33.2.1 Hydrogen Production Methods

Hydrogen can be produced from both renewable (hydro, wind, solar, biomass, and geothermal) and nonrenewable (coal, natural gas, and nuclear) resources [22]. Hydrogen is mainly produced through fossil-fuel processing. In the entire world, 48% of hydrogen is produced from natural gas, 30% from oil, 18% from coal, and only 4% from renewable sources [23].

The main hydrogen production methods are steam reforming, gasification, partial oxidation, thermochemical cycling, photolysis, and electrolysis. Steam reforming may be used with natural gas, gasification with coal and waste, partial oxidation with oil, thermochemical cycling with nuclear and solar, photolysis with solar, electrolysis with wind and solar, etc. [23,24]. Producing hydrogen with a low cost means reforming it from fossil fuel such as natural gas, which may give rise to pollution by forming carbon dioxide. Manufacturing hydrogen is relatively more expensive [18,25].

Hydrogen production through electrolysis of water is more promising as it avoids carbon emission. Water can be decomposed into its elementary components by passing electric current between two electrodes separated by an electrolyte. According to Faraday's law, hydrogen production rate of an electrolyzer cell is directly proportional to the electric current in the equivalent electrolyzer circuit.

Electrolysis process has been proposed especially for renewable systems. The power generated by these systems highly depends on weather conditions. For example, during cloudy periods and at night, a PV system would not generate any power. In addition, it is difficult to store the power generated by a PV system for future use. To overcome this problem, a PV system can be integrated with other alternate power sources and/or storage systems, such as electrolyzer, hydrogen infrastructure, and FC systems [26]. When assessing recent developments in hydrogen applications, renewable energy sources have been used to generate hydrogen. Besides, energy demand/supply management can be satisfied using renewable sources and hydrogen infrastructure by including FCEVs, smart grids, and hydrogen-fueling systems. The renewable hydrogen cycle coupled with smart grids is shown in Fig. 33.2.

33.2.2 Hydrogen Storage

The driving range of the FCEVs depends on its onboard hydrogen storage capability and other energy management systems. According to the improvements of the hydrogen storage tanks, FCEVs can meet to match driver expectations [5,23]. The use of hydrogen as a vehicle fuel requires an onboard storage that offers inherent safety and both volumetric and gravimetric efficiencies. Onboard storage in vehicular systems is one of the major barriers to the acceptance of hydrogen-powered vehicles [27]. Since onboard storage systems increase safety concerns especially for drivers and passengers during dangerous situations such as car accidents, the storage system gives a hazardous impression. The problems associated with hydrogen storage change from one storage technology to another. Thus, hydrogen storage technologies are evaluated as the first step of the current deliverable presentation. There are four technologies available today to store hydrogen aboard vehicles [16,17,28]:

• Compressed hydrogen gas in high-pressure tanks

• Liquefied hydrogen

• Metal hydrides

• New methods currently under development

The most used technique for hydrogen storage is compression of hydrogen into different kinds of high-pressure tanks [16]. According to the Department of Energy (DoE), compressed hydrogen technique will continue to be the most popular type of hydrogen storage for vehicular systems until 2020. Most vehicles currently in the on-road testing phase and on the road commercially are equipped with such a composite high-pressure tank. This is because of its simple structure and charge-discharge easiness. In general, vehicular pressurized hydrogen storage tanks made of very light and robust composite materials [29]. Storage density (gravimetric ratio) of above 0.05 kg of hydrogen per 1 kg of total weight, which means a stored hydrogen ratio of 5%, is easily achievable [16]. This ratio can reach up to 11.3% in this approach. There are two working pressures commonly used in commercialized vehicles such as 350 bar (35 MPa–5000 psi) and 700 bar (70 MPa–10000 psi) [17]. Leading FCEV automakers have mounted the high-pressured storage tanks on their models with their own preferences. For instance, while Toyota, Honda, and Hyundai use 700 bar (10,000 psi), Nissan uses 350 bar (5,000 psi) pressurized tank [5,21].

