZEV Factory, Toyota Motor Corporation, gave a presentation on "Accelerating Technological Innovation and Creating Partnerships for a Hydrogen Society.” In addition, he introduced the "Toyota FC Module" and Toyota’s activities to develop partnerships in order to utilize the FC stack installed in the new Toyota Mirai for various applications.

  In the "Honda's Fuel Cell Vehicle Development" presentation by Mr. Shuichi Togasawa, Chief Engineer, Block 1, High Voltage PU Development Office, Advanced Power Unit and Energy Research Institute, Honda R&D Co., Ltd., he outlined the history of Honda FCV development leading to the Clarity Fuel Cell, and explained the New Energy and Industrial Development Organization’s (NEDO) efforts on the technical development of fuel cell stacks and FCV-related issues. In the final Q&A session, he also introduced the atmosphere of its joint development activities with GM.

Related Reports:
Smart Energy Week 2021: Electrification-related Technologies (FC edition) (Mar. 2021)
FCV Developments at Daimler and Hino and Efforts toward the Realization of a Hydrogen Society (Feb. 2021)
The Routes to Carbon-neutral Freight Transport (Dec. 2020)
SAE China 2020 (2): Electrification of Commercial Vehicles (Dec. 2020)
Electric Powertrain Market Forecast in Major Countries (Oct. 2020)
Fuel cell commercial vehicles: Toyota jointly develops FC systems with major Chinese OEMs (Aug. 2020)

New Mirai released in December 2020 (Source: Toyota)

  Toyota released a new model of the Mirai, a fuel cell vehicle, in December 2020. In February 2021, Toyota announced the Toyota FC Module, a fuel cell system package that utilizes the technology of the new model. The system is designed to be easily utilized by FC product companies for a wide variety of applications, including mobility types such as trucks, buses, trains, and ships, and stationary power generators.

  This presentation focused on the various possibilities of fuel cells, and explained the technological innovations and enhancements for deployment to expand the use of fuel cells, as well as the efforts made in cooperation with local communities and businesses to promote the use of fuel cells in society.

Efforts to popularize FCs

  The use of hydrogen is accelerating around the world, and fuel cell technology is required for speed, increased hydrogen usage, ease of use in various applications, and the expansion of applications.

  Fuel cell technology, which started with the Mirai, will be used in the powertrains of commercial vehicles, trains, ships, and other forms of mobility, but it also has the potential to play a major role as a fundamental technology that enriches people's lives, as it provides solutions for industry, daily life, the global environment, and energy issues.

  To promote "cheaper and more convenient technology" and "easy-to-use technology", efforts are being made for (1) improved functionality, (2) strengthened deployment, and (3) the advancement of creating partnerships.

Evolution of fuel cell technology

History of fuel cell technology development (Created by MarkLines based on Toyota materials)

  Toyota's development of fuel cell technology started in 1992, and the first generation Mirai has sold more than 11,000 units and traveled more than 200 million kilometers.

  The power density has increased 30-fold from 0.11kW/L in the experimental FCEV in 1996 to 3.5kW/L in the first-generation Mirai, and at the same time, tests have been repeated to simulate various environments, including collision safety, bullets (shot to test safety and durability), freezing at low outside temperatures, etc.

  In the new Mirai released in 2020, the power density has been further improved to 5.4kW/L.

  The second-generation FC stack installed in the new Mirai has a volume of 24 liters instead of 33 liters and a mass of 24kg instead of 41kg, making it more compact and lighter while increasing the maximum output by 15% from 114kW to 128kW and the range by 30% from 650km to 850km.

