Ferromagnetic Hybrid\n2D FeS/FeS<sub>2</sub> Nanostructures\nas Electrocatalysts for the Hydrogen Evolution Reaction

The development of highly effective and durable catalysts\nfor the\nhydrogen evolution reaction (HER) using abundant earth materials is\ncrucial for advancing the hydrogen economy. In this work, we present\nan approach for synthesizing two-dimensional (2D) combined phase materials\nwith tunable catalytic and magnetic properties. We successfully synthesized\nferromagnetic pristine pyrite (FeS<sub>2</sub>) nanoparticles (NPs)\nand hybrid 2D troilite (FeS) nanosheets utilizing the hot-filament\nmetal–chemical vapor deposition (HFMCVD) technique. The mixed\nphase of 2D FeS/FeS<sub>2</sub> exhibited an exceptional HER catalytic\nperformance, achieving a low overpotential of 40 mV at 10 mA·cm<sup>–2</sup> current density. Additionally, the magnetic saturation\nand magnetic moments of the mixed phase 2D FeS/FeS<sub>2</sub> materials\nwere significantly higher compared to pristine FeS<sub>2</sub> NPs.\nThis increase is attributed to a higher density of unpaired electrons\nand spins in the mixed phase hybrid materials. These enhanced magnetic\nproperties facilitate more efficient electron transfer, leading to\nsuperior catalytic performance with low overpotentials during HER.\nThe ferromagnetic 2D FeS/FeS<sub>2</sub> material holds promise as\nan electrocatalyst for next-generation water splitting as well as\nenergy conversion applications. Moreover, our computational results\nbased on DFT are consistent with the experimental findings.