Transition Metal-Driven Variations in Structure, Magnetism, and Photocatalysis of Monoclinic M3Se4 (M = Fe, Co, Ni) Nanoparticles

The transition metal selenides (MxSey) have gained attention for their unique physical and chemical properties, especially those associated with the transition metal (M). Despite advancements in synthesis, fabricating these selenides is challenging due to their complex stoichiometry and high asymmetry. One such system is monoclinic iron selenide (Fe3Se4), which can be used in permanent-magnet technologies and serve as a model system for understanding magnetism. This study focuses on fabricating monoclinic M3Se4 (M = Fe, Co, or Ni) compounds via thermal decomposition, examining how solution chemistry influences their morphology and properties. With a Curie temperature of about 322 K, Fe3Se4 is ferrimagnetic, whereas Co3Se4 and Ni3Se4 are paramagnetic between 5 and 300 K. The latter two compounds also show higher catalytic activity for hydrogen evolution in water splitting, with maximum H2-evolution rates of 1.01, 5.16, and 6.83 mmol h-1g-1 for Fe3Se4, Co3Se4, and Ni3Se4, respectively.