Development Trends and Popularization Scenario for Fuel Cell Vehicle. 1 Toyota-cho, Toyota, Aichi, Japan. 1 Toyota-cho, Toyota, Aichi, Japan

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1 / The Electrochemical Society Development Trends and Popularization Scenario for Fuel Cell Vehicle T.Yoshida a, K.Kojima b, T.Yokoyama c and S. Sekine b a Fuel Cell System Development Div. TOYOTA Motor Corporation, 1 Toyota-cho, Toyota, Aichi, Japan b Fuel Cell System Engineering Div. TOYOTA Motor Corporation, 1 Toyota-cho, Toyota, Aichi, Japan c Advanced Powertrain, FC Hybrid Group, Toyota Technical Center Toyota Motor Engineering & Manufacturing North America, Inc W.186th St, Gardena, CA 90248, USA The Toyota FCHV-adv that was released in 2008 has a cruising range in actual driving conditions of more than 500 km and can be started in temperatures as low as -30, thereby overcoming two of the major obstacles to the practical adoption of FCVs. Toyota is continuing to resolve technical issues to popularize FCVs. For example, Toyota aims to reduce the cost to about 1/20 by further development work. In addition to improving commercial appeal, the widespread adoption of FCVs depends on the establishment of basic hydrogen infrastructure. Toward 2015, car manufactures including Toyota are continuing to cooperate with governments and energy businesses to establish infrastructure and make the necessary modifications to laws and regulations. This article summarizes the technical progress for FCVs. Introduction Toyota Motor Corporation plugs away at developing various types of advanced transportation technologies that contribute to the development of a society based on sustainable mobility. One technology that is recognized as having significant potential for the future is the fuel cell vehicle (FCV). Toyota began fuel cell development in 1992, and was the first company in the world to begin leasing an FCV (the Toyota FCHV) in In 2005, model certification was obtained for a revised version of this vehicle that complied with the Japanese government s new safety standards. Subsequently, Toyota developed the FCHV-adv (Fuel Cell Hybrid Vehicle-advanced) with the latest fuel cell technology. This vehicle was introduced into the Japanese market in 2008 and the North American market in 2009 [1]. The vehicle s exterior appearance and basic specifications are shown below (Fig. 1 and Table 1). There are two primary points where the FCHV-adv has been improved in comparison to the 2005 model. 1. A cruising range in practical driving conditions of more than 500 km has been achieved by increasing the hydrogen storage capacity through improvements in the hydrogen tanks and by increasing efficiency to optimize the FC system. 2. The system can now be started in temperatures as low as -30 C, due to improvements in the FC stack and the adoption of new technology called rapid warm-up operation. 3

2 Fig. 1: Toyota FCHV-adv at Yellow Knife, Canada. Vehicle Fuel Battery type Table 1: FCHV-adv Specifications Item Data Overall length/ width/height [mm] 4,735/1,815/1,685 Maximum speed [km/h] 155 Maximum cruising range [km] test cycle JC08 test cycle Fuel consumption [km/kg] 139 (38)@ test cycle (Gasoline conversion [km/l]) 126 (34.5)@ JC08 test cycle Seating capacity [person] 5 Type Hydrogen Storage system High-pressure storage tanks Maximum storage pressure[mpa] 70 Tank capacity [L] 156 Tank capacity [kg] 30 C Nickel-metal hydride Cruising Range Actual cruising range can only be extended by two ways: (1) Increasing hydrogen storage capacity (2) Improving fuel efficiency Therefore, the new hydrogen tanks used in the Toyota FCHV-adv were made to increase the filling pressure to 70 MPa. The carbon fiber layer which covered outside of the tank was optimized to reduce its thickness. The tank valves were made smaller using new materials, and the amount of residual (unusable gas) was reduced. Therefore, Our new tank has 1.9-times the hydrogen storage capacity of the 2005 model [1]. Better fuel efficiency was accomplished by the accumulation of small improvements. Principally by reviewing the system, this development reduced losses occurring in the auxiliary units (such as the air compressor and the hydrogen pump) that are needed to operate the FC stack, and increased the amount of regenerative energy recovered from braking. These efforts achieved an approximately 25 % improvement in vehicle fuel efficiency compared with the 2005 model. Consequently, the efficiency of the FC system 4

