Enhanced charge storage performance of MXene based all-solid-state supercapacitor with vertical graphene arrays as the current collector

摘要

The dwindling depletion of fossil fuels and ever-growing energy demand are the two sole persuasive reasons of the search for renewable clean green energy sources and the storing of these energy sources are called for im-mediate attention for the fabrication of supercapacitor like efficient energy storage devices. Variety of electrode materials have been investigated over the past years to surpass the shortcomings (low energy density, poor stability, high internal resistance etc.) of the two main category of supercapacitors i.e., electric double layer (EDL) capacitor and pseudocapacitor. To tie the advantages of both of these types of supercapacitive materials, herein we have fabricated a two-electrode symmetric device using Ti3C2Tx MXene and passivated vertical gra-phene nanosheets (VGN) as a current collector material. The easily synthesized material was investigated through several characterization techniques like X-ray diffraction, field emission scanning electron microscopy, high resolution transmission electron microscopy, contact angle measurements, surface area analysis and finally the electrochemical measurements. The device displayed a high areal capacitance of 199 mF/cm2 at 0.08 mA/ cm2 along with an excellent stability and columbic efficiency of 90 % and nearly 100 % over 6000 repetitive charge-discharge cycles. The energy density and corresponding power density were also found to be remarkable and as high as 13.57 mu Wh/cm2 and 31.07 mu W/cm2 respectively. To corroborate our experimental observations qualitatively, we have carried out the extensive Density Functional Theory (DFT) simulations and presented the structural and electronic properties of pristine VGN and MXene sheets and MXene@VGN. The interaction be-tween VGN and MXene is due to charge transfer from Ti 3d orbital of MXene to C 2p orbital of VGN. Enhanced quantum capacitance and lower diffusion energy barrier for the electrolyte's ions in MXene@VGN justify the superior charge storage performance in the modified structure compared to pristine VGN and MXene as observed in the experiment. The computed quantum capacitance follows the trend MXene@VGN >MXene >VGN, matching nicely with the trend of specific capacitance obtained in the experiment