Research On 2D MOFs/Conductive Polymer Composited Electrodes For All Solid State Transparent Supercapacitors

With the rapid development of intelligent electronic devices,flexible and transparent energy storage devices to match them have become important research fields.As one new generation of energy storage equipment,transparent supercapacitors have unique properties such as good electrochemical performance,strong mechanical flexibility and high optical transparency,having attracted extensive attention by numerous researchers.However,the practical applications of conventional flexible supercapacitors are still restricted by the low transmittance.As one of the most crucial components,the preparation of flexible transparent electrodes palys a siginificant role in transparent supercapacitors.Therefore,the design of advanced electrodes with high specific capacitance and transmittance is of great significance for developing the flexible transparent supercapacitors.Due to rich active site,large specific surface area and easy functionalization,metal-organic framework materials（MOFs）have been used as promising electrode materials.In particular,the two-dimensional MOFs,with an ultra-thin nanosheet structure make it pervious to ligh,thereby achieving high transparency of the electrode.However,the intrinsic low conductivity of MOFs,limits their applications in transparent energy storage devices.Interestingly,PEDOT:PSS exhibits relatively high conductivity,good pseudocapacitance and the ability to form a smmoth film.As a result,the combination of PEDOT:PSS and two-dimensional MOFs can effectively improve the conductivity of transparent electrodes,which may offer high capacitive performance for flexible transparent supercapacitors.The specific research work and results are as follows:（1）A two-dimensional nickel cobalt bimetallic MOF（NiCo-BDC）was prepared via a facil ice bath ultrasonic method,which was subsequently subjected to spun coating onto the ITO/PET substrate for the preparation of transparent film electrodes.The symmetric all solid sandwich transparent supercapacitor was assembled using the transparent film electrodes with PVA/KOH as gel electrolyte.The thickness and transmittance of thin film electrodes were regulated through altering the concentration of MOF solution.The experimental results showed that the transparency of obtained transparent thin film electrode and device could reach 80%and 60.2%at the wavelength of 550 nm,respectively.At the current density of 100μA cm^-2,the area specific capacitance of the symmetrical device could reach 2.1 m F cm^-2.It was worth noting that the assembled supercapacitor could still keep a capacitance retention rate of 68.8%even after repeatedly folding it to 180°,demonstrating good cycling stability.（2）In order to improve the energy storage performance of two-dimensional MOFs material,NiCo-BDC/PEDOT:PSS composite film electrode was prepared by spraying PEDOT:PSS on the surface of NiCo-BDC film.The symmetric all solid sandwich transparent supercapacitor was assembled using the transparent film electrodes with PVA/KOH as gel electrolyte.By changing the number of layers of PEDOT:PSS,the thickness,transmittance and conductivity of the composite electrode could be adjusted.The experimental results showed that the addition of PEDOT:PSS significantly improved the conductivity of the composite electrode and the capacitive performance of the transparent supercapacitor.The transparency of obtained transparent thin film electrode and the device could reach 64%and 56%at the wavelength of 550 nm,respectively.At the current density of100μA cm^-2,the area specific capacitance of the symmetrical device could reach 4.0 m F cm^-2.It was worth noting that the transparent supercapacitor still had 90%capacitance retention after 180°bending and folding,which indicated that the device had high cycle stability.