Synthesis And Properties Of Co-based Electrocatalyst With Nano-assembly Structures

Nowadays,with the depletion of traditional fossil fuels,various social and ecological problems have become increasingly serious.Energy has become one of the global hottest topics.The development of green and renewable energy is a practical solution to this challenge.In the past few decades,a large number of potential energy conversion and storage devices have been extensively studied,such as rechargeable metal-air batteries,water splitting devices,and fuel cells.It is worth noting that these systems are highly dependent on a series of electrochemical reactions,including oxygen reduction reaction（ORR）,oxygen evolution reaction（OER）,and hydrogen evolution reaction（HER）.However,slow kinetics of these electrochemical reactions result in large overpotentials and low energy conversion efficiency.At present,Pt,Ir,Ru and their derivatives enjoy excellent electrocatalytic activity,however,their scarcity and high cost have substantially hindered their large-scale commercial application.Therefore,it is necessary to develop low-cost,effective and stable electrocatalysts to increase the reaction rate.As one of the most abundant elements on earth,cobalt（Co）has different oxidation states(Co^II/Co^III),and the metal redox potential is close to the potential for reducing oxygen to water（E=1.23 V vs.RHE）.Therefore,Co-based catalysts have attracted widespread attention as a substitute for traditional noble metals.In this paper,we have synthesized a series of Co-based catalysts with special nano-assembly structures by metal/non-metal doping and template methods and systematically study the main mechanism and catalytic performance.The main contents are as follows:Firstly,we summarized the electrocatalytic energy conversion device and the electrochemical reactions involved,briefly described the research progress of electrocatalysts,emphasized the importance of developing inexpensive,stable and efficient catalysts in the process of electrocatalytic energy conversion,and explained the background and research content of this article.Secondly,bimetal Co/Mn-ZIF was synthesized by self-assembly with Co and Mn as central ions and2-methylimidazole as the organic ligand.Then,the bimetal Co/Mn-ZIF was used as the template for anion exchange with[Fe（CN）₆]^3-ion at room temperature to obtain a Co/Mn-ZIF@Fe-Co PBA composite catalyst（PBA:abbreviation for Prussian Blue Analogues）.The structure and morphology of the catalyst were characterized,and the results showed that the prepared catalyst well retained the shape of the dodecahedron and had a core-shell structure.The prepared catalyst was tested for electrochemical performance,and the results showed that the composite catalyst exhibited better electrocatalytic activity than the advanced noble metal catalyst Ru O₂.Further mechanism studies show that the amorphous hydroxide formed in situ during the oxygen evolution reaction of the Co/Mn-ZIF@Fe-Co PBA catalyst acts as an active material,which greatly promotes the electrocatalytic performance.And based on the advantages of the core-shell structure,the catalyst has a higher specific surface area,which is more conducive to the mass transfer process.Thirdly,Co-Ni glyceric acid as the precursor was sulfurized with thioacetamide.Subsequently,non-noble metal Mo components were introduced to synthetic Mo-doped Ni Co₂S₄ catalyst successfully.The structure and morphological characterization results show that the synthesized catalyst is a nanosphere with Yolk-Shell structure,and the surface has folds assembled from sheet-like structures,and the components Mo and S are evenly distributed throughout the nanosphere.The electrical performance test results show that the Mo-doped Ni Co₂S₄ catalyst performs good ORR and OER bifunctional electrocatalytic activity.Theoretical analysis shows that the Yolk-Shell structure make the catalyst possess a larger specific surface area and more active sites,and Mo doping can effectively adjust the electronic structure,accelerate the reaction and improve the electrocatalytic activity.Fourthly,The precursor of Co-Ni glyceric acid was treated with glucose,urea,and thioacetamide to achieve carbon coating,co-doping with sulfur and nitrogen,and finally calcined to form hollow waxberry-like Co Ni O₂/SNC catalyst.The hollow structure facilitates the exposure of more active sites and provides sufficient space for electrochemical reactions.In addition,the synergistic coupling between the metal oxide and the co-dopant of S and N into carbon materials help further improve the electrocatalytic performance of the catalyst.The electrical performance test results show that the Co Ni O₂/SNC catalyst has good ORR,OER and HER electrocatalytic activity.In summary,in this paper,we designed and synthesized a series of nano-assembled Co-based catalysts,characterized the microstructure and composition of these catalysts,and studied the electrocatalytic performance of these catalysts.The results show that these Co-based catalysts have excellent ORR,OER or HER catalytic activity,providing new opathways to meet global energy challenges.