Influence of Co doping on physiochemical properties of MnFe2O4/C nano compounds toward oxygen reduction reaction

Highlights: • Co doped MnFe_2−xCo_xO₄/C(x = 0.25–0.75) for ORR was for the first. • MnFe_2−xCo_xO₄/C shows enhanced ORR performance. • The MnFe_2−xCo_xO₄/C shows uniform particles size of ~11–15 nm. • Co doping lead to Mn³⁺ ion increased that is favorable site for ORR. • Co doping result to cathodes redistribution on tetrahedral and octahedral site. -- Abstract: Recently, several researchers have found that the manganese ferrite (MnFe₂O₄) nanoparticle can be a promising candidate for the oxygen reduction reaction (ORR). However, the MnFe₂O₄ nanoparticles still face challenges on their ORR activity and stability for practical application. In this work. The Co-doped MnFe₂O₄ electrocatalysts are explored to improve their intrinsic activity for the ORR in alkaline electrolytes. The MnFe_2−xCo_xO₄/C (x = 0.25–0.75) electrocatalysts show significant improvements on the ORR performance, particularly the MnFe_1.5Co_0.5O₄/C electrocatalyst exhibits the best ORR performance with 80 mV positive shift in half-wave potential compared to the pristine MnFe₂O₄. Meanwhile, the MnFe_1.5Co_0.5O₄/C nanoparticles display a uniform spherical shape with a size of ~11–15 nm, compared to the irregular shapes of the MnFe₂O₄/C nanoparticles with sizes in the range of ~8-~70 nm. The Co doping has redistributed the cations between the tetrahedral and octahedral sites in the MnFe₂O₄ structure from the XRD, TEM, FTIR, and XPS analysis. Furthermore, the particles sizes of the doped MnFe₂O₄/C nanoparticles are smaller and uniform, with more oxygen vacancies. In addition, the Co doping has enriched the surface Mn³⁺ ions and improved the conductivity of the MnFe₂O₄/C nanoparticles. The above results are closely related to the enhanced ORR activity of the Co-doped MnFe₂O₄/C compared to the pristine of the MnFe₂O₄/C.