How Exactly Do Hydrogen Fuel Cell Cars Work?

As I mentioned in my ‘How Exactly Do Electric Cars Work?’ article, many of us have grown up around gasoline-powered cars with an internal combustion engine, so we’re familiar with how they work. However how green cars work is sometimes seen as a mystery, especially hydrogen cars (because people will have used electric-powered devices many times, but probably not hydrogen-powered devices!)

So I have written this article to look at exactly what happens after the drivers presses the acceleration pedal, to make the car move forward. Please note that I’ll often use terms like FCEV (Fuel-Cell Electric Vehicle) or FCV (Fuel-Cell Vehicle) in lieu of ‘hydrogen car’, but they all mean the same thing – as the Brief Overview section shows!

Brief Overview

Hydrogen cars are also known as ‘fuel cell’ cars, or fuel cell electric cars. This is because whilst such cars are powered by hydrogen (stored within a fuel tank), the actual chemical reaction which converts this fuel into power happens within a fuel cell – which is a similar idea to an internal combustion engine.

In other words, hydrogen [fuel] & oxygen [oxidant reactant] (is converted into) electricity [power] & water [waste product] as shown in this handy video of the Toyota Mirai:

The chemical reaction which converts hydrogen (and oxygen) into electricity (and waste water) happens continuously and this is why hydrogen cars are sometimes called fuel-cell electric vehicles (FCEVs) or fuel-cell vehicles (FCV).

So in many ways, hydrogen cars are a bit of a middle ground between electric cars and traditional gasoline cars: the former runs entirely off electricity and its electrical motor (same as hydrogen cars after the chemical reaction), whilst the latter relies on a continuous generation of a fuel source based on a chemical reaction (same as hydrogen cars via hydrogen being ‘fed’ into the fuel cell).

The Fuel Cell (Stack)

Since it’s such an important component, it’s worth looking at the fuel cell (stack) in more detail – thanks to Javier Zarracina of the Los Angeles Times for the following handy diagram:

Bottom half of LA Times fuel-cell car diagram, showing just the fuel-cell component
Bottom half of LA Times fuel-cell car diagram, showing just the fuel-cell component

Each fuel cell sees hydrogen interacting with a negative electrode, whereby the catalyst causes a chemical reaction which utilises oxygen and produces electricity, along with waste water. Whilst batteries are a store of already-generated electrical power, fuel cells do not ‘store’ anything – they are purely an electrochemical cell which continuously produces an output (electricity) via an input (hydrogen – and oxygen).

Because each hydrogen fuel cell only produces 1 volt or less of electricity – but cars need hundreds of volts of electricity to function – multiple fuel cells are combined together into a fuel cell stack.

Overall Hydrogen Fuel-Cell Car Components

Now that we’ve looked at the main difference of a hydrogen car (the fuel-cell), it’s worth looking at the overall components that make up a hydrogen fuel-cell vehicle – thanks to diagram of all main components within a hydrogen fuel-cell car diagram of all main components within a hydrogen fuel-cell car
  • The hydrogen tank is one of the most important components here. These are heavy-duty, high-pressure storage tanks which connect directly to the fuel filler port. They are usually located below the floor of the vehicle, under the back seats or trunk/boot of the car. These tanks usually store hydrogen at 5,000 or 10,000 psi and they are very heavy. For example, the Toyota Mirai’s tanks store hydrogen at 10,000 psi and weight around 44 kg (97 lb) each. They usually only hold around 5 kg each of fuel – in other words, a hydrogen car can hold up to 10 kg of hydrogen fuel, despite their tanks weighing almost 9x this!
  • You may notice a battery pack near the hydrogen tanks. This stores electricity which has been generated from braking, in a process known as regenerative braking. This electricity can be used to help acceleration, in lieu of hydrogen power…
  • .. the process of using hydrogen or battery power is managed by the controller (also called the power control unit). This is the ‘heart’ of a hydrogen (and electric) car, and it’s connected to the acceleration (and brake) pedals. Essentially when the driver accelerates, small sensors called potentiometers ‘tell’ the controller how much power is needed. The controller will then manage the available power sources (mainly the power from the hydrogen, via the fuel cell stack; but also from the battery pack), and ‘pass’ this power onto the motor.
  • The electrical motor is the component which actually moves the car forward. After being supplied power, magnetic field forces start interacting with the motor – which then turns the output (the drive shaft, in this case). The drive shaft is connected to the wheels, naturally meaning that once the motor turns, the wheels turn – and the car moves forward!

To Conclude

That’s pretty much all there is to it. It’s fairly interesting to see the similarities with both electric cars and gasoline-powered cars. And in some ways, this is the potential advantage of FCEVs: assuming fuel cell and storage tank prices fall, car manufacturers should hopefully be able to produce hydrogen cars in a fairly cost effective way. After all, their configuration/design and many of the components are the same as the ‘old’ technology in gasoline cars, and also the new technology of electric cars.

But naturally, hydrogen as a fuel source is plentiful: estimates say that up to 90% of the universe is hydrogen-based. Naturally not all that can be used to power FCVs, and the current cost of producing hydrogen fuel to pump into your car is expensive. However if these costs can be overcome, hydrogen cars do seem to have many advantages design-wise.

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