There are 3 main types of a Fuel Cell.

1. Hydrogen Fuel Cell. This is the main one people use nowadays.

2. Solid Oxide Fuel Cell.

3. Alkaline Fuel cell. Made from Alkaline metals.

Fuel cell vehicle is the vehicle which is using fuel cell stack as a moving force instead of conventional combustions engines. They can be fed by H2 - so it will hydrogen fuel cell, or work on the solid oxide fuel cell principles.

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No, iron oxide is a solid.

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Potato power does not technically count as a fuel cell because of its electrochemical processes and solid fuel source.