- Email: [email protected]
Fuel Cell System for Honda CLARITY FUEL CELL
Journal Pre-proof Fuel Cell System for Honda CLARITY FUEL CELL Shintaro Tanaka, Kenji Nagumo, Masakuni Yamamoto, Hiroto Chiba, Keiko Yoshida, Ryu Okano PII:
S2590-1168(20)30003-5
DOI:
https://doi.org/10.1016/j.etran.2020.100046
Reference:
ETRAN 100046
To appear in:
eTransportation
Received Date: 22 September 2019 Revised Date:
12 December 2019
Accepted Date: 1 February 2020
Please cite this article as: Tanaka, S., Nagumo, K., Yamamoto, M., Chiba, H., Yoshida, K., Okano, R., Fuel Cell System for Honda CLARITY FUEL CELL, eTransportation, https://doi.org/10.1016/ j.etran.2020.100046. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier B.V.
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Fuel Cell System for Honda CLARITY FUEL CELL a
Shintaro Tanaka *, Kenji Nagumoa, Masakuni Yamamotoa, Hiroto Chibaa, Keiko Yoshidaa, Ryu Okanoa a
Honda R&D Co., Ltd. Automobile Center, 4630 Shimotakanezawa, Haga-machi, Haga-gun, Tochigi, 321-3393 Japan *Corresponding author. Email: [email protected]
Abstract Honda started to lease the world's first fuel cell vehicle (FCV) in December 2002 and has since continuously provided FCVs with advanced technologies. In March 2016, Honda leased the CLARITY FCV with a high-performance and durable downsized fuel cell system realized by optimizing the structure of the fuel cell stack, controlling water distribution in the catalyst-coated membrane, and extending the fuel cell lifetime. As a result, the fuel cell system, voltage control unit, and motor unit are integrated into one fuel cell powertrain system. This highly integrated design allowed the CLARITY FCV to become the world's first production five-seater fuel cell sedan to install the entire fuel cell powertrain system under the front hood. Thus, this study aimed to develop novel measurement methods that will allow the simulation of different parameters of FCV. Particularly, the following key findings are introduced: prediction model for the performance degradation of the catalyst layer, effects of atmospheric impurities on performance degradation, chemical degradation of electrolyte membrane, and water content optimization for catalyst coated membrane. Keywords: Fuel cell stack, Performance degradation, Membrane degradation, CCM water distribution.
1. Introduction Since the latter half of the 1980s, Honda has focused on urban air pollution, global warming, and energy issues as the areas to be addressed in its automotive developments. The company has worked to realize measures to respond to these issues. Honda considers fuel cell vehicles (FCV) as the ultimate next-generation clean automobile with the potential to address all these issues. With this, the company is continuously engaged in FCV development (Fig. 1). Fuel cells produce electricity and water through the reaction of hydrogen and oxygen. In automotive applications, they do not emit atmospheric pollutants (such as CO2), making them an effective solution to air pollution and global warming. The hydrogen used by the fuel is a secondary energy carrier, which can be produced from various forms of primary energy and can be easily converted into electricity using means including fuel cells and gas turbines (Fig. 2). CO2 emissions during existing hydrogen production pose an environmental issue. However, future hydrogen production using renewable energy can potentially offer an energy source that does not emit CO2. Fuel cells are also prospects in addressing the uneven distribution of fossil fuels; thus, presenting further advantages for energy security.
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Fig. 2 Source and application of different energies
Fig. 1 Solutions of environmental and energy issues aimed by FCV
2. Development of FCVs To respond to environmental and energy issues, Honda has been engaged in the development of technologies that increase the efficiency of internal combustion engines (ICE) and further efficiency increase through electrification (Fig. 3). Among these efforts, Honda began the research on fuel cells at the end of the 1980s and since then, progressed to the development of fuel cell stacks. The company was the first to lease a marketed FCV in December 2002 [1, 2]. In 2004, the first Honda-built fuel cell stack [3, 4] was installed. The lease marketing of the sedan-type FCX Clarity began in 2008 [5, 6] and that of the CLARITY fuel cell in March 2016 (Fig. 4) [7]. At 3.1 kW/L, the fuel cell stack in CLARITY FUEL CELL has world-class volume power density 60% higher than previous stacks (Fig. 5).
Fig. 3 Environment-friendly initiatives of Honda 2002.12 FCX
2004.11 FCX
2008.6 FCX Clarity
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Fig. 4 Evolution of Honda FCV
2016.3 CLARITY FUEL CELL
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Door
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Passenger
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-20 ℃
-30 ℃
-30 ℃
Cold Temp. Performance
>0 ℃
FC L/O
Under floor
Under floor
Center tunnel
Under hood
Separator
Carbon
Stamped metal
Stamped metal
Stamped metal
Body
EV-Plus
EV-Plus
New body
New body
Body Type
Small 2 box
Small 2 box
Sedan
Sedan
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360 km
470 km
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750 km
The size reduction of the stack was accompanied by increased impact toughness at collision. This allowed the realization of a fuel cell powertrain comprising a hydrogen supply system, air supply system, voltage converter, and motor sized equivalent to a V6 powertrain (Fig. 6). Therefore, the developed fuel cell powertrain can fit in the same position of an existing gasoline powertrain, allowing the use of a five-seater gasoline vehicle chassis. In addition, the use of a 70-MPa hydrogen tank helped in ensuring a driving range of approximately 750 km and hydrogen tank filling of approximately 3 min.
Fig. 5 Output density of different fuel cell stack
Fig. 6 Fuel cell system for CLARITY FUEL CELL
3. New fuel cell stack and development method 3.1. Overview of the new fuel cell stack The multiple cell layers in the fuel cell stack are composed of a membrane electrode assembly (MEA) and separators that form gas channels (GCs). MEA comprises a polymer electrolyte membrane (PEM), catalyst layers (CL), and gas diffusion layers (GDL). PEM with formed CL is referred to as a catalyst-coated membrane (CCM) (Fig. 7). In normal fuel cell stacks, the unit formed by a MEA and two separators is considered one cell (Fig. 7). Honda reduced the size of its fuel cell stacks by employing a wave configuration that increases the gas diffusion performance of GCs and a cooling configuration in which two MEA and three separators represent one unit (two cells) (Fig. 8).This configuration has been further developed for the CLARITY FUEL CELL. In addition to using a thinner MEA, the developed fuel cell stack circulates water from power generation through counter flows of hydrogen and air. This achieves a uniform distribution of the CCM water content
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using an optimal gas distribution structure realized through the use of a resin frame. Furthermore, the level of water content is reduced by the humidity feedback control. These technologies reduces the depth of the gas flow channels and increased compactness by 20%, thereby helping in enabling a 1-mm cell thickness (Fig. 9). The depth reduction of the GCs can further contribute to the pitch reduction. This reduced the water condensation and accumulation produced by generation in the gas diffusion layers, increasing gas diffusion performance, and realizing a 1.5 times performance increase per cell (Fig. 10). With thinner cells and increased generation performance, the CLARITY FUEL CELL achieved a 60% increase in volume power density, 30% reduction in the number of cells in the stack, and 33% reduction in the stack size.
