Whats stopping the general use of hydrogen in cars?

Answer 1

Currently, hydrogen fuel cells are costly to produce and fragile.

Freezing conditions are a major consideration because fuel cells produce water and utilize moist air with varying water content. Most fuel cell designs are fragile and cannot survive in such environments at startup but since heat is a byproduct of the fuel cell process, the major concern is startup capability. Although service life is coupled to cost, fuel cells have to be compared to existing machines with a service life in excess of 5000 hours Hydrogen has a very low volumetric energy density at ambient conditions, equal to about one-third that of methane. Even when the fuel is stored as a liquid in a cryogenic tank or in a pressurized tank, the volumetric energy density (megajoules per liter) is small relative to that of gasoline.

In order to distribute hydrogen to cars, the current gasoline fueling system would need to be replaced, or at least significantly supplemented with hydrogen fuel stations. information from wikipedia