The Study Of Patterned Graphene In Supercapacitors

The rise of smart electronics,such as smartphones,sport bands and intelligent?household?robots has stimulated the rapid development of high-performance energy storage devices.As typical energy storage devices,supercapacitors have been extensively studied.Supercapacitors arise as new energy storage devices that work based on the electric double layer of the electrode-electrolyte interface.According to different working mechanisms,they can be divided into electric double layer capacitors and pseudocapacitors.Generally,supercapacitors possess high power density,long cycle life,and good stability.Therefore,they are widely used in production,dalily life,and military fields.However,supercapacitors suffer from low energy density.In order to make full use of the superior characteristics of supercapacitors,problems of lower energy density,especially insufficient capacitance must be solved firstly.There are many strategies to improve the energy density of supercapacitors,in which developing efficient electrode materials is of critical importance.Recently,graphene-based supercapacitors have been considered as promising energy storage devices,since graphene using as electrode material shows excellent physical and chemical properties,such as outstanding electrical conductivity,flexibility,mechanical strength,and high surface area.However,the preparation of graphene electrodes still faces huge challenges,including?1?realizing mass production of graphene electrodes,?2?modifying graphene electrodes,?3?developing graphene hybrids,?4?exploring novel wearable and flexible graphene device,?5?advancing integrated and miniaturized devices and so on.For example,as an alternative,graphene oxide?GO?prepared by simple chemical oxidation of graphite has been considered a potential precursor for mass production of graphene-related materials.Yet,because of the chemical oxidation treatments,GO has a lot of oxygen-containing groups?OCGs?,and thus it is insulating,which makes it unsuitable for applications as electrodes.Therefore,it is necessary to adjust the OCGs on GO sheets by using suitable reduction treatments.Meanwhile,electrode patterning should be taken into consideration,which involves multiple complex processes.What's more,open problems with regard to compatibility between materials processing and device fabrication are still challenging.To solve the above-mentioned problems,we have carried out a series of experimental works using GO as a precursor.Through laser processing,GO is photoreduced,patterned and modified during one simple direct laser writing step.The main results are as follows:1.Micro-nano structured graphene supercapacitor.By using simple two-beam laser interference?TBLI?technologies,we achieved hierarchically structuring and synchronous photoreduction of GO.After TBLI process,hierarchical micro-nanostructures including microscale gratings and layered nanoporous structures formed.Interestingly,the morphology and reduction degree of TBLI reduced GO are highly dependent on the laser intensity,which provides the possibility to control the micronanostructures,chemical composition and conductivity of graphene electrode.As comparison,thermal reduced GO?TRGO?samples were controlled to obtain similar oxygen contents as TBLI reduced GO.What's more,the TBLI reduced GO based supercapacitors exhibit higher specific capacitances and better device performances compared to the devices based on TRGO.2.Laser-assisted nitrogen-doped graphene supercapacitors.Facing the insufficient capacity of graphene electrodes,it's still of great challenge to further improve the capacitance of such photoreduced graphene oxide-based supercapacitors and simplify multiple fabrication steps into single one.We have demonstrated the preparation of nitrogen-rich carbon nanoparticles?NCNPs?as a solid-state doping agent,which can be effectively doped in GO during the laser direct writing photoreduction process.Since both the NCNPs and GO could be well-dispersed in water,a composite?NCNPs@GO?with tunable contents of the two materials could be easily obtained,in which NCNPs could be uniformly distributed.Therefore,the resultant reduced NCNPs@GO?R-NCNPs@GO?composites not only have a high N content of?7.78 atom % but possess good electrical conductivity and porous structure.Supercapacitors based on R-NCNPs@GO showed much higher rate performance and relatively better specific capacitance value as compared with that based on bare RGO prepared in the same way.The enhanced device performance was due to the introduction of uniform distribution of NCNPs in the composite.3.Flexible planar supercapacitors based on graphene oxide and black phosphorus quantum dots nanocomposites.We demonstrate simple direct laser writing?DLW?of flexible planar supercapacitors based on GO and black phosphorus quantum dots?BPQDs?hybrids.The photoreduction effect of DLW process can render fair conductivity to the hybrid material and lead to planar interdigital electrode patterns on flexible