Audi's commitment to hydrogen dates back to 2004, when the company released the Audi A2H2. Featuring three hydrogen tanks, a Ballard PEM (Proton Exchange Membrane) fuel cell stack and an electric drivetrain with regenerative braking, it was the company's first proper foray into hydrogen technology.
The trend continued in 2009 with the Q5 HFC (Hydrogen Fuel Cell) and then in 2011 with the second generation Q5 HFC.
The latest vehicle to be powered by hydrogen is the Audi A7 h-tron quattro. Featuring four hydrogen tanks that hold up to 5kg of hydrogen, the car is capable of travelling up to around 540km and will do the 0-100km/h dash in 7.9 seconds.
We had the chance to drive this car at the Audi Future Performance Days event and came away pleasantly surprised with the experience. The A7 h-tron looks and feels just like any other A7. Aside from a giant emergency stop button, the interior of the vehicle is ostensibly the same as the regular diesel or petrol powered A7.
Under the bonnet, though, you won't find a drop of diesel or petrol. The A7 h-tron's hydrogen fuel stack produces power, which sends torque through two electric motors (one at the front and one at the rear) that produce 170kW of power in combination.
Over 300 individual cells form part of the fuel cell stack, with the core of each featuring a polymer membrane. Hydrogen is supplied to an anode, which breaks the hydrogen down into protons and electrons. The protons then move through the membrane to a cathode where they react with air to create water.
At the same time, the electrons are used to supply power to the motors. Each individual cell features around 0.6-0.8 Volts.
Audi then went a little further with the A7 h-tron by making it a plug-in hybrid. So while the hydrogen fuel stack is used to power the car and charge the batteries, a driver can also charge the 8.8kWh battery stack from a wall socket.
Driving the h-tron is quite unique because it makes next-to-no noise. Every now and then you hear a sound from the hydrogen system and a whir from the electric drivetrain, but the rest of the time it's silent and quite pleasing to drive.
With 540Nm of torque available, it sprints along nicely and feels like a genuine driving and ownership proposition.
The fifth generation hydrogen vehicle from Audi will take this further by offering a premium package (the company is yet to confirm which model it will be based on) that can operate at higher temperatures without decreases in performance.
Currently the A7 e-tron suffers significant performance degradation at ambient temperatures above 40 degrees Celsius. The other challenge faced by Audi is increasing the compression of air in the hydrogen fuel cell stack to increase performance.
There is also a power requirement of around 10kW to operate the hydrogen fuel stack, which presents in itself a considerable issue as you need to use a great deal of power to then produce more power.
Dr Armin Burkardt, Audi's head of concept development TDI HEV & fuel cell, said that it has been quite challenging to develop a production vehicle that is lighter, faster and more efficient than the current A7 h-tron, revealing that the fifth generation car will forego plug-in hybrid technology.
"We will change from plug-in technology to just hybrid technology, because we don't need the extra distance from the batteries and it adds additional weight and package demands. It doesn't make sense."
Will there ever be a hydrogen sports car? Dr Burkardt said that it's a challenge, but they wouldn't rule out the possibilities.
"That's hard to say. A sports car is way up higher in terms of power demands and that's a big challenge to increase power, but why not. We are just starting. Throttle response isn't as fast as an electric vehicle, but it is better than a regular combustion engine."
Click on the Photos tab to see more images of the Audi A7 h-tron quattro.