Making hydrogen fuel, however, is not emission free: today, making most hydrogen fuel involves natural gas in a process that releases CO2 into the atmosphere. (sciencedaily.com)
However, most hydrogen on earth is already locked into H2O (or other molecules), and can not be used for power. (sciencedaily.com)
But most hydrogen today is made from natural gas, which brings the cost of hydrogen down closer to that of gasoline but makes the FCEV about 50 percent less carbon - intensive than a gasoline vehicle. (scientificamerican.com)