Carbon Based Microelectrodes' Surface Engineering And Electrochemical Performance

To increase the device density and deliver energy at higher efficiency,microsupercapacitors?MSCs?are attracting much attention.Among the MSCs,interdigital MSCs,with relatively high specific area and short ion diffusion pathway,are of great potential for the next generation energy storage micro-devices.Carbon materials are often used for the fabrication of interdigital MSCs for their large specific surface area and good conductivity.During the fabrication of carbon based MSCs,methods like inkjet printing,vapor deposition and electrodepositions are always used.However,these methods have shortcomings like high-cost,complex procedure and can't optimize the carbon based microelectrodes'performance easily and effectively.Compared with those methods,photolithography is widely used to fabricate MSCs for capability of facile control of interdigital electrode configuration and compatibility with the current microtechnologies.Additionally,the photoresist used in photolithography can be directly carbonized into porous carbon as microelectrodes for MSCs,thus the fabrication process of MSCs can be simplified,and the cost can be reduced.In this work,by developing SU-8 1060 the photoresist after exposing in the mixture of propylene glycol methyl ether acetate?PGMEA?and active materials?multi-wall carbon nanotubes?MWCNTs?,nitride acid treated MWCNTs?n-MWCNTs?and reduced graphene oxide?rGO??,patterned photoresist with active materials on its surface is obtained.Subsequent pyrolysis of the patterned photoresist is conducted in N₂ ambient at 900oC and 1 M PVA/H₂SO₄ electrolyte is applied to assembly the all solid-state MSCs.The results are as follows:1.The active materials?MWCNT,n-MWCNT and rGO?can be well dispersed in PGMEA after sonication,even after 24 hours.By developing the photoresist after exposing in the mixture,patterned photoresist with active materials on its surface are derived.Then the photoresist is pyrolyzed and assembled into high performance MSCs.This method shortened the production cycle and cost of the surface modified carbon based MSCs to a large extent.2.From the SEM results,it's found that the photoresist derived carbon possesses amorphous porous structure with wide pore size distribution,active materials can be effectively attached to the surface of electrode.For MWCNT and n-MWCNT,net-like structure is formed on the surface of the electrode with parts of the active materials rooted in the electrode.As to rGO modified electrode,most of the rGO are separately dispersed on the electrode with part of the rGO rooted in the electrode.Based on the results of electrochemical test of the microsupercapacitors,it's found that the capacity of MWCNT modified electrodes is 4.8 mF·cm^-2(10 mV·s^-1),the capacity of unmodified electrodes is 3.52 mF·cm^-2(10 mV·s^-1).Before modification,the maximum energy density of the electrodes is 2.08 mW·cm^-3(power density 0.094W·cm^-3),the maximum power density is 1.41 W·cm^-3(energy density 0.62mWh·cm^-3);After modified by MWCNT,the maximum energy density increases to2.85 mWh·cm^-3(power density 0.123 W·cm^-3),and the maximum power density increases to 1.98 W·cm^-3(energy density 0.88 mWh·cm^-3)?3.The improvement of the performance of carbon based MSCs mainly attribute to that the specific surface area of the microelectrodes is increased due to the MWCNTs on their surface,thus more ions can be absorbed during the charge,and the EDLC is increased,as well as the specific capacitance and energy density.Also,the conductivity of the microelectrode is improved due to the highly conductive MWCNTs,leading to faster charge transportation and result in the increment of power density.