Preparation And Performance Studies Of Heteroatom Doped Three-dimensional Graphene Composites

Three-dimensional graphene was synthesized by facile hydrothermal method with graphene oxide?GO?.The three-dimensional graphene has superior specific surface area,strong mechanical strengths and high electrical conductivities,which are attractive for supercapacitance,sensor and catalytic system.Especially in the field of supercapacitor,huge surface area of three-dimensional graphene can overcome the disadvantage of restacking of graphene and enhance the electric double layer capacitors.In order to further improve its property,we take the method that heteroatom doped three-dimensional graphene and prepared its composites.In this work,we prepared heteroatom doped three-dimensional graphene and its composites in order to synthesize excellent electrode materials.The structures and morphologies of the heteroatom doped three-dimensional graphene and its composites were characterized by various techniques,and electrochemical properties were also investigated.The main research results and conclusions are as follows:?1?Three-dimensional graphene?RGO?,nitrogen doped three-dimensional graphene?RGN?and nitrogen,sulfur co-doped three-dimensional graphene?RGNS?were synthesized by facile hydrothermal method with graphene oxide?GO?;GO and and urea;GO and thiourea as raw materials,respectively.The structures and morphologies of GO,RGO,RGN and RGNS were characterized by various techniques,and electrochemical properties were also investigated.The results exhibit GO,RGO,RGN and RGNS are three-dimensional structure.The specific capacitance and cyclic stability of RGN and RGNS are higher than RGO.?2?Three-dimensional nitrogen-doped graphene/polyaniline hydrogels?RGNP?was synthesized by facile hydrothermal method with graphene oxide?GO?and polyaniline nanorods?PANI-NRs?,and urea as the reducing agent and nitrogen source.The structures and morphologies of the composites were characterized by various techniques,and electrochemical properties were also investigated.X-ray photoelectron spectroscopy?XPS?demonstrated nitrogen atom was doped into graphene and scanning electron microscopy?SEM?indicated PANI-NRs fully inset into the three-dimensional graphene layers.The RGNP composite electrode exhibited the significantly improved electrochemical performances compared to the undoped equivalents or the separate components.The specific capacitance is up to 589.3 F g^-1 at current density of 3 m A cm^-2 in 1M H2SO4 electrolyte,which also displays superior pseudocapacitive cycling stability?retention of 80.5% after 500 cycles?.In addition,good capacitance retention rate(80.2% at 30 m A cm^-2)has been achieved.These results indicate that the RGNP composite electrode can be applied for high performance supercapacitor.?3?Three-dimensional nitrogen,sulfur co-doped graphene/polyaniline hydrogels?RGNSP?was synthesized by facile hydrothermal method with graphene oxide?GO?and polyaniline nanorods?PANI-NRs?,and thiourea as the reducing agent and nitrogen,sulfur source.X-ray photoelectron spectroscopy?XPS?demonstrated nitrogen,sulfur atoms was co-doped into graphene.The specific capacitance is up to 735.2 F g^-1 at current density of 2 m A cm^-2 in 1M H2SO4 electrolyte,which also displays good capacitance retention rate(570 F g^-1 at 20 m A cm^-2)has been achieved.However,PANI only exhibits the capacitance of 210 F g^-1 at current density of 2m A cm^-2.The capacitance retention of RGNSP of 66.7 % is attained after 500 cycle tests compare with 52.5 % for that of pure PANI at current density of 2 m A cm^-2.?4?In this work,3D nitrogen-doped graphene/cobalt-nickle layered double hydroxide?RGN/Co Ni-LDH?is synthesized by a facile co-precipitation method.Scanning electron microscopy?SEM?images indicate 3D nitrogen-doped graphene can lead to the good dispersion of Co Ni-LDH nanolayer.The specific capacitance is up to 2092.3 F g^-1 at current density of 5 m A cm^-2 in 6 M KOH electrolyte.In addition,good capacitance retention rate(86.5% at 50 m A cm^-2)has been achieved.The capacitance retention of RGN/Co Ni-LDH of 80% is attained after 1000 cycle tests at current density of 10 m A cm^-2.In two-electrode asymmetric system,the energy density of RGN/Co Ni-LDH is 49.4 Wh kg^-1 at the power density of 101.97 W kg^-1.