Japan, China and South Korea have set ambitious targets to put millions of hydrogen-powered vehicles on their roads by the end of the next decade at a cost of billions of dollars.

But to date, hydrogen fuel cell vehicles (FCVs) have been upstaged by electric vehicles, which are increasingly becoming a mainstream option due to the success of Tesla Inc.'s luxury cars as well as sales and production quotas set by China.

Critics argue that FCVs may never amount to more than a niche technology. But proponents counter that hydrogen is the cleanest energy source for autos available, and with time and more refueling infrastructure it will gain acceptance.