FC stack performance improvement (Source: Toyota) 2008 model → 1st generation FC stack 3.5kW/L, 33L/41kg → 2nd generation FC stack 5.4kW/L, 24L/24kg (Vertical axis: Volumetric power density, Horizontal axis: Mass power density)	Second-generation FC stack and cell (Photo taken at the World Smart Energy Week 2021 venue)

  As for the performance improvement of the FC stack, the output per cell area has been improved by 26% by increasing the output per electrode unit area by 15%, and the maximum output of the stack has been improved by 12% while reducing the number of cells by 40.
  The key technology is the evolution of material technology, which reduces the amount of precious metals used per unit output by 58% by dispersing the platinum inside the porous carbon support to increase the utilization efficiency and promote the diffusion of ionomer (an electrolyte polymer, meaning ion + polymer).
  The flow path of the FC stack has been improved to drain the generated water in the cell by narrowing the flow path to drain the stagnant water in the separator and GDL (gas diffusion layer) catalyst layer to improve the performance on the high load side.

  Regarding extending the range, by downsizing the stack and storing it under the hood, and adding one high-pressure hydrogen tank under the floor to increase the hydrogen loading capacity by 1 kg, the vehicle’s performance was improved by 1.5%, the unit performance was improved by 6.2%, and the control was improved by 2.3%, for a total of 10% improvement in fuel efficiency, realizing a 30% improvement in range from 650km to 850km.

Evolution of materials technology (Source: Toyota) Top center: 1st generation solid carbon carrier Bottom center: 2nd generation porous carbon carrier (Green: Ionoma, Red: Pt on surface, Blue: Pt inside) Left graph: 15% increase in output per electrode unit area (Vertical axis: Cell voltage, Horizontal axis: Current density) Right graph: Reduction of Pt amount 2008 model → 1st generation: 72% reduction → 2nd generation: 58% reduction (Vertical axis: Amount of Pt per output)

Improvement of range (Source: Toyota) (Blue graph: First generation Mirai, Red graph: New Mirai) Upper right graph: Improved range (+ 30%) The range has been improved by 30% by expanding the amount of hydrogen loaded and improving fuel efficiency (distance that can be traveled with 1 kg of hydrogen). Central figure: Expansion of hydrogen loading capacity It is equipped with three tanks (4.6kg to 5.6kg) without sacrificing passenger space, while also utilizing the space in the center tunnel. Lower right graph: Improved fuel economy (+10%: vehicle performance +1.5%, unit performance +6.2%, control improvement +2.3%) By changing the FC boost converter to SiC, improved unit performance such as the use of Li batteries, and improved control such as refresh control, an approximate 10% improvement in fuel economy has been achieved.

Strengthening the foundation of production and development

Reduction of cell production cycle time (Source: Toyota) Blue graph: 1st generation: 10s of minutes Red graph: 2nd generation, a few seconds (Vertical axis: Cell production cycle time)

  As for speeding up production, the the production capacity of the stack and tank of the new Mirai is 30,000 units/year, 10 times that of the original Mirai, and manufacturability is 2.5 times that of the original Mirai.
  In addition, the amount of in-house capital investment has been reduced by 70% compared to a 10-fold increase in the scale of the business, contributing to cost reduction.

  In the production of the FC stacks (2nd generation stacks) for the new Mirai, productivity has been improved by speeding up the coating and rolling processes, speeding up cell assembly, and faster and more accurate quality control and inspection.
  In the transport of the electrolyte membrane and the diffusion layer in the roll process, the tension difference during transport is measured and the difference in tension between the left and right sides is controlled to suppress processing irregularities and achieve high-speed transfer.
  In the cell assembly process, the electrodes are sandwiched between separators and bonded by resin, and the cycle time has been reduced from several tens of minutes to several seconds by changing from conventional vulcanized adhesion to thermoplastic adhesion.

  To speed up the development process, an example of improvement of the development process using modeling and simulation was introduced, where the catalyst layer was modeled and the structure of ionomer and carbon was linked to performance, and the drying conditions that suppressed agglomeration were linked to the production process. It is said that the speed was increased by incorporating conditions for non-defective products such as drying conditions.

Toyota FC modules explanation panel (Photo taken at the venue of World Smart Energy Week 2021) Upper figure: Realization of an eco-friendly hydrogen society Center figure: Extensive product lineup (all-in-one FC module, lightweight hydrogen tanks of various sizes) Lower figure: FC components of the new Mirai

  When FC systems are to be used in various applications other than automobiles, it is difficult to create FC systems because (1) power supply voltage and output, (2) space limitations, (3) various connections (interfaces), etc. vary depending on the usage environment and needs.

