Taxi driver Theo Ellis, the first person in Europe to drive Toyota Motor Corp.'s hydrogen-powered Mirai sedan for business, loves telling passengers about the technology that emits nothing but water.

They ask him about its costs, greenness, and the majority inquire about safety. To his passengers, the word "hydrogen" evokes memories of the Hindenburg, the airship that was destroyed in half a minute when it caught fire in 1937, or the hydrogen bomb, a successor to what the U.S. dropped on Japan to end World War II.

"That will put people off," Ellis, who drives for London-based Green Tomato Cars Ltd., said in an interview. "A lot of people mention that. As soon as you mention hydrogen it's the first thing on their mind."