Controlled Synthesis Of Cobalt-based Nanocatalytic Materials And Their Defect Regulation And Electrocatalytic Performance

The rapid consumption of fossil fuels and the use of non-renewable energy have caused serious pollution to the environment,which has promoted the vigorous development of advanced energy conversion and storage systems.Metal-air batteries and water electrolysis devices have attracted much attention as new clean energy conversion systems.The main reactions involved are oxygen reduction reaction(ORR),oxygen evolution reaction(OER),hydrogen evolution reaction(HER),etc.However,due to the slow kinetics of these reactions,it is very important to choose an electrocatalyst with excellent performance to increase the reaction rate and energy conversion efficiency.So far Pt-based catalysts and Ir-/Ru-based catalysts are considered to be the most effective ORR and OER electrocatalysts,respectively.Nevertheless,these noble metal-based electrocatalysts cannot meet the needs of large-scale applications due to their high price,low content,and poor stability.For the moment,the challenge is to develop a dual-functional electrocatalyst with high activity and low cost to promote the catalytic reaction.Transition metals are widely used because of their abundant reserves,low price and environmental friendliness.Among them,cobalt-based metals(oxides,sulfides,etc.)have the characteristics of high activity and good electrochemical stability under alkaline conditions,and are considered to be a class of promising catalytic materials.In this paper,cobalt-based transition metal nanocatalytic materials was used as the research object.Cobalt-based metal catalysts with excellent electrocatalytic performance are designed and synthesized by adjusting the microscopic crystal structure,morphology,defects and surface/interface structure.The specific research content of this paper is as follows:(1)Firstly,a spherical spinel CoFe₂O₄nanoparticle was synthesized as a precursor by hydrothermal method.Afterwards,a dual-functional catalytic material CoFe@Fe₃N-CNT with carbon-oxygen double defects and heterogeneous interface was successfully synthesized by inducing alloy precipitation and chemical vapor deposition(CVD).The structure,composition,and morphology of the catalyst were characterized by XRD,XPS,SEM,TEM and other methods in detail,and density functional theory(DFT)calculations were performed on the catalyst.The results show that the catalyst has a unique pea pod-like heterogeneity.Interface structure,and rich carbon and oxygen defects are built in it.Under the synergistic effect of heterogeneous interface and defects,the electronic structure of the catalyst is effectively adjusted to promote the improvement of electrocatalytic performance.In this chapter,through a simple CVD method,a heterogeneous interface and a large number of carbon and oxygen defects are constructed in the carbon nanotubes derived from spinel CoFe₂O₄.At the same time,the ORR reaction mechanism of the catalyst under alkaline conditions is deeply studied.(2)A precursor of Co(OH)F nano-needle array supported on carbon cloth was synthesized by hydrothermal method.Then,a nitrogen-doped carbon nanotube-coated elemental cobalt electrocatalyst was constructed in situ by the CVD method.Finally,by introducing the element S,a dual-functional catalyst Co@Co_1-XS-NCNT with a heterojunction structure of Co@Co_1-XS and CNTs was successfully synthesized,and the catalyst was rich in sulfur vacancies.The structure,composition,and morphology of the catalyst were systematically studied through SEM,TEM,EPR and XPS characterization tests.The results show that it has a unique heterojunction structure and a large number of sulfur defects,which is conducive to the transport of oxygen and electrons,effectively enhances the conductivity of the catalyst,and provides more active sites for the reaction.The catalyst has excellent OER electrocatalytic activity and zinc-air battery performance.(3)The sol-gel method was used to successfully synthesize perovskite oxide SrCoO_2.52 nano-catalytic material.An amorphous cobalt-based electrocatalyst with ultra-high oxygen evolution reaction performance was successfully synthesized through surface engineering strategy.The structure,composition and oxygen vacancy defects were systematically studied by TEM,XRD,EPR and other characterization methods.The research results show that by introducing Ru³⁺ions,Ru³⁺is hydrolyzed and deposited on the surface of the perovskite,and the well-crystallized perovskite structure is destroyed and finally reconstructed into an amorphous structure,and a large number of oxygen vacancy defects are constructed.Through the structural transformation and the regulation of the metal valence state,the oxygen evolution reaction performance of the catalyst is greatly improved,and the corresponding potential is 1.42 V at a current density of 10m A·cm^-2.