  “Diversity" and "affinity" are important for many applications, and the Toyota FC Module, a packaged fuel cell system with Mirai as a starting point, was announced on February 26, 2021, taking into account factors such as the FC stack output lineup, tank size variations, packaging, and safety/reliability support.

  Toyota FC modules can be used for the FC of a variety of products by combining small 8kW, vertical 60/80kW, and horizontal 60/80kW FC modules, and the tanks are lightweight and a diverse lineup is available.

  An FC system can be created simply by assembling the water pump, air compressor and other peripheral components compactly in a FC module equipped with a DC-DC converter capable of 450 to 750V and connecting to a drive platform (power control unit, motor, battery, etc.) prepared by the customer and connecting air circulation system, hydrogen circulation system, and cooling system. It also provides support for handling hydrogen and high voltage.

FC module specifications (Created by MarkLines based on materials from Toyota Industries Corporation and Toyota Motor Corporation)	FC system schematic (Source: Toyota)

Expansion of FC development through collaboration

FC heavy-duty truck verification testing with logistics companies (Source: Toyota)

  Toyota is expanding the framework for commercial vehicle collaboration on fuel cell technology globally in Japan, the U.S., Europe and China.

  Since trucks account for a high percentage of transportation volume and a high percentage of CO2 emissions, they are highly effective as a low-carbon initiative, and Toyota is planning to conduct field testing with logistics companies on the use of FC heavy-duty trucks for trunk line hauling transport.
  In addition, Toyota is considering conducting field testing of 3-ton class FC trucks with convenience store operators.
  With regard to port logistics in North America, Toyota has started field testing of FCs on long-distance trailer trucks (Class 8) at the Port of Long Beach, Los Angeles.

  The company is also working on the expansion of FC to applications other than automobiles such as power generation equipment and railways, and is working on a fuel cell powered ship in Europe.

  As an initiative to further expand the potential of FC, the company is bringing up the possibility of applying FC from the perspective of "utilizing mobility" (e.g., minimum turning radius, vehicle width) and "utilizing space" (e.g., interior space, passenger capacity, tank capacity).

Creating new value for sustainable evolution

Moving e: Demonstration testing for a power generation/supply system (Source: Toyota)

  Moving e, which is being tested in collaboration with Honda, is a system for demonstrating a mobile power generation and power supply system that combines an FC bus with a portable external power supply and a portable battery. By combining Honda's inverter and small battery technologies with Toyota's FC bus, the system aims to supply power to evacuation centers in the event of a disaster and to supply clean energy to events during normal times.

A mindset of continuous challenge

Lunar mobility "Lunar Cruiser" under joint research with JAXA (Source: Toyota)

  As a challenge for 2050 and beyond, Toyota is also working with JAXA (Japan Aerospace Exploration Agency) to explore the possibility of using fuel cell technology in space.

  Since experiments in outer space are difficult, evaluation and various new challenges are required from experimentation, and new challenges lead to breakthroughs in existing technology. For example, on the moon, the gravity is 1/6 that on the earth, so the behavior of the water generated in fuel cells is greatly affected. Mr. Yoshida of Toyota said that “we can evolve our technology by constantly thinking about the behavior and challenging ourselves to devise new ways of doing things, and that the greatest source of creating new things is to keep challenging ourselves.”

  A Q&A session was held after the presentation, the contents of which are introduced below.

Q: Why did you set the output of the FC module at 80kW?

A: We are thinking of making it possible to respond to various applications by combining modules, but at the moment, we are first focusing on commercial vehicles based on the second-generation FC as a starting point. The difference between the 128kW of the Mirai and the 80kW of the FC module is the difference in maximum output and continuous output, but basically the same module is used.

Q: What is the difference between Type 4 and Type 3 hydrogen storage tanks, and what is your view on storage and FC performance?

A: It is important that the tank is made of resin and is light, and especially for commercial vehicles range is important, so we are increasing the amount of hydrogen stored on board to extend the range. Since the battery is important in producing peak power for a short period of time, the package is configured in combination with the battery.

