Interface engineering of the dz2 electrons mobility for single atom catalytic activity and selectivity

Transition metal singlet embedded in nitrogen-doped carbon material (M-N-C) has been demonstrated as a promising electrochemical oxygen reduction reaction (ORR) catalyst; however, the unsatisfying activity and production selectivity have hampered its widespread applications in energy storage and conversion technologies. Herein, interface engineering by facilitating M-N-C catalysts (M from 3d to 4d electron-containing elements) with MXene has been utilized to regulate their ORR performance. It is found that the charge transfer occurring within the interface not only tunes the electron occupancy of the 3d/4d orbitals of the metal site, but also delocalizes the population of the d states. This alternation enhances the mobility of the electrons and promotes the 4e catalytic process thermodynamically. Meanwhile, the formation of ∗HOOH, the key reaction intermediate for 2e reaction, is hindered due to the alleviation of the binding capacity, which is beneficial to improve production selectivity. This study provides foundational understanding for the ORR catalytic mechanism at the atomic level and opens up new avenues for designing high-demanded electrocatalysts.