Construction And Electrocatalytic Properties Of Cobalt@Nitrogen-doped Carbon Nano Bowls

On account of the rising energy demand,climate change and pollution resulting from fossil energy,it is necessary to develop clean and renewable energy technologies.Fuel cells and metal–air batteries are expected to be an alternative to conventional batteries.However,the electrochemical oxygen reduction reaction（ORR）is slow,limiting the energy conversion efficiency.Although noble-metal catalyst is applied to commercial batteries,it is hindered by high cost and low stability.Hence,general researches have been devoted to developing low-cost,durable and highly efficient nonprecious metal ORR catalysts.A large number of studies have shown that the transition metals（Fe,Co,Ni）with low cost and catalytic activity can replace noble metals,and the transition metal-nitrogen-carbon（M-N-C）catalysts have excellent ORR catalytic activity.But,the actual application of the catalyst also needs to have a good durability.Therefore,it is of great practical value to construct a stable and efficient M-N-C type ORR catalyst material.In this dissertation,nitrogen-doped carbon bowls with cobalt nanoparticles loading（Co@NCB）was obtained through hydrothermal,etching,impregnation and high-temperature sintering.The composition and structure of the materials were characterized by the corresponding test method,and the electrocatalytic properties of the materials and the contrast samples as oxygen reduction catalysts were studied.The main research results of this dissertation are as follows:1.Using resorcinol,tetraethyl orthosilicate,formaldehyde and cobalt acetate as the main raw materials,nitrogen-doped carbon bowls with cobalt nanoparticles loading（Co@NCB）was obtained through hydrothermal,etching,impregnation and high-temperature sintering.The phase,composition,structural morphology,graphitization degree and specific surface area of Co@NCB were characterized.2.The electrocatalytic performance of Co@NCB as ORR catalyst is tested.The electrochemical measurements show that Co@NCB owns excellent electrocatalytic performances.The half-wave potential(E_1/2)of the ORR moves 6 m V forward compared to the Pt/C catalyst in a solution of 0.1 M KOH.Mealwhile,the constant voltage stability test show that Co@NCB can remain 95.5%of initial maximum current in 0.1 M KOH after 10 h,much higher than that of Pt/C catalyst（84.1%）.In addition,Co@NCB also show a much better anti-methanol toxicity performance than Pt/C,and the addition of methanol to the electrolyte basically do not affect its performance.The structures and properties of Co@NCB are compared with carbon nanobowls（CB）,nitrogen-doped carbon nanospheres（NCS）,nitrogen-doped carbon nanobowls（NCB）,cobalt decorated carbon nanobowls（Co@CB）,Co@NCB with acid treatment（Co@NCB-AT）and commercial Pt/C,and the results display that the loading of Co nanoparticles and the structural morphology of carbon nano bowls are of great significance to the ORR catalytic performance.Finally,Co@NCB also shows excellent performance in zinc-air battery.