In another approach, the hydrogen gas is liquefied and stored under lower temperature and pressure compared with the high-pressure approach in liquefaction technique [16]. In this method, the ratio of stored hydrogen per tank weight is around 26%. However, the usage of liquid hydrogen storage system is limited because of its properties, cost of the manufacturing material, and cost of the tank. Besides, the whole process is relatively inefficient because a lot of energy is already consumed in the first stage of hydrogen liquefaction [30]. In this technique, nearly 26% of the stored hydrogen energy is consumed during the hydrogen liquefaction process [28]. In addition, liquid hydrogen tanks suffer from hydrogen leaks due to the unavoidable thermal losses that lead to pressure increase in the tank. This hydrogen self-discharge of the tank may reach to 3% daily, which means a 100% self-discharge in 1 month [31]. Hydrogen liquefaction and use of liquid hydrogen are usually practiced only where achieving high storage density is absolutely essential, such as in aerospace applications [28,16]. Some prototype hydrogen-powered automobiles also use specially developed liquefied hydrogen tanks [16].

Metal hydrides offer alternatives to the storage of hydrogen in gaseous and liquid form. Storing hydrogen as hydride in metals provides some advantages especially for safety in many applications. However, the tank weight provides a significant problem in this approach especially for applications like vehicular systems. The commercially available metal hydride hydrogen tanks offer a stored hydrogen ratio of 4.5% [27]. Besides, the repetition of hydrogen storage (absorption)/release (desorption) further decreases this ratio. Moreover, heat is released during the absorption process, which must be removed in order to achieve the continuity of the reaction. Similarly, during the hydrogen desorption process, heat must be supplied to the storage tank [16]. To overcome these limitations, some new techniques in metal hydride hydrogen storage approach are under investigation, which is expected to reach a hydrogen storage ratio of 10.5% in the near future [31].

New hydrogen storage methods have potential for providing higher energy densities than the conventional methods. These methods contain hydrogen storage in carbon nanotubes, storage in glass microspheres, boron-based storage, or storage in polyhydride chemical complexes [29]. Among them, the nanotube technique seems to be promising according to the recent developments in nanotechnology, which is anticipated to reach to a hydrogen storage ratio of 68% [17]. As another novel hydrogen storage method, boron-based chemical storage materials (like borohydrides and ammonia borane) are promising compounds with their high-hydrogen capacities. However, these hydrogen storage materials create ongoing problems from the kinetic and thermodynamic limitations in practice [32]. Besides, the current costs of these methods are extremely high that prevents the commercial utilization of these approaches [33,34].

33.2.3 Hydrogen Delivery and Fueling Station

It is expected that the FCEVs will have a significant market share in upcoming years. To that end, an effective and efficient utilization of the currently existing hydrogen infrastructure should be reconsidered for widespread penetration of FCEVs. Considering that proof-of-concept experiment with R&D studies for hydrogen generation has been already shown; construction of hydrogen generation and distribution infrastructure is a requirement for commercialization of FCEVs to achieve a sustainable process [19,21].

Hydrogen has poor volumetric energy density, and hence, FCEVs have a limited storage capacity, which makes hydrogen generation and distribution infrastructure a must-have. In addition, to ensure acceptance by public, hydrogen-refueling stations should be constructed and mounted.

Despite the expensiveness and complexity of hydrogen storage, it has been reported that delivering hydrogen by pipeline or tanker trucks to the refueling stations is possible with some adaptive alterations to the current infrastructure [17]. It is significantly important for both developed and developing countries to realize these studies in a timely manner in order to prevent/reduce the possible future technological dependence on other countries about this issue. Several such studies are realized worldwide, especially in countries such as Japan, the United States, Germany, China, South Korea, and Italy, where renewable sources are used with a high ratio with a vision of future hydrogen economy and hydrogen generation, and distribution infrastructure has been already established or planned [17,19].

