FOR decades, hydrogen has been the Dracula of automotive fuels: Just when you think a stake has been driven through its zero-emissions heart, the technology rises from the grave.

In 2015, even with gasoline cheaper than it has been in years, hydrogen is back to haunt those who insist that battery electric vehicles are the long-term solution for reducing fossil fuel consumption and carbon dioxide emissions.

This time — with hydrogen fuel cell costs falling significantly, and a tiny yet budding network of public fueling stations — automakers are placing their latest long-odds bet on hydrogen cars.

Hyundai has been first in the latest wave of fuel cell models, which are actually electric cars with one important difference: Instead of a plug-in battery that draws power from the electrical grid, a fuel cell generates power from an electrochemical reaction between onboard hydrogen and oxygen in the air. Clean water trickles out the tailpipe as the only byproduct.