Fig. 7 Schematic image of fuel cell
Fig. 9 Schematic image of counterflow and in-plane gas distribution with resin frame
Fig. 8 Schematic image of Honda’s fuel cell structure
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Fig. 10 Comparison of liquid water and performance
3.2. Development of fuel cell stack models High-level power generation in a compact and lightweight stack and standard level of durability of fuel cells are both required in developing fuel cell stacks in FCVs. To evaluate durability, hundreds of cells are manufactured and assembled in a stack, which results in an extended development period. At Honda, the development of the new fuel cell stack was accelerated by incorporating advance evaluations using simulation models. To help ensure the durability of the fuel cells, it is necessary to maintain the active surface area of the catalyst layers and the thickness of the electrolyte membrane. The active surface area of the catalyst layers considerably affects the cell output, and the thickness of the electrolyte membrane separates the oxygen and hydrogen fuel and electrically insulates the anode and cathode, respectively. The maintenance of the catalyst layer surface area and PEM thickness is greatly affected by the content of CCM water. When the water content is high, the coalescence of the catalyst due to dissolution, agglomeration, and re-deposition result in the decrease of the catalyst layer surface areas. Chemical degradation occurs due to chemical reactions. Factors, such as impurities and hydrogen peroxide, accelerate the PEM degradation and promote the loss of membrane thickness. In addition, due to the iron-based material employed in the separators, the water accumulation from generation in separator channels results in the elution of iron, especially the contact area of the separators and the MEA, accelerating the chemical degradation of the PEM. When a fuel cell stack is installed in a FCV, the generation operating conditions, including the hydrogen/air stoichiometry, the stack temperature and humidity change in response to the vehicle states, such as acceleration and deceleration. Furthermore, this affects the water content of the CCM. In a fuel cell stack, the large CCM area of approximately 300 cm2 poses difficulty in realizing uniform water distribution within the generating plane. Thus, it is important to create a simulation model to evaluate the durability of the catalyst layers and electrolyte membrane in advance through consideration of the water content distribution in the CCM.
3.3. Simulation model of performance degradation in the catalyst layer
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3.3.1. Parameters for evaluation Degradation results in the reduced performance in a fuel cell stack when the vehicle is running, starting up, and stopped. The size of the material (Pt) in the cathode catalyst layer increases and its performance declines due to the recurring high-potential loads when the vehicle starts and stops. With this, the potential cycles when output fluctuates during vehicle operation (Fig. 11).
Fig. 11 Pt on the carbon support
Fig. 12 General CV depicting features
To quantify the effect of potential cycles on the degradation of the cathode catalyst layer, the relationship between the loads produced by potential cycles and the degree of degradation of the catalyst layer was investigated using cyclic voltammetry (CV). CV is a method to express electrochemical reactions in the catalyst layer in response to the potential in terms of current. Fig. 12 shows the current-potential characteristic of a normal Pt catalyst. A current can be observed in the electrochemical double-layer capacitance of the cell at approximately 0.5 V. From 0.6 to 1.0 V, a transition occurred from the adsorption reaction between the Pt and water to a reaction that forms an oxide film on the Pt surface (Pt oxidation). On the other hand, a reduction reaction occurs in the platinum oxide (PtO) layer (platinum reduction) and Pt returns to its metallic state when from 1.0 to 0.6 V. At potentials lower than 0.5 V (between 0 V and approximately 0.45 V), a proton (H+) adsorption and desorption reaction (hydrogen adsorption and desorption: HAD) occurs on the Pt. The total HAD charge (QHAD) and effective electrochemical surface area (ECSA) of Pt are proportional, as expressed in Equation (1). With this, the ECSA indicating the catalyst performance can be determined based on the total HAD charge. (1) ECSA cm
3.3.2. Numerical expression of the effect of attained potential In this study, the effect of the projected maximum potential attained during start-up (upper-level potential, ULP) was investigated (Fig. 13). Results indicated that higher ULP causes a greater increase in the reduction current (Q1) in the PtO film formed from the increased potential. In addition, the reduction current in the PtO differed not only with ULP but also with the holding time. The effect of the minimum potential attained during acceleration and deceleration of a running vehicle (lower-level potential; LLP) was also investigated (Fig. 14). When LLP was manipulated, Q1 produced by the ULP was reduced from a to b by the holding LLP. Due to the holding LLP, the PtO formed at the ULP was reduced and the charge declined due to the partial return of the PtO to its metallic state.
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Fig. 13 Effect of upper level potential (ULP)
Fig. 14 Effect of lower level potential (LLP)
Based on these results, Pt stress (∆Q) is defined, which is the indicator of the cathode catalyst layer degradation to clarify the effect of potential cycles due to the vehicle start, stop, acceleration, and deceleration (Equation (2)) [8]. Pt stress：ΔQ ≡ Q Q (2) Here, Q1 is the total charge in the PtO film at the ULP, and Q2 is the residual charge in the PtO film after reduction due to the LLP. To establish the correlation between performance and ∆Q, ECSA as a factor of performance and its relationship with ∆Q were investigated. Potential cycle tests using test cells were conducted to determine the relationship between the ECSA loss rate and ∆Q. ∆Q was set by modeling the potential changes in a fuel cell stack and applying different conditions of the vehicle such as the projected potential and temperature upon starting, stopping, accelerating, and decelerating. Fig. 15 shows the relationship between the ECSA loss rate and ∆Q. These results indicate that the ECSA loss rate can be expressed by ∆Q with comprehensive consideration of the changes in potential, temperature, and other factors during the vehicle start and operation.
Fig. 15 Correlation of ECSA loss rate and ∆Q 3.3.3. Verification in the actual fuel cell stack To verify the developed model, the catalyst degradation in stack evaluation acceleration mode was studied using an actual fuel cell stack. ∆Q was calculated based on the average voltage profile of the stack (ULP and holding time, LLP) and temperature. Moreover, the water content of the cells was estimated based on impedance and ECSA loss rate was predicted. Fig. 16 shows the ECSA measured and estimated in a cell (Dry Condition: 25% RH gas, Wet Condition: 45% RH gas).The dashed lines in the plot show the ECSA predictions from the developed model. The
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predicted and measured values corresponded well, demonstrating the potential of the model to estimate the catalyst degradation in an actual fuel cell stack. In addition, results indicated the reduced deterioration under conditions with lower water content. Therefore, the water content of the cathode catalyst layers was controlled during start-up and shutdown to reduce the ECSA decline.
