 With either method, the only byproduct from the spent hydrogen is water, however during combustion with air NOx can be produced.Honda introduced its fuel cell vehicle in 1999 called the FCX and have since then introduced the second generation FCX Clarity.Limited marketing of the FCX Clarity, based on the 2007 concept model, began in June 2008 in the United States, and it was introduced in Japan in November 2008.