1. Fuel Cells: Fundamentals and Applications
1.1. Fundamentals of Fuel Cells
Fuel cells are a direct electro-chemical energy conversion technology capable of generating direct current (DC) from low mW to higher kW applications. Fuel cells are comparable to batteries, considering the fact that they both have electrolytes, electrodes, and generate DC through electro-chemical reactions. The ultimate difference between them is that a fuel cell requires a constant supply of fuel and oxidant to generate power, whereas a battery discharges its stored potential per load demands. Faster recharging time for fuel storage and higher driving range in comparison with batteries makes fuel cells more versatile and comparable in the transportation sector
[1][2].
1.2. Classification of Fuel Cells
Fuel cells are classified based on the type of electrolyte.
Although most of the physics associated with fuel cells are common across types, PEMFCs stand out as the significant technology in the transport sector due to its quick startup, simplicity, and viability. These solid polymer membrane fuel cells are associated with an efficiency of 83%, which is much higher than IC engines. The technology, by itself, does not generate any emissions and the only byproducts are unused oxidant and water. The modularity and simple design of fuel cells allows for the mass production of individual units. Fuel cell stacks are built by adding each unit cell in series to provide a desired voltage and power. The concept of stacking fuel cell units in series to achieve the desired power became necessary in lieu of the cabling requirements and resistive losses associated with single cell-scaled up systems
[3].
1.3. Basic Components and Working of Fuel Cells
A brief overview of the components that constitute a fuel cell unit along with its working principles are discussed in this section. The below figure and associated tables
[4] explain the materials, functions, and processes associated with PEM fuel cells, considering that it caters to the transport market, which accounts for 90% of the global fuel cell market.
Some Design Challenges Associated with PEMFC Systems
Some of the key challenges in PEM fuel cell system design have been addressed by researchers worldwide. Certain studies on flow channel modifications showed improved performance of fuel cells due to the uniform distribution of reactants and effective water removal from cells. For example, one of the studies by Magesh Kannan et al., on the development of a sinuous flow field for the cathode exhibited a significant improvement in power density by 14%
[5]. Certain experimental studies were performed to improve the temperature uniformity of PEMFCs in order to achieve better performance in the system. One such study was performed by Dineshkumar et al., to evaluate the optimal number of passes to be machined in the graphite plates with the objective of maintaining temperature uniformity in the system.
1.4. Applications of Fuel Cells: Transportation Sector
A commercial vehicle that meets the expectations of fast refueling times and zero or low tail-pipe emissions is the fuel cell electric vehicle of today
[6]. Presently, these FCEVs have a driving range of 240–435 miles, with a better fuel efficiency than conventional fuels. The market for hydrogen-based fuel cells in the transportation sector is increasing, which is very evident by the fact that numerous auto-manufacturers have begun purchasing fuel cell businesses
[7]. Some manufacturing businesses have begun constructing environmentally friendly hydrogen generating facilities, while traditional gasoline bunkers are making room for hydrogen refueling stations
[8].
1.5. Architecture of Fuel Cell Electric Vehicles
Fuel cell direct mode: The fuel cell is used as the direct source to drive the power train. A 12 V battery is present to assist with startup. Hydrogen-based fuel cells are used in this architecture. The fuel cell controls associated with these systems have a poor response
[9].
Parallel-hybrid mode: In a parallel hybrid fuel cell architecture, the fuel cell looks after the base load and the battery is used to accommodate fluctuations. The battery dynamically responds to the peak conditions and the fuel cell assists with cruising of the vehicle.
Series-hybrid mode: In a series-hybrid fuel cell architecture, the battery drives the vehicle and looks after instantaneous loads in the vehicle. The fuel cell is used to charge the battery. A trade-off between the sizes of the battery and fuel cell are made by the designer.
1.6. Components of FCEVs
The idea of using fuel cells in EVs is to make use of its ability to generate DC power, which is required for the propulsion of any EV. EV designers and manufacturers define their power requirements through the rated capacity of the DC electric motor and the fuel cell-battery combination is decided accordingly to meet this requirement. In today’s scenario, the technical aspect of designing battery algorithms to optimally save energy during regenerative braking, shorter acceleration stints, and adhering to the load-following strategy is gaining importance
[10].
Battery: As with all electric vehicles (AEVs), a traditional auxiliary battery (12 V) is used to start the vehicle and assist with powering the accessories of the vehicle. In the case of battery electric vehicles (BEVs), a traction battery takes over the propulsion part. In FCEVs, based on the architecture, a fuel cell-battery combination is applied.
Battery pack: During braking, the potential energy of the flywheel is restored through regenerative braking technology. A high-voltage battery bank is used to store this energy. In the case of BEVs, this can be used to power the traction battery so that it provides increased autonomy to the vehicle in AEV mode.
