Studies On Preparation And Performance Of Multi-doped Graphene-based Electrocatalysts

Due to the synergistic electronic effect of heterogeneous dopants,the multi-atom doped carbon nanomaterials have become promising fuel cell electrocatalysts.However,their electrochemical performance largely depends on the structural design of the doped atoms,and the study on their electrocatalytic mechanism is still a huge challenge.Multi-atom co-doped graphene can not only utilize the synergistic effect of heteroatoms to further enhance the catalytic performance,but also enrich the active sites of graphene for better deposition of metal nanoparticles,so it has been widely concerned and recognized by researchers.However,the current methods and processes for the synthesis of multi-atom doped graphene are relatively complicated,and there are many kinds of precursors involved,especially the frequent use of surfactants or toxic organic solvents,which results in the serious environment pollution and is not conducive to commercial development planning.Consequently,it is necessary to further develop green,simple and efficient synthesis method and process of multi-atom doped graphene,so as to reduce the types of precursors,cut the cost,and improve the catalytic efficiency of the catalyst.This thesis has mainly focused on the following aspects:（1）A simple sulfonated iron phthalocyanine pyrolysis strategy was used to design and prepare Fe,N,S tri-doped graphene composites（Fe-N-S-GR）,which were used as support materials for dendritic Pt nanoparticles（Pt NDs）.Transmission electron microscope（TEM）,X-ray energy dispersive spectroscopy（EDX）,Raman spectroscopy（Raman）,X-ray diffraction（XRD）,ultraviolet-visible absorption spectroscopy（UV-vis）,thermogravimetric analysis（TGA）,X-ray photoelectron spectroscopy（XPS）and X-ray absorption fine structure（XANES）techniques are used to characterize the prepared composites and explore the morphology and electronic structure of the materials.Several electrochemical testing methods were used to study the electrocatalytic activity,long-term electrochemistry durability,and anti-poison ability of the prepared Pt NDs/Fe-N-S-GR,Pt/Fe-N-GR,Pt/GO and commercial Pt/C catalysts for methanol oxidation.In addition,density functional theory（DFT）calculations were used to reveal the synergistic effect between Pt nanoparticles and multiple doped atoms on enhancing catalyst performance.（2）With sulfonated metal phthalocyanine（TSMPc,M=Cu,Fe,Co,Ni）as the precursors,M-N-S tri-doped graphene composites and four Pt electrocatalysts（Pt/M-N-S-G）were prepared.Various physical characterization methods were used to characterize the morphology and electronic structure of the prepared samples.At the same time,electrochemical tests show that compared with commercial Pt/C catalyst,the prepared Pt/M-N-S-G greatly improves their electrochemically active surface area,and the electrocatalytic activity and stability for methanol oxidation.Among them,Pt/Cu-N-S-G exhibits the best methanol oxidation electrocatalytic performance(2368 m A mg_Pt^-1),and the performance order for the catalysts based on different TSMPc is Cu>Ni>Co>Fe.In addition,the DFT calculations were also used to study the effect of adsorption and bonding ability of Pt atoms on the M-N-S tri-doped graphene on the performance enhancement of the catalyst.（3）2,5-dimercaptothiadiazole and ferric hydroxide colloid were used as the precursors to prepare Fe₃O₄ functionalized S,N co-doped graphene composite support,and then the Pt/Fe₃O₄-SNG catalyst for methanol oxidation could be obtained through the deposition of Pt nanoparticles.The morphology and electronic structure of the prepared samples were characterized by various physical characterization methods.Several electrochemical testing methods were used to study the electrocatalytic performance of Pt/Fe₃O₄-SNG,S,N-doped graphene supported Pt（Pt/SNG）,Fe₃O₄ functionalized graphene supported Pt（Pt/Fe₃O₄-G）and commercial Pt/C catalysts.Due to the strong interaction between Pt nanoparticles and Fe₃O₄functionalized S,N-doped graphene,the Pt/Fe₃O₄-SNG exhibits greater electrochemical active surface areas(162.06 m² g^-1),higher electrocatalytic activity(1129.07 m A mg_Pt^-1)and stability,and anti-CO poisoning ability for methanol oxidation.（4）With perfluoro copper phthalocyanine as the precursor,N and F co-doped graphene supported Cu single-atom catalyst（Cu-NFG SAC）was synthesized for catalyzing oxygen reduction.Meanwhile,Cu-NFG SAC was also used as the support to deposit Pt nanoparticles with a network structure（Pt/Cu-NFG SAC）,which is applied to methanol oxidation.Various physical characterization techniques were used to reveal the morphology and electronic structure of the materials.The electrochemical tests show that Cu-NFG SAC has higher oxygen reduction electrocatalytic activity(the limiting current density is 5.93 m A cm^-2,the half-wave potential is0.89 V,and the current density at 0.9 V is 2.00 m A cm^-2)and stability than Cu,N-doped graphene（Cu NG）,N-doped graphene（NG）and commercial Pt/C catalysts.In addition,compared with Pt/Cu NG,Pt/NG and commercial Pt/C catalysts,Pt/Cu-NFG SAC has the highest electrocatalytic activity,stability and anti-poisoning ability for methanol oxidation.This thesis mainly focuses on the studies of the controllable construction methods of the novel and highly efficient heteroatom-doped graphene,and reveals the internal relationship and law between the surface structure of as-prepared multidoped graphene supporting Pt or metal single atom catalysts and the electrocatalytic reaction performance.It is found that,the prepared catalysts can greatly improve the electrocatalytic activity,stability and anti-toxicity for methanol oxidation or oxygen reduction reactions,and also improve the utilization efficiency of precious metal Pt.The research contents have important theoretical and practical significance for the design and construction of high-performance heteroatom doped carbon nanomaterial-based fuel cell catalysts.