Enhancing PEM Fuel Cell Efficiency with an Integrated Organic Rankine Cycle Using Low-GWP Working Fluids

Abstract

Proton exchange membrane fuel cells (PEMFCs) offer high-efficiency, zero-emission electricity, yet 45 % to 60 % of their input chemical energy is lost as low-grade waste heat. In response to this problem, this study presents a thermodynamic analysis of a 50 kW PEMFC thermally integrated with a sub-critical organic rankine cycle (ORC) to convert this waste heat into additional power. Using a high-fidelity model validated with errors below 5 %, this study compares low-global warming potential (GWP) working fluids (R1233zd(E), R1234yf, R1234ze(Z)) against the legacy R245fa under a practical fixed-state-point control strategy. The results demonstrate up to 3 % increase in total electrical efficiency, driven by the successful conversion of the PEMFC’s low-grade waste heat into additional net power output by the ORC bottoming cycle. The main novelty of this research lies in the first comprehensive demonstration that a 3 % system efficiency enhancement can be sustainably achieved by integrating low-GWP working fluids and a practical fixed-state-point control strategy to ensure stable operation. The analysis confirms that the thermodynamically limited 10 % ORC thermal efficiency can be realized without compromising energy recovery potential, proving that the pursuit of sustainability is compatible with enhanced system performance. R1234yf is identified as the superior low-GWP fluid for high-load operations, while R1233zd(E) proves optimal for low-load conditions, validating a robust pathway for designing next-generation, eco-friendly fuel cell systems.