Porous-Structured Graphene Materials As Electrodes For Electrochemical Applications

Graphene,the single layer of carbon atoms patterned in a hexagonal lattice,has attracted great attention all over the world for its potential applications in sensors,catalysis,energy storage devices,and environmental fields due to the brilliant mechanical,electronic,and thermal properties.Such as the formation of the three-dimensional(3D)porous architectures of graphene as anode materials is an effective strategy to achieve high-performance lithium ion batteries,such architectures not only allow fast access of electrolyte into the three-dimension 3D porous structure but also improves electron transportation and Li ion diffusion in the electrode.Therefore,to assembly 3D porous structure will be a good way to solve the problems in many applications.The research work is mainly comprised of two major applications that include several(3D)porous structured materials with specifically designed morphologies.The porous-structured materials in the first project was used as anode materials for Li-ion batteries.The second project deal with detection of heavy metal ions by electrochemistry using microporous graphene thin films(MGTF)as electrode.1.The morphology of electrode materials plays an important role in determining the performance of(LIBs).However,studies on determining the most favorable morphology for high-performance LIBs have rarely been reported.In this study,a series of F-doped SnOx(F-SnO2 and F-SnO)materials with various morphologies was synthesized using ethylene diamine as a structure-directing agent in a facile hydrothermal process.During the hydrothermal process,the F-SnOx was embedded in situ into the 3D architecture of reducedgraphene oxide(RGO)to form F-SnOx@RGO composites.The morphologies and nanostructures of F-SnOx,i.e,F-SnO2 nanocrystals,F-SnO nanosheets,and F-SnO2 aggregated particles,were fully characterized using electron microscopy,X-ray diffraction,and X-ray photoelectron spectroscopy.Electrochemical characterization indicated that the F-SnO2 nanocrystals uniformly distributed in the 3D RGO architecture exhibited higher specific capacity,better rate performance,and longer cycling stability than the F-SnO,with other morphologies.These excellent electrochemical performances were attributed to the uniform distribution of the F-SnO2 nanocrystals,which significantly alleviated the volume changes of the electrode material and shortened the Li ion diffusion path during lithiation/delithiation processes.The F-SnO2@RGO composite composed of uniformly distributed F-SnO2 nanocrystals also exhibited excellent rate performance,as the specific capacities were measured to be 1158 and 648mA h g-1 at current densities of 0.1 and 5 A g-1,respectively.2.Macroporous graphene thin films were prepared on ITO substrates(MGTFs@ITO)via an ice crystal-induced phase separation process and were used as electrodes for the electrochemical detection of heavy metal ions.The MGTF@ITO electrodes have been characterized by scanning electron microscopy,Raman spectroscopy and contact angle measurements.The results demonstrate that the MGTF@ITO has a high specific area with robust macroporous framework and a hydrophilic surface.The MGTFs@ITO as electrodes are found to exhibit enhanced currents at the redox peaks and decreased charge transfer resistances.Based on these outstanding properties,the MGTF@ITO electrodes exhibit excellent stripping performance for the analysis of Ag(I)with a detection limit of 0.005 ?g L-1.The high sensitivity of the MGTF@ITO electrodes can be ascribed to the well-defined macroporous framework,high electrical conductivity,high specific area and good wettability.The MGTF@ITO electrodes are further demonstrated applicable to the simultaneous detections of Zn(?),Cd(?),Pb(?),Cu(?)and Ag(?)ions with outstanding sensing performance.