Investigation And Analysis Of Transiation Metal Decorated Graphene-based Carbon Material For High-effective Oxygen Reduction Reaction

In recent years,due to the increasing global energy consumption and depletion of natural resources,thus,research on sustainable energy conversion and storage devices is pertinent.Currently,various energy devices,such as fuel cells,metal-air batteries,solar cells and supercapacitors are the most common used.Among these electrochemical device,PEMFCs and Zn-air batteries can directly convert chemical into electrical energy.Compared with other devices,which are environmentally friendly.Whether PEMFCs or Zn-air batteries,the sluggish kinetics of electrochemical oxygen reduction reaction?ORR?process retrict their further development.Platinum-based materials have long been regarded as the best active catalysts for ORR,yet their high cost and poisonous nature negatively influence their large-scale applicaton.Furthermore,in the practical electrochemical reaction,Pt-based hybrids often suffer from particle dissolution and poisoning.These will greatly reduce their stability.In this thesis,we have reviewed successful experience of researchers in the field of ORR,we prepared several different non-noble ORR catalysts.The relatived characterization and discussion were summarized as following.1.Synthesis and Investigation Co,Co₃O₄ decorated graphene aerogel electrocatalyst for high-effective oxygen reduction reactionDue to the high cost,poisonous nature negatively,and poor stability of Pt/C,and this is a fatal problem for the actual development of oxygen reduction reaction.In this work,small Cobalt nanoparticles uniform in situ grown in three-dimentional grapheme?3DG?under the help of ascorbic acid?AA?by hydrothermal process.After further annealing in argon and hydrogen,thin carbon layers wrapped on the surface of Co nanoparticles were viewed by TEM.The exist of carbon layers can greatly improve the stability of the catalyst and prevent its corrosion.The Co/3DG catalyst was subjected to25 mV negative shifts for the half-wave after 5000 potential cycles.The electron transfer n values to be 3.81 to 3.94 for Co/3DG from-0.7 to-0.1 v,conforming that the ORR process almost through a four electron pathway.On the basis of the first work,we report a kind of tiny hollow nano-Co₃O₄ anchored 3D grapheme aerogels?3DG?in the first time,which derived from direct oxidation carbon wrapped Co/3DG through Kirkendall effect.Due to its unique structure and high specific surface area,hollow Co₃O₄/3DG hybrids shows excellent ORR catalytic activity with almost four-electron reduction pathway,high methanol tolerance and long-term durability in alkaline media.2.Nitrogen-doped graphene-like carbon with Fe₂N encapsulated in gaphitic layers as a catalyst in oxygen reduction reactionIn our second work,we report a novel soft-template method to construct Fe₂N/N-doped graphene-like carbon?NC?hybrid.NC and Fe-N_x units play different roles,and synergistic enhancement of catalyst performance.It is interesting that the a few carbon layers wrapped on the surface of Fe₂N nanoparticles,which facilitated to form Fe-N-C catalytic sites.Fe₂N@NC compounds show a good catalytic activity,including positive onset potential and almost half-wave potential towards Pt/C.Furthermore,the catalyst of Fe₂N@NC was applied to air catalyst of zinc-air batteries,which display a better open circuit voltage and adjacent power density than Pt/C.These results futher suggest that the catalyst of Fe₂N@NC can be use for a alternative catalyst to Pt/C in practical applications.3.Design and synthesis Co/N/S decorated porous carbon architectures as a high-effective catalysis in ORRIn our last work,we use cysteine,melamine and cobalt salt control synthesis Co/N/S decorated graphene-like material.The performance of catalyst is further improved?mainly in half-wave potential and limiting current density?after acid corrosion.Based on the related literature and analysis our experiment data,we believe that metal cobalt did not directly involved in the reaction and it is not the true active center.At the same time,we think some cobalt atoms may infiltrated into the carbon shell and bond with N,S and C form Co-N-C or Co-N-S active centers.In addition,the as-prepared Co@NSC-acid catalyst also exhibited a good electrochemical properties?including open circuit voltage,power density and good stability?in zinc-air batteries.