| Currently,the demand for energy storage devices is growing rapidly and these devices are moving toward implantability,easy portability,and foldability,which also puts higher demands on the performance of energy storage devices including micro-supercapacitors（MSCs）.Planar on-chip MSCs have characteristics such as high power density,long cycle life,and fast charge/discharge rate,and the electrode material largely determines the performance.Therefore,how to achieve an overall improvement of the electrochemical performance of MSCs by replacing or improving the electrode materials has received increasing attention.Graphene quantum dots（GQDs）are very small special graphene fragments that can improve the electrochemical activity of electrodes.Related reports indicate that theπ-πbonds between different layers of graphene or GQDs will have a gravitational force,resulting in an increase in the number of layers and stacking.The overall performance is that the graphene or GQDs film becomes thicker,which will severely reduce the specific surface area and the diffusion rate.Functionalized graphene quantum dots（Aminated graphene quantum dots,A-GQDs）can weaken the interaction betweenπ-πbonds,thereby increasing the specific surface area and the ion diffusion rate,improving the overall electrochemical performance of MSCs.In addition,the reduction of epoxy groups in A-GQDs may be due to the nucleophilic reaction of this material with ammonia during the preparation process,thus converting some of the groups to amino groups,and it is also due to the presence of amino groups that improves the transfer rate between electrodes and the surface chemical activity of the electrode material.In this paper,A-GQDs aqueous solution was used as a new electrode material,the electrode films and the planar on-chip MSCs were fabricated and by improved liquid-air interface self-assembly,photolithography,magnetron sputtering,etching processes and other crafts.According to the characterization results of the electrode films,A-GQDs contain abundant edge defects and functional groups,the average particle size is about 1.62 nm and obvious lattice stripes can be observed in the quantum dots under high resolution.A-GQDs were used as the electrode material to fabricate MSCs for several electrochemical tests,the minimum scan rate of the devices could be measured as 0.1 V s-1,at which the surface capacitance and energy density of the devices were 73.53μF cm-2and 10.21 n Wh cm-2,respectively,and the power density of the devices reached the maximum value of 113.55μW cm-2when the scan rate was increased to 10000 V s-1and the time constant was calculated to be1.23μs based on the maximum characteristic frequency of the impedance spectrum of 813 k Hz.Using the same fabrication process,four different planar on-chip MSCs with electrode width/gap width of 2μm/2μm,6μm/2μm,30μm/10μm and 100μm/100μm,respectively,were prepared by the controlled variable method.Chemical tests and drawing comparisons.According to the experimental results,reducing the electrode width can improve the overall performance of MSCs.When the electrode width is reduced to a certain value,it is necessary to consider whether the electrolyte can penetrate completely.Insufficient penetration will affect ion transport and lead to device performance reduce.Finally,by controlling the ratio of electrode width to gap width to be 6μm/2μm,three kinds of MSCs with different film thicknesses were prepared and electrochemical tests were carried out,which showed that the thinner the electrode film,the better the device performance.The characterization test and electrochemical analysis in this paper show that A-GQDs as the electrode material can significantly improve the rate capability and power density of MSCs on the planar sheet,which has a good development prospect. |
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