The Preparation Of Transition Metal Cobalt And Its Compound Supported On Biomass Porous Carbon Materials And Their Electrochemical Performance

At present,porous carbon materials with transition metal and its oxides and hydroxides supported on the surfaceexhibit potential application in electrochemical fields.However,some popular carbon materials,such as graphene and CNTs,always have high costs,complex process of preparation and harsh preparation conditions in spite of their large surface areas and good conductivity as the support of metal and its oxides and hydroxides.Thus,it is still a challenge to develop a facile and scalable synthesis method of carbon materials with excellent electrochemical performance for commercial application.In this work,a series of transition metal and its oxides and hydroxides supported on porous carbon materials have been designed and prepared using chitosan,cobalt acetate as carbon,cobalt precursors,respectively.Their morphology,structure,forming process and the electrochemical performance?including HER,supercapacitor and OER?were studied.The main contents and conclusions are as follows:?1?A facile method is proposed to prepare cobalt supported on nitrogen-doped porous carbon material with high graphitization degree by using chitosan as carbon source,urea as soft template and poloxamer as dispersant.With the optimum condition of the mass ratio of Co?Ac?₂to F127 of 1:4 and the mass ratio of chitosan to urea of 1:6,the obtained cobalt-carbon composite?Co@NPC?shows uniformly distributed cobalt nanoparticles that are encapsulated in nitrogen-doped porous carbon bundle with large specific surface area.The testing results show that as electrode for hydrogen evolution reaction?HER?,Co@NPC exhibits superior electrocatalytic performance with low overpotential(?₁₀=259mV),small tafel slope(99 mV dec^-1)and high stability in 1 M KOH electrolyte?83%of its original current density retained after 6 hours of chronoamperometric testing?.After oxidizing Co@NPC under the optimum conditions of 250 ^oC for 3 hours,the obtained cobalt oxide-carbon material?Co₃O₄@NPC?shows a yolk-shell structure,and exhibits a high specific capacitance(661 F g^-1 at the current density of 0.5 A g^-1),good rate capability(71.5%of its capacitance retained with the current density increasing from 0.5 A g^-1 to 10 A g^-1)and excellent cyclic stability(82.3%of its original capacitance kept after 2000 cycles at the current density of 20 A g^-1).?2?Cobalt supported on porous carbon material?Co@C?were prepared via high temperature pyrolysis of the mixture of chitosan,cobalt acetate and sodium chloride.In the process of removing sodium chloride template by water washing for 96 h,the composite with Co and Co?OH?₂ supported on porous carbon materials?Co/Co?OH?₂@C?were obtained by galvanic reaction.Thermodynamic calculations show that the gibbs free energy of this reaction is?G₈)=-42.846 KJ/mol<0.Thus,the reaction can occur spontaneously in theory.And the hydrotalcite-like Co?OH?₂ with a thickness of 3 to 5 nm forms in the optimized sample Co/Co?OH?₂@C?the mass ratio of chitosan to sodium chloride is 1:6?.Meanwhile,the carbon material presents a morphology of regular skeletal structure.In 1 M KOH alkaline solution,Co/Co?OH?₂@C shows good OER catalytic activity with the potential of 1.62 V at the benchmark current density and the tafel slope of 78 mV dec^-1.Compared with Co@C,the potential of Co/Co?OH?₂@C for OER has reduced by 50 mV,and tafel slope has reduced by 23mV dec^-1.Therefore,the introduction of Co?OH?₂ to Co@C can greatly improve the catalytic performance of Co/Co?OH?₂@C for OER.