JAES Learning

VISIT OUR YOUTUBE CHANNEL
Jaes Sponsor - Basket



How do hydrogen cars work?

There has been quite a discussion lately about an alternative fuel car: the HYDROGEN CAR! This is the green alternative to the classic combustion engine.

When talking about hydrogen cars, we don’t mean an hydrogen fuelled engine, but an electric engine getting power from an hydrogen fuel cell.

Today there are two ways to make an electric engine car move:

1. LITHIUM-ION batteries, which is the most common technology, and in 2020 1,42 million pieces have been sold, 147% more than 2019;
2. The FUEL CELLS, that are hydrogen fuel cells, part of innovative vehicles we’re going to talk about.

The first thing to say about hydrogen powered cars is that they have zero pollutant emissions. The only by-product coming out from the exhaust pipe is water vapour, which represents a great alternative in a world, where the rate of pollution has been increasing every year.

Let’s go deeper on how these kind of vehicles work.

Hydrogen cars use a fuel cell put in the centre of the vehicle; a fuel cell is an electrochemical device that converts chemical energy directly into electricity. The operating principle of fuel cells was discovered in 1839 by the British physicist William Grove. Next to the fuel cell there is a carbon fibre tank, which can resist to a 700 bar pressure during refuelling.

In the fuel cell takes place the reverse process to the electrolysis, that we analysed in another video (“How to produce hydrogen”), and combining hydrogen and oxygen generates electricity that powers the motors of the vehicle.

The fuel cell consists of an anode and a cathode, that are a negative and a positive electrodes. The anode is saturated with oxygen, the cathode instead oxidises hydrogen; by combining the two elements there is a chemical reaction (H2 + ½ O2 ? H2O) that generates electricity obtaining heat and water as waste material.
The electricity produced flows directly into the electric motor making the car move.

One of the best qualities of hydrogen is its very high specific energy density, 40,000 watt/kg, 236 times more than lithium-ion battery specific energy. This means that hydrogen cars are lighter and have more autonomy; moreover, refuelling a hydrogen tank takes few minutes compared to a lithium battery which takes hours.
With all these advantages, an obvious question comes: why then aren’t hydrogen cars widespread?
The main problem is the production itself. There are several ways to produce hydrogen: the most common one is called “steam reforming”, but it is very polluting and requires fossil fuel to operate. Another big issue is distributing hydrogen to the service stations. Unfortunately all these complex processes have fuel price and air pollution increased.
A valid alternative that many companies are developing is to produce hydrogen in small plants built inside the service stations, possibly by electrolysis process, that is far less polluting than steam reforming. Thanks to this method they can reduce costs and polluting emissions caused by transport of fuel.

We’ve talked about peculiarities of hydrogen as a fuel, but there’s also a lot to say about the particular storage process. Hydrogen has a very low density as a gas, and there are two ways to increase its actual density:

1. By compressing the element with a force of 790 atmospheres and injecting it into pressurised tanks; however energetic efficiency decreases by 13%;
2. Or by cooling process; we must say that the hydrogen is the most difficult element to liquefy, after helium, so it must reach the temperature of -253° causing though an efficiency decrease by 40%.

Liquefying hydrogen by cooling allows to use smaller tanks than the pressurised ones, however reaching such low temperatures means an enormous effort. That’s why pressurisation is preferred rather than cooling.

When hydrogen gets stored, it’s ready to be injected into vehicles’ tanks from a special fuel station, specifically designed for that purpose. Hydrogen is compressed, then stored in special pipes called BUFFERS, and passes through a heat exchanger to be cooled right before flowing into the vehicle.

At gas station methane and LPG are usually compressed at 350 bar pressure. Due to its characteristics, instead, hydrogen is compressed at 700 bar pressure, permitting us to fill the tank in few minutes.

We’ve just made a complete overview of these amazing hydrogen vehicles, which aim to achieve great results for the environment since they don’t have pollutant emissions. Many companies are investing in R&D to make hydrogen cars become the future of sustainable mobility.

Do you really think that hydrogen cars will be the right path to save our planet from pollution? Let us know.