Condensation model to reproduce experimentally observed liquid water distributions in gas diffusion layer for polymer electrolyte fuel cells with variation of cell temperature and relative humidity of inlet gas

Improving the performance of polymer electrolyte fuel cells requires reducing the concentration overpotential at high current densities. Since liquid water accumulation in the gas diffusion layer (GDL) prevents oxygen diffusion to the catalyst layer, water management is a critical issue in fuel cell design and optimization. For such a purpose, the use of numerical simulation is desired. In the present study, a new macroscopic condensation model and a two-fluid model are developed. By using a condensation rate constant that depends on the relative humidity, the present simulation successfully predicts the liquid water content in the GDL quantitatively under a wide range of cell temperature and relative humidity conditions, which is experimentally validated using operando synchrotron X-ray radiography. The simulation also provides the state of water oversaturation. At 313 K, the relative humidity exceeds 100% extensively in the GDL except near the gas channel, while oversaturation is mitigated by higher temperatures. Thus, a simulation method incorporating finite phase change rates must improve prediction accuracy at lower cell temperatures and is expected to broaden the applicability of numerical prediction across various temperature and relative humidity conditions.