Structural parameters, energy states and magnetic properties of the novel Se-doped NiFe2O4 ferrites as highly efficient electrocatalysts for HER

This study is devoted to NiFe2O4 with different masses of Se (NFO + x%Se) (x = 0.0-4.0%) spinel ferrite nanoparticles production and investigation. The results of the crystal structure, microstructure and magnetic properties are presented as a function of the chemical content of the NFO + x%Se. Superparamagnetic (at 300 K) and ferrimagnetic (at 10 K) states are observed for all samples in the wide magnetic field range. The field de-pendencies of the magnetization show that Se-substitution does not change the main magnetic characteristics when x < 2.0%. We observe a non-linear dependence of magnetic parameters for sample with x & GE; 2.0% (for NFO+2%Se, we determine the increase of the main magnetic parameters for 20% of the average values and the minimum values belong to the NFO+3%Se). The undoped sample and NiFe2O4+x%Se are soft magnets and characterized by the low coercivity (varying in the range 560-647 Oe). At T = 10 K squareness ratio (Sq. = Mr/Ms) is in a range of (0.216-0.318). This indicates a preferable single-domain state of crystallites, which differs from the magnetic structure at T = 300 K. Furthermore, the NFO + x%Se (x = 2.0) have a low overpotential of about -327 mV, and a small Tafel slope of 91 mV/dec, which makes it a better for HER (hydrogen evolution reaction) catalyst than the undoped NiFe2O4.