In the past year, three automakers--Toyota, Honda, and Hyundai--have debuted new hydrogen cars. The biggest launch is likely the Toyota Mirai, which will hit U.S. streets this fall. Fuel cell vehicles (FCVs) have for years been the white whales of the clean-vehicle set. They emit only water; they fill in three minutes (vs. up to several hours for a traditional electric); and their range is comparable to gas-powered cars, about 300 miles. But automakers have avoided them, mainly because of infrastructure concerns: There are only a dozen hydrogen filling stations in the U.S., mostly in Southern California. That, too, is changing. Last year, the state set aside $200 million to build 100 more hookups by 2020. And that just may drive a national trend.