If hydrogen-fueled vehicles are used instead of natural gas delivery systems, using central hydrogen delivery system would be more convenient. Furthermore, decentralized and distributed hydrogen stations combined with electrolyzers and renewables will be built to meet the variable demands for hydrogen [5].

In this regard, the fueling and P2G operations of FCEVs should be controllable under the smart grid umbrella. Besides, hydrogen storage of FCEVs in parking condition can be utilized as a backup gas unit when the gas demand increases or fuel cells of FCEVs with suitable power-conditioning unit can supply power to electric loads and appliances. Thus, FCEVs can be considered as multicarrier energy sources. Likewise, BEVs and PHEVs are also considered as both storage and a flexible load resource with a connection to smart grids (including renewables) under a suitable smart charging and discharging approach. Furthermore, smart grids have the potential of exploiting renewable sources and providing the required infrastructure for BEVs and FCEVs [19]. Additionally, CHP of the electrolyzer can be considered as a supplementary.

In this context, Honda proposed and developed novel and efficient complementary applications of hydrogen value chain such as FCEV, compact/smart hydrogen station (SHS), high-pressure storage tank, fuel cell stack, electrolyzer, and power-conditioning units. After accomplishing their proof-of-concept experiments, commercialization by Honda has already started and currently being deployed in some regions [21]. To this end, some governments and automakers are cooperating, aiming to support hydrogen infrastructure development by methods by partially subsidizing operation costs of infrastructure firms [21,35]. However, the abovementioned issues cannot be evaluated independent from smart energy technologies.

33.3.1 Alkaline Fuel Cell

Alkaline fuel-cell system is one of the first developed fuel-cell technology with the simplest structure. It is the first type widely used on space applications [37,41]. AFCs use a liquid solution of potassium hydroxide (KOH) as an electrolyte that conducts ions between two electrodes: anode and cathode. Because the electrolyte is alkaline, the ion conduction mechanism has differences from PEMFCs [24]. At the basic structure of AFCs as given in Fig. 33.3, at the anode side, hydrogen undergoes oxidation reaction that turns hydrogen into a positively charged ion and negatively charged electron. The negatively charged electrons travel through an external circuit that generates electricity and unifies with oxygen atoms at the cathode side [42]. The alkaline electrolyte only lets the composed hydroxyl (OH⁻) go through the anode side. By this reaction, hydrogen ions and hydroxyl reunite producing water. Eventually, water, heat and the electricity will be obtained.

Some key advantages of AFC systems can be specified as [43] the following:

• Low operation temperatures (50–200°C)

• Quick start-up range (<0.1 h)

• High efficiency (50%–70%)

• Low catalyst requirement reducing content costs

• Simple structure

• Low weight and volume

Some key disadvantages of AFC systems can be specified as [13,43–45] the following:

• Short operating life since they use a liquid solution of potassium hydroxide (KOH) as an electrolyte that is highly corrosive, thus eroding its parts

• Required oxygen must be provided after purification since they are very intolerant to carbon dioxide

• High cost for commercialized applications and current R&D studies are focusing on reducing costs

33.3.2 Molten Carbonate Fuel Cell

The main principles of MCFCs are based on SOFCs and the other types of fuel cells. In the mid-1960s, Texas Instruments developed several MCFCs for US Army that led to a widespread use of MCFCs in the field [43].

MCFCs use lithium potassium carbonate salts as an electrolyte as shown in Fig. 33.4. They operate at high temperatures (650°C); therefore, catalysts can be made of low-priced metals to reduce cost, and the heat/exhaust can be utilized [37]. If the heat/exhaust can be utilized (with CHP), the efficiencies of MCFCs can be increased from 60% to 85%. Additionally, higher temperature makes the FC system more tolerant to poisoning (carbon monoxide) than lower temperatures. These systems can use either carbon dioxide or oxygen as a fuel. Currently, there are many molten carbonate systems available with capacities ranging from 100 kW up to 2 MW.

