Unveiling Enhanced Oxygen Reduction in Multi-Walled Carbon Nanotube-Supported MnCo₂O₄: Experimental and Theoretical Insights into Tin Substitution for Octahedral Cobalt

In this work, Sn-doped manganese cobaltite (Snx-MnCo2O4) was synthesized by using a solvothermal method followed by an annealing process. To further increase its catalytic efficiency, it was integrated onto a carbon support, carboxylic acid-functionalized multiwalled carbon nanotubes (fMWCNTs). Among the synthesized materials, fMWCNT-supported Sn-doped MnCo2O4 exhibits the highest onset potential for oxygen reduction and shows a distinctly selective four-electron oxygen reduction, as demonstrated by the rotating disc electrode and rotating ring disc electrode experiments. X-ray photoelectron spectroscopy reveals a shift in the binding energy of Mn 2p owing to alterations in the electronic structure of the crystal upon incorporation of Sn into MnCo2O4. Computational studies proved the replacement of octahedral Co ions in the MnCo2O4 crystal structure by Sn4+ ions. The withdrawal of electron density by Sn4+ species from the active centers (Mn3+) leads to an increased electropositive character at the Mn3+ centers. Since Mn3+ centers are the effective active centers in this catalyst, oxygen is efficiently adsorbed at these active centers, resulting in enhanced electrocatalytic activity.