Laser micromachining strategies for high quality perforation of thin titanium foils to produce microporous layers for polymer electrolyte membrane electrolysis

Microporous layers (MPLs) have emerged as a promising approach to enhancing the efficiency of polymer electrolyte membrane electrolysis cells. While there are many studies addressing the mass-perforation of foil materials, the process of perforation of thin titanium foils remains challenging. A significant challenge in the processing of titanium foils pertains to effective heat management during laser processing. Even at low fluences and ultrashort pulses, thermal deformation occurs, resulting in the displacement of the foil material and, therefore, loss of perforation. This deformation is observed to be fluence-dependent. Furthermore, experimental evidence has demonstrated that a titanium foil does not undergo significant oxidation during the perforation process, which is a fundamental prerequisite for utilization in an electrolysis cell. Energy-dispersive x-ray spectroscopy analyses provide corroboration for this finding. The present study investigates three “on-the-fly” strategies for the production of MPLs: a conventional drilling process, an optimized drilling process, and an optimized multispot (9 × 1) drilling process. The experiments are conducted with a 10 μm-thick titanium foil, which is perforated over an area of 20 × 20 mm2 using a femtosecond laser. The objective is to achieve the highest possible perforation rates, while maintaining high quality. The perforation is analyzed by examining the ablation rates and the hole geometry. This allows for the production of hole exit diameters in the single-digit micrometer range while using comparatively high focal lengths (f = 100 mm). Finally, the processing times are analyzed and an estimate is given for scaling to larger areas.