Preparation And Activity Regulation Of Transition Metal-Based Electrocatalysts

Since the end of the 20 th century,we have faced a severe energy crisis and increasingly serious environmental pollution.Therefore,saving the limited energy andcurbing environmental pollution are top priorities.Electrocatalytic reactions are widely used in the fields of energy and environment,especially some new energy conversion devices such as fuel cells,metal-air batteries,and electrolyzed water cells,which involve three electrochemical reactions:oxygen reduction?ORR?,oxygen evolution?OER?,and hydrogen evolution?HER?reactions.Due to the huge reaction energy barrier in these catalytic reactions,catalysts are usually needed to reduce the reaction barrier and thus decrease energy consumption.Commonly used catalysts are all noble metal-based materials such as Pt/C,RuO₂,IrO₂,etc.,but they are expensive and scarce.In order to reduce the reliance on precious metals,the development of non-precious metal-based catalysts with low cost and excellent performance have attracted widespread attention from researchers.Catalysts based on transition metals?Fe,Co,Ni,etc.?have rich active sites and high electrical conductivity,and therefore have great potential to replace precious metal-based catalysts in the field of the electrocatalytic science.In this dissertation,the following three kinds of transition metal-based electrocatalysts have been designed and prepared.Their morphological and structural properties are characterized and their electrocatalytic performances are tested.The as-generated electrocatalysts show excellent performance for applications in zinc-air batteries oroverall water splitting.?1?A bimetallic iron-cobalt polyphthalocyanine containing sulfur atomsinthe peripheral ringsis synthesized by a solvothermal method,and then its surface is coated with silica.The Co₈FeS₈ nanoparticles-loaded N,S-codoped carbon material?Co₈FeS₈/NSC?is obtained after pyrolysis of silica-protected bimetallic polyphthalocyanine.In the resulting material,its active components are greatly retaineddue to the protection of silica during pyrolysis.Co₈FeS₈/NSC shows excellent electrocatalytic performance for both ORR and OER,comparable to that of precious metals.When Co₈FeS₈/NSC is used as the air electrode,the assembled zinc-air battery has high peak power density and excellent cycling stability.?2?Using copper foam after acid washing and oxidation treatment as a conductive substrate,a layer of iron polyphthalocyanine containing sulfur atoms in the peripheral rings?FeSPPC?is grown in situ on the surface of copper foam?CF?.The electrochemical performance of the obtained catalyst is much higher than that of bare copper foam.In view of its excellent electrochemical performance and stabilityfor both HER and OER,the assembled water electrolyzer using FeSPPC/CF as the cathode and anodedisplaysexcellent performance for overall water splitting.?3?Using nickel foam as a conductive support,Co₂Fe?CN?₆/Fe₂O₃ microspheres are grown on the surface of nickel foam by a simple one-step hydrothermal method.The obtained catalyst inherits the macroporous structure of the nickel foam material,and has large electrochemically active surface area,high conductivity and small charge transfer resistance.These advantages makeithighly active in catalyzing HER and OER.It can be applied as a bifunctional electrocatalyst for overall water splitting and shows excellent performance.