Defect Regulation And Electrocatalytic Properties Of NiCo-based Spinel

Oxygen reduction reaction（ORR）and Oxygen evolution reaction（OER）play an essential role in the development and storage of energy,particularly in the development of rechargeable batteries,and the development of efficient OER/ORR catalysts is therefore urgent.Although commercial noble metal catalysts are representative of catalysts with excellent reaction kinetics and catalytic activity,they are expensive and constrain industrial applications.Spinel-based catalysts attract great interest due to their low cost,spinel is mainly divided into ortho-spinel and anti-spinel,controlled morphology and abundance of sites,and there are many ways to modulate spinel materials,such as morphology modulation,introduction of defects and so on.In this work,Co Ni₂S₄ and Ni Co₂O₄ are represented by anti-spinel and used as the target of this study,with defect engineering as the starting point to improve the ORR and OER catalytic activity of spinel by regulating electron transfer.The specific research contents are as follows:1.A surface modified strategy on the surface of Co Ni₂S₄ via introducing Mo-S bridging.As expected,the oxygen reduction reaction（ORR）activity of Mo-S bridged Co Ni₂S₄ showed an optimal performance with a half-wave potential of 0.802 V,superior to primitive Co Ni₂S₄ and many spinel-based catalyst materials reported recently.Both experimental characterization and density functional theory calculations indicate that the improved ORR performance derives from the more electron-deficient sites and anion vacancies by driving electrons transfer between Ni,Co,and S,and thus results in the creation of more active sites.These results propose a new direction of surface reconstruction for optimizing spinel-based electrocatalyst.2.A series of CeO₂ and Ni Co₂O₄（NCO）composite materials were synthesized by adopting hydrothermal and annealing methods,of which Ce O₂/NCO was selected as a representative sample.Through the relevant electrochemical tests,it can be found that Ce O₂/NCO has improved performance compared with the original sample NCO,with a voltage reduction of 34 m V at an overpotential of 10 m A·cm^-2 and the C_dl value of3.30 m F·cm^-2for Ce O₂/NCO,indicating that it has abundant active sites on its surface.The Tafel slope and R_ct of Ce O₂/NCO were 99 m V·dec^-1 and 36.4Ω,respectively,which were both better than the as-built samples,which fully demonstrates the higher reaction kinetics of Ce O₂/NCO.In addition,Ce O₂/NCO composite material exhibited excellent stability in the 60 h i-t test.The presence of oxygen defects in the Ce O₂/NCO structure,as revealed by XPS and ESR analyses,further indicates the formation of certain oxygen defects during the composite process with Ce O₂.This work synthesizes a complex of spinel Ni Co₂O₄ with Ce O₂,which is rich in active sites and has certain oxygen defects,which broadens the idea of regulating the catalytic activity of spinel.