Construction Of Co-based MOFs-derived Alloy Carbon-based Oxygen Electrocatalyst And Its Performance In Zn-air Batterie

Considering the energy crisis and environmental problems associated with the usage of conventional fossil fuels,the development of renewable energy sources with economically and environmentally friendly characteristics has been actively pursued.In this regard,rechargeable zinc-air batteries,which combine the main features of secondary batteries and fuel cells,are considered as highly promising next-generation energy storage/conversion devices,where oxygen electrocatalysts loaded on air electrodes,due to their slow catalytic reaction kinetics,become a key constraint to the commercialization of zinc-air batteries.Therefore,in this work,a series of multi-metal composite carbon-based oxygen electrocatalysts were synthesized by the construction of alloy-metal oxide heterogeneous interfaces,electrostatic spinning,introduction of nitrogen-doped carbon and high entropy of the system using polymetallic organic frameworks as carbonization precursors,and the electrochemical and cell performance of these catalysts were investigated.Firstly,Ox-MnCoNi-C（4h）,an oxygen electrocatalyst with the alloy/polymetallic oxide heterogeneous interfaces,was prepared by alloy reoxidation.The catalyst has a high oxygen reduction half-wave potential（0.8 V）and a low oxygen evolution overpotential（360 m V）.The rechargeable zinc-air batteries assembled with this catalyst exhibited excellent power density(125 m W cm^-2)and long-term cycling stability of more than 100 h.This excellent performance results from the encapsulation of a heterogeneous interface and a graphitic carbon layer with high electron transfer rate,the presence of heterogeneous interface enhances the oxygen trapping and charge conversion process.Meanwhile,the encapsulation of the graphitic carbon layer prevents excessive oxidation and contamination of the catalyst surface and improves the stability of the catalyst.Subsequently,MnCoNi-MOF and PAN were co-spun using an electrostatic spinning method to obtain MnCoNi-MOF@PAN fibers.Then,operations of pre-oxidation and carbonization under inert gas were performed to successfully synthesize a nitrogen-doped carbon nanofiber-coated MnCoNi alloy catalyst.The catalyst exhibited an oxygen reduction half-wave potential of 0.81 V and good stability in a three-electrode measurement.The battery subsequently assembled with mixed Ru O₂as the oxygen electrode also exhibited good discharge characteristics.The excellent oxygen reduction properties of the catalysts are attributed to the abundant nitrogen doping and the high specific surface area of the carbon nanofibers,which facilitate to ensure the dispersion of the alloy catalytic sites and improve the interaction between the carrier and the catalyst.Finally,a high-entropy alloy MnCoRu FeNi embedded nitrogen-doped carbon catalyst was synthesized by a simple room-temperature crystallization and carbonization method using2-methylimidazole as the ligand and nitrogen source.The prepared MnCoRu FeNi-NC has a high specific surface area of 403 m²g^-1and abundant nitrogen content.The assembled rechargeable Zn-air batteries exhibited a peak power density of 162 m W cm^-2and a charge/discharge cycling stability of more than 130 hours.The excellent bifunctional properties of the catalyst stem from the synergistic effect of abundant nitrogen-doped carbon,ultra-high specific surface area and strong lattice distortion effect of the high-entropy alloys,while the slow diffusion effect of the high-entropy alloys contributes to the better stability,which greatly avoids the leaching of metal sites in the electrolyte.