Cars powered by fuel cell
a) Do not emit carbon dioxide but water vapor
b) They are quieter but
c) They are still much more expensive than conventional both in their construction and in their use and maintenance.
d) In order this type of vehicles to become common station selling liquid hydrogen are required.
e) These station selling liquid hydrogen as well as the cars' tanks should be constructed to resist high pressure.
f) Also a safe way to transport hydrogen from the place of manufacture to station selling liquid hydrogen should be established.  This task is a very difficult one because hydrogen reacts instantly with oxygen and therefore any leak will cause explosion.
Explosion will also happen, if such a car will be involved in a nasty crash.
It should be understood that fuel cells are not energy form but "energy store". When hydrogen is burned produces water. In order to extract hydrogen from the water electrical energy is needed in order to split water into hydrogen and oxygen. Thus, any pollution of the environment shifts to the area where the electricity is generated.