MCFCs do not demand an external reformer; thus, the primary fuel used may not be hydrogen gas. The basic components of natural gas, methane, and steam are processed at a reformer in the MCFC system, and electricity will be produced. The internal reformer reduces the costs compared with the other FC technologies with external reformers.

Some key advantages of MCFC systems are specified below [43,46]:

• Using the fuel converted in the system

• Producing so much heat/exhaust that can be cogenerated

• High efficiencies

• Relatively fast response to load changes in steady-state conditions

• Require low-cost catalysts

• Lower sensitivity to poisoning

Some key disadvantages of MCFCs include the following [46]:

• Slow start-up range (5–10 h)

• Demand redesigning with more resistant components to corrosion

• Problems in contenting the liquid electrolyte in the structure

• Requirement of preheating before starting work

• Short operating life especially when using for high-power production systems

33.3.3 Polymer Electrolyte Fuel Cell

Among the various next generation power supplies, the polymer electrolytes or PEMFCs have been found to be one of the most promising energy sources due to their high efficiencies and environment-friendly operations [47].

The basic structure of PEMFC, shown in Fig. 33.5, consists of three segments: the anode (negative characteristic electrode), the cathode (positive characteristic electrode), and the electrolyte membrane sandwiched between the two that allows only positively charged ions/protons to move between the two electrodes. The anode and the cathode have a catalyst, which speeds up the reactions at the electrode. Hydrogen goes to the anode side, and oxygen from the air flow goes to the cathode side. At the anode side, hydrogen undergoes oxidation reaction that turns hydrogen into a positively charged ion and negatively charged electron. After the reaction, protons are being transferred from anode to cathode through the electrolyte membrane, while the electrons travel through an external circuit. When the ions/protons reach the second electrode cathode, they will unify again with electrons and react with oxygen to form water. Eventually, electricity, water, and heat will be generated [39].

Some key advantages of PEMFCs include the following [16]:

• Low operation temperatures (50–100°C)

• Quick start-up range (<0.1 h)

• High efficiencies (40%–60%)

• Structure of electrolytes is more reliable, secure, and stable than other FCs

• High power density is the highest among all the available types of FCs

• High tolerance capability to differential pressures of the reactants

• Robust and simple structural design

Some key disadvantages of PEMFCs are listed below:

• Possess a structure highly depending on the purity of hydrogen

• Very poor tolerance to carbon monoxide and sulfur particles

• Gases require to be moisturized before reacting

• Comprised of a fairly expensive platinum catalyst and a solid polymer membrane

PEMFCs are a good candidate to substitute conventional technologies with their higher efficiencies and lower environmental impacts. The cost of PEMFCs is expected to down to consumer affordable levels in the near future [13].

Many advantages of PEMFCs, including fast response time, low operating temperature, high power density, and life cycling, have made the PEMFCs attractive and promising energy devices from the transportation and mobile applications to stationary applications as a distributed generation [5,16]. Therefore, lots of big companies such as Ballard, UTC, Nuvera, PlugPower, General Electric, Toshiba, and Sanyo produce PEMFCs commercially. Leading automaker companies such as Honda, Toyota, Daimler-Chrysler, General Motors, BMW, Nissan, Ford, Hyundai, and Renault and worldwide brand-mark companies like Samsung and IBM use this shining technology for their own commercial applications [48].

33.3.4 Direct Methanol Fuel Cell

FCs either use hydrogen directly or reform hydrocarbon fuels like methanol, which is the simplest organic fuel that can be most economically and efficiently produced from relatively plentiful fossil fuel [24]. Thus, the operation of the DMFC is based on oxidation of water mixed with methanol. After the oxidation, methanol goes to the FC anode side [37]. DMFCs use a liquid fuel methanol, which is easier to transport for public using with current infrastructure [41]. DMFCs are often used to supply power for portable electronics and emergency power supply.

