Electrocatalysis Performances Of Cobalt-based Carbon Nanomaterials From Pyrolysis Of Cobalt-triazole Complex

The combination of electro-catalytic energy conversion and storage technology and renewable energy is an efficient and clean new energy system that gradually replaces fossil energy and reduces pollution.Among them,electrocatalyst materials play an important role in the conversion of clean energy,such as electrolyzed water and fuel cells.Although platinum?Pt?,ruthenium oxide?RuO₂?and iridium oxide?IrO₂?are currently highly catalytically active,they are not commercially available on a large scale due to their low content on the earth and their high cost.Therefore,there is an urgent need to prepare and develop non-noble metal catalyst materials for electrocatalysis.In recent years,metal-organic materials have been used as precursors and templates to form various forms of nanomaterials with different ways for electrochemical applications.In this paper,cobalt-based carbon nanomaterials were prepared using Co?tzbc?₂?H₂O?₄?tzbc=4-?1H-1,2,4-triazole?-benzoic acid?.The morphology and electrochemical properties of the catalyst materials were investigated by a variety of characterization techniques.The main contents of this thesis are as follows:?1?Surface enwrapped Co nanocrystals?NCs?embedded into the 2D N-doped graphitized carbon layers are synthesized successfully by simple in situ pyrolysis of Co?tzbc?₂?H₂O?₄ complex,which have highly active and ultra-stable electrocatalytic performances towards HER and OER.In particular,Co@NC-3 shows an outstanding HER activity with a low overpotential of 122 mV at a current density of 10 mA.cm^-2(?₁₀)and small Tafel slope(53.7 mV.decade^-1)in acidic electrolyte.For OER,the Co@NC-3exhibits a lower overpotential(?₁₀=365 mV)than that of RuO₂(?₁₀=384 mV)in 1.0 M KOH.Moreover,the electrocatalyst affords good durability both in acidic and alkaline condition.Through various characterization methods,the surface enwrapped cobalt NCs and 2D N-doped graphitization carbon can act synergistically electrocatalytic properties.Simultaneously,Co@NC-3 maintains the stability due to the surface enwrapped Co NCs,which inhibits the gradually corrosion of Co in a wide pH range.?2?Heteroatom-doping can change the electronic structure of carbon materials,improving the catalytic activity.Based on this,Co?tzbc?₂?H₂O?₄ was pyrolyzed through the CVD?Ar/NH₃?method by adjusting the pressure to obtain N-doped cobalt-based carbon materials.A number of characterizations indicate that Co@C-N-0.26?0.26 means a pressure of 0.26 Kpa?has a large specific surface area,more Co-N active sites,pyridine nitrogen and graphite nitrogen,allowing the catalyst to have better OER and ORR performance under this pressure.Co@C-N-0.26 shows an outstanding OER activity with a low of potential of 1.574V vs.RHE at a current density of 10 mA.cm^-2,and a lower Tafel slope(66.7 mV.decade^-1).Cathodic reduction peak position of Co@C-N-0.26 is similar to the commercial Pt/C,which has good ORR catalytic properties.?3?B,N double-doped cobalt-based carbon materials were synthesized by simple one-pot thermal treatment of complex Co?tzbc?₂?H₂O?₄ and H₃BO₃,which apply in HER,OER and ORR.The experimental results show that the content of B can be used as the key to regulate the electrochemical performance.Different B/N ratios can result in different electronic structures and morphologies,which can be applied to different electrochemical properties.The B/N of 0.25:1 has good oxygen reduction catalytic properties.Such excellent performances are attributed to the fluffy graphitization carbon layer structure,strong the O-B-C bonds and the B-C bonds.For hydrogen evolution reaction and oxygen evolution reaction,compared with other materials,there are smaller Co nanoparticles as catalytic active sites at a B/N ratio of 0.5:1,which is favorable for the catalytic performance of HER and OER.