How do Hydrogen Cars work?
The above diagram shows the basic required components needed for a hydrogen powered car. Some components are shared with a Battery Electric Vehicle (BEV) such as battery, and traction motor, these are still required.
Compressed hydrogen and oxygen from the atompshphere is fed into fuel cell where a reaction occurs which generates electricity, water and heat. This reaction happens at a fixed rate, this is used to charge the battery which acts as a buffer for the power used by the traction motor. 
- The overall energy efficiency of hydrogen fuel cell can be seen in the diagram above, the main issue is the massive energy losses when converting electricity to hydrogen and back again it can be seen in the above diagram.
- These losses will push up the price of usage considerably as much more energy is required.
- Currently hydrogen is generated from fossil fuels .
- Hydrogen is classed by the NFPA 70s explosive rating of 4 which is the highest, this is due to the fact only a small amount of oxygen (4%) is required to start a reaction, this makes it more dangerous than petrol when there is a leak. 
- Hydrogen fuel cell cars still require a battery, though smaller as a fuel cell will output a fixed amount of energy which requires buffering to allow of acceleration. Effectively you have a battery ev with a lot of extra equipment.
- With range of BEV’s increase every year and costs coming down, Hydrogen fuel cell cars will be just too expensive to justify for consumer cars.