By far, the most promising alternative source of energy for cars is the hydrogen-based fuel-cell engine, which USES hydrogen to electricity that, in turn, powers the car.

By far, the most promising alternative source of energy for cars is the hydrogen-based fuel-cell engine, which USES hydrogen to create electricity that, in turn, powers the car.

Then comes the cost of hydrogen-based vehicles. Just the platinum for the catalyst inside a fuel cell costs as much as an internal-combustion engine of equivalent power, according to a recent study.