Enhanced hydrogen evolution activity and magnetic/electrodynamic properties of Fe/Bi co-doped nano CoNiV spinel oxides

In this study, Fe/Bi co-doped CoNiV nano spinel oxides (Co_0.5Ni_0.5Fe_xBi_xV_2–2xO₄ (x ≤ 0.040) NSOs) were synthesized through a hydrothermal approach. Employing M-H curves at 300 K (Room temperature, RT) and 10 K, magnetic properties of Fe/Bi doped CoNiV (x ≤ 0.040) NSOs are examined. It is observed that they possess paramagnetic and superparamagnetic nature at RT and 10 K, respectively. Substitution of V atoms with Fe/Bi yields fluctuations of magnetic parameters (with a maximum at x = 0.030) with growing doping content at 10 K. The accompanying saturation magnetization (Ms) at 10 K is estimated through the Langevin function, giving rise to the highest (lowest) M_s value at x = 0.030 (0.000, undoped NSOs). Our findings demonstrate that magnetic characteristics of Fe/Bi doped CoNiV (x ≤ 0.040) NSOs can be adjusted by controlling Fe/Bi dopants. The electrocatalyst Fe/Bi doped CoNiV (x = 0.04)@CS nanoelectrocatalyst demonstrated notable performance in the HER, with an overpotential of 271 mV, a Tafel slope of 131.07 mV/dec, and remarkable stability up to 20 h using chronopotentiometry methods. The surface and electrochemical analyses demonstrated that the sample, which underwent dual doping with 4.0 % Fe⁺³ and 4.0 % Bi⁺³ concentrations, had enhanced performance in the HER. Additionally, electromagnetic studies revealed superior EMI shielding effectiveness (SET), with the x = 0.03 composition achieving ∼30 dB over a broad frequency range. These results establish Fe/Bi doping as an effective strategy to tailor structural, magnetic, electrochemical, and EMI shielding properties, highlighting its multifunctional potential.