Fig. 16 Verification results of the degradation by CCM water control
3.4. Effects of atmospheric impurities on performance degradation 3.4.1. Typical atmospheric impurities to affect performance Most reports on the effect of atmospheric impurities on power involve tests using commercial mini cells, such as JARI cell [9]. To date, no known cases of using actual automotive cells has been reported. Mini cells typically use a serpentine flow-field that differs from the flow-field of an actual automotive cell. Hence, the diffusion behavior of air and its impurities also differ. Thus, the effect to reduce power may differ from that in an actual vehicle. Table 1 shows the typical atmospheric impurities that affect fuel cell stack power [9]. These impurities include sulfur-based gases (H2S and SO2) and nitrogen-based gases (NO2 and NH3). The concentrations of these impurities are affected by various factors, such as the geographical environment and weather conditions. This makes the quantitative evaluation of the effects of various impurities using only field trials impractical. Therefore, this study conducted bench tests that generated power under simulated atmospheric gases containing different impurity concentrations to the cathode side of an actual automotive cell. Table 1 Atmospheric impurities that affect fuel cell performance Impurities Concentration H2S 1700 ppb 250 ppb SO2 19 ppb NO2 600-6000 ppb 21 ppb NH3 38 ppb
Hot spot Hot Spa Volcano Heavy Traffic Tunnel Livestock Industry
3.4.2. Effects of atmospheric impurities using actual automotive cell The performance evaluation used a stack consisting of ten actual automotive cells. Fig. 17 shows a schematic figure of the power generation evaluation apparatus. High-purity hydrogen was humidified and heated using a bubbling system to achieve the conditions similar to the supplied fuel gas of the stack in an actual vehicle. The air with impurities removed (hereafter, “clean air”) was humidified and heated, then the
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specified impurity was mixed via a T-shaped joint connected to the gas inlet pipe of the stack cathode. The mixture was then supplied as the oxidant gas to the stack.
Fig. 17 Experimental scheme of gaseous contaminants injection The evaluation was performed by simulating the load variation produced by the vehicle start, stop, acceleration, and deceleration, referred to as the “running mode”. During the running mode, the cathode flow rate changes according to the set load variation. The maximum power during clean air supply was extracted and used as the reference for the decrease in power over time. The power slopes with various atmospheric impurities (∆P2/∆t) and that with clean air (∆P1/∆t) are defined as the power decay rate. It is used as the index for evaluating the effect of atmospheric impurities on power (Fig. 18). Fig. 19 shows the relationship between the concentration of each impurity and the power decay rate.
Fig. 18 Power decay rate by subtracting rate in clean air for correction This study confirmed the previously reported [9] tendency where the power drop increases with the concentrations of atmospheric impurities. By examining the characteristics of each gas type, two types of sulfur-based impurities (H2S and SO2) exhibited similar behavior between the power decay rate dependence and concentration. Reference [10] proposed Pt catalyst surface reactions for H2S and SO2. In both cases, the adsorption reaction to the Pt surface active sites in SO42– form. Thus, the power dependence on impurities concentration is presumed to be similar for both H2S and SO2.
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Fig. 19 Relationship between power decay rate and impurities concentration As described in Reference [9], with similar concentrations of different impurities, NO2 shows a smaller effect on the power reduction compared to sulfur-based impurities. However, Table 1 shows that the maximum atmospheric concentration of sulfur-based impurities is 1000 ppb, whereas some environments have NO2 concentrations of more than 1000 ppb. Hence, power may also be affected in regions with high NO2 concentrations. NH3 did not affect power at the anticipated actual concentration of 100 ppb. Similar to Reference [9], this study confirmed that NH3 concentrations of less than 1000 ppb have no effect.
3.5. Simulation model of chemical degradation in PEM The PEM is believed to be subject to degradation due to the OH radicals produced by the reaction of hydrogen and oxygen passing through the membrane. Fe ions are known to accelerate chemical degradation through generation of OH radicals. On the other hand, there are metal ions or organic molecules with conjugated systems that scavenge radicals. However, it is necessary to use appropriate quantities of these additives as they can reduce the conductivity of H+. A map of the degree of acceleration of chemical degradation in relation to the amount of Fe ions and amount of radical quencher used as an additive was formulated (Fig. 20). The PEM thickness was set using this map to predict the lifetime of the membrane. In addition, present Fe particles became Fe ions, thereby producing local thinning of the PEM thickness (Fig. 21).
Fig. 20 3D visualized map of accelerating factor a
Fig. 21 X-Ray and PEM thickness measurement using SEM
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3.6. Simulation model for in-plane water content in CCM 3.6.1. Evaluation parameters The operating conditions of the fuel cell stacks fitted in FCV change with the vehicle state. The CCM water content changes with the operating conditions. The in-plane CCM water content in the cells differs in different positions. With this, the development of the simulation model for evaluation of the in-plane water content distribution of the CCM proceeded with the development of the water content sensor during actual real-time vehicle operation, including the acceleration and deceleration. 3.6.2. Measurement of in-plane water distribution in CCM Honda employs analyses using the neutron RG to study the water status in the fuel cell interior. Since this measurement method involves beaming neutrons in one cell direction, it can obtain the total water content encompassing in the separator channels, within the CP and CCM in the said direction. However, it is not suitable in measuring the isolated CCM water content. With this, a method using impedance was developed, together with the simulation model [11], to measure the water content of the cells fitted in a vehicle. This method was applied in developing a sensor that can measure the in-plane CCM water distribution in fuel cells. Fig. 22 shows the developed sensor for the impedance measurement of the in-plane water distribution of the CCM. The sensor was designed in the same shape as the MEA. It can be fitted between separators in an actual fuel cell stack and take measurements without special separators or seals. Both surfaces of the sensor feature 75 square sensor pads that measure the impedance of the CCM. An alternating current is superposed on the entire fuel cell stack to conduct the measurement. Resistance values are calculated from the current and voltage values measured by the sensor and are converted to the water content of the CCM.
Fig. 22 Water content distribution measurement sensor 3.6.3. Simulation model of in-plane water distribution in CCM There is several fuel cell simulation software available. This study selected a market fuel cell simulation software with adequate simulation accuracy and speed for the fuel cell stack development employed in FCV. The simulation model of the in-plane water distribution in the CCM was developed by incorporating the experimental results of the water distribution in Section 3.6.2 and applying original Honda functional modifications. Fig. 23 (a) and (b) show the simulation results of in-plane water distribution in the CCM and the comparison of simulation and measurement results, respectively. As exhibited in the figure, there is a good correspondence between the simulation and measurement results. Moreover, the application of a resin frame to optimize the hydrogen and air distribution has minimized variations in the water distribution of the CCM in the direction of the shorter side of the generating area.
