Why is fuel cell energy conversion efficiency unrestricted by the Carnot cycle?
Fuel cell chemistry can be converted directly into electrical energy by an electrode reaction, which is irrelevant to the Carnot cycle and is certainly not limited by the Carnot cycle.
Carnot cycle is the heat machine, as long as the heat through the expansion of heat generated by the heat engine will be limited by the maximum efficiency of the carnot cycle. The fuel cell is a chemical reaction that converts chemical energy directly into electrical energy.
Carnot cycle is the use of heat, while the fuel cell is basically no heat, or very little, its principle is different.
