Designed Synthesis Of Functionalized Graphene For Electrochemical Energy Storage

Various aerospace power systems were needed in order to insure all kinds of spacecraft instruments and equipment work properly.Chemical energy device is an important part of the space power system which including various ion batteries and fuel cells.For the complex space environment,one of the main research focuses on chemical energy device is to develop electrode materials with high capacity and high stability.Graphene has the characteristics of large specific surface area and high conductivity have potential applications in various electrochemical energy storage device.In this paper,a variety of methods was developed for synthesis of functionalized graphene used for high performance electrode materials of batteries.First,inorder to alleviate the capacity reduction caused by the poor conductivity and volume effects of lithium electrode materials during charging and discharging,a method for preparing high conductivity 3D macroporous graphene(3DMG)by heating-quenching cycles was developed.The as prepared 3DMG has large specific surface area and high conductivity which was used to modify P25(Ti O2)and Fe2O3 lithium ion battery(LIBs)anode materials.The 3DMG/P25 composites feature excellent electrochemical performance with a higher capacity of 130 mAh g-1 which is 5.2 times larger than that of P25 after 50 cycles.At lower and higher test temperature conditions(0 oC and 40 oC),the 3DMG/P25 composites exhibit higher capacity of 91.7 and 89.1 mAh g-1 which is significantly better than those of the pure P25(10 and 27.8 m Ah g-1,respectively).XANES measurements demonstrate the formation of Ti–O–C bonds that ensure rapid electron transfer in the 3D MG/P25 nanocomposite,consequently leading to improved electrochemical performance.Furthermore,the 3D porous graphene also used for the modification of Fe2O3,and the modified materials exhibited higher capacity compared to bare anode materials at all test temperature.The results showed that the modified material can be used as anode materials under 0 to 40 oC,which has potential application in the space power supply system.Sodium-ion batteries(SIBs)is an important kind of electrochemical energy storage device.The main research goal for SIBs is to develop electrode materials with high capacity and high stability.However,the increase in ionic radius of Na+ ion as compared to Li+ ion will cause a larger volume expansion upon intercalation.At present,carbon materials,especially graphene,have good electrical conductivity and mechanical properties can be used as stable anode materials for SIBs.Here,3D N doped graphene structure was synthesized via a microreactor consisting of melamine fiber with a coated protective GO layer process.Such 3D N doped graphene structures show reversible sodium storage capacities up to 265 m Ah g-1 after 50 cycles at room temperature.At lower and higher test temperature conditions(0 oC and 40 oC),the 3D N doped graphene exhibit high capacity of 196 and 184 m Ah g-1 after 50 cycles The pores combined with N doping in the as synthesized 3D N doped graphene would facilitate ion transport and provide access of the electrolyte to the surface active sites.The results showed that the 3D N doped graphene can be used as SIBs anode materials under 0 to 40 oC,which provide a reference for its further application in the space environment.At present,doped graphene was used for fuel cell oxygen reduction catalyst,however,the catalytic active site in the doped graphene is not comfirmed.A novel one-pot strategy to synthesize N doped graphene through a direct transformation from bulk g-C3N4 was development.The N contents and species in doped graphene can be controllable adjusted via post annealing under 800 to 1000 oC.The as-prepared N doped graphene exhibited excellent catalytic activity for ORR.The electrochemical tests in combination with XPS analysis proved that the high electrocatalytic activity could be attributed to a high ratio of graphitic-N/pyridinic-N.Furthermore,S-N dual-doped graphene was synthesis via a simple pyrolysis of a mixture of melamine and dibenzyl sulfide as efficient electrocatalysts for ORR.The S-N dual doped graphen show enhanced activity towards ORR as compared with mono-doped counterparts and the S1N6C900 showed the most promising activity for ORR.In S-N dual doped carbon nanosheets,a high content of graphitic-N and pyridinic-N is necessary for ORR electrocatalysts,but an appropriate amount of S atoms further contributes to the improvement of ORR activity.Superior ORR of the performance from the as-prepared doped graphene implies great promises in practical applications in fuel cells.