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Fig. 23 (a) Simulation result of water content distribution
Fig. 23 (b) Comparison of simulation and experiment result
3.6.4. Optimization of in-plane CCM water distribution The generation system employed in the CLARITY FUEL CELL is provided with a humidifier with its bypass valve connected in parallel (Fig. 24 (a)). Based on the water content of the CCM and stack impedance characteristics (Fig. 24 (b)), the necessary CCM water content for the durability of the stack is controlled within the upper and lower limits shown in the figure depending on the measured stack impedance, which is the average value of in-plane impedance.
Fig. 24 (a) In-plane water content of CCM control system in 2016 FCV model
Fig. 24 (b) Relationship between CCM water content and stack impedance Considering the in-plane CCM water distribution, the measurement error and water content distribution are indicators incorporated in the graph of stack impedance/CCM water content characteristics (Fig. 24 (b)). Target impedance shows the range for the control of stack impedance. A lower variation in the in-plane CCM water distribution results in the increased possible expansion of the range for control. Therefore, simulations were conducted under different fuel cell operating conditions using the simulation model discussed in Section 3.6.3 to optimize the in-plane CCM water distribution.
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3.6.5. Verification in the actual fuel cell stack Finally, to verify the in-plane CCM water content has been optimized using the simulation and is within the upper and lower limits in all positions, a sensor for the measurement of in-plane CCM water content was installed to the on-board generation system as shown in Fig. 25 (a). Measurements were conducted in vehicle operating mode. The blue curves in Fig. 25 (b) show the time series results for maximum water content, while the red curves show the minimum water content. The in-plane CCM water content changes during operation mode, such as increasing when the vehicle accelerates and decreasing when it decelerates. The blue plots and the red plots in Fig. 25 (c) respectively showed the maximum and minimum values for the in-plane CCM water content in the direction of the shorter side of the generating area. These results show that the in-plane CCM water content is highest in the center of the cells in the gas flow direction. This is because of the increased output during acceleration resulting in the highest current density in the center of the cells and a lot of produced water. Fig. 25 (d) shows the measurement results for the in-plane CCM water distribution at its minimum water content during deceleration. When the vehicle transitions from acceleration to deceleration, the in-plane CCM water content at the air inlets declines approximately to the lower limit. When the current is high and a lot of water is produced by the generation, the in-plane CCM water content also increases, as shown in Fig. 25 (b). However, when the vehicle decelerates, the amount of water produced declines with the current.
Since high-current generation immediately preceding deceleration had increased the stack temperature, the volume of saturated water vapor was high and the water discharge outside the stack increased. 13
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During deceleration, the volumetric airflow becomes excessive due to a delay in the response of the air supply control. These factors have a synergistic effect, resulting in a decline in the in-plane CCM water content near the air inlets. In each case, the necessary in-plane CCM water content for stack durability was maintained within the upper and lower limit values.
4. Conclusion (1) Pt stress was newly developed as a function quantification of the effects of potential cycle in the FC and humidity around the catalyst on catalyst degradation. (2) The effect of atmospheric impurity concentrations on the fuel cell performance at an actual FCV operating environment was evaluated by bench tests using an actual FCV stack. Comparison of nitrogen-based and sulfur-based impurities at equal concentrations showed the larger effect of sulfur-based impurities on power. (3) A three-dimensional map was created to represent the accelerating factor of PEM degradation as a function of the amount of ferrous ion contamination and radical quencher additive. (4) An impedance measurement sensor shaped like an MEA was developed to incorporate in systems mounted in actual vehicles. The sensor can measure real-time CCM water content distribution in an actual vehicle operating environment. Honda has positioned FCV as the ultimate clean car, offering the response to environmental and energy issues that will soon be demanded from future vehicles. Particularly, the company is engaged in technological development efforts in this area. The realization of a hydrogen-based society, centered on the use of hydrogen and fuel cells, will be essential in enabling society to continue to experience the joy of mobility while addressing environmental and energy issues. Honda will continue to actively advance research and development efforts, collaborating in the realization of a new automotive society and establishment of infrastructure towards the advent of a sustainable society.
Acknowledgements We thank Dr. Weibo Zhen for supporting the completion of this article.
References [1] Kawasaki S, Ogura M, Ono T, Kami Y. Development of the Honda FCX Fuel Cell Vehicle, Honda R&D Technical Review, Vol. 15, No. 1; 2003, p. 1–6. [2] Ogawa T, Kimura K, Uchibori K, Fujimoto S, Shimizu K. Development of New Power Train for Honda FCX Fuel Cell Vehicle, Honda R&D Technical Review, Vol. 15, No. 1; 2003, p. 7–12. [3] Kawasaki S, Uchibori K, Murakami Y, Shimizu K, Fujimoto S. Development of New Honda FCX with Next-generation Fuel Cell Stack, Honda R&D Technical Review, Vol. 18, No. 1; 2006, p. 45–50. [4] Inoue M, Saito N, Uchibori K. Next-generation Fuel Cell Stack for Honda FCX, Honda R&D Technical Review, Vol. 17, No. 2; 2005, p. 8–13. [5] Matsunaga M, Fukushima T, Ojima K, Kimura K, Ogawa T. Fuel Cell Powertrain for FCX Clarity, Honda R&D Technical Review, Vol. 21, No. 1; 2009, p. 7–15. [6] Saito N, Kikuchi H, Nakao Y. New Fuel Cell Stack for FCX Clarity, Honda R&D Technical Review, Vol. 21, No. 1; 2009, p. 16–23. [7] Kimura K, Kawasaki T, Ohmura T, Atsumi Y, Shimizu K. Development of New Fuel Cell Vehicle CLARITY FUEL CELL, Honda R&D Technical Review, Vol. 28, No. 1; 2016, p. 1–8. 14
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[8] Yamamoto M, Matsumori H. Empirical Model for Polymer Electrolyte Fuel Cell Electrocatalyst Degradation Using Platinum Stress, Honda R&D Technical Review, Vol. 28, No. 1; 2016, p. 41–49. [9] New Energy and Industrial Technology Development Organization: Heisei 17-21 Nendo Seika Hokokusyo Kotaikoubunshigata Nenryodenchi Seru no Rekka Mekanizumu Kaiseki to Yojumyo Hyoka Shuho no kaihatsu; 2010. (in Japanese) [10] Franco A. Polymer Electrolyte Fuel Cells: Science, Applications, and Challenges, Pan Stanford; 2013, p. 428–485. [11] Egami M, Watanabe S. Fuel Cell Nyquist Plots in Transient States Using FFT Methods with a Space-average Noise Reduction Algorithm, JSAE Transaction, Vol. 45, No. 6; 2014, p. 995–1000.