Q: How much will the newly adopted SiC (silicon carbide) power semiconductors contribute to increasing the range?

A: They do not make a significant contribution to range, but do contribute to the reduction of losses.

Clarity Fuel Cell (Source: Honda)

  Honda launched its fuel cell vehicle, the Clarity Fuel Cell, in March 2016 (leased to government and corporate customers), and in 2020 began offering it to individuals on a leased basis.

  In the Honda seminar presentation, after talking about the environmental issues surrounding fuel cell vehicles, Mr. Togasawa introduced the history of Honda's FCV development, the outline of the Clarity Fuel Cell, the issues encountered in development, and the strategies for popularization.

History of FCV development and overview of the Clarity Fuel Cell

  Honda began leasing and selling the FCX in 2002, followed by the FCX Clarity in 2008 with improved low-temperature performance to -30°C, and the volume production FCV, the Clarity Fuel Cell, in 2016.

  The range has been increased from 360km to 750km due to the high pressure tank and optimal layout.

  In the Clarity Fuel Cell, the fuel cell powertrain is mounted under the engine hood, and the battery and hydrogen tank are optimally placed to create a spacious cargo area.

History of FCV development (Created by MarkLines based on Honda materials)	Power density of new FC stack (Source: Honda) Clarity FUEL CELL 33% smaller (compared to previous model) World-class output density (*2) 3.1kW/L (*2) As of February 2016, according to Honda research (Vertical axis: Volumetric power density, Horizontal axis: Power density)

  The FC stack used in the Clarity Fuel Cell is 33% smaller than conventional stacks and has a volumetric power density of 3.1kW/L.

  The cell (in a fuel cell) consists of a Membrane Electrode Assembly (MEA) in which an electrolyte membrane is sandwiched between an electrode layer and a diffusion layer of hydrogen and air electrodes, and these are sandwiched between separators provided with a flow path for hydrogen and air and a flow path for refrigerant. However, the cooling structure that makes up one unit (2 cells) with 2 MEAs and 3 separators has been further developed to make the cells 20% thinner, achieving a thickness of 1 mm per cell and improving the power generation performance per cell.

Thinning the cell of the new FC stack (Source: Honda)

Fuel cell system integrated with drive unit (Source: Honda)

  The fuel cell system is integrated with the drive unit.

  The voltage control unit, which boosts the stack voltage to drive the motor at high voltage, uses SiC power modules to achieve compact size and high output. The power control unit is also integrated with the drive motor and gearbox.

  The air compressor is an electric turbocharger type that increases the air supply pressure by 1.7 times that of conventional compressors. The powertrain size is almost as small as that of a V6 engine due to the downsizing of the fuel cell powertrain.

  As for the issues for the popularization of FCVs, there are some prospects with regards to range (750km), environmental compatibility (-30°C), and power output performance (3.1 kW/L). But for large commercial vehicles, it is necessary to further improve durability and reliability (currently several thousand hours). And, it is necessary to solve these issues in a balanced design process with a focus on quality assurance and cost reduction.

  To improve the durability and reliability of fuel cells, it is important to be able to measure the internal environment of the fuel cell, as degradation varies depending on how the fuel cell is used. Honda is engaged in measuring detailed events such as moisture content distribution, dry/wet cycles, contamination effects, and start/stop cycles.

Toward improving durability

  As for the influence of contamination in the atmosphere, fuel cells are easily affected by harmful gases because they operate and generate power by the intake of air, and if the concentrations of H₂S in volcanic areas and SO₂ in tunnels are high, the rate of output reduction will increase, so the filter must have the performance to catch such substances.

  The issue of fuel cell heat resistance is that the temperature difference between the cells in the center and the cells at the ends of the stacked cells in the stack changes the condensation state and the water content of the tabs, which affects the durability.

  The temperature transition can be predicted accurately by simulation, and it is necessary to build simulation technology to improve durability performance.

