Hydrogen Fuel Cell vs Hydrogen Combustion
“Hydrogen car” is a generic term referring to vehicles powered by hydrogen. But one of the unique things about hydrogen is that there’s more than one way to convert it to forward motion. In fact, hydrogen cars can be roughly divided into two categories. Hydrogen fuel cell vehicles operate similarly to electric cars. On the other hand, hydrogen combustion vehicles operate similarly to gasoline cars.
Both types of vehicles produce zero emissions – but they work in very different ways.
Hydrogen Fuel Cell
Hydrogen fuel cell cars may sound like a new thing – the first mass-production fuel cell cars for America, the Hyundai Nexo and Toyota Mirai, were delivered in late 2022 – but fuel cells are technology that pre-date the automobile.
In 1838, a Welsh physicist combined hydrogen and oxygen in the presence of an electrolyte to produce an electric current – though the amount of current generated wasn’t enough to power a vehicle. But, by the 1960s, fuel cell technology was being used in America’s Gemini and Apollo spacecraft, where it provided crews with electricity and water, which were generated by stored hydrogen and oxygen.
Why hydrogen? Hydrogen is the most abundant element on earth by quantity, if not by weight. The lightest element in the universe can be produced from a number of domestic resources, and there are ways to produce it sustainably. In fact, the goal of the U.S. Hydrogen Council is the widespread use of decarbonized hydrogen for transportation by 2030.
A hydrogen fuel-cell vehicle is an electric vehicle – just without a plug. There’s no big battery to recharge. Instead, you simply fill a tank with compressed hydrogen gas, which takes about five minutes, a similar amount of time to refueling a gas vehicle.
From that pressurized fuel tank, hydrogen gas flows to a fuel cell system, which combines the hydrogen with oxygen from the air. A chemical reaction produces electric current – and water, the car’s only emission, which drops out of a vent pipe underneath the car.
At the same time, electricity generated by the fuel cell (as well as the vehicle’s regenerative braking system) is stored in a lithium-ion battery. Pressing the vehicle’s accelerator pedal yields an immediate flow of electric power from the fuel cell and/or battery to an electric motor, which drives the wheels. In the Mirai, the electric motor and the fuel cell stack both live in the rear of the car, but fuel cells and electric motors are small and easy to locate, offering engineers lots of packaging flexibility.
The advantage of a fuel cell drivetrain, compared to a battery-electric drivetrain, is that the battery can be much smaller than those in a battery-electric car. This means the vehicle can be much lighter and more efficient overall. Because hydrogen fuel cell cars don’t rely on a huge battery to derive decent driving range, they are more responsive to drive, lighter on their feet, and better performing than battery-powered electric vehicles.
Hydrogen Combustion
Fuel cells aren’t the only way to convert hydrogen to forward motion, though. For instance, Toyota, who has always been a big believer in hydrogen, has also invested in hydrogen combustion.
Unlike a hydrogen fuel cell vehicle, which creates electricity that powers an electric motor, a hydrogen combustion engine looks, sounds, and behaves like a gasoline engine – except for the fact that it burns hydrogen and produces no noxious tailpipe emissions. Yet like a fuel cell car, a hydrogen combustion car only emits water.
The advantage of hydrogen combustion? Faster time to market – because traditional automakers can adapt existing engineering – as well as, likely, an easier deployment of refueling infrastructure. Gas stations could be adapted to serve hydrogen – which can be stored in gaseous or liquid form on-board a vehicle.
From a driving perspective, hydrogen combustion cars will feel familiar to anyone who has driven a gasoline car – with an engine, gears, and a bit of noise. Hydrogen burns quicker than gasoline, making hydrogen combustion powertrains very responsive and exciting.
On the other hand, hydrogen combustion cars are more mechanically complex than hydrogen fuel cell cars, which consist of a simple, reliable electric motor and a fuel-cell system. Lots of moving parts, like a gasoline car, will mean more maintenance over time.
Drivers of hydrogen combustion cars will also share some of the drawbacks of hydrogen fuel cell vehicles. These include an expensive pressurized hydrogen storage tank and a lack of refueling infrastructure in much of the U.S.
Hydrogen-combustion technology is moving fast with the latest versions offering upgraded power, performance, and reliability. At a recent event at Fuji Speedway in Japan, Toyota unveiled a Corolla Cross running on liquified hydrogen, instead of hydrogen gas, as its power source. The improved density of on-board fuel storage helps the driving range of the vehicle.
Toyota, Hyundai, and other car brands like Renault and BMW, are serious about hydrogen combustion. Koji Sato, the head of Toyota’s hydrogen combustion racing program, has said the company is about 40 percent of the way towards commercializing hydrogen combustion – and it is already part of the production development cycle for new vehicles for both Toyota and Lexus. BMW demonstrated hydrogen combustion in a 7 Series sedan almost 20 years ago and continues to develop the technology for high-performance vehicles.
The Future
As we head to a zero-emissions future, battery electric vehicles may end up being the dominant form of transportation, but batteries will not be the only technology helping us to reduce our carbon footprint. Hydrogen power, with its quick refueling times, will be a key component of transforming long-haul transportation – for goods as well as people.
While all international carmakers are plowing hundreds of billions of dollars to go from gasoline to full-electric, Toyota and other brands are being more cautious and open-minded, knowing there will be room for other zero-emissions technologies for certain use cases. As we are still in the infancy of the transition to zero-emissions driving, carbon neutrality will look different for different kinds of customers – and automakers will have to offer these customers diversified options to stay relevant.
