Oxygen Electrocatalytic Performance Of Copper Oxide Supported On ZIF-67-derived Hollow Carbon Cube

The large-scale utilization of sustainable energy forms the core of the contemporary energy revolution.Energy storage and conversion devices are considered to be the key technologies for effectively capturing and utilizing renewable energy to construct modern sustainable energy systems.Among the various energy storage and conversion devices,metal-air batteries(such as zinc-air batteries)are promising candidates due to their high efficiency,environmental friendliness,and wide application potential in future sustainable energy systems.The core reaction of the zinc-air battery is the oxygen reduction and oxygen evolution reaction(ORR/OER),which typically require catalysts to overcome high overpotentials to initiate the reactions.Precious metal catalysts are often regarded as benchmarks for their excellent performance;however,their application is often limited by high costs and poor stability.Recent studies have shown that many transition metal oxides can significantly enhance their catalytic activity by increasing surface area and active sites,and thus can potentially replace noble metal catalysts.Therefore,it is a far-reaching task to rationally construct electrocatalysts with high activity structures.The aim of this paper is to prepare bifunctional electrocatalysts with high performance and long-term stability for ORR and OER.We choose regular ZIF-67 nanocube as precursor and non-noble metal oxide composite Cu2O/HZCNC-x and Cu2O/CoFe2O4-x materials as objects.A variety of materials characterization techniques,electrochemical(ORR/OER)performance testing methods,and practical applications in zinc-air batteries are employed to analyze the material composition,elemental valence states,apparent morphology,half-wave potential,and practical value of the catalysts,which allowed for reasonable inferences about the catalytic mechanism.In this study,we use density functional theory(DFT)calculations to investigate the activity origins of Cu2O-Co3O4-based catalysts for ORR/OER.According to the calculation results,a novel structure composed of hollow ZIF-67-derived carbon nanocube(HZCNC,with skeleton Co3O4)and Cu2O nanoparticles is constructed.By etching with tannic acid,hollow ZIF-67 nanocube is used as the precursor for preparation of the Cu2O/HZCNC electrocatalysts via a two-step pyrolysis.Meanwhile,Co3O4 as an active component is in situ formed in the carbon framework(HZCNC).Tannic acid etching can adjust the morphology and porosity of metal/carbon-based material to provide more pore channels to promote the mass transport.Due to the hydrophilic surface of HZCNC,the catalysts can realize the uniform distribution of Cu2O nanoparticles on the HZCNC to improve the utilization efficiency of active species(Cu2O/Co3O4).Moreover,it is expected that Cu atoms have a very high affinity for Co atoms to form the nanostructured heterojunction.Cu2O particles covered on the surface of HZCNC can form a thin shell to protect the active sites on Co3O4 from damage.As expected,Cu2O/HZCNC catalysts should exhibit ultra-high catalytic activity and extreme stability in alkaline media.Cu2O/CoFe2O4-0.425 bilayer nanoboxes have been successfully prepared by anion sequential exchange and annealing strategy.The Cu2O/CoFe2O4-0.425 catalyst is transformed from a ZIF-67 nanocube into a double-shell hollow structure coated with Cu2O particles.The structure has a large specific surface area,which can expand the contact area between electrolyte and reactant,enhance the charge transfer ability,and promote the electrolyte/reactant-electrode diffusion/penetration process.The thin shell of Cu2O with Cu+ active sites and structural stability is firmly fixed on the surface of CoFe2O4,which not only protects the main active center of CoFe2O4 nucleus from erosion,but also forms a highly active Cu2O/CoFe2O4 heterojunction with Cu/Co synergies for significantly increasing OER/ORR activity.As expected,the combined advantages of Cu2O/CoFe2O4-0.425 catalyst should give it higher activity and stability than commercial Pt/C(ORR)and RuO2(OER).In this paper,ZIF-67 nanocube is used as the precursor to prepare transition metal oxide multilayer hollow structure composite materials,which provides a viable pathway to create hollow bifunctional oxygen electrocatalysts by modulating the synergy between interfacial engineering and active substances.