Improving mass transfer with surface patterning of the porous transport layer for PEM water electrolysis

<h2>Summary</h2> Proton exchange membrane (PEM) water electrolyzers suffer from mass transfer limitations under high current densities. To reduce the mass transfer losses, we develop a surface patterning strategy to treat the titanium felt by laser processing and polytetrafluoroethylene hydrophobic treatment. It achieves a voltage of ∼2.28 V at 5 A/cm², reducing mass transfer losses by approximately 85.4%. Both the visualization characterization and numerical simulation results indicate that the surface patterning titanium felt has sufficient bubble detachment sites, possessing a minimum average bubble diameter of 192 μm and robust bubble dynamics. The surface patterning structure efficiently restricts the bubbles' growth and accelerates their removal, thereby achieving an efficient separate pathway for gaseous oxygen and liquid water transport. These insights not only shed light on the fundamentals of porous transport layer wettability and bubble dynamics but also provide design guidelines for porous media to enable low overpotentials of mass transportation.