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Highlights 1. Simulation model of performance degradation in catalyst layer 2. Effects of atmospheric impurities on performance degradation 3. Chemical degradation of electrolyte membrane 4. Water content optimization for catalyst coated membrane
Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☒The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
Shintaro Tanaka
S2590-1168(20)30003-5
DOI:
https://doi.org/10.1016/j.etran.2020.100046
Reference:
ETRAN 100046
To appear in:
eTransportation
Received Date: 22 September 2019 Revised Date:
12 December 2019
Accepted Date: 1 February 2020
Please cite this article as: Tanaka, S., Nagumo, K., Yamamoto, M., Chiba, H., Yoshida, K., Okano, R., Fuel Cell System for Honda CLARITY FUEL CELL, eTransportation, https://doi.org/10.1016/ j.etran.2020.100046. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier B.V.
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Fuel Cell System for Honda CLARITY FUEL CELL a
Shintaro Tanaka *, Kenji Nagumoa, Masakuni Yamamotoa, Hiroto Chibaa, Keiko Yoshidaa, Ryu Okanoa a
Honda R&D Co., Ltd. Automobile Center, 4630 Shimotakanezawa, Haga-machi, Haga-gun, Tochigi, 321-3393 Japan *Corresponding author. Email: [email protected]
Abstract Honda started to lease the world's first fuel cell vehicle (FCV) in December 2002 and has since continuously provided FCVs with advanced technologies. In March 2016, Honda leased the CLARITY FCV with a high-performance and durable downsized fuel cell system realized by optimizing the structure of the fuel cell stack, controlling water distribution in the catalyst-coated membrane, and extending the fuel cell lifetime. As a result, the fuel cell system, voltage control unit, and motor unit are integrated into one fuel cell powertrain system. This highly integrated design allowed the CLARITY FCV to become the world's first production five-seater fuel cell sedan to install the entire fuel cell powertrain system under the front hood. Thus, this study aimed to develop novel measurement methods that will allow the simulation of different parameters of FCV. Particularly, the following key findings are introduced: prediction model for the performance degradation of the catalyst layer, effects of atmospheric impurities on performance degradation, chemical degradation of electrolyte membrane, and water content optimization for catalyst coated membrane. Keywords: Fuel cell stack, Performance degradation, Membrane degradation, CCM water distribution.
1. Introduction Since the latter half of the 1980s, Honda has focused on urban air pollution, global warming, and energy issues as the areas to be addressed in its automotive developments. The company has worked to realize measures to respond to these issues. Honda considers fuel cell vehicles (FCV) as the ultimate next-generation clean automobile with the potential to address all these issues. With this, the company is continuously engaged in FCV development (Fig. 1). Fuel cells produce electricity and water through the reaction of hydrogen and oxygen. In automotive applications, they do not emit atmospheric pollutants (such as CO2), making them an effective solution to air pollution and global warming. The hydrogen used by the fuel is a secondary energy carrier, which can be produced from various forms of primary energy and can be easily converted into electricity using means including fuel cells and gas turbines (Fig. 2). CO2 emissions during existing hydrogen production pose an environmental issue. However, future hydrogen production using renewable energy can potentially offer an energy source that does not emit CO2. Fuel cells are also prospects in addressing the uneven distribution of fossil fuels; thus, presenting further advantages for energy security.
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Fig. 2 Source and application of different energies
Fig. 1 Solutions of environmental and energy issues aimed by FCV
2. Development of FCVs To respond to environmental and energy issues, Honda has been engaged in the development of technologies that increase the efficiency of internal combustion engines (ICE) and further efficiency increase through electrification (Fig. 3). Among these efforts, Honda began the research on fuel cells at the end of the 1980s and since then, progressed to the development of fuel cell stacks. The company was the first to lease a marketed FCV in December 2002 [1, 2]. In 2004, the first Honda-built fuel cell stack [3, 4] was installed. The lease marketing of the sedan-type FCX Clarity began in 2008 [5, 6] and that of the CLARITY fuel cell in March 2016 (Fig. 4) [7]. At 3.1 kW/L, the fuel cell stack in CLARITY FUEL CELL has world-class volume power density 60% higher than previous stacks (Fig. 5).
Fig. 3 Environment-friendly initiatives of Honda 2002.12 FCX
2004.11 FCX
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Fig. 4 Evolution of Honda FCV
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The size reduction of the stack was accompanied by increased impact toughness at collision. This allowed the realization of a fuel cell powertrain comprising a hydrogen supply system, air supply system, voltage converter, and motor sized equivalent to a V6 powertrain (Fig. 6). Therefore, the developed fuel cell powertrain can fit in the same position of an existing gasoline powertrain, allowing the use of a five-seater gasoline vehicle chassis. In addition, the use of a 70-MPa hydrogen tank helped in ensuring a driving range of approximately 750 km and hydrogen tank filling of approximately 3 min.
Fig. 5 Output density of different fuel cell stack
Fig. 6 Fuel cell system for CLARITY FUEL CELL
3. New fuel cell stack and development method 3.1. Overview of the new fuel cell stack The multiple cell layers in the fuel cell stack are composed of a membrane electrode assembly (MEA) and separators that form gas channels (GCs). MEA comprises a polymer electrolyte membrane (PEM), catalyst layers (CL), and gas diffusion layers (GDL). PEM with formed CL is referred to as a catalyst-coated membrane (CCM) (Fig. 7). In normal fuel cell stacks, the unit formed by a MEA and two separators is considered one cell (Fig. 7). Honda reduced the size of its fuel cell stacks by employing a wave configuration that increases the gas diffusion performance of GCs and a cooling configuration in which two MEA and three separators represent one unit (two cells) (Fig. 8).This configuration has been further developed for the CLARITY FUEL CELL. In addition to using a thinner MEA, the developed fuel cell stack circulates water from power generation through counter flows of hydrogen and air. This achieves a uniform distribution of the CCM water content
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using an optimal gas distribution structure realized through the use of a resin frame. Furthermore, the level of water content is reduced by the humidity feedback control. These technologies reduces the depth of the gas flow channels and increased compactness by 20%, thereby helping in enabling a 1-mm cell thickness (Fig. 9). The depth reduction of the GCs can further contribute to the pitch reduction. This reduced the water condensation and accumulation produced by generation in the gas diffusion layers, increasing gas diffusion performance, and realizing a 1.5 times performance increase per cell (Fig. 10). With thinner cells and increased generation performance, the CLARITY FUEL CELL achieved a 60% increase in volume power density, 30% reduction in the number of cells in the stack, and 33% reduction in the stack size.
