Like electricity, hydrogen is more of a energy storage mechanism than an energy source. The most popular application of hydrogen in transportation (and other applications) is in a fuel cell. A fuel cell operates by passing hydrogen across a membrane that strips away electrons, thus generating electricity, and emitting only water (H2O) as a byproduct. In fuel cell vehicles, that electricity is used to power an electric motor, as with an EV; thus, a fuel cell is essentially just a different sort of battery. Fuel cell vehicles enjoy all of the benefits of electric motors (quiet, efficient, durable), but the fuel cells themselves have been expensive with limited life. The most notable advantages of fuel-cell vehicles over electric vehicles are more rapid recharging time and the relative ease with which extended ranges can be achieved.
The other way to use hydrogen as a fuel is in combustion. Directly burning hydrogen is much cleaner than gasoline or diesel combustion, and some companies are exploring hydrogen combustion in passenger vehicles.
As with electric vehicles (EVs), the main appeal of hydrogen for Valley 25x’25 is the hope that in the intermediate term it can be produced using renewable sources. Thus far, most hydrogen is produced from natural gas (a fossil fuel). Unlike EVs, however, hydrogen-powered vehicles are not widely available and have lower well-to-wheel efficiency than EVs.