Recently, concerns about the poisonous effects of methanol have emerged; thus, companies prefer using ethanol instead of methanol [37]. DMFCs have immature technology, low power density, slow power response, and low efficiency compared with direct hydrogen FCs [24].

33.3.5 Phosphoric Acid Fuel Cell

Phosphoric acid fuel cell is the first developed FC technology and first to be used commercially. They are considered as first generation of modern FC. PAFCs use liquid phosphoric acid as an electrolyte. The PAFC systems have about 40% energy production efficiency and high operating temperatures (150–220°C) [42]. With cogeneration of heat/exhaust, the efficiency can be increased up to 85% [43]. Currently, there are PAFCs with capacities ranging from 200 kW to 11 MW. Necessary improvements for widespread use of PAFCs will require reducing the operating cost while increasing the operating life.

These FC systems have a drawback of weight; therefore, these FCs are not preferable on transport applications. Some key advantages of PAFC systems can be specified as follows [43,46]:

• Tolerant till 30% carbon dioxide content, hence direct usage of atmosphere air

• High efficiency (85%) with cogeneration of heat/exhaust (CHP)

• Operate trouble-free at temperatures (150–220°C)

Some key disadvantages of PAFCs include the following [42,43]:

• Slow start-up range (1–4 h)

• Low tolerant to carbon monoxide component

• Exhausting water content can damage acidic electrolyte (corrosion)

• Massive and heavy structure

• Requirement of external reformer

• Requirement of preheating before starting to operate

33.3.6 Solid Oxide Fuel Cell

SOFCs operate at high temperatures (700–1000°C), and every single solid oxide cell produces 0.8–1 V voltages [43]. The heat/exhaust (around 500–850°C) generated by SOFCs is attractive for cogeneration. SOFC systems are currently used in stationary applications such as backup power units. Furthermore, recent R&D studies are focusing on feasibility of SOFCs at transportation appliances [49,50].

Solid oxide fuel cells are promising with their inherent advantages for industrial applications such as its independence from pure fuel. Therefore, hydrogen and CO, CH₄, and other hydrocarbons can be used as fuel [37] in a SOFC. Since SOFCs operate at high temperatures, these systems can use low-cost catalyst components to enhance operational performance. SOFCs use a solid electrolyte, generally a ceramic material called yttria-stabilized zirconia (YSZ). Because the electrolyte does not involve a liquid-phased reaction, a problem such as fuel flooding does not occur. Also, SOFCs can be manufactured for many configurations, although other FC types with liquid electrolyte cannot [46].

In SOFCs, fuel is supplied to the anode side, and oxygen from the air flow goes to the cathode side as shown in Fig. 33.6. At the anode side, hydrogen undergoes oxidation reaction that turns hydrogen into a positively charged ion and negatively charged electron. The separated electrons travel through an external circuit from anode to cathode to produce electricity and oxygen atoms absorb the electrons. The solid electrolyte membrane only permits the transition of negative charged oxygen ions from cathode to anode. When oxygen ions reach anode, they react with hydrogen ions to form water.

SOFCs have about 45% efficiency that can reach 85% by capturing and utilizing the heat/exhaust. Additionally, the SOFC systems have low gas emissions [51].

