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.

Automated summary

This study focuses on the production and investigation of NiFe2O4 spinel ferrite nanoparticles doped with different masses of Se. The results show that the chemical content of Se has an impact on the crystal structure, microstructure, and magnetic properties. Superparamagnetic and ferrimagnetic states are observed in a wide magnetic field range. The magnetic characteristics do not change significantly when Se-substitution is less than 2.0%. However, a nonlinear dependence of magnetic parameters is observed for samples with Se-substitution greater than or equal to 2.0%. The undoped sample and NiFe2O4+x%Se exhibit soft magnetic behavior.