Basically, the only by-product (=the pollution) of the hydrogen oxidation is water. Can it be any more clean?Originally Posted by Johanna
However, the total environmental footprint depends on the way this hydrogen was obtained. It is yet to be proved (=unknown) that hydrogen could be mined from the certain geological formations. Presently, the most common way to produce hydrogen is to extract it from water by means of electricity. So, technically, hydrogen is more like an energy carrier. If the clean energy (solar, wind, geothermal, etc.) is used for the extraction, the environmental impact of operating such plane is very low (i.e. there are other factors unrelated to fuel emissions).