Downsizing NiCoS Pentlandite by Laser Fragmentation in Liquids for Enhanced HER Performance

Pentlandites have demonstrated promising hydrogen evolution reaction (HER) performance and are particularly attractive due to their earth abundance and direct utilization as naturally occurring ores. However, their micrometer-scale particle size limits the accessible surface area and effective catalyst utilization. Laser fragmentation in liquids (LFL) offers an approach to overcome this limitation by producing nanoparticles while largely preserving the structure and composition of the pristine material. Therefore, picosecond LFL was employed to fragment Ni 2.25 Co 6.75 S 8 pentlandite microparticles into nanoparticles with the aim of enhancing their HER performance. By systematically varying the laser fluence (200‑800 mJ/cm²) and the induced pulses per volume (24-72 PPV), optimal fragmentation conditions were identified, while the resulting structural and chemical composition as well as the HER performance were comprehensively investigated using electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, thermogravimetric analysis, electron paramagnetic resonance spectroscopy, and electrochemical characterization. The microparticles were successfully fragmented into 10-40 nm nanoparticles while largely preserving their crystal structure, however with indications of composition changes at higher fluences. Laser processing at fluences of ≥600 mJ/cm² reduced the HER overpotential by up to 50 mV (≈15%) compared to the pristine material. This enhancement is most likely associated with the formation of a thin carbon shell and an increased concentration of paramagnetic species, indicating a higher defect density in the laser-fragmented nanoparticles. The laser-fragmented catalysts were further successfully integrated into a zero-gap electrolyzer, demonstrating their applicability under a technologically relevant reaction environment. This approach demonstrates the potential of LFL as a promising tool for converting micrometer-sized catalyst powders into nanostructured materials while preserving their crystal structure and improving their catalytic performance, thereby enabling catalyst optimization beyond the capabilities of conventional processing methods.