Fig. 7 Schematic image of fuel cell
Fig. 9 Schematic image of counterflow and in-plane gas distribution with resin frame
Fig. 8 Schematic image of Honda’s fuel cell structure
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Fig. 10 Comparison of liquid water and performance
3.2. Development of fuel cell stack models High-level power generation in a compact and lightweight stack and standard level of durability of fuel cells are both required in developing fuel cell stacks in FCVs. To evaluate durability, hundreds of cells are manufactured and assembled in a stack, which results in an extended development period. At Honda, the development of the new fuel cell stack was accelerated by incorporating advance evaluations using simulation models. To help ensure the durability of the fuel cells, it is necessary to maintain the active surface area of the catalyst layers and the thickness of the electrolyte membrane. The active surface area of the catalyst layers considerably affects the cell output, and the thickness of the electrolyte membrane separates the oxygen and hydrogen fuel and electrically insulates the anode and cathode, respectively. The maintenance of the catalyst layer surface area and PEM thickness is greatly affected by the content of CCM water. When the water content is high, the coalescence of the catalyst due to dissolution, agglomeration, and re-deposition result in the decrease of the catalyst layer surface areas. Chemical degradation occurs due to chemical reactions. Factors, such as impurities and hydrogen peroxide, accelerate the PEM degradation and promote the loss of membrane thickness. In addition, due to the iron-based material employed in the separators, the water accumulation from generation in separator channels results in the elution of iron, especially the contact area of the separators and the MEA, accelerating the chemical degradation of the PEM. When a fuel cell stack is installed in a FCV, the generation operating conditions, including the hydrogen/air stoichiometry, the stack temperature and humidity change in response to the vehicle states, such as acceleration and deceleration. Furthermore, this affects the water content of the CCM. In a fuel cell stack, the large CCM area of approximately 300 cm2 poses difficulty in realizing uniform water distribution within the generating plane. Thus, it is important to create a simulation model to evaluate the durability of the catalyst layers and electrolyte membrane in advance through consideration of the water content distribution in the CCM.
3.3. Simulation model of performance degradation in the catalyst layer
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3.3.1. Parameters for evaluation Degradation results in the reduced performance in a fuel cell stack when the vehicle is running, starting up, and stopped. The size of the material (Pt) in the cathode catalyst layer increases and its performance declines due to the recurring high-potential loads when the vehicle starts and stops. With this, the potential cycles when output fluctuates during vehicle operation (Fig. 11).
Fig. 11 Pt on the carbon support
Fig. 12 General CV depicting features
To quantify the effect of potential cycles on the degradation of the cathode catalyst layer, the relationship between the loads produced by potential cycles and the degree of degradation of the catalyst layer was investigated using cyclic voltammetry (CV). CV is a method to express electrochemical reactions in the catalyst layer in response to the potential in terms of current. Fig. 12 shows the current-potential characteristic of a normal Pt catalyst. A current can be observed in the electrochemical double-layer capacitance of the cell at approximately 0.5 V. From 0.6 to 1.0 V, a transition occurred from the adsorption reaction between the Pt and water to a reaction that forms an oxide film on the Pt surface (Pt oxidation). On the other hand, a reduction reaction occurs in the platinum oxide (PtO) layer (platinum reduction) and Pt returns to its metallic state when from 1.0 to 0.6 V. At potentials lower than 0.5 V (between 0 V and approximately 0.45 V), a proton (H+) adsorption and desorption reaction (hydrogen adsorption and desorption: HAD) occurs on the Pt. The total HAD charge (QHAD) and effective electrochemical surface area (ECSA) of Pt are proportional, as expressed in Equation (1). With this, the ECSA indicating the catalyst performance can be determined based on the total HAD charge. (1) ECSA cm
3.3.2. Numerical expression of the effect of attained potential In this study, the effect of the projected maximum potential attained during start-up (upper-level potential, ULP) was investigated (Fig. 13). Results indicated that higher ULP causes a greater increase in the reduction current (Q1) in the PtO film formed from the increased potential. In addition, the reduction current in the PtO differed not only with ULP but also with the holding time. The effect of the minimum potential attained during acceleration and deceleration of a running vehicle (lower-level potential; LLP) was also investigated (Fig. 14). When LLP was manipulated, Q1 produced by the ULP was reduced from a to b by the holding LLP. Due to the holding LLP, the PtO formed at the ULP was reduced and the charge declined due to the partial return of the PtO to its metallic state.
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Fig. 13 Effect of upper level potential (ULP)
Fig. 14 Effect of lower level potential (LLP)
Based on these results, Pt stress (∆Q) is defined, which is the indicator of the cathode catalyst layer degradation to clarify the effect of potential cycles due to the vehicle start, stop, acceleration, and deceleration (Equation (2)) [8]. Pt stress：ΔQ ≡ Q Q (2) Here, Q1 is the total charge in the PtO film at the ULP, and Q2 is the residual charge in the PtO film after reduction due to the LLP. To establish the correlation between performance and ∆Q, ECSA as a factor of performance and its relationship with ∆Q were investigated. Potential cycle tests using test cells were conducted to determine the relationship between the ECSA loss rate and ∆Q. ∆Q was set by modeling the potential changes in a fuel cell stack and applying different conditions of the vehicle such as the projected potential and temperature upon starting, stopping, accelerating, and decelerating. Fig. 15 shows the relationship between the ECSA loss rate and ∆Q. These results indicate that the ECSA loss rate can be expressed by ∆Q with comprehensive consideration of the changes in potential, temperature, and other factors during the vehicle start and operation.
Fig. 15 Correlation of ECSA loss rate and ∆Q 3.3.3. Verification in the actual fuel cell stack To verify the developed model, the catalyst degradation in stack evaluation acceleration mode was studied using an actual fuel cell stack. ∆Q was calculated based on the average voltage profile of the stack (ULP and holding time, LLP) and temperature. Moreover, the water content of the cells was estimated based on impedance and ECSA loss rate was predicted. Fig. 16 shows the ECSA measured and estimated in a cell (Dry Condition: 25% RH gas, Wet Condition: 45% RH gas).The dashed lines in the plot show the ECSA predictions from the developed model. The
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predicted and measured values corresponded well, demonstrating the potential of the model to estimate the catalyst degradation in an actual fuel cell stack. In addition, results indicated the reduced deterioration under conditions with lower water content. Therefore, the water content of the cathode catalyst layers was controlled during start-up and shutdown to reduce the ECSA decline.
