Preparation And Electrocatalytic Investigation Of Co-N-C Based Materials

With the increasing depletion of traditional fuels and the increasing demand for environmental protection awareness,researchers have begun to devote themselves to the development of clean energy and recyclable conversion and storage technologies,including water electrolysis devices,fuel cells,and zinc-air batteries（ZABs）.Among them,hydrogen evolution reaction（HER）,oxygen evolution reaction（OER）and oxygen reduction reaction（ORR）are important components of these clean energy conversion systems.Currently,platinum-based catalysts are the well-known benchmark catalysts for HER and ORR,while ruthenium and iridium-based oxides are considered to be the most effective catalysts for OER reactions.However,the natural scarcity and high cost of these precious metal catalysts hinder their large-scale commercialization.Therefore,it is necessary to find high-efficiency,stable,and economical multifunctional catalysts to provide a source of power for the large-scale development of new energy.In recent years,transition metal（Fe,Co,Ni,Mo,etc.）based materials and carbon materials have been considered as ideal substitutes due to their good electrocatalytic activity and easy availability of raw materials.This article mainly focuses on the preparation and the electrocatalytic performances（ORR,OER and HER）of Co-N-C materials,and used in Zn-Air batteries and water electrolysis devices to explore its application prospects.The obtained results were summarized as follows:（1）Polypyrrole（PPy）nanowires is deposited on a carbon fiber paper（CFP）substrate via electrodeposition,then Co²⁺is impregnated on PPy via an impregnation method.Finally,through pyrolyzing in the decomposition atmosphere of dicyandiamide（DCA）,Co/MMCs is in-situ prepared.DCA is acted as the chemical vapor deposition（CVD）solid source here,and its introduction promotes the diversification of carbon morphology（MMCs are composed of carbon nanorods,nanospheres and nanowires）and the hierarchization of carbon structure（rods,balls,and wires all are comprised by small carbon nanosheets）.Simultaneously,the introduction reduces the average size of Co nanoparticles,and increases the content of interfacial Co-N and pyridine-N.Due to the combined regulation on morphology and defect,Co/MMCs exhibits desirable HER,OER and ORR electrocatalytic activities.In addition,the catalyst also exhibits favorable performances in water electrolysis and Zn-Air batteries.（2）Co-precursor array is grown firstly via a water-bath deposition on CFP substrate,and then through polydopamine（PDA）wrapping and CVD annealing,an interlaced/fused structure of nitrogen-doped carbon nanotubes is obtained,wherein the metallic Co nanoparticles are mainly distributed on the top of the carbon nanotubes.The ORR half-wave potential of Co@NCNT_0.4is 0.91 V,the overpotential of OER is 180 m V at the current density of 10 m A cm^-2,and theΔE is 0.5 V.The assembled flexible ZABs also has a superior performance.（3）A kind of Co-N polymer is firstly obtained via a solvothermal method,and then mixed with DCA and annealed in Ar atmosphere,Co NC（1:4）electrocatalyst is prepared,where atomically dispersed and nanoscaled Co species embedded in micro-/mesoporous carbon nanosheet/nanotube architecture.The ORR half-wave potential of Co NC（1:4）is 0.87 V,the potential of OER is 1.55 V at a current density of 10 m A cm^-2,and theΔE is 0.68 V.Revealed by control and SCN^-poisoning experiments,N species and atomically dispersed Co species are the main active centers for ORR;whereas the metal Co nanocrystals are the chief active species for OER.Importantly,the catalyst also exhibits favorable performances in water electrolysis and Zn-Air batteries.