Fuelling a Hydrogen Car

21 August 2012

Interview with

Aman Dhir, University of Birmingham

Meera -   The plan for a hydrogen economy involves the increased use of hydrogen as a fuel for transport, particularly in hydrogen powered cars.  However, in this context, hydrogen isn't used as a direct energy source like coal or oil, but is instead used as an energy carrier and it needs to go through a fuel cell in order to produce the electricity needed to power a motor, as Aman Dhir explained when I met him on campus alongside one of the university's hydrogen cars.

Aman -   There are 6 different types of fuel cells and the simplest to explain probably is a so-called proton exchange membrane fuel cell (PEM fuel cell), which conceptually just joins hydrogen ions and oxygen ions together to produce water and the electrons are then released around an external circuit which can be used in the application.  The fuel cell is made up of several different layers.  The so-called membrane electrode assembly which consists of a catalyst layer, a gas diffusion layer, and a membrane: times 2.  So you have a catalyst layer and a gas diffusion layer on both sides of the electrode.  One electrode is used for the fuel, so in this case, hydrogen so H2 comes in and is broken down to H+ ions.  On the other side, the air comes in and oxygen is grabbed, so it's the oxygen side.  The oxygen O2 is broken to O2 - and the H+ ions migrate from one side through the membrane and join with the O2 - on the other side to produce the water and the electrons then travel around the external circuit which can then be applied to any load that requires electricity such as a motor, a light bulb, whatever.

Meera -   Well we are in the engineering lab here at the university and you've got a hydrogen car in front of us.  So it's about the size of say, a smart car.

Aman -   So it's approximately 2 ½ meters in length and about 1 ½ meters to 1.8 meters in height, and about 1½ meters in width.  So yes, it's a super mini-sized vehicle.

Meera -   How is this really designed then?  So you've got the fuel cell here at the front of the car.  How is this all combined together to make this car move?

Aman -   Well, the powertrain behind this hydrogen hybrid vehicle - the key thing it's actually a hybrid; it's not a pure hydrogen vehicle - is that the fuel will come in and be stored in a hydrogen tank at 350 bar.  It is then fed into the fuel cell and the fuel cell does its job of converting the hydrogen into H+ ions and then the electrons are freed.  And the electrons then go forward to either charge a set of batteries or power an electric motor.  So primarily, it will charge an electric battery and the batteries will then drive the motor, and the motor then drives the wheels.  So this vehicle will give you a 0-60 of 6.1 seconds.  So essentially, it's no different to an electric vehicle.  80% is similar.  The only difference is that you don't plug it into a wall to get your electricity.  We generate our own electricity on-board.

Meera -   The hydrogen used by the fuel cell is compressed and stored on-board the vehicle within a cylindrical tank holding 600 grams of the gas at a pressure of 350 bar or roughly 345 atmospheres.  But because hydrogen is highly flammable, the design also needs to take this into account.

Aman -   Along each step in the design is designed to the ISO standards.  It is as safe as any other vehicle on the road, if not safer.

Meera -   What does the tank consist of?  What say, makes this safe?

Aman -   This tank is actually extra light.  It's road aluminium reinforced with carbon fibre and Kevlar, so the thing is bullet proof.  It's that well-designed.  If you compare that to let's say a plastic petrol tank or diesel tank, if you don't get out of your vehicle within 4 minutes, they'll assume you're dead because they're designed to collapse after 4 minutes.  This thing will stay alive, so you are inherently safe in this vehicle.

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