Metal–organic framework-derived MnO/CoMn₂O₄@N–C nanorods with nanoparticle interstitial decoration in core@shell structure as improved bifunctional electrocatalytic cathodes for Li–O₂ batteries

Core@shell-structured, hierarchically porous manganese oxide/cobalt manganite@nitrogen-doped carbon (MnO/CoMn₂O₄@N–C) nanorods with interstitially decorated CoMn₂O₄ nanoparticles are synthesized via one-step carbonization of metal–organic framework (MOF)-coated α˗manganese oxide (α-MnO₂@ZIF-67) nanorods and are evaluated as bifunctional electrocatalytic cathodes for Li–O₂ batteries (LOBs) to improve the bifunctionality, specific discharge capacity, and cyclability of α˗MnO₂ nanorod cathode-based LOBs. The MnO/CoMn₂O₄@N–C nanorods feature a MnO nanorod core with CoMn₂O₄ nanoparticle interstitial decoration, both coated by an N–C conductive shell. The MnO core renders Mn active sites and oxygen vacancies, while the CoMn₂O₄ interstitial decoration gives additional Mn, Co active sites, thereby enhancing bifunctional electrocatalytic ORR–OER. The N–C shell increases electronic conductivity, hierarchical porosity, specific surface area, and protects the core and interstitial decoration against lithium peroxide (Li₂O₂) passivation. The improved structural features allow the MnO/CoMn₂O₄@N–C nanorod cathode-based LOB cells to exhibit superior full specific discharge capacity of 8,625 mAh·g⁻¹ and cyclability of 48 discharge–charge cycles at 200 mA·g⁻¹ specific current and 2000 mAhg⁻¹ limited specific discharge capacity compared to their α˗MnO₂ nanorod counterparts. An ORR–OER mechanism is proposed to describe the interesting formation of particle- and film-type Li₂O₂ deposits at different cycles for the MnO/CoMn₂O₄@N–C nanorod cathodes. Such MOF-derived, interstitial nanoparticle-decorated nanoarchitectures can lead to high-performance tunable bifunctional electrocatalysts.