3 in the Toyota FCHV-adv was improved to a maximum of 64 %. This equates to a wellto-wheel efficiency of approximately 40%, around twice that of a gasoline vehicle. Due to these improvements, the FCHV-adv has achieved cruising range in practical driving conditions of more than 500 km, or about 2.4 times the cruising range of the previous FCV. This figure is similar to the 450 to 650 km practical average cruising range of current gasoline vehicles. In mode, the cruising range is 830 km (Table 1). This is the longest cruising range of any FCV in the world. In a long-distance cruising test on actual roads from Osaka to Tokyo (about 560 km or 350 miles) with the air conditioning running, the vehicle arrived at Tokyo without any hydrogen refueling and actually had some hydrogen to spare (Fig. 2).The rest fuel amount to over 100km drivable. Osaka Japan Tokyo 560 km (350mile) Figure 2: Long distance travel of Toyota FCHV-adv without refueling. Cold Startability In addition to cruising range, cold startability is one of the major issues confronting FCVs. The following sections describe the efforts to improve the cold startability of the Toyota FCHV-adv. To start the FC system at subfreezing temperatures, it is important to control the generated water to prevent it from freezing. The water, which accumulates in the FC membrane electrode gasket assembly and gas channels, freezes and reduces gas diffusion. This may prevent the continuation of power generation in the FC or cause operational defects in system components. This paper explains four items that are important to overcome this issue: (1) the water content control system, (2) visualization inside the FC, (3) rapid warm-up operation, and (4) electric power control using FC capacitance characteristics. The first point is important when the system is stopped, the others when the system is started. Water Content Control System The first key item to enable cold startability is the sub-system that controls the water content in the FC stack at the beginning of power generation (at the end of the previous driving operation). A correlation between water content and electrical resistance in an actual cell (i.e., PEM resistance or the same as impedance) is applied to the sub-system, Figure 3 shows a block diagram of the developed AC impedance measurement system [4]. 5

4 ECU Converter control Data sampling FFT analysis Filter (LPF) V=Asin(ωt) V fc I fc HV battery High voltage converter Voltage sensor Current sensor AC impedance (to other ECU) PCU + - Fuel cell stack Figure 3: Sub-system for AC impedance measurement of FC. VISUALIZATION INSIDE FC By the visualization of the inside of the FC under power generation below freezing point, it was found that the generated water is initially super-cooled when the FC generates power at subfreezing temperatures [2, 3]. In addition, power generation cannot be continued, when gas exchange was inhibited by the frozen water at the interfacial surface between the membrane electrode assembly (MEA) and the gas diffusion layer (GDL). Rapid Warn-Up Operation Based on the visualization results, it is necessary to quickly raise the system temperature before the water generated by the chemical reaction freezes and prevents FC operation. For this reason, while reducing the thermal capacity of the parts that compose the FC stack, the third item, called rapid warm-up operation, was developed. This operation is based on the idea of using the actual FC as a massive heater to increase the calorific value of the FC [5-7]. To realize this idea, the supply of oxygen to the fuel cell is limited to increase the concentration overvoltage and lower the reaction efficiency. This intentionally reduces the efficiency of power generation and increases the amount of self-generated energy to stimulate warming up of the fuel cell (Fig. 4). A normal operation point is relatively higher voltage shown in Fig. 4. However, the fuel cell is operated at lower voltage than the normal operation point in order to increase the self-generated energy while satisfying the requirement power under rapid warm-up operation. Increasing the self-generated heat in this way rapidly warms up the fuel cell beyond the freezing point. 6

5 FC s heat generation under normal operation FC voltage [V] 1.0 Normal operating point FC s heat generation under Rapid warm up operation Operating point for rapid warm up FC current [A] Figure 4: Rapid warm-up operation point of FC. Electric Power Control Using FC Capacitance Characteristics After the temperature of the fuel cell has been increased above freezing by the rapid warm-up operation, the vehicle can run but the warm-up phase is continued during vehicle operation, until approximately 70 C, to enable efficient fuel cell operation. If driver release accelerator pedal in this operation, surplus power is generated by the late air compressor response is not so quick compared with accelerator pedal release because of its inertia. This surplus power may overcharge the secondary battery. To manage surplus power, we focus on fuel cell stack electric capacity [8]. FC has sufficient capacity to absorb the surplus power. we set in this capacity to control surplus power and allowed the rapid warm-up V_FC [V] Voltage rise I Air ICapacitor I Voltage decrease FC I_Air I_CAP FC capacitance FC current increase Voltage decrease (V 0 V 1 ) Modeling 0 25A I_FC [A] Cyclic Voltammogram of a 400 cell (25V/s and 25A of air supplied) FC I_Air (a) When FC Voltage decreases I_CAP FC capacitance FC current decrease Voltage rise (V 0 V 1 ) (b) When FC Voltage rises Figure 5: FC Capacitance Characteristics As shown in Fig. 6, these improvements have enabled a start up time of 30 seconds at -20 C, which is the best cold start capability of any FCV in the world. 7

