Case Study 607 Fuel Cell Component Study
This case study, authored by Daniel Burnett of Surface Measurement Systems Ltd., investigates how relative humidity (RH) influences the surface thermodynamic properties of proton exchange membrane fuel cell (PEMFC) components. Using Inverse Gas Chromatography (IGC SEA), the dispersive and specific surface energies of two membranes (Nafion 1135 and BPSH‑30) and three gas diffusion layers (GDLs) with different hydrophobic treatments (plain, BA, bilayer) were measured at 30 °C under 10 %, 50 % and 90 % RH. Dynamic Vapour Sorption (DVS) provided water sorption isotherms for the same samples. Results show that for both membranes, dispersive surface energy decreases with increasing RH while specific surface energy rises, reflecting greater water adsorption (up to ~13 % of dry weight). BPSH‑30 exhibits higher water uptake and a stronger RH dependence than Nafion. For GDLs, dispersive energy also declines with humidity, but specific energy trends differ: the BA‑treated GDL’s specific energy increases, whereas plain and bilayer GDLs generally decrease, likely due to competitive adsorption of water versus probe molecules. Water uptake for GDLs is orders of magnitude lower (<0.12 % of dry weight) than for membranes. The study concludes that humidity markedly alters surface energetics, which in turn affects water transport mechanisms such as electro‑osmotic drag, back‑diffusion, and pore flooding, underscoring the need to consider RH‑dependent surface properties in PEMFC design and long‑term operation.
Topics
Relative Humidity as a Critical Parameter for PEMFC Performance
Explanation of why feed‑stream humidity governs ionic conductivity, water management, and overall fuel‑cell efficiency.
IGC SEA Methodology for Quantifying Dispersive and Specific Surface Energies
Details of the inverse gas chromatography approach, probe molecules, van Oss equations, and rescaling corrections used to extract surface energy components.
Dynamic Vapour Sorption (DVS) for Water Sorption Isotherms
Procedure for measuring mass change of membranes and GDLs across 0–95 % RH at 25 °C, yielding quantitative water uptake data.
Humidity‑Dependent Surface Energy Trends in Nafion 1135 vs BPSH‑30 Membranes
Comparison of how dispersive energy decreases and specific energy increases with RH for the two membranes, highlighting BPSH‑30’s greater water uptake and stronger RH sensitivity.
Surface Energy Behaviour of GDLs with Different Hydrophobic Treatments
Investigation of plain, BA, and bilayer GDLs, showing uniform decrease in dispersive energy with RH but divergent specific‑energy responses (BA increases, plain/bilayer decrease).
Comparative Water Uptake: Membranes versus GDLs
Quantitative contrast showing membranes absorb >13 % of their dry weight at high RH, while GDLs absorb <0.12 %, indicating vastly different wetting regimes.
Implications of Surface Energy Changes for Fuel‑Cell Water Management
Discussion of how altered surface energetics affect electro‑osmotic drag, back‑diffusion, pore flooding, and long‑term performance of PEMFCs.
Conclusions and Recommendations for Future Fuel‑Cell Component Testing
Summary of key findings and suggestion to extend IGC SEA/DVS studies to other components and broader temperature/RH ranges.