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 (Sn x -MnCo 2 O 4 ) 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 MnCo 2 O 4 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 MnCo 2 O 4 . Computational studies proved the replacement of octahedral Co ions in the MnCo 2 O 4 crystal structure by Sn 4+ ions. The withdrawal of electron density by Sn 4+ species from the active centers (Mn 3+ ) leads to an increased electropositive character at the Mn 3+ centers. Since Mn 3+ centers are the effective active centers in this catalyst, oxygen is efficiently adsorbed at these active centers, resulting in enhanced electrocatalytic activity.