Hydrogen fuel cells are emerging as a sustainable way to decarbonize transportation on land, sea and air. The technology generates electricity through an electrochemical reaction between hydrogen and oxygen, producing only water and heat as byproducts.

The basic elements of a hydrogen fuel cell power system are the fuel system, air management, thermal management, a fuel cell stack and an electric motor. Fuel cells are fed hydrogen from the fuel system and oxygen through a compressor in the air management system to produce electricity and heat. The heat is rejected by the thermal management system, and the electricity drives motors that provide power for propulsion.

With their potential for high energy efficiency, zero emissions and fast refueling, fuel cells offer an intriguing alternative to traditional internal combustion engines (ICEs) and pure battery-electric systems.

They provide improved energy density, which enables greater range between fueling. That’s why the technology appeals to manufacturers of airplanes, automobiles, buses, ships, tractors, trucks and trains.

On land, hydrogen fuel cell vehicles (HFCVs) are particularly attractive for long-haul trucking and commercial transportation applications. That’s why legacy automakers such as Honda, Hyundai and Toyota are focusing on the technology, which has also attracted the attention of start-ups like Hyzon Motors Inc. and Nikola Corp.

At sea, hydrogen is powering yachts and ships with clean energy systems. Companies like Sunreef Yachts are exploring technologies like compressed hydrogen storage and onboard hydrogen generation through methanol reforming.

In the air, fuel cells could present a pathway to more sustainable aviation, with leading players such as Boeing and Honeywell developing hydrogen-powered aircraft for short-haul routes.

Despite its many benefits, hydrogen fuel cell technology still faces major hurdles, such as public acceptance, high costs, limited infrastructure and the complexity of hydrogen storage.
 

Rolling Along

With land-based vehicles, hydrogen is stored onboard until it is needed. Electricity generated by the fuel cell is used in combination with a battery to power an electric motor that drives the wheels.

An HFCV is electrically driven, like a battery electric vehicle (BEV), and in many cases these vehicles even use an identical electric motor. The main difference is the energy storage system. Instead of carrying electrical power in a battery, gaseous hydrogen is stored in tanks and then converted by fuel cells into electricity to power the vehicle.

The higher energy density of hydrogen allows for greater range, a crucial factor for commercial vehicles and long-haul trucking. Additionally, the refueling speed of HFVCs is comparable to traditional fossil fuels, making them practical for industries that rely on quick turnaround times.

“Hydrogen fuel cell vehicles are electric vehicles at their core,” says Jerome Gregeois, director of commercial vehicle development at the Hyundai Kia America Technical Center.

The vehicles generate electricity on demand using a fuel cell stack, which combines hydrogen from onboard pressurized tanks with oxygen from the air in an electrochemical reaction. This electricity powers an electric motor, with any excess stored in a small battery for later use, such as during regenerative braking.

Hyundai is a major player in HFCV development, with a growing portfolio of hydrogen-powered vehicles, including the Nexo SUV and the Xcient Class 8 semi-truck.

According to Gregeois, a light-duty HFCV can refuel in just three to four minutes, while the company’s Xcient trucks achieve full refueling in 20 to 30 minutes. The goal is to reduce that to under 10 minutes.

Hyundai’s commercial vehicles, including Xcient trucks and hydrogen-powered buses, are manufactured in a dedicated facility in South Korea. The assembly process for hydrogen vehicles mirrors that of ICE vehicles in many ways.

The fuel cell stack, which occupies a space comparable to a four-cylinder or V6 engine, is installed in the engine compartment. Hydrogen storage tanks are positioned where gasoline tanks would traditionally be located, with pipes connecting the tanks to the fuel cell stack.

While BEVs typically require fewer assembly processes, due to the absence of complex air processing systems, HFCV architectures ensure a seamless transition for manufacturers familiar with ICE vehicle production.
 

Infrastructure Challenges

Hydrogen fuel cell vehicles also avoid some of the infrastructure challenges associated with BEVs, such as the strain on local power grids from widespread electric vehicle charging.