Confirmation of commercial vehicle potential through taxi field testing

  Taxi field testing was conducted for three years beginning in 2017 using six vehicles in the Japanese prefectures of Tokyo, Kanagawa, Saitama, and Miyagi, and their potential as commercial vehicles has been confirmed. By learning the characteristics of a taxi that has a long operating time in relation to the distance traveled, these characteristics can then be fed back to the durability protocol for future development.

Cost reduction initiatives

Productivity improvement: MEA material yield improvement (Source: Honda) Comparison of production processes (hydrogen electrode) Conventional model: Atypical MEA (membrane-electrode assembly) The base layer is applied to the diffusion layer in a single row and at intervals, requiring die-cutting work to match the shape of the MEA and generating scrap material. Clarity FUEL CELL (rectangular MEA) Because of its rectangular shape, the base layer can be applied to the diffusion layer continuously in multiple rows, greatly reducing the amount of scrap material. For the hydrogen electrode, the electrode layer is also applied continuously.

  Honda has been working on measures such as simplifying the laminated structure, changing to a simple structure by integrating hydrogen distribution devices, and improving the material yield of MEA. However, to cope with the increase in production volume in the future, it will be necessary to automate processes that rely on human labor and to automatically measure cells. It is expected that standardization will be promoted to lower the barrier to entry and accelerate the development of production technology.

Higher performance and higher durability of materials and parts by sharing NEDO issues

FCV Issue Sharing Forum issues (Source: NEDO) >>> Translation of the table

  Regarding the current status and issues of fuel cells for FCVs, at the "FCV Issue Sharing Forum" sponsored by NEDO, Toyota and Honda jointly categorized and addressed the challenges of applying fuel cells to automobiles to improve performance, increase durability, and reduce costs. Electrolyte membranes, catalysts, GDLs (gas diffusion layers), seals, production technologies, and analysis and evaluation technologies are being studied to reduce costs, mainly in the stack area.

External power supply by "connecting technology"

Usage scenarios for the Power Exporter 9000 external power supply device (Source: Honda)

  The fuel cell vehicle's power can be extracted and used by the Power Exporter 9000, an external power supply with a maximum output of 9kVA. Honda has a track record of supporting disaster-stricken areas with external power output devices in times of disasters.

  Honda is also conducting the aforementioned Moving e field testing in collaboration with Toyota.

Strategies for popularization

  Honda established a joint venture with GM in 2017 to jointly develop and manufacture fuel cell systems, and is preparing to install them in the next FCV. It is expected to enable Honda to expand its sales during the period of widespread popularization in the future.

  Honda's fuel cell roadmap is to expand from passenger cars to commercial heavy-duty mobility, as well as to the electrification of various mobility types such as trains and ships, and it is conducting joint research on FC heavy-duty trucks with Isuzu Motors Limited.

  A Q&A session was held after the presentation, the contents of which are introduced below.

Q: When will the next Clarity Fuel Cell be equipped with the new FC that is being jointly developed with GM?

A: We are working with GM on a joint development project that combines the strengths of both companies. But, there are cultural differences between our companies in Japan and the U.S. in terms of thinking and how to proceed, and it takes time to harmonize the technologies, so we are a little behind schedule. In addition to the technological barriers due to the high goals we have set, there are also differences in way our companies think, but development is progressing, so I hope everyone will be patient.

Q: You said that you have ascertained a forecast for range, but does that mean that there will be no problem once the infrastructure is in place?

A: The current number of hydrogen stations is far fewer than gas stations, so "ascertained a forecast" for range may be a bit of an exaggeration. Especially in the winter, this range may not be sufficient, as the actual range realized will be lower due to the use of heaters and air conditioners, but we believe that if the number of hydrogen stations increases, I think that it will be a car that can be used reasonably even if the cruising range is 750km.

Q: How do you calculate fuel consumption?

A: The value is calculated from the amount of hydrogen taken from the hydrogen tank running in the same mode as gasoline vehicles.

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Keywords.
Electric, FCV, Fuel Cell, FC Stack, Hydrogen Tank, Toyota, MIRAI, FC Bus, LUNAR CRUISER, Honda, CLARITY FUEL CELL, Power Exporter 9000, NEDO

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