Preparation And Electrochemical Performance Research Of Silicon-Based TiO₂ Nanotube Arrays Film Composite Electrode

With the ever-increasing deployment of micro/nano electronic systems,the need grows for smart and efficient energy-storage devices with high-performance and long lifetime.Planar micro-supercapacitors（MSCs）have drawn extensive research attention owing to their unique structural design and size compatibility for microelectronic devices.Titanium dioxide nanotubes with the high specific surface area have been used in various fields for its structural advantages and physicochemical properties.However,the preparation of TiO₂nanotubes arrays（TNTAs）is difficult to integrate with microelectronics technology.To solve this problem,in this work,for the first time we demonstrate an integration of TiO₂ nanotube arrays as a high-surface-area scaffold for on-chip supercapacitors.In this particular fabrication,TiO₂ NTAs were grown over silicon substrate through magnetron sputtering.The ordered TNTAs were grown by directly anodizing Ti film sputtered on planar silicon substrate.The effect of voltage,electrolyte composition,and anodization time on the morphology of nanotubes was investigated by scanning electron microscopy（SEM）and the optimized experimental parameters were obtained.It is found that the nanotubes with length about 2.00μm were prepared in ammonium fluoride electrolyte at constant voltage of 50V.The TNTAs were then electrochemically reduced to enhance their electrical conductivity.The reduced TNTAs（r-TNTAs）exhibit an extremely low series resistance of 5.7Ω.It is noted that the r-TNTAs present an optimized specific capacitance of 5.6mF·cm^-22 at 0.05 mA·cm^-2,which is 5 times higher than that of pristine TNTAs on silicon substrate.Furthermore,the r-TNTAs were used as scaffolds to support MnO₂ nanoparticles by electrochemical deposition.The MnO₂ decorated r-TNTAs show maximum specific capacitance 20.6 mF·cm^-2(volumetric specific capacitance of 103 F·cm^-3)at 0.05 mA·cm^-2 as well as excellent cycling stability with 82.1%capacitance retained after 3000 charge-discharge cycles.Such integration of silicon based TNTAs might open up new opportunities to construct 3D nanostructured electrodes for high-performance on-chip supercapacitors.Besides,tungsten oxide stand out among these electrode materials because of the low-cost and multiple oxidation states(W⁶⁺/W⁵⁺).WO₃ decorated TiO₂nanotube arrays（NTAs）film electrode for on-chip MSCs was fabricated via an efficient and facile approach.The chemical bath deposition（CBD）of tungsten trioxide is utilized to enhance the capacitive behavior.The integrated electrode demonstrated maximum electrochemical performance with an area capacitance of 27.45 mF·cm^-2 in 1 M H₂SO₄ aqueous electrolyte(with volume specific capacitance of 137.25 F·cm^-3)and 17.58 mF·cm^-2 in 1 M Na₂SO₄ electrolyte.Moreover,the Si/r-TNTAs@WO₃ electrode shows an excellent electrochemical performance with long cyclic stability（96.7%after 2000 cycles）.This study provides a new route to understand intrinsic electrochemical behaviors.The planar silicon integration of TiO₂ nanotube film electrode boasts a broad prospect and gigantic potentiality for highly efficient on-chip miniature energy storage equipment.