Fig. 16 Verification results of the degradation by CCM water control
3.4. Effects of atmospheric impurities on performance degradation 3.4.1. Typical atmospheric impurities to affect performance Most reports on the effect of atmospheric impurities on power involve tests using commercial mini cells, such as JARI cell [9]. To date, no known cases of using actual automotive cells has been reported. Mini cells typically use a serpentine flow-field that differs from the flow-field of an actual automotive cell. Hence, the diffusion behavior of air and its impurities also differ. Thus, the effect to reduce power may differ from that in an actual vehicle. Table 1 shows the typical atmospheric impurities that affect fuel cell stack power [9]. These impurities include sulfur-based gases (H2S and SO2) and nitrogen-based gases (NO2 and NH3). The concentrations of these impurities are affected by various factors, such as the geographical environment and weather conditions. This makes the quantitative evaluation of the effects of various impurities using only field trials impractical. Therefore, this study conducted bench tests that generated power under simulated atmospheric gases containing different impurity concentrations to the cathode side of an actual automotive cell. Table 1 Atmospheric impurities that affect fuel cell performance Impurities Concentration H2S 1700 ppb 250 ppb SO2 19 ppb NO2 600-6000 ppb 21 ppb NH3 38 ppb
Hot spot Hot Spa Volcano Heavy Traffic Tunnel Livestock Industry
3.4.2. Effects of atmospheric impurities using actual automotive cell The performance evaluation used a stack consisting of ten actual automotive cells. Fig. 17 shows a schematic figure of the power generation evaluation apparatus. High-purity hydrogen was humidified and heated using a bubbling system to achieve the conditions similar to the supplied fuel gas of the stack in an actual vehicle. The air with impurities removed (hereafter, “clean air”) was humidified and heated, then the
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specified impurity was mixed via a T-shaped joint connected to the gas inlet pipe of the stack cathode. The mixture was then supplied as the oxidant gas to the stack.
Fig. 17 Experimental scheme of gaseous contaminants injection The evaluation was performed by simulating the load variation produced by the vehicle start, stop, acceleration, and deceleration, referred to as the “running mode”. During the running mode, the cathode flow rate changes according to the set load variation. The maximum power during clean air supply was extracted and used as the reference for the decrease in power over time. The power slopes with various atmospheric impurities (∆P2/∆t) and that with clean air (∆P1/∆t) are defined as the power decay rate. It is used as the index for evaluating the effect of atmospheric impurities on power (Fig. 18). Fig. 19 shows the relationship between the concentration of each impurity and the power decay rate.
Fig. 18 Power decay rate by subtracting rate in clean air for correction This study confirmed the previously reported [9] tendency where the power drop increases with the concentrations of atmospheric impurities. By examining the characteristics of each gas type, two types of sulfur-based impurities (H2S and SO2) exhibited similar behavior between the power decay rate dependence and concentration. Reference [10] proposed Pt catalyst surface reactions for H2S and SO2. In both cases, the adsorption reaction to the Pt surface active sites in SO42– form. Thus, the power dependence on impurities concentration is presumed to be similar for both H2S and SO2.
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Fig. 19 Relationship between power decay rate and impurities concentration As described in Reference [9], with similar concentrations of different impurities, NO2 shows a smaller effect on the power reduction compared to sulfur-based impurities. However, Table 1 shows that the maximum atmospheric concentration of sulfur-based impurities is 1000 ppb, whereas some environments have NO2 concentrations of more than 1000 ppb. Hence, power may also be affected in regions with high NO2 concentrations. NH3 did not affect power at the anticipated actual concentration of 100 ppb. Similar to Reference [9], this study confirmed that NH3 concentrations of less than 1000 ppb have no effect.
3.5. Simulation model of chemical degradation in PEM The PEM is believed to be subject to degradation due to the OH radicals produced by the reaction of hydrogen and oxygen passing through the membrane. Fe ions are known to accelerate chemical degradation through generation of OH radicals. On the other hand, there are metal ions or organic molecules with conjugated systems that scavenge radicals. However, it is necessary to use appropriate quantities of these additives as they can reduce the conductivity of H+. A map of the degree of acceleration of chemical degradation in relation to the amount of Fe ions and amount of radical quencher used as an additive was formulated (Fig. 20). The PEM thickness was set using this map to predict the lifetime of the membrane. In addition, present Fe particles became Fe ions, thereby producing local thinning of the PEM thickness (Fig. 21).
Fig. 20 3D visualized map of accelerating factor a
Fig. 21 X-Ray and PEM thickness measurement using SEM
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3.6. Simulation model for in-plane water content in CCM 3.6.1. Evaluation parameters The operating conditions of the fuel cell stacks fitted in FCV change with the vehicle state. The CCM water content changes with the operating conditions. The in-plane CCM water content in the cells differs in different positions. With this, the development of the simulation model for evaluation of the in-plane water content distribution of the CCM proceeded with the development of the water content sensor during actual real-time vehicle operation, including the acceleration and deceleration. 3.6.2. Measurement of in-plane water distribution in CCM Honda employs analyses using the neutron RG to study the water status in the fuel cell interior. Since this measurement method involves beaming neutrons in one cell direction, it can obtain the total water content encompassing in the separator channels, within the CP and CCM in the said direction. However, it is not suitable in measuring the isolated CCM water content. With this, a method using impedance was developed, together with the simulation model [11], to measure the water content of the cells fitted in a vehicle. This method was applied in developing a sensor that can measure the in-plane CCM water distribution in fuel cells. Fig. 22 shows the developed sensor for the impedance measurement of the in-plane water distribution of the CCM. The sensor was designed in the same shape as the MEA. It can be fitted between separators in an actual fuel cell stack and take measurements without special separators or seals. Both surfaces of the sensor feature 75 square sensor pads that measure the impedance of the CCM. An alternating current is superposed on the entire fuel cell stack to conduct the measurement. Resistance values are calculated from the current and voltage values measured by the sensor and are converted to the water content of the CCM.
Fig. 22 Water content distribution measurement sensor 3.6.3. Simulation model of in-plane water distribution in CCM There is several fuel cell simulation software available. This study selected a market fuel cell simulation software with adequate simulation accuracy and speed for the fuel cell stack development employed in FCV. The simulation model of the in-plane water distribution in the CCM was developed by incorporating the experimental results of the water distribution in Section 3.6.2 and applying original Honda functional modifications. Fig. 23 (a) and (b) show the simulation results of in-plane water distribution in the CCM and the comparison of simulation and measurement results, respectively. As exhibited in the figure, there is a good correspondence between the simulation and measurement results. Moreover, the application of a resin frame to optimize the hydrogen and air distribution has minimized variations in the water distribution of the CCM in the direction of the shorter side of the generating area.