“Hydrogen refueling stations can provide the same speed and convenience as gas stations, without requiring adjustments to grid capacity,” claims Gregeois, who says that Hyundai is investing in R&D to improve refueling protocols for commercial vehicles.

Faster refueling times—potentially even shorter than for diesel trucks—promises to make hydrogen a more attractive option for logistics firms and freight carriers.

Hyundai is working to increase the power output of its fuel cell stacks, aiming for more energy-efficient systems that rely less on onboard batteries. For commercial vehicles, durability is a key focus, with a target of 1 million miles for large trucks.

However, while Hyundai continues to push the boundaries of hydrogen technology, the success of HFCVs will ultimately depend on a robust infrastructure network and widespread market adoption.

“Infrastructure and vehicle deployment go hand in hand,” notes Gregeois. As hydrogen stations expand beyond major West Coast hubs like Los Angeles and San Francisco, he expects to see wider adoption of HFCVs in other markets.

Engineers at Toyota Motor Corp. have been developing fuel cell vehicles for almost 30 years. Today, they’re focusing on the efficiency and cost-effectiveness of next-generation cars such as the Mirai sedan, which is marketed in California as a “plug-less electric vehicle.”

Instead of having to charge a battery in a BEV, which can take several hours, an FCEV driver simply fills the tank with hydrogen. The fuel is a nontoxic, compressed hydrogen gas rather than liquid gasoline. Electricity generated by the Mirai’s fuel cell and the regenerative braking system is stored in a lithium-ion battery.

The Mirai is assembled at Toyota’s Motomachi plant in Japan. The automaker also produces fuel cell stacks and tanks in Japan, but assembles fuel cell power train kits and modules for commercial and heavy-duty applications at its factory in Georgetown, KY.

“We see hydrogen as part of a multi-pathway strategy to help reduce carbon dioxide emissions as quickly as possible,” says Justin Ward, general manager of fuel cell development for Toyota Motor North America R&D.

Toyota’s fuel cells feature a polymer electrolyte membrane that allows for low heat generation and high-efficiency operation.

The Mirai uses Toyota’s TNGA-L platform, which is very similar to the Lexus LS full-size sedan. That allows for most of the architecture to be similar.

“Where the vehicles are different is that the Mirai has three multi-layer carbon fiber-reinforced tanks underneath the structure for high-pressure hydrogen storage,” explains Ward.

One tank runs longitudinally where a driveshaft to the rear wheels would be in a Lexus LS. The other two are just under the rear seat and in the rear where a gas tank would normally be located. All three tanks are inboard of the vehicle structure and sit low in the body.

“Instead of an engine block under the front hood, the Mirai has a fuel cell stack,” Ward points out. “The rear of the vehicle carries an inverter, battery and electric motor for propulsion. They are vehicles that are powered by hydrogen and electricity, designed to share the roads with vehicles of all kinds of propulsion systems.”

Now in its second generation, the Mirai is currently sold in California, Europe and Japan, but it is not the company’s only hydrogen vehicle.

“We sell second-generation fuel cell vehicles in Europe as buses, [and we are] continuing to develop hydrogen [technology] for other heavy applications,” says Ward. “We have produced fuel cell-powered boats, port equipment and stationary [equipment] for years.”

Sales Challenges

Despite the promise of hydrogen technology, the lack of refueling infrastructure still remains a significant hurdle to wide-scale adoption.

Hydrogen molecules are measured in kilograms instead of gallons of fuel. A higher pressure rating for the tank indicates that it can hold more hydrogen. The tanks in the Toyota Mirai, for example, have a total capacity of 5.6 kilograms at 700 bar, allowing for a driving range up to 402 miles.

“There are retail stations open across California,” says Ward. “Refueling the Mirai takes approximately five minutes, on par with conventional internal combustion vehicles.”

Hydrogen fueling stations are like conventional gas stations apart from the nozzle and receptacle interface, since hydrogen is a gas.