Some key advantages of SOFC systems can be specified as follows [42,45,46]:

• Producing massive amount of heat/exhaust that can be utilized

• Fast chemical reactions

• High efficiency

• The solid electrolyte is more reliable than a liquid electrolyte

• Nonrequirement of external reformer

• No corrosion problems

Some disadvantages of SOFC systems include the following:

• Slow start-up range (1–5 h)

• Requirement of R&D studies on decreasing volumetric and gravimetric parameters

• Low tolerant to sulfur element

• Requirement of long-term proof-of-concept studies

33.5.1 Design Architectures for PEMFC Powered Hybridizations

In general, FCEVs are configured as series vehicles [60]. However, the architecture of a FCEV can be configured in series, series-parallel, and parallel. The selection of the hybrid power-train topology is very important for an efficient operation and better market penetration of FCEV systems. Effective and efficient power conversion technologies are strategic for the progress of FCEVs [62]. Interfacing the load/power-train unit requirements with the different operational modes of onboard generation and storage systems call for suitable power electronic converter configuration and control. The selection of power-conditioning unit for hybrid systems including PEMFC is based on some significant factors like lower cost, space requirement, compact structure, higher efficiency, electric isolation, and ripple-free and reliable operation [15,62].

Despite the fact that hybridization concept brings remarkable benefits, the main challenge is to find the appropriate combination of energy sources. Each energy source has unique characteristics and energy conversion efficiency. Thus, each combination is expected to show different performance, efficiency, and fuel/energy consumption. Moreover, in a hybrid topology, these energy sources can be connected to dc bus either directly or via a power converter. In case of utilizing a power converter, which allows higher flexibility in load sharing, an improved hydrogen economy may be expected. However, system efficiency may decrease due to additional conversion stage, which might worsen the equivalent fuel economy.

Considering the abovementioned factors and the load/drivetrain requirements, various topologies may be used for the operation of PEMFC hybrid systems. One of the simplest architectures for the parallel operation of PEMFC hybrid systems includes the direct integration of PEMFC system with the auxiliary power unit as shown in Fig. 33.9. During low power demand, the FC system generates up to its load limit, and the excess energy between the load demand and the FC output power is used to charge the auxiliary unit. In this period, the S1 switch is closed, and S2 switch is open. During high-power-demand periods, both the FC system and the auxiliary units supply the load demand. During this period, S1 switch is kept open, and S2 switch is closed. The direct integration topology is attractive, because it does not require a high-power dc/dc converter; thus, the complexity, cost, weight, and volume of the system are significantly reduced [15]. For example, the UC system integration can be achieved with or without power electronic converter via series and parallel connection. Because of the high specific power and power density of UC bank, it may be possible to eliminate the dc/dc converter for voltage regulation so that it can deliver higher output. This topology is proposed by Honda [63] for a combined PEMFC-/UC-powered vehicular system. Also, the direct integration of the FC with the UC bank is possible for relatively low-voltage applications with a dc bus of less than 50 V [64]. The UC bank and the load terminal voltages depend on the FC system terminal voltage, which prevents the power capability of the UC bank from being fully utilized. Therefore, the UC bank size is restricted by the terminal voltage of the FC system, as in the battery/UC hybrid system of Ref. [65].

Different designs of a topology with only one dc/dc converter unit are shown in Figs. 33.10 and 33.11. The topology in Fig. 33.10 regulates the output power of the FC system, while the rest of the energy between the load demand and the FC output power is naturally supplied by the auxiliary unit. Besides, the topology in Fig. 33.11 is based on the regulation of the auxiliary system output power or the regulation of the DC bus voltage. There are many studies in the literature using these two topologies. Some previous studies on these topologies are reviewed and summarized in Ref. [15].

The most common topology for hybrid systems is composed of multiple dc/dc converters as shown in Fig. 33.12. In this kind of topology, the dc/dc converter of one of the available power sources is employed for the dc bus voltage regulation, which is called voltage-oriented-control, and the rest of the converters are controlled for power tracking by power-oriented-control methodology. Thus, the proposed power-conditioning unit provides the capability of delivering the desired power value from the hybrid power sources while keeping the bus voltage at a desired level. Additional architectures for the usage of multiple converter topologies for transportation area are available in Refs. [53,66–70].

