A hydrogen-powered supercar that can speed from 0-60mph in 3.5 seconds is to be unveiled at this year's Speciality Equipment Market Association (SEMA) show in Las Vegas.The Scorpion from Ronn Motors looks like a gas guzzler with sleek design and aerodynamics clearly taken into account, but under the hood it is an altogether different creature.It carries a 1.5 gallon tank for water electrolysis and uses hydrogen to reach speeds at over 200 mph.The car's Hydrorunner system injects hydrogen directly into the motor, adding an extra 20 per cent to 40 per cent to the vehicle's mileage compared to when it is running on gasoline.Ronn Motors, which started less than a year ago in Austin Texas, is also working on capturing condensation from the air conditioning system to that the water tank self replenishes.Unlike other hydrogen cell vehicles which need regular topping up with the gas, the Scorpion tops itself up, using a battery to carry out electrolysis on the water it carries on board.