DC-DC converter: This semi-conductor circuit is a means to step up or step down the voltage of operation in EVs. In BEVs, the converter helps in stepping down the voltage to charge an auxiliary battery from the battery pack. In FCEVs, this converter is used to step up the voltage to charge an on-board battery for range-extended EVs (EREV).
Electric traction motor: Based on the vehicle architecture, the traction motor is coupled with a fuel cell-battery combination. These DC traction motors are often coupled with generators for regeneration purposes.
Fuel cell stack: Based on the design of the FCEV, a fuel cell stack is capable of operating at the rated voltage and power to suit the case.
Fuel filler: Hydrogen is stored in a compressed state in FCEVs. A suitable nozzle-based receptacle technology is used to connect the fuel tank with the refueling station.
Fuel tank: Stores hydrogen at the required pressure for its usage in FCEVs.
Power electronic controllers: This technology manages the powertrain configuration in FCEVs. It controls the amount of energy delivered to the traction motor to receive the desired speed-torque characteristics based on the load-following strategies used between the fuel cell-battery combination.
Thermal cooling system: The entire fuel cell-battery energy system must be thermally protected for prolonged operation and sustainable performance.
1.7. Demonstrations of FCEVs in Transportation Sector
This section compiles only some of the key historical demonstrations of FCEVs and details about the scientific and technological advancements in FCEV products.
GM electro van: In 1966, the first hydrogen-based electro van
[11] was developed (32 individual stacks of 1 kW fuel cell modules each) by Craig Marks, GM, with a nominal power output of 32 kW and peak load of 160 kW. The maximum attainable speed was limited to 70 mph, with a range of 120 miles. Due to the high cost, large fuel storage space, and poor hydrogen infrastructure at that period, commercialization of the product did not happen.
Daimler-Benz NECAR: In 1994, Daimler-Benz came up with their NECAR
[12], which housed a 50 kW Ballard-manufactured PEMFC system. The top speed was limited to 56 mph, with a range of 81 miles. This car also was not commercialized due to its limitation in carrying cargo because of the large hydrogen storage tanks.
Toyota FCHV: In 2002, the world’s first fuel cell hybrid vehicle was available to lease in the USA and Japan
[13]. It contained a 90 kW fuel cell unit coupled with a Ni-MH battery that provided a combined range of 155 miles.
Honda FCX Clarity: Launched in 2007, the vehicle housed a 100 kW fuel cell stack, with a driving range of 354 miles and top speed of 100 mph
[14]. This was one of the first fuel cell electric vehicles to be produced commercially, although on a very low scale with only 200 units produced between 2008–2010. The leasing limitations were restricted to southern California and Japan.
Toyota Mirai: In 2014, Toyota launched its first commercially successful Mirai
[15], a mid-size fuel cell electric vehicle that had reached a global sales volume of 21,475 units as of November 2022
[16], starting at USD 49,500. It houses a 114 kW fuel cell unit fuelled by 2 × 700 bar hydrogen storage units, with a total capacity of 122.4 L. It features a Ni-MH battery unit (224.8 V
rated) that takes control as per the loading requirements during peak conditions. The top speed of the vehicle is 200 mph, with a combined driving range of 360 miles.
Hyundai Nexo: In 2018, the Hyundai Nexo (FCEV) was launched with the capabilities of a high-performance air filtering unit that was able to eliminate micro-air particulates for its cathode fuel supply system as it runs. The hydrogen refueling time is restricted to less than 5 min, and the vehicle has a driving range of 372.8 miles with a top speed of 111.2 mph
[17]. It houses a fuel cell unit of 95 kW capacity compressed in 700 bar units with a capacity of 156 L, a battery unit of 64 kWh for energy storage, and the cost of this automobile starts at USD 59,435
[18]. The permanent magnet synchronous motor (PM-SM) that drives the transmission unit is designed for a maximum power of 120 kW. Around 1321 units have been sold since its market inception.
1.8. Applications of Fuel Cells: Stationary Sector
Unlike the utilization of PEMFCs for transport applications, stationary fuel cell energy systems are capable of operating in a wide range of temperatures (AFC, SOFC, PAFC, and MCFC are also utilized)
[19][20]. Based on their capacity, they can be classified as small to medium (10 kW–300 kW) and large (300 kW–20 MW) stationary power generation systems.
Based on the architecture and interconnection with other power systems/grid
[21], they can be classified as:
Standalone: The fuel cell unit is used as the predominant power source and a battery bank is used to supplement peak needs.
Grid parallel: The fuel cell unit is designed as the base power supply for the consumer’s need. In the case of peaks, the grid will supplement these demand needs. Since these systems (fuel cell unit and grid) do not communicate with each other directly, interconnection standards are not required.
