Preparation And Oxygen Reduction Reaction Performance Of NiCo₂O₄ Nanomaterials

Oxygen reduction reaction?ORR?is an important cathode reaction of fuel cell and metal air battery.Due to its sluggish kinetics,it is urgent to develop highly efficient catalysts to overcome the disadvantages of high overpotential and accelerate the ORR process.Spinel-structured NiCo₂O₄ with advantages of high electrochemical activity,low cost,abundant resources,etc.has attracted considerable interests.However,NiCo₂O₄suffers the problems of poor electrical conductivity,low durability and insufficient active sites.Previous results showed that employing carbon as substrate is an efficient method to enhance conductivity and improve specific surface area of NiCo₂O₄,and the introduction of oxygen vacancy could modify electron distribuction of material,thus leading to optimized electrocatalyst performance.In this study,the NiCo₂O₄/hollow carbon sphere nanocomposite with abundant oxygen vacancies?NiCo₂O₄/HCS-V?is prepared by hydrothermal method.The phase,crystal structure and valence state of samples are characterized by various characterization methods,and their electrochemical performances are measured.Finally,the theoretical mechanism of oxygen vacancies enhanced ORR kinetics of NiCo₂O₄ is confirmed by density functional theory?DFT?calculations,and the main research contents and results are as follows:?1?With the help of electrostatic adsorption,NiCo₂O₄ nanosheets with abundant oxygen vacancies are grown on conductive hollow carbon sphere via a facile hydrothermal process and a subsequent annealing treatment.The electrochemical results show that NiCo2O4/HCS-V exhibits a positive onset potential?0.9 V?,high limiting current(-5.8 mA cm^-2),and favorable stability?⁹0%retention after 40000 s?.?2?DFT calculation results show that hollow carbon sphere and oxygen vacancies enhance the density of states near Fermi level and decrease the work function of NiCo₂O₄.The introduction of HCS facilitates the adsorption of oxygen for NiCo₂O₄.Besides,the calculated ORR overpotential of NiCo₂O₄ is lowered by introducing oxygen vacancies,which plays a key role in optimizing electrocatalytic performance.