What are hydrogen cars and how do they work?

Hydrogen cars
Hydrogen cars

Hydrogen. It’s the most abundant element in the universe and the third-most on Earth but did you know it can also also fuel cars?

Although the hydrogen car and its use in the fight against greenhouse gas emissions is still relatively niche, manufacturers are dedicating more resources to research and development leading to advances in safety and efficiency and new models in market.

While the expenses involved in rolling out hydrogen refuelling infrastructure means it will more likely fuel long-haul trucks and trains than be freely available to motorists, hydrogen is set to play a crucial role in the future of transport and it’s worth understanding this evolving technology.

What is a hydrogen car?

By its most basic definition, a hydrogen car is one powered by a chemical reaction involving hydrogen.

The most popular form of hydrogen car is known as a fuel cell electric vehicle (FCEV), whereby hydrogen stored in an onboard tank undergoes chemical reactions in a fuel cell to create electrical energy which powers electric motors.

How does a hydrogen car work?

There are five main components that make a hydrogen car/FCEV work:

1. Hydrogen storage

The hydrogen storage system is the fuel tank of a hydrogen car. Made of composite materials like fiberglass, carbon fibre and aluminium, it is far stronger than LPG tanks or conventional petrol tanks, and can safely store hydrogen at 700 bar (10,000psi).

2. Battery

A high-voltage lithium-ion battery, like what is found in a conventional EV, can store electricity generated from the fuel cell stack and be used to give the vehicle an extra boost under acceleration.

3. Fuel cell

The fuel cell stack is where the magic happens. Hydrogen stored in the vehicle’s tank enters the fuel cell stack with oxygen from the atmosphere and is broken down to protons and electrons.

The flow of electrons created in the fuel cell provides electricity, and the protons, electrons, and oxygen combine to produce water molecules.

4. Inverter

The inverter converts high-voltage direct current from the cell into alternating current, which is used to operate the electric motor.

5. Electric motor(s)

The electric motor(s) and reducer are the powertrain that connects to the wheels and converts electrical energy into mechanical torque.

When the vehicle slows, the motor also converts mechanical torque into electricity stored in the battery. The reducer plays the role of a gearbox, amplifying torque by adjusting rotational speed of the motor.

Toyota Mirai hydrogen car

Above: Toyota's Mirai hydrogen FCEV

So are hydrogen cars considered electric vehicles?

Hydrogen cars as they exist today are considered electric vehicles if they make use of a fuel cell. Seeing as one byproduct of the reaction in the fuel cell is electricity that drives electric motors, this puts the ‘EV’ in FCEV.

However, some manufacturers – namely Toyota – have been testing hydrogen’s application as the combustible fuel in an internal combustion engine (ICE), replacing the need for petrol or diesel. In this application, the vehicle would not be considered electric.

What are the pros and cons of hydrogen cars?

Hydrogen cars present some benefits compared to conventional types of EVs and ICE vehicles:

Firstly, their range and refilling time is comparable with ICE vehicles, exceeding the capabilities of current battery electric vehicles (BEVs).

Toyota’s Mirai FCEV, for example, has a claimed range of approximately 500km with a filling time between two to three minutes, while Hyundai’s Nexo FCEV can cover 666km after a fill taking less than six minutes.

By comparison, a Tesla Model 3 Long Range takes roughly 90 minutes for a complete charge, with its 75kWh battery pack providing a claimed 547km of range.

Like BEVs, hydrogen cars have zero harmful tailpipe emissions. The only two byproducts of converted hydrogen is pure water and heat.

So – infrastructure permitting – hydrogen cars could provide all of the convenience of an ICE vehicle with all of the environmental benefits of an EV.

However, hydrogen also comes with cons. At this stage, hydrogen refuelling infrastructure is considerably more expensive to roll-out than EV refuelling infrastructure. Hydrogen is also very difficult to store and transport due to its very low density and less efficient in energy transfer compared to an EV. 

Although technology and methods used to refine hydrogen are constantly improving, as it is now, the process is still also very energy-intensive.

Are hydrogen cars safe?

Hydrogen cars have received a bad rap in terms of safety due to the volatility of hydrogen and the large amount of energy it stores.

While these concerns are not unfounded, the reality is all vehicles – including conventional ICE and electric vehicles – have inherent risks when involved in crashes.

Manufacturers specialising in hydrogen are constantly refining safety measures for hydrogen cars and they will only become safer over time.

One leg-up in these efforts is the fact hydrogen is roughly 14 times less dense than air, meaning any onboard hydrogen can be vented into the atmosphere rapidly if the car detects a serious accident has occurred.

Often the most dangerous situation in a crash involving an ICE vehicle is flammable petrol or diesel pooling underneath a damaged car if a fuel line is ruptured. This is all but negated in a hydrogen car.

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