6 However, further improvement is required from the standpoint of product quality. In particular, progress must be made in reducing both scavenging time when the vehicle stops and start-up time, and in improving durability after repeated cold starts. 60 Test locations :Canada :Japan 40 :US Startup time [s] FC temperature at start [ ] Figure 6: Start-up time of Toyota FCHV-adv. Durability of FC Stack To ensure the viability of the FCHV as a commercial product, it is necessary to focus on the durability of the FC stack and the cost reduction of the FCHV system. There are many cases we consider for durability such as high cell potential, high temperatures, high or low humidity including humidity/potential cycling and start/stop operation [12,16]. Two major issues to improve the durability of the FC stack are the prevention of crossover due to fractures in the electrolyte membrane, and reduction of performance decay as a result of catalytic electrode deterioration. There have been significant improvements in crossover durability in the past several years by the market in the FCHV-adv(Figure 7). Of course there is no fear of crash when the reduction of performance decay, but it s not convenient for customers. From this view points, we set our target of the durability of cell performance to 15years.However, we does not satisfy this target. Crossover Amount MEA1 Reduction of physical deterioration MEA2 Reduction of chemical deterioration MEA3 Durability test by FC system bench in simulated continuous driving Ave speed: 63km/hr Threshold limit value FCHV-adv MEA4 Maximum Output MEA1 MEA2 MEA3 Threshold limit value MEA4 FCHV-adv Durability (year equivalent) Figure 7. Durability of FC Stack 8

7 Elements of MEA Core Shell Catalyst One effort towards the reduction of platinum usage is development of the core-shell catalyst. The aim is to reduce the total amount of Pt used in an FCV by replacing the center of the catalyst particle with a non-precious metal and placing precious metal only on the particle surface, which is the location of chemical activity. Toyota is grateful for the support of the U.S. Department of Energy (DOE) toward research and development in this area, and there are expectations that this technology will be practically applied[19] [16]. Catalyst Ink Catalyst ink of which components are carbon, platinum, water, and ionomers, is important to generate good performance catalyst layer. Contrast-variation small-angle neutron scattering (CV-SANS) is a powerful technique to study this ink since it allows one to decompose scattering intensity functions to partial scattering functions[18]. From the CV-SANS analysis, the following is revealed: (1) The partial scattering functions for carbon-carbon, polymer-polymer, and carbon-polymer correlations, were successfully obtained. (2) The microscopic structure of the catalyst ink consists of dendric clusters of carbon particles surrounded by ionomers. (3)Ionomers have an ionic cluster peak around q 0.1Å-1, which maintain its structure even in the ink mixed with carbon/pt. (4)The cross term of carbon-polymer correlations indicates a percolated structure of carbon clusters mediated by ionomers. Simulation Various simulations have been applied to the development of FCV reducing the development time and cost[9-11]. Toyota has been developing CAE which covers the entire fuel cell technology from a molecular model for the material R&D to the vehicle system model for the system and control design. Catalyst Durability It is essential to understand the influence of the operation condition and design factors on the Pt/C catalyst durability in PEMFC. We explain one of examples of these our simulation. The influence of the catalyst layer thickness on the electrochemical surface area (ECSA) loss was examined with the same Pt loading MEAs (Figure 8)[20]. The thin catalyst layer lost large ECSA, as Pt loss area formation was dominant. On the other hand, the thick catalyst layer showed less ECSA loss. The influence of Pt diffusion was located around the catalyst layer / membrane interface. The model calculation results supported this assumption. ECSA loss causes the MEA performance decay. This decay was also analyzed by modeling [21]. 9

8 Normalized ECSA Experiment Calculation Catalsyt layer thickness, m Figure 8. Investigation of influence of cathode catalyst layer thickness on ECSA loss under H2/N2 condition at80,100%rh. Cost reduction The cost of the previous FCHV system was too expensive for many customers to buy it as a mass produced vehicle. However, currently, the cost has been reduced to about 1/10 by simplifying the design and reducing the cost of materials. Toyota aims to reduce the cost even more about 1/2 by further development work. The additional cost reduction with the effect of mass production technology is expected to achieve the commercialization of FCV. In general, the higher durability we want, the higher cost we need. But cost and durability must go together. It is very important to develop the elements of PEFC[17]. FC vehicle cost FCHV-adv (2008) FC system cost Body, chassis, hybrid system components, etc. 1/10 or less Vehicle cost 10 million yen or less 1/2 or less Further cost reduction Limited release phase Current status (2011) Initial phase of market penetration (2015) Growth phase of market penetration Overcoming technical challenges Reducing costs Design and production technologies Figure 9. Cost reduction of FC system Economies of scale 10

