Fabrication And Catalytic Performance Of Graphene Based Carbon Materials

Carbon materials have become the hotspots in current research due to their rich forms and diverse structures.Carbon-based materials represented by graphene have outstanding optical,thermal,electrical,magnetic and mechanical properties,and are widely used in many fields such as energy,environment,electronics and life science.In order to overcome the shortcomings of easy accumulation and agglomeration of graphene,chemical modification and structural construction have been carried out to ensure the stability of the material.In this paper,graphene-based carbon materials have been constructed from the top-down design method of modifying large-scale carbon materials and the bottom-up design method of assembling small molecular carbon sources to form complex structural systems,and their catalytic performance in energy and environment fields have been explored.The main research results are as follows:Based on the top-down design method,graphene oxide was obtained by oxidative exfoliation of graphite and then combined with transition metal oxides and noble metal nanoparticles to prepare partially reduced graphene oxide supported Au,Ag andγ-Fe₂O₃ magnetic trimetallic nanocomposites,and the heterogeneous catalytic performance of the as-prepared materials toward the reduction of 4-NP was investigated.It was found that the reducing agent with stronger reduction property promoted a faster nucleation of metal nanoparticles,resulting in a smaller particle size,and the synergistic effect between Au and Ag effectively improved the catalytic activity.Moreover,the nanocomposites could be easily separated from the reaction system with the help of superparamagnetism,and the catalyst can still maintain good catalytic activity after repeated reuse.Graphene hydrogel-based nitrogen-carbon materials with tunable nitrogen configuration were synthesized by hydrothermal and ammonia pyrolysis of graphene oxide,and the electrocatalytic performance of the as-prepared materials toward oxygen reduction reaction（ORR）was investigated.The abundance of various N-moieties formed under elevated pyrolysis temperature was quantified to study their roles in the reaction mechanism in detail,and it was found that the pyrrolic-N is conducive to a higher onset potential,while quaternary-N is beneficial to the four-electron ORR pathway.The sample with the best performance achieves an onset potential of 0.95 V versus RHE,electron transfer number of 3.61-3.99,along with methanol tolerance and superior long-term stability.Based on the exploration of the construction of nitrogen-doped graphitized materials,Fe NC materials were prepare by further introduction of metal elements,and the electrocatalytic performance of the as-prepared Fe NC materials toward ORR was investigated.It was found that the catalytic activity center was derived from Fe₂N structure,and the hydrogel-based preparation process can ensure the uniform dispersion of active sites.The best-performing sample has better catalytic activity than commercial Pt/C catalysts,with an onset potential of 1.06 V versus RHE,electron transfer number of 3.88-3.99,along with methanol tolerance and long-term stability.Based on the bottom-up design method,three-dimensional carbon and nitrogen materials with skeleton structure were synthesized by starch hydrosol using rapid freezing and freeze-drying processes with salt as template,and the electrocatalytic performance of the as-prepared materials toward ORR was investigated.The preparation process based on the template method brings a rich pore structure for the material.The stress change of carbon layer caused by the two-step pyrolysis process increases the carbon layer spacing,which is conducive to mass transfer.The sample with the best performance is comparable to commercial Pt/C,with an onset potential of0.96 V versus RHE,electron transfer number close to 4,and long-term stability.