Toyota is working collaboratively between Japan and the U.S. to create hydrogen fuel cells that are scalable in size and application, whether for a light passenger vehicle or a heavy-duty truck.

“We don’t envision hydrogen fuel cell research as simply an island,” explains Ward. “We are engaging in collaboration with other companies and organizations to share best practices to raise awareness of hydrogen, and opportunities to spread the technology and diffuse costs.”

“We need to see more stations and a larger distribution network to make hydrogen more affordable and accessible,” adds Hyundai’s Gregeois.

Currently, hydrogen fueling stations are concentrated in key markets like California, limiting the deployment of HFCVs to specific regions.

Another challenge for HFCVs is the high cost of fuel, particularly green hydrogen produced from renewable energy sources. It can be anywhere from 1.5 to eight times more expensive than gasoline, depending on the region and the time of year.

“Using renewable electricity, 75 percent of that energy makes it to the wheels of a BEV,” says James Edmondson, research director at IDTechEx. “For a hydrogen fuel cell vehicle, that figure is around 25 percent, as a lot of energy is lost converting to and from hydrogen at each end.”

In addition, fuel cells require greater than 99.99 percent purity of hydrogen.

Edmondson predicts that hydrogen-powered vehicles will make up 12 percent of zero-emission medium-duty trucks in 2034 and 15 percent of zero-emission heavy-duty trucks, primarily once regions with a strong push for a hydrogen economy start to use it in other sectors, such as agriculture and construction equipment.

“We are continuing to reduce costs so that we can pass the savings on to consumers,” says Toyota’s Ward. “We also continue to work with infrastructure providers and suppliers to emphasize the importance of hydrogen fuel cells, and how they can benefit society.”
 

Waterborne Applications

Hydrogen fuel cell systems can benefit many types of ships. One of the first segments of the marine industry to see the benefits of the technology are custom yacht builders.

Sunreef Yachts is a luxury boat builder based in the historic shipyard of Gdansk, Poland, the birthplace of the anti-communist Solidarity movement in the early 1980s. The company has carved a niche by specializing in sustainable power boats and sailboats, such as the 80 HYECO and the Zero Cat.

The former is based on compressed hydrogen storage, while the latter boasts onboard hydrogen production by means of methanol reforming.

“At the moment, we are in a very advanced stage with the realization of the project powered by fuel cells supplied with pure hydrogen gas where gas fuel is stored in pressure tanks up to 350 bar,” says Nicolas Lapp, chief technology officer at Sunreef.

The 80 HYECO (Hydrogen ECO) uses proton-exchange membrane fuel cells. The Zero Cat is based on a similar fuel cell technology, but the source of fuel is different. Gas fuel is produced by a hydrogen generator installed onboard to produce pure hydrogen from methanol in a reforming process that uses electric power generated by solar cells.

“Thanks to our high-end solar technology, we have the advantage of integrating solar cells in every possible surface of the bodywork,” explains Lapp.

However, Lapp and his colleagues are facing several challenges. One is non-existent or unclear rules and regulations from various maritime administrations.

“Hydrogen is a strong industry trend with a possible impact on the infrastructure worldwide, so it is vital to not only follow, but to shape its future in the yachting world,” says Lapp. “[However], safety regulations impose additional stringent requirements for nautical engine rooms where alternative fuels [such as hydrogen] are used.”
 

Up in the Air

Hydrogen fuel cell technology is also emerging as a viable way for the aviation industry to reduce its carbon footprint. Unlike traditional jet fuel-powered engines, zero-emission alternatives could revolutionize short- and medium-haul flights with cleaner and quieter options.

Joby Aviation Inc., an air taxi start-up, recently completed a long-duration hydrogen-powered flight, and Universal Hydrogen has conducted test flights with retrofitted aircraft. However, commercial deployment is still quite a few years away, due to the challenges of certification, infrastructure and scaling.

“A hydrogen fuel cell aircraft works by converting hydrogen into electricity through a chemical reaction rather than combustion,” says Phil Robinson, senior director engineering for zero-emission aviation at Honeywell International Inc.