substrates at the same time.Due to the synergistic effect of high conductivity derived from reduced GO?RGO?and abundant active sites at the surface of BPQDs,the resultant supercapacitors showed enhanced specific capacity and superior rate performance compared to that based on solo RGO electrode.Furthermore,the as-fabricated hybrid device exhibited outstanding flexibility.After 1000 bending cycles,no obvious performance degradation can be observed.In addition,DLW technology can also facilitate the integration of such supercapacitors.The integrated device presented reasonable performance uniformity with a voltage extension of 3 V,which could easily power a light-emitting diode?LED?.4.Planar and flexible supercapacitors based on graphene oxide and manganese dioxide nanoparticles composite on paper substrate.Most of the traditional paper-based supercapacitors adopted sandwich structure.However,to satisfy the tremendous demand of wearable electronics,developing planar paper-based device is still challenging.Herein,we use simple direct laser writing?DLW?technique to fabricate in-plane supercapacitors based on graphene oxide?GO?and manganese dioxide?MnO₂?nanoparticles on paper substrate.Taking all advantage of porous structure and absorptive surface properties of the paper substrate and the pseudocapacity of MnO₂,the obtained device based on reduced composite?R-MnO₂+GO?shows enhanced specific capacitance value.What's more,integrated device including three in series interdigital electrodes can be easily achieved via DLW fabrication method,which can power a LED.In addition,it's worth noting that through exquisitely designing the substrate structure,the paper-based device presents excellent flexibility,which remains a high specific capacitance retention after repeated test cycles.5.Fetomsecond laser direct writing of graphene-based microcapacitors.In order to meet the urgent requirements of integrated electronic devices,it is of great significance to develop micro-supercapacitors?MSCs?for integrated and miniaturized applications.We reported the ultraminiaturized nitrogen-doped reduced graphene oxide micro-supercapacitors?MMSCs-NRGO?fabricated by fetomsecond laser direct writing?FsLDW?of GO under ammonia atmosphere.The MMSCs-NRGO interdigital patterns are 130 ?m long and 90 ?m wide.The resultant device MMSCs-NRGO delivers promoted specific capacitance of 1980 mF/cm²,which much higher than that of FsLDW of GO?MMSCs-RGO??326 mF/cm²?.Besides,the MMSCs-nrgo exhibits high energy density of 0.417 mWh/cm²at power density of 50 mW/cm².The enhanced electrochemical performance of MMSCs-NRGO was attributed to the introduction of nitrogen doping of reduced GO and the rational design of interdigital pattern of electrode.What's more,MSCs arrays and the integrated MMSCs-NRGO of in series and in parallel could be easily achieved by FsLDW.It's worth noting that the integrated MMSCs-NRGO could power a LED,which demonstrates successful miniaturization of MMSCs-NRGO without sacrificing its potential as the power source.In summary,we start with laser processing of patterned graphene oxide.During laser fabrication,complicated multiple procedures were simplified into single step,including tunable oxygen content,hierarchically structuring and synchronous photoreduction of GO,laser-assisted heteroatom doping,laser-assisted preparation of composite materials and development of flexible/miniaturized devices.By using simple two-beam laser interference?TBLI?technologies,we achieved hierarchically structuring and synchronous photoreduction of GO,providing the feasibility for controlling the micronanostructures,chemical composition and the conductivity of the graphene electrodes.Laser assisted the fabrication of nitrogen-doped graphene electrodes,during which tunable properties of R-NCNPs@GO could be easily obtained by adjusting the contents of GO/NCNPs.What's more,photoreduction and nitrogen doping were simultaneously accomplished.Direct laser writing of flexible planar supercapacitors based on GO and black phosphorus quantum dots hybrids can render fair conductivity to the hybrid material and lead to planar interdigital electrode patterns on flexible substrates at the same time.The simple laser fabrication process demonstrated the compatibility of electrode preparation with integrated processes.Direct laser writing of graphene oxide and manganese dioxide nanoparticles composite on paper substrate can take all advantage of porous structure and absorptive surface properties of the paper substrate and the pseudocapacity of MnO₂.The resultant R-MnO₂+GO based device possesses excellent electrochemical performance and shows great potential for developing planar devices.Fetomsecond laser direct writing of graphene oxide makes microelectrode patterning in micro size true and makes it easy to achieve integration,such as microelectrode arrays,series and parallel connection.Finally,the electrochemical performance and potential applications of laser-processed patterned graphene electrode devices were explored.