How do hydrogen fuel cells work?

The drive to reduce global emissions is a huge priority for car manufacturers (whether through their own initiative or by government regulation), but many alternative fuel sources have drawbacks.

Hybrid vehicles can switch to pure electric power for relatively short periods, and although fully electric cars are becoming more popular as their driving ranges increase we’re still some way from matching the range offered by conventional combustion engines.

This is where hydrogen cars come in.

What are hydrogen fuel cell cars?

In many ways, hydrogen fuel cell vehicles work much like regular electric vehicles – they use electric motors to transmit power through the wheels. The differences lie in the power source which drives those motors. EVs make use of a large number of batteries (usually lithium-ion – as you’d find in a laptop computer) whereas a fuel cell vehicle is fuelled by power generated in a hydrogen fuel cell. The hydrogen is stored inside a tank in much the same way that petrol or diesel is, and the process of refuelling is almost identical too.

The ‘sciencey’ bit

Electricity is generated in a fuel cell via a relatively simple chemical reaction – similar to how batteries work. Hydrogen from the tank is pumped towards a positively charged terminal, while at the same time air is fed from outside towards a negatively charged terminal. The positive end is made from platinum, which acts as a catalyst in this process.

The system essentially forces the hydrogen electrons to generate electricity as they move through the cell towards the positive end. The power the flows through the electric motor, which drives the wheels just like any other electric car. This circuit terminates at the negative terminal of the cell. Meanwhile, the protons are directly attracted to the negative terminal.

So what’s the significance of the air?

This is where the clever stuff happens. To remove all the leftover products, the air feed allows them to react with the oxygen in the air, which is then fed along an exhaust pipe. The by-product of this reaction? Water. Pure, clean water. The only thing emitted from a hydrogen car’s tail pipe is water vapour and steam, making it one of the cleanest fuels available.

Who produces fuel cell vehicles?

Two of the biggest makers of hydrogen powered cars are Honda and Toyota. The latter recently released the Mirai, which can achieve a highly reasonable 300 mile range from its practical – yet highly aerodynamic – saloon body shape. It produces 153hp and 247lb ft of torque, and it only takes five minutes to fill the tank.

Honda is due to create a replacement for its hydrogen-powered FCX next year, which will offer a similar range to the Toyota. Meanwhile, BMW is working on its own vehicles, too – and the mighty Volkswagen Group’s hydrogen cars don’t look far away either (see photo below).

If it’s so clean, why isn’t everyone driving a hydrogen car?

Unfortunately there are a few hurdles to overcome before the technology becomes mainstream. Despite the fact that hydrogen is the most abundant chemical element in the universe, it generally likes to hang about stuck to other elements in chemical compounds. That means that other substances (such as fossil fuels or water) must be broken down into their constituent parts in order to extract pure hydrogen.

This can often be complicated and take a lot of energy to achieve, though through the electrolysis of water, it is possible to extract it cleanly (as long as the source of the electricity is renewable).

Once the hydrogen has been extracted, the next issue is the need for infrastructure to make it a viable alternative. There are approximately 11,000 petrol stations throughout the UK, whereas hydrogen stations can be pretty much counted on your fingers and toes.

Storing hydrogen – whether in your car or at a filling station – is also a potential issue. If you wish to store it under pressure, you have to use energy compressing it, effectively wasting the energy you’d save using hydrogen. If you store it under atmospheric pressure it doesn’t use energy but it takes up a lot of space, making it impractical.

As it stands, there has been nowhere near as much investment in fuel cell tech as there has been in pure electric cars, let alone the hundred-or-more years of development of the internal combustion engine. As a result, the technology is far more expensive than either of the most viable alternatives.

The costs are reducing all of the time though, and once they’re cheap enough, fuel cell vehicles will offer a genuinely renewable energy source for our cars of the future.

Hydrogen high-noon

Hopefully, like us, you’re waiting for the arrival of hydrogen cars with baited breath. If you can’t wait for technology to catch up with your eco-friendly ambitions, why not take a look at our best electric cars article. For more options, head over to our deals page to see our latest discounts.

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