Which is more efficient way to generate energy using hydrogen: direct hydrogen combustion or through fuel cell? Please explain so that even a primary school student can understand.
If you want energy as heat, the best way to generate energy is combustion. If you want energy as electricity, the best way is a fuel cell (which also produce some heat). If you want mechanical work, using hydrogen like gas or oil in a usual combustion engine, the yield would be a maximum of $30$%. The best yield would be to produce electricity in a fuel cell, then use this electricity to run an electric motor. Here the yield is of the order of $60$%, twice as much as the combustion engine.