The idea of using hydrogen as a clean fuel in internal combustion engines is great in theory as the only emission, as it burns, is water; however the problem lies in the creation of the hydrogen in the first place. Manufacturing hydrogen (by electrolysis of water) is hugely inefficient, requiring a lot of electrical energy. This can be accomplished using renewable energy sources, so called Green Hydrogen, but the amount of green hydrogen available currently is minimal. I still think its important to explore this idea of using clean fuels to run old technology but until an efficient method of creating hydrogen is developed I don't think we're really any better off.