Preparation And ORR Catalytic Activity Of Cobalt/carbon Composite Nanoparticles

Oxygen Reduction Reaction（ORR）is the key reaction between Fuel Cells（FCs）and metal air battery cathode.However,the reaction kinetics is slow,and high efficiency catalyst is needed to reduce the reaction energy barrier of ORR and accelerate the ORR process.Although noble metal Pt/C catalysts show excellent ORR catalytic activity,their large-scale application is still limited by high cost and poor stability.Therefore,the development of efficient,stable and low-cost non-precious metal ORR catalysts has become the key to overcome the above difficulties.Among many non-noble metal catalysts,transition metal cobalt-based catalysts have been widely reported for their excellent performance and high stability.Among many non-noble metal catalysts,transition metal cobalt-based catalysts have been widely reported for their excellent performance and high stability.At present,MOF pyrolysis and template pyrolysis are the main synthesis ways of cobalt carbon-based ORR catalysts,but they still have many problems such as complicated process and long preparation cycle.In order to solve the above problems,Co@C catalyst and Co@C（N）catalyst were prepared by dc arc plasma method,and their structural morphology and ORR catalytic activity were characterized and analyzed.Using DC arc plasma as heat source,cobalt powder as raw material and methane as reaction gas,the Co@C nanopowders were prepared at working voltage/current of 30 V/90 A.The structural morphology of Co@C was analyzed by XRD,TEM,Raman and other characterization methods.Co@C is a carbon coated structure with cobalt as the core.The size of the particles is related to the amount of methane in the reaction gas,and the high amount of methane provides more carbon.After nucleation,the carbon coating is thicker,and the size of the composite nanoparticles is larger.The ORR catalytic activity of Co@C was tested in alkaline environment.It was found that the half-wave potential of Co@C 0.01 NPs prepared in0.01 MPa methane was 0.63 V,the limit current density was 3.68 m A cm^-2,and the tafel slope was 227.09 m V dec^-1.And it has a four-electron ORR pathway.Co@C 0.01 NPs has relatively high ORR activity,because the particle size of Co@C 0.01 NPs is small,the specific surface area of the material is large,that is,the contact area between the catalyst and O₂ during the ORR process is large,which improves the ORR activity of the material.In order to further improve the ORR activity of Co@C 0.01NPs,Co@C 0.01NPs was calcined in a tube furnace with nitrogen to obtain Co@C（N）NPs.TEM observation showed that the samples were overburned and agglomerated among the particles after three hours of calcination.XPS analysis showed that nitrogen was successfully doped into Co@C（N）NPs,and the nitrogen content in the sample increased with the increase of calcination time.The ORR activity of Co@C（N）NPs was tested.The half-wave potential of Co@C（N）-2h obtained by calcination for 2 hours was 0.76 V,and the Tafel slope was 76.5 m V dec^-1,which was the same as that of commercial Pt/C catalyst.After 5000 CV cycles,the half-wave potential of Co@C（N）-2h decreased by only 10 m V,showing extremely high durability.The ORR activity of Co@C（N）-2h was significantly higher than that of Co@C.