Hydrogen Fuel Cell vs Combustion: Efficiency Duel

The same hydrogen fuel supply feeds two rival ways of extracting its chemical energy. On the left, H2 and O2 burn directly, and the heat has to pass through a Carnot-limited heat engine before any of it becomes useful work. On the right, a PEM fuel cell splits H2 into protons and electrons at the anode, routes the electrons through an external circuit to do work directly, then recombines everything with O2 at the cathode. Watch the live efficiency bars: the fuel cell's ceiling is not set by reservoir temperatures at all.