Structural Design,Synthesis And Electrocatalytic Performance Of Cobalt-Based Carbon Nanomaterial Electrocatalyst

Oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)catalysts are the key points of fuel cells.At present,noble metals such as Ir O₂and Ru O₂are used as oxygen evolution catalysts,and Pt-based noble metals are mainly used as oxygen reduction catalysts.Researchers mainly focus on the preparation of composites of non-noble metals and carbon-based metals,with the goal of reducing the cost of catalysts and improving the catalytic activity of catalysts to meet modern energy needs.This paper is dedicated to developing low-cost cobalt-based carbon nanomaterial oxygen catalysts with high catalytic activity and high stability,and combining a variety of material characterization methods and electrochemical research methods to study oxygen catalysts.The main research contents and innovations are as follows:1.CoN_x/HCN-CNTs as cheap and efficient ORR electrocatalystIn this study,a new two-step pyrolysis strategy was used to synthesize cobalt-based nitrogen-doped carbon nanotubes with a helical coiled structure and uniform diameter.Among them,CoN_xnanoparticles are uniformly distributed on the entire carbon nanotubes,not just distributed at the tip.Firstly,ZIF-67 is pyrolyzed to obtain Co-based nanoparticles supported on carbon materials,and then the ZIF-67 pyrolyzed derivative and melamine are physically mixed and pyrolyzed.CoN_x/HCN-CNTs as highly efficient ORR electrocatalysts benefit from the synergistic effect between nitrogen-doped carbon nanotubes and CoN_x-based active sites.Compared with the commercial 20%Pt/C catalyst under the same test conditions,CoN_x/HCN-CNTs showed stronger catalytic activity,durability and methanol tolerance.Compared with the various carbon nanotubes previously reported,they have a higher initial potential and half slope potential for ORR.Through this research,multiple pyrolysis has revealed the high hope of directly manufacturing electrocatalysts for lithium-ion batteries and supercapacitors.2.Preparation of E-NiCo₂S₄/SBS-NCNTs bifunctional oxygen electrocatalyst by electrodeposition methodIn this study,encapsulated NiCo₂S₄-based nanoparticles were prepared by electrodeposition and procedural calcination strategies.Nano-mediated rigid bamboo-shaped nitrogen-doped carbon nanotubes were prepared.Firstly,Ni-Co-based nanosheets were introduced on the surface of foamed nickel by electrodeposition.,And then foamed nickel physically mixed with melamine,calcined and vulcanized,and finally formed E-NiCo₂S₄/SBS-NCNTs electrocatalyst.The straight bamboo-shaped nitrogen-doped carbon nanotubes show an average diameter of about 500 nm.What makes us more excited is that the nanoparticles are evenly dispersed on the surface of the carbon nanotubes,not just at the tip or inside.We chose thiourea as the heteroatom source to construct the encapsulated NiCo₂S₄-based nanoparticles of rigid bamboo-shaped nitrogen-doped carbon nanotubes,because it has more states than the oxidation state to promote the redox reaction and conductivity.It is expected to improve the intrinsic conductivity of nanoparticles to enhance catalytic activity.The introduction of heteroatoms into nanostructures provides a promising solution to promote the formation of rigid bamboo-shaped carbon nanotubes,which may be attributed to the changes in carbon hybridization caused by changes in the microscopic surface chemical environment of NiCo₂S₄-based nanostructures.The starting potential of E-NiCo₂S₄/SBS-NCNTs in OER is 1.52V(compared to RHE),and the starting potential of E-NiCo₂S₄/SBS-NCNTs in ORR application is 0.95V(compared to RHE).Compared with20%Pt/C,it has better durability and methanol tolerance.3.CP@NC-Co Fe₂O₄/C as a cheap and efficient OER electrocatalystIn this study,we covered the surface of carbon paper with PANI nanowire arrays by electrochemical polymerization,and successfully synthesized MOF-74-Co/Fe on the surface with the help of PANI arrays.Through pyrolysis,a nitrogen-doped carbon nanoarray material loaded with cobalt ferrite was successfully prepared.Its synthesis is mainly due to the introduction of PANI.It can not only be used as a kind of"adhesive",grow MOF on its surface and cover carbon paper,but also can form nitrogen-doped carbon materials through pyrolysis to improve conductivity.And its unique 3D nano-array structure not only greatly increases the surface area,but also provides more attachment sites for Co Fe₂O₄,thereby accelerating electron transport and improving OER performance.High specific surface area,high utilization rate of catalyst,enhanced electron transport characteristics and retention of original carbon paper characteristics ensure excellent OER activity.CP@NC-Co Fe₂O₄/C has a small overpotential(290 m V),fast electron transfer,low charge transfer resistance and stable catalytic current,which can achieve long-term durability,which helps to obtain excellent OER performance.