A gradient porous transport layer enabling a high-performance proton-exchange membrane electrolysis cell

Large-scale green hydrogen production through proton-exchange membrane electrolysis cells (PEMECs) is constrained by high costs. Operating PEMECs at high current densities while minimizing overpotentials, particularly the mass transport overpotential due to intense water-oxygen two-phase flow, is crucial. The porous transport layer (PTL) plays a key role in facilitating water-oxygen two-phase flow and affecting ohmic resistance and catalyst utilization. In this study, a gradient PTL has been developed by introducing titanium mesh with tunable pores between the titanium felt and the flow field. The woven mesh structure with large pores facilitates water transport under the ribs, while the titanium felt reduces ohmic resistance and improves catalyst utilization. Experimental results demonstrate that the gradient PTL with a single layer of titanium mesh (pore size: 0.6 mm) can reduce the mass transport overpotential from 0.478 V to 0.206 V at 5 A/cm2 and maintain low ohmic and activation overpotentials compared with the conventional PTLs. Additionally, the gradient PTL with two titanium mesh layers (pore sizes: 0.6 mm and 0.28 mm) can further facilitate water transport, reducing mass transport overpotential to 0.149 V at 5 A/cm2. Numerical simulations reveal that the developed gradient PTL increases the volume fraction of liquid water and ensures uniform water distribution in the catalyst layer. The combined results indicate that the gradient PTL design is promising for enhancing mass transport performance while maintaining low ohmic resistance and high catalyst utilization, making PEMECs more viable for large-scale hydrogen production.