The electricity powers electric motors, and when hybridized with batteries, it provides a seamless power source for aircraft. At the heart of this system is a fuel cell stack, where the chemical magic happens. Surrounding the stack is the balance of plant (BOP), which includes cooling systems, hydrogen regulators and air compressors that maintain optimal performance.

“The fuel cell stack combines hydrogen and oxygen, often with a catalyst like platinum, to generate electricity,” explains Robinson. “The BOP ensures the stack operates in its ‘happy place,’ regulating temperature, air intake and hydrogen flow. Without the BOP, the system wouldn’t function.”

The fuel cell provides steady power, while the batteries deliver bursts of energy when there’s a sudden need, like during takeoff or quick maneuvers. The batteries also allow the fuel cell to ramp up slowly to recharge them, creating a more efficient and balanced power system.

An additional benefit specific to hydrogen fuel cells is the elimination of in-flight nitric oxide and nitrogen dioxide emissions.

Honeywell is focusing on the development of hydrogen propulsion systems ranging from small drones to manned aircraft.

“For unmanned drones, we develop the entire system from scratch, including the stack, BOP and integration into the airframe,” says Robinson. “For manned aviation, the approach is more collaborative.”

In Europe, under the Clean Aviation initiative, Honeywell leads the Newborn Consortium, which includes 12 partners including Pipistrel, PowerCell and the University of Nottingham. Together, they’re building hydrogen propulsion systems tailored for commercial aircraft.

“In the Newborn project, Honeywell acts as the integrator, pulling together various technologies into a cohesive system that can be installed into aircraft,” Robinson points out. Two of the biggest challenges they face involve weight and hydrogen storage.

“Power density—or the weight of the system—is a significant hurdle,” says Robinson. “Jet engines are incredibly efficient at delivering high power with minimal weight. Fuel cells, on the other hand, are heavier for the same amount of power output, so weight reduction is a primary focus for us.”

Storage of hydrogen is another complex issue: Hydrogen is very lightweight by mass, but extremely bulky by volume, even when compressed.

“Most test flights today use gaseous hydrogen, but compressed gas doesn’t provide the range needed for commercial aviation,” notes Robinson. “That’s why we’re working on developing lightweight, robust tanks for liquid hydrogen storage, which can significantly increase energy density and range.”

The challenges extend to aircraft design as well. Hydrogen-powered aircraft often require a complete redesign, starting from the propulsion system and building the airframe around it.

“You can’t just retrofit a jet fuel-powered aircraft with a hydrogen propulsion system,” warns Robinson. “It’s a time-consuming and expensive process, but one that’s necessary to integrate these new systems effectively.”

That’s one reason why Robinson believes the first commercially viable hydrogen aircraft will be small, commuter-class planes. “Smaller aircraft are easier to build and require less investment in infrastructure, making them ideal for early adoption,” he explains. “Over time, we expect the technology to scale to larger aircraft. But, transoceanic hydrogen flights are unlikely in my lifetime.”

According to Robinson, widespread adoption of hydrogen fuel cell aircraft will require technological breakthroughs and infrastructure development.

“Reducing the weight of the fuel cell stack, BOP and storage systems is critical,” claims Robinson. “We’re also exploring how to use the waste heat from fuel cells for other aircraft systems, like cabin heating or wing de-icing, to offset weight elsewhere.”

As with land-based vehicles, refueling infrastructure is another challenge that must be addressed, as hydrogen refueling stations will be essential for commercial deployment. While some airports in the U.S. and Europe are starting to install hydrogen infrastructure, the industry is far from having the widespread network needed for regular operations.

Despite these challenges, Robinson remains optimistic about hydrogen’s role in decarbonizing aviation. “Hydrogen aircraft are a crucial part of the broader roadmap to reduce aviation emissions,” he points out. “While sustainable aviation fuels will continue to dominate long-haul flights, hydrogen offers a zero-emission solution for shorter routes, which account for a significant portion of global air travel.”