Tuning the electronic structure of the Mn–N–C catalyst through XO2 group (X = S, Se, Te) doping for proton-exchange membrane fuel cells†

Single-atom catalysts towards the oxygen reduction reaction (ORR) often suffer from unsatisfactory activity and poor stability. Herein, for the first time, we successfully modulated the electronic structure of the Mn–N–C catalyst by introducing chalcogen oxygen groups (XO₂, X = S, Se, Te), which induce changes in the Mn–N bond length in the MnN₄ structure, thereby modulating the electronic structure of the metal center Mn. The experimental results demonstrate that the introduction of XO₂ groups results in the rearrangement of Mn 3d electrons, which can be strongly correlated with the ORR activity of the Mn–N–C catalysts, among which the SeO₂ modification increases the kinetic current density of the Mn–N–C catalyst achieving a half-wave potential (E_1/2) of 0.79 V versus the reversible hydrogen electrode, approaching that of Fe–N–C catalysts along with significant stability in acidic media. The promising performance of the Mn–N–C catalyst as a PGM-free cathode was confirmed through fuel cell testing. First-principles calculations demonstrate that the introduced XO₂ group downshifts the d-band center of the Mn center, thus successfully optimizing the adsorption of oxygen intermediates. This finding significantly facilitates the activity enhancement of Mn–N–C catalysts via the construction of a geometric structure–electronic structure–catalytic property relationship.