Combining the features of multiple converter-based topology, some researchers focused on utilizing multiple-input single-output design architecture as depicted in Fig. 33.13. This topology provides the advantage of reduced number of elements (multiple inputs of power sources can be connected to a dc bus via only one output capacitor) used in power electronics interface design. For example, Ferreira et al. [71], Perez et al. [72], and Napoli et al. [73] utilized the multi-input converter topology for an electric vehicular system consisting of PEMFC, battery, and UC.

The design of the abovementioned single- or multi-input converters can be realized as insulated or uninsulated, unidirectional, or bidirectional according to the area of application. The basic uninsulated unidirectional and bidirectional dc/dc converter topologies are shown in Fig. 33.14. The proposed multi-input and bidirectional converter-based PCU offers the following advantages:

• Voltage levels of the input power sources can be different.

• The input sources can deliver the requested power individually and simultaneously.

• Electrically isolation prevents damage on input sources.

• The proposed PCU can work bidirectionally, that is, the power can flow in either direction between individual input and output.

However, there are different advanced, more advantageous but complex topologies developed by power electronics researchers [15].

33.5.2 Vehicular Power Control Strategy and Energy Management

Due to the different characteristics of multiple power sources, the efficiency and the fuel economy of hybrid systems mainly depend on proper energy management strategy (EMS), which is very important for PEMFC-powered hybrid systems.

An FCEV energy control system must provide good acceleration and high recovery of braking energy. The power sharing between the FC system and energy storage system (battery or UC bank) is determined according to the load sharing and control algorithm. Main requirements of the control algorithm are satisfaction of the power demand and management of the power flow in accordance with efficient operation of the different power sources. Coupled with this, the control system should utilize the FC system and energy storage system to match the vehicle load profile by considering different features of power sources.

Since stable operation of the FC system is vital for efficiency, lifetime and cost, FC system should deliver the base load power without responding to peak power demand. Another purpose of the control system is to adopt the battery or UC bank in stabilizing the dc link voltage. This enables power transfer to/from battery or UC bank and improves the driving performance.

Hybrid systems can provide improved efficiency when a well-designed energy splitting algorithm that considers the individual characteristics of each hybrid system is applied. There are many techniques for energy management that have been investigated in the literature, such as intelligence-based strategies, optimization-based strategies, and frequency decoupling strategies [74].

33.5.3 Current Status and Future Trends of Fuel Cell based Vehicles

Leading automakers have started to make their light-duty hydrogen FCEVs for testing and commercial applications. Available FCEVs are on the road in selected regions like California, Europe, Japan, where access to hydrogen stations are available. Some of these vehicle models include Honda FCV (2016), Toyota Mirai (2017), Mercedes-Benz B-Class F-Cell (2015), Hyundai Tuscon, and SUV (2016). All of these FCEVs uses 100 kW fuel cell stack. They also have quick refueling time of less than 10 min and driving range of around 200–300 mi [21,54,87–89].

The California Fuel Cell Partnership (CaFCP) plays a vital role in preparing to demonstrate and commercialize the vehicle technology of the twenty-first century. This organization is a unique collaborative of automakers, energy and FC technology companies, and government agencies. Currently CaFCP is focused on the marketization and industrialization and while emphasizing the importance for market introduction of FCEVs [90].

Although automakers have produced FC-based commercial vehicles, actually, they started to develop FCEV prototypes many years ago. For example, Toyota has developed various types of FCEVs, after it began its fuel-cell efforts in 1992. Ballard developed and demonstrated a hydrogen-fueled transit bus in 1993. GM demonstrated an FC/battery hybrid FCEV in 1998. Nearly 200 B-Class FC-based Mercedes-Benz vehicles have been with customers in the United States and Europe since 2010 [89]. AC Transit has the most comprehensive program to obtain real-world driving impressions and experiences and realize the earlier phase of the hydrogen FCEVs in North America [17,90]. The new Mercedes GLC F-CELL and next generation Honda FCEVs combine fuel cell and energy storage unit (lithium-ion battery) using plug-in hybrid technology that is planned to come to the market in 2017 and 2018, respectively [21,91].

