What are the positives of changing to hydrogen powered cars?

Positives of using Hydrogen to power internal combustion engines include that the exhaust is non-polluting and that the engine runs cleaner, internally.

Explanation:

Using Hydrogen to power a car engine provide power by internal combustion of Hydrogen, H2, and Oxygen O2. The resulting exhaust is almost totally water. Mixing H2 and O2 causes the exhaust to become H2O, water:

2H2 + O2 → 2H2O

The operation of Hydrogen internally cleans the valves and other internal parts. The oil remains clean even after many hours of operation