Analyze the thermodynamic efficiency limits of fuel cells compared to heat engines.

Fuel cells directly convert chemical energy to electricity without combustion, bypassing Carnot limitations. Theoretical efficiency is ΔG/ΔH where Gibbs free energy ΔG represents available work and ΔH is enthalpy change. For hydrogen fuel cells, this is 83% at standard conditions, much higher than Carnot efficiency at practical temperatures. However, actual efficiency depends on activation, ohmic, and concentration overpotentials that increase with current density. Practical fuel cell efficiency is 40-60% for power generation. At partial loads, fuel cells maintain high efficiency unlike heat engines. When considering hydrogen production efficiency (electrolysis 70-80%, reforming 65-75%), well-to-wheel efficiency becomes comparable to advanced heat engines.