Some governments (e.g., US and Japan) and automakers (e.g., Honda, Toyota, Daimler, Nissan, and Ford) are working together to support hydrogen infrastructure, public awareness, decrease operational costs of infrastructure firms. By cost reduction and mass production of competitive parts such as the FC stack, hydrogen, fueling stations, compact packaging, storage (battery and ultracapacitors), silicon carbide-based innovative power electronics, and electric motor technologies, these vehicles can be commercialized and introduced to the market for widespread use [18,21,37].

It is necessary to carry out further investigation on the performance, reliability, durability, and cost reduction of FC systems. FCEV design architecture plays a significant role while considering the performance, packaging, interior-space, efficiency, real-world performance, and durability issues. FCEV systems should be environmentally safe and commercially viable. Without doubt, technologies of a stable supply of highly pure hydrogen and inexpensive cell components are a prerequisite for market penetration of FC systems. In this case, since the number of renewable energy sources is increasing rapidly, new business models and marketing strategies can be developed. For example, the production of green hydrogen from renewable sources (biomass, biowaste, electrolyzers powered by photovoltaic, and wind energy systems) and also other feasible and viable hydrogen production methods can be used to feed the FCEVs and to balance the electric and gas grids under the smart grid concept [5,20]. Besides, as a part of sustainable energy and transportation chain, FCEVs, and their modular infrastructures like power inverter and hydrogen stations can contribute to the efficiency of the smart energy systems (as V2G, V2H, flexible load, storage, combined heat power, grid balancing, energy exchange, feed-in tariffs, and emerging application concepts). These kinds of EVs, like FCEVs, can also be used as an investment tool and as a major player of energy market in the future smart grids and smart cities.

Demonstration infrastructure should be sufficient for envisioned commercialization roadmap [5]. Demonstration projects and proof of concept experiments will act as a seed in addressing problems associated with practical applications, data collection for standardization, durability of FCEVs and accelerate awareness of using hydrogen in our daily life [5,17,21,92]. From the viewpoint of FCEVs market penetration, currently, there are limited commercial FCEVs, but in medium- and long-term periods, there will be huge numbers of FCEVs on the road depending on the abovementioned strategies of developed and developing countries. Thus, they can contribute significantly toward sustainable transportation and hydrogen chain.

33.5.4 Safety

Hydrogen FCs can revolutionize many sectors, since hydrogen is as safe as or even safer than other flammable fuels such as gasoline or natural gas. However, with the lack of professional design and management, hydrogen fuel cells pose several other risks that other flammable fuels do not.

Nowadays, FCEVs, hydrogen refueling stations and other values of hydrogen chain started to operate in different regions, despite pending answers to potential questions (How safe is hydrogen? What are potential hazards of hydrogen? Which improvements does it require to avoid danger?) [5]. Hazards and associated risks for hydrogen fuel cells should be considered by all stakeholders such as designers, regulators, and users in various situations when FCEVs are inoperable, in normal operation and in collision [5,16].

The main potential hazards can be listed as follows [5,16,21]:

• Hydrogen burns (rather than explosion)

• Higher flammability range

• Danger posed by invisible hydrogen flames (adding chemicals like odorant for required luminosity can provide an easier detection)

• Hard detection of hydrogen leak

• Higher tendency to leak since hydrogen is the smallest molecule (professional design may prevent leaks)

• Potential of hydrogen to asphyxiate people

• Frostbite/cold burns of liquid hydrogen

• Refueling station accidents

These hazards may be prevented or the impacts can be decreased with more R&D studies, administrative supports, efforts of all stakeholders, etc. For instance, Honda improved several designs to prevent FCEVs from collision impacts such as fastening bar as an impact resistant to prevent cells, straight frame structure to protect components, and load path structure to disperse the collision load and for efficient absorption of energy [21].