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Fig. 23 (a) Simulation result of water content distribution
Fig. 23 (b) Comparison of simulation and experiment result
3.6.4. Optimization of in-plane CCM water distribution The generation system employed in the CLARITY FUEL CELL is provided with a humidifier with its bypass valve connected in parallel (Fig. 24 (a)). Based on the water content of the CCM and stack impedance characteristics (Fig. 24 (b)), the necessary CCM water content for the durability of the stack is controlled within the upper and lower limits shown in the figure depending on the measured stack impedance, which is the average value of in-plane impedance.
Fig. 24 (a) In-plane water content of CCM control system in 2016 FCV model
Fig. 24 (b) Relationship between CCM water content and stack impedance Considering the in-plane CCM water distribution, the measurement error and water content distribution are indicators incorporated in the graph of stack impedance/CCM water content characteristics (Fig. 24 (b)). Target impedance shows the range for the control of stack impedance. A lower variation in the in-plane CCM water distribution results in the increased possible expansion of the range for control. Therefore, simulations were conducted under different fuel cell operating conditions using the simulation model discussed in Section 3.6.3 to optimize the in-plane CCM water distribution.
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3.6.5. Verification in the actual fuel cell stack Finally, to verify the in-plane CCM water content has been optimized using the simulation and is within the upper and lower limits in all positions, a sensor for the measurement of in-plane CCM water content was installed to the on-board generation system as shown in Fig. 25 (a). Measurements were conducted in vehicle operating mode. The blue curves in Fig. 25 (b) show the time series results for maximum water content, while the red curves show the minimum water content. The in-plane CCM water content changes during operation mode, such as increasing when the vehicle accelerates and decreasing when it decelerates. The blue plots and the red plots in Fig. 25 (c) respectively showed the maximum and minimum values for the in-plane CCM water content in the direction of the shorter side of the generating area. These results show that the in-plane CCM water content is highest in the center of the cells in the gas flow direction. This is because of the increased output during acceleration resulting in the highest current density in the center of the cells and a lot of produced water. Fig. 25 (d) shows the measurement results for the in-plane CCM water distribution at its minimum water content during deceleration. When the vehicle transitions from acceleration to deceleration, the in-plane CCM water content at the air inlets declines approximately to the lower limit. When the current is high and a lot of water is produced by the generation, the in-plane CCM water content also increases, as shown in Fig. 25 (b). However, when the vehicle decelerates, the amount of water produced declines with the current.
Since high-current generation immediately preceding deceleration had increased the stack temperature, the volume of saturated water vapor was high and the water discharge outside the stack increased. 13
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During deceleration, the volumetric airflow becomes excessive due to a delay in the response of the air supply control. These factors have a synergistic effect, resulting in a decline in the in-plane CCM water content near the air inlets. In each case, the necessary in-plane CCM water content for stack durability was maintained within the upper and lower limit values.
4. Conclusion (1) Pt stress was newly developed as a function quantification of the effects of potential cycle in the FC and humidity around the catalyst on catalyst degradation. (2) The effect of atmospheric impurity concentrations on the fuel cell performance at an actual FCV operating environment was evaluated by bench tests using an actual FCV stack. Comparison of nitrogen-based and sulfur-based impurities at equal concentrations showed the larger effect of sulfur-based impurities on power. (3) A three-dimensional map was created to represent the accelerating factor of PEM degradation as a function of the amount of ferrous ion contamination and radical quencher additive. (4) An impedance measurement sensor shaped like an MEA was developed to incorporate in systems mounted in actual vehicles. The sensor can measure real-time CCM water content distribution in an actual vehicle operating environment. Honda has positioned FCV as the ultimate clean car, offering the response to environmental and energy issues that will soon be demanded from future vehicles. Particularly, the company is engaged in technological development efforts in this area. The realization of a hydrogen-based society, centered on the use of hydrogen and fuel cells, will be essential in enabling society to continue to experience the joy of mobility while addressing environmental and energy issues. Honda will continue to actively advance research and development efforts, collaborating in the realization of a new automotive society and establishment of infrastructure towards the advent of a sustainable society.
Acknowledgements We thank Dr. Weibo Zhen for supporting the completion of this article.
References [1] Kawasaki S, Ogura M, Ono T, Kami Y. Development of the Honda FCX Fuel Cell Vehicle, Honda R&D Technical Review, Vol. 15, No. 1; 2003, p. 1–6. [2] Ogawa T, Kimura K, Uchibori K, Fujimoto S, Shimizu K. Development of New Power Train for Honda FCX Fuel Cell Vehicle, Honda R&D Technical Review, Vol. 15, No. 1; 2003, p. 7–12. [3] Kawasaki S, Uchibori K, Murakami Y, Shimizu K, Fujimoto S. Development of New Honda FCX with Next-generation Fuel Cell Stack, Honda R&D Technical Review, Vol. 18, No. 1; 2006, p. 45–50. [4] Inoue M, Saito N, Uchibori K. Next-generation Fuel Cell Stack for Honda FCX, Honda R&D Technical Review, Vol. 17, No. 2; 2005, p. 8–13. [5] Matsunaga M, Fukushima T, Ojima K, Kimura K, Ogawa T. Fuel Cell Powertrain for FCX Clarity, Honda R&D Technical Review, Vol. 21, No. 1; 2009, p. 7–15. [6] Saito N, Kikuchi H, Nakao Y. New Fuel Cell Stack for FCX Clarity, Honda R&D Technical Review, Vol. 21, No. 1; 2009, p. 16–23. [7] Kimura K, Kawasaki T, Ohmura T, Atsumi Y, Shimizu K. Development of New Fuel Cell Vehicle CLARITY FUEL CELL, Honda R&D Technical Review, Vol. 28, No. 1; 2016, p. 1–8. 14
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[8] Yamamoto M, Matsumori H. Empirical Model for Polymer Electrolyte Fuel Cell Electrocatalyst Degradation Using Platinum Stress, Honda R&D Technical Review, Vol. 28, No. 1; 2016, p. 41–49. [9] New Energy and Industrial Technology Development Organization: Heisei 17-21 Nendo Seika Hokokusyo Kotaikoubunshigata Nenryodenchi Seru no Rekka Mekanizumu Kaiseki to Yojumyo Hyoka Shuho no kaihatsu; 2010. (in Japanese) [10] Franco A. Polymer Electrolyte Fuel Cells: Science, Applications, and Challenges, Pan Stanford; 2013, p. 428–485. [11] Egami M, Watanabe S. Fuel Cell Nyquist Plots in Transient States Using FFT Methods with a Space-average Noise Reduction Algorithm, JSAE Transaction, Vol. 45, No. 6; 2014, p. 995–1000.
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Highlights 1. Simulation model of performance degradation in catalyst layer 2. Effects of atmospheric impurities on performance degradation 3. Chemical degradation of electrolyte membrane 4. Water content optimization for catalyst coated membrane
Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☒The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
Shintaro Tanaka