Tipped as the future of green motoring, hydrogen cars are virtually emissions-free and both simple and fast to refuel.
So what are they and how soon will we be driving them?
How do hydrogen cars work?
As their name suggests, they use hydrogen as a fuel to power the car.
Colourless, odourless hydrogen gas passes through a fuel stack, where it interacts with oxygen. This process both generates the electricity and creates water, which is the car's only emission and dribbles out from a little tube at the back.
Like electric cars, hydrogen cars using hybrid technology are quiet to drive. But the hydrogen models are quicker to refuel and have a longer range.
For example, the tank of Toyota's Mirai holds 5 kilograms of compressed hydrogen. The car's range has not been tested in Australia but in Europe it takes about three minutes to refuel a tank, which will last about 550 kilometres.
It's worth pointing out that hydrogen fuel cell technology is not new — NASA used them to power rockets for decades — but car manufacturers are now able to make fuel cells small and mobile enough to fit inside passenger cars.
How green are they?
They have the potential to be one of the cleanest cars on the road.
Their only emission is water, but the biggest hurdle to fulfilling their green potential is that the hydrogen to power the cars in Australia is now almost entirely sourced from fossil fuels, such as natural gas.
This could change if plans for a home-grown renewable hydrogen industry are successful.
It would ensure a source of hydrogen generated via renewable energy like wind or solar power.
What's it like to drive one?
It feels like driving a hybrid car, which is not surprising because they use similar technology.
You press a button to turn the car on and there's a barely audible hum as the motor starts.
There are only two obvious signs that it's a hydrogen car.
One is the H20 button, which prompts the purge of water from the system (this also happens automatically when the car is turned off), and the other is an interactive infographic on the dashboard which shows the chemical activity going on behind the scenes.
How long until we will be driving hydrogen cars on our roads?
Your neighbour is unlikely to be pulling into their driveway in the latest hydrogen car anytime soon.
Firstly, you can't buy hydrogen cars in Australia yet. In fact, there are only four demonstration models in Australia — one owned by Hyundai and the remaining three by Toyota.
And secondly, even if you had one, you would have nowhere to refuel it.
As everyone in the industry acknowledges, the biggest impediments to widespread take-up of the cars are the sheer logistics and expense of building the refuelling infrastructure for everyday use.
For example, Toyota estimates it costs up to $2.3 million to build a medium-sized retail refuelling station in Europe or the US. The company has built itself a portable refueller, while Hyundai has one at its Sydney head office.
For these reasons, industry pundits agree it makes sense to promote hydrogen car use in densely populated areas of big cities.
How about other vehicles?
Toyota's manager of advanced technology vehicles, Matthew Macleod, said there is a lot of interest from government and industry in using hydrogen to power trucks and buses which could use a common refuelling hub.
For example, in Melbourne, Moreland City Council plans to convert some of its diesel trucks to hydrogen and build a commercial refuelling station.
South Australia last week released its hydrogen road map, which outlines its intent to take the national lead in driving a hydrogen economy, including a $8.2m trial of a hydrogen bus fleet and refuelling station.
Western Australia trialled hydrogen buses last decade, but found it difficult to find an affordable and reliable source of hydrogen.