Grid interconnected: Interconnection standards become part of these systems, wherein the fuel cell unit will export excess power to the grid at times of lower demand. The fuel cell unit is designed to produce constant power and the grid is used to supplement peaks.
1.9. Ballard’s Technological Products (Fuel Cell Market and Products)
Ballard has been developing fuel cell systems since the technology’s inception. Ballard’s main offerings can be divided into four categories: stationary power systems, fuel cell stacks, marine systems, and heavy-duty modules. These classifications, albeit relevant to many industries, are inspired by the basic fuel cell stack advancements attained by Ballard in its 40 years of research and development. In the domain of stationary power generation and backup applications, Ballard connects its fuel cell stack to power modules and solutions such as H2PM, Wave, and Clear Gen II as tabulated, thus providing more flexible, modular, and dependable power for cutting-edge systems. Finding a location that can deliver hydrogen on a sustainable basis is an important consideration when buying or investing in these stationary power systems. These fuel cell modules take up less area on the floor than other renewable technologies, such as solar panels or wind turbines, which is a basic characteristic of these renewable systems
[22][23][24][25].
Fuel cell stacks from Ballard are equipped with air-cooled and liquid-cooled technologies that employ clever cooling algorithms as tabulated to control the thermal effects on fuel cell operation. Ballard’s unique membrane electrode assembly (MEA), which has been standardized across all of its products and can be changed depending on the application, is a single component. The automated manufacturing of these units allows them to keep costs down and production running continuously, as evidenced by the fact that they have deployed more than 670 MW of goods as a fuel cell producer.
2. Technical Challenges and Market Drivers of Fuel Cell Energy Systems
2.1. Opportunities
In the automotive industry, globally acclaimed automakers are planning to ramp up their production of green mobility solutions. For example, the business activities and product portfolios of Hyundai in 2022 reflected that the firm is routing towards hydrogen-based energy technologies through its sophisticated and robust 90 kW fuel cell stacks for heavy-duty applications
[26]. Other similar automakers, such as Daimler, Toyota, BMW, and Tata Motors, are supposedly investing in the design and development of fuel cell transportation systems. As another example, Tata Motors in India as tabulated is showing a clear inclination towards its fuel cell electric bus development to boost the green hydrogen utilization of the nation.
2.2. Fuel Economy and Long Travel Range
According to DOE testing results, a gasoline engine is less than 20% efficient in converting the chemical energy of gasoline into propulsive power in a conventional engine. This corresponds to 50% less fuel consumption of hydrogen for the same amount of energy. The cost of the generation of hydrogen in the near future is expected to drop with developments in hydrogen infrastructure
[27]. The nominal driving range of present day FCEVs ranges between 300–700 km (240–435 miles), which is comparable to vehicles with conventional engines and better than BEVs. These factors will eventually drive the accelerated growth of the FCEV market.
2.3. Threats
The aspects of hydrogen production, including its sustainability, storage, safety, and high cost of investment, are some of the obstacles in the development of hydrogen infrastructure. This infrastructure must be digitally equipped with systems that optimally govern hydrogen generation, storage, and distribution mechanisms for safer operation. This poses a serious threat for the market of FCEVs in developed as well as emerging economies
[28].
2.4. Segmentation
Based on the power output from fuel cells, the sector is categorized as 150 kW applications, 150–250 kW applications, and more than 250 kW applications. Almost all of the FCEV applications demonstrated in the market belong to the less than 150 kW criteria. This block has dominated the fuel cell market until 2022 and will continue to do so in the near future. The more than 250 kW segment corresponds to long-haul heavy-duty buses and trucks, which is one of the fastest growing utility sectors in the fuel cell market
[29]. As an example, Hyundai declared a milestone achievement in its premium heavy-duty fuel cell vehicle, the Xcient 6 × 8, after surpassing 5 million kilometers by 47 units deployed in Switzerland in October 2022
[30]. This truck has a 350 kW motor with a torque of 2237 Nm and driving range of 400 km on a single charge. The vehicle has two 90 kW fuel cell stacks and is dependable and robust for client operations. The vehicle has three sets of 72 kWh batteries for assistance and seven big hydrogen tanks with a combined capacity of 31 kg. The 150–250 kW segment constitutes medium-sized utility vehicles for transit applications. Based on the demand for these systems in the near future, growth is predicted.
2.5. Market Generation for Local Components and Analysis
As previously mentioned, the commercialization of hydrogen-based technologies and fuel cell products occurs side-by-side, thus the components that constitute the systems for both hydrogen and fuel cell technologies are in demand. For example, nearly 60% of the total cost of FCEVs is attributed to the fuel cell energy system itself
[31]. Batteries constitute the second greatest share in the market. The auxiliary battery and supplementary battery pack are essential components of FCEVs and the demand for these batteries is correspondingly increasing with FCEV market growth. Other significant increases in the market for hydrogen storage tanks, drive systems (power electronic solutions), electric motors, and power controller units are also expected with growth in the fuel cell market. Robert Bosch GmbH is considered to be one of the critical players in the development of auto-components associated with valves, regulators, fuel cell electric drives
[32], and technologies associated with fuel cell power trains and their realization. The recent official statements from the firm confirmed their interests in hydrogen generation and utilization in addition to component- and system-level development.