9 Hydrogen Infrastructure Issues The development of a hydrogen infrastructure is critical for the popularization of FCVs. This is not simply a matter of building hydrogen stations, but will also require the development of hydrogen manufacturing, transport, and supply technologies to minimize CO2 emissions and costs, as well as the creation of regulations and standards for safe handling of large amounts of hydrogen. Therefore, cooperation among the government, energy producers, and auto manufacturers will become increasingly important. In July 2008, a scenario for the popularization of the FCV and the spread of hydrogen stations was announced at the Fuel Cell Commercialization Conference of Japan (FCCJ). In this scenario, the major Japanese auto manufacturers and energy suppliers agreed upon a target to start popularization in 2015 and to build infrastructure from 2015, in advance of vehicle popularization. To promote hydrogen station establishment, 13 Japanese companies issued a joint statement concerning the introduction of FCVs in the Japanese market and the development of hydrogen supply infrastructure on January 13, 2011 [23]. The companies plan to approach local governments and other concerned parties to discuss strategies, targeting Japan s four major metropolitan areas (Tokyo, Nagoya, Osaka, and Fukuoka) (Fig.10) Early commercialization In 4 major metropolitan areas 100 stations Deployment on highways 2025 Commercialization expanding 47 prefectural capitals covered 1,000 stations from 2030 onward Mass commercialization Nation-wide hydrogen net established 5,000 stations Advance deployment in 4 major metropolitan areas Commercialization start in 2015 Based on the proposal of Council of Competitiveness-Nippon (COCN) Figure 10. Deployment plan of hydrogen stations in The Research Association of Hydrogen Supply/Utilization Technology (HySUT) is an association founded 31st July 2009, with an approval of Minister of Economy, Trade and Industry (METI).[24]. HySUT operates two demonstration projects. For example, "Hydrogen Highway Project" is a regular long distance service of fuel cell vehicles and buses on an expressway connecting between downtown Tokyo and Haneda / Narita airport. A target has been set reduce the supply cost of hydrogen below that of gasoline by 2030, and research is being actively advanced by NEDO [25]. Conclusion For the improvement of the cruising range of FCVs, the Toyota FCHV-adv has 1.9- times the hydrogen storage capacity of the 2005 Toyota FCHV and 25% improved fuel efficiency. As a result, the Toyota FCHV-adv has achieved an actual cruising range equivalent to a gasoline vehicle of 500 km, and a cruising range in the LA#4 test cycles 11

10 of 790 km, which is the longest of any FCV in the world. For cold startability, the Toyota FCHV-adv has also achieved the start-up under subfreezing temperatures in the world. In the future, to increase the viability of the FCV as a commercial product, we intend to increase durability and reduce costs. Car manufactures including Toyota wish to reach a consensus with energy suppliers and governments on infrastructure technology establishment, regulation revision, technical and social demonstrations, and initial infrastructure development and then implement these matters, with the aim of starting the popularization of FCVs from References 1. M.Kizaki, Y.Nonobe, H.Mizuno, T.Takahashi, A.Yamashita, in EVS24 / Y. Ishikawa, T. Morita, K. Nakata, K. Yoshida, M. Shiozawa, Behavior of water below the freezing point in PEFCs, Journal of Power Sources (2006) 3. Y. Ishikawa, M.Shiozawa, H. Hamada, M. Uehara,in 212th ECS meeting / N.Kitamura, K.Manabe, Y.Nonobe, M.Kizaki, in SAE International/ United States Patent Application United States Patent US 6,329,089 Ballard Power Systems Inc., 7. K.Manabe, Y.Naganuma, Y.Nonobe, M.Kizaki and T.Ogawa, in SAE International/ H.Imanishi, K.Manabe, Y.Nonobe and T.Ogawa, in SAE International / A. Z. Weber and J. Newman, J. Electrochem. Soc., 151, A326 (2004). 10. R.M. Darling and J.P. Meyers, Journal of the Electrochemical Soc.,150, A1523 (2003). 11. S. Um and C. Y. Wang et al., J. Electrochem. Soc., 147, 4485(2000) 12. M. F. Mathias,et al et al., Electrochem. Soc. Interface, 14, 24 (2005). 13. N.Takeuchi, T.F.Fuller, J. Electrochem. Soc., 157,B135 (2010) 14. N.Takeuchi, T.F.Fuller, J. Electrochem. Soc., 155 B770 (2008) 15. J.Farnsworth, T.Bono, H.Mizuno, Y.Tano, M.Toida,in SAE International/2010, 16. T.Yoshida. Toyota Technical Review,57,48 (2011) 17. M. Takami, T. Yoshida and M. Ueda, in First CARISMA International Conference/ K.Amemiya,et al. JSAE 2011 annual congress autumn(in Japanese) 19. K.Sasaki et al. Angew. Chem. Int. Ed. 49,8602, (2010) 20. N.Takeuchi, K.Kato and T.Yoshida, in printed. 21. S.Jomori, N.Nonoyama and T.Yoshida, in printed. 22. Fuel Cell Commercialization Conference of Japan (FCCJ) Ministry of Economy, Trade and Industry (METI), Japan The Research Association of Hydrogen Supply/Utilization Technology (HySUT) Press Release. Fuel Cell and Hydrogen Group, New Energy Technology Department, New Energy and Industrial Technology Development Organization /nedoothernews / 12