2.6. Global Fuel Cell Shipments
It is evident that there has been a net rise in nominal power generation from individual fuel cell units over the past five years, observable by the growth in fuel cell shipments from 75,000 to 130,000 units per year as listed and the accompanying power transition from 1 to 2.3 GW. The saturation in the sheer volume of fuel cell shipments during the years 2019–2020 can be attributed to the strict norms followed by nations as part of COVID 19 protocols. The two-fold increase in shipments in 2021 is a clear indication of national interests in fuel cell-based technologies
[33]. The transportation sector accounts for around 90% of these fuel cell shipments, followed by the stationary power generation sector.
2.7. Commitment and Deployment Status
The International Partnership for Hydrogen and Fuel Cells in the Economy (IPHE), a consortium that currently has 22 member nations as is listed, is working to expedite the adoption of hydrogen and fuel cell technology across a range of industries and uses. Reports from the IPHE
[34] confirm that more than 19,000 FCEVs are currently in operation in South Korea and more than 13,000 FCEVs are in operation in the USA as of 2022. The numbers are expected to increase as other major economies, such as China, Japan, and India, are investing in the development of hydrogen infrastructure and FCEV adoption.
2.8. Hydrogen Policies and Roadmaps towards Commercialization
Certain major economies, such as Japan and the USA, are taken into consideration in this section. On some level, there is a consensus amongst these nations in implementing the hydrogen economy. However, this depends on the individual aspirations and funding opportunities in these nations towards hydrogen-specific areas.
2.8.1. Japan
In the strategic energy plan of 2014, hydrogen was given a boost to play a central role in Japan’s energy supply
[35][36]. The plan discussed the potential of the hydrogen economy to create sustainable, cost-efficient technologies and improved energy security for the nation since about 1/5th of the energy requirement for transport was imported from oil-turbulent economies. This shift in hydrogen import would reduce the stress on fuel prices and the economy. By 2050, the market for the hydrogen economy is expected to reach JPY 8 trillion, as more patents are being filed for hydrogen-based technologies around the world. Another policy of concern is the cross-ministerial strategic innovation promotion program, which aims to promote the development of hydrogen production technologies, including CCU-based units. Japan aims to introduce 5.3 million fuel cell units across the domestic market by 2030. The strategic roadmap for hydrogen and fuel cells for Japan was developed in 2014, defining three phases towards hydrogen economy realization:
Phase 1 (2015-): Hydrogen popularization and utilization (stationary and FCV market)
Phase 2 (2025-): Hydrogen supply and implementation of hydrogen for unused energy sectors
Phase 3 (2040-): Realization of CO2-free hydrogen generation systems
Japan’s main target in the hydrogen technology roadmap includes the capability of producing domestic fuel cells by 2021 and to sell 200 thousand units of FCEVs in the market by 2025.
2.8.2. The USA
Hydrogen investment and talks about promoting the hydrogen economy in the USA began in the early 2000s. The workshop organized by the US Department of Energy (DOE) in 2002 stressed the sustainability of hydrogen as a fuel for domestic and industrial applications. Some of the implications of promoting these hydrogen policies are expected to reduce gasoline consumption to less than 40% by 2035. The technological changeover would also lead to potential employment opportunities and a study indicated a creation of 675,000 jobs related to this field by 2050. Nevertheless, the challenges due to cost pose a serious impedance to transitioning the economy. Stationary fuel cells cost around 3000–7000 USD/kW, which is relatively higher than conventional power plants. On the other hand, automotive fuel cells cost around 49 USD/kW, which is still higher than 30 USD/kW for conventional IC engine technology. With respect to durability aspects too, the practical durability of fuel cells in stationary and automotive applications are limited to 20,000 and 2500 h against targets of 40,000–80,000 and 5000 h, correspondingly.
The US DOE is revising its strategies to improve the targets
[37][38][39]. For example, the cost of fuel cells in automotive applications was set to a new target of 30 USD/kW in 2017, whereas the hydrogen production and delivery costs were set to a target of 2–4 USD/gge (gallon gasoline equivalent) by 2020 against the 4–6 USD/gge mark set in 2011. One of the critical aspects in promoting the hydrogen economy is federal support and funding. Funds are provided for high-impact R&D related to this field, which includes non-Pt based catalyst development, hydrogen storage, renewable hydrogen generation, and liquid-based fuel cell technologies.
This entry is adapted from the peer-reviewed paper 10.3390/en16062748