Pseudocapacitance of Amorphous TiO2 Thin Films Anchored to Graphene and Carbon Nanotubes Using Atomic Layer Deposition

Abstract

Amorphous TiO2 thin films were conformally coated onto the surface of both graphene (G) and multiwalled carbon nanotube (CNT) samples using atomic layer deposition (ALD). An ultrathin Al2O3 adhesion layer was employed to obtain the conformal TiO2 ALD films. Using 1 M KOH as the electrolyte, the electrochemical characteristics of TiO2 ALD films grown using 25 and 50 TiO2 ALD cycles were then determined using cyclic voltammetry, galvanostatic charge/discharge curves, and electrochemical impedance spectroscopy. Because the TiO2 ALD films were ultrathin, the poor electrical conductivity and low ionic diffusivity of TiO2 did not limit the ability of the TiO2 ALD films to display high specific capacitance. The specific capacitances of the TiO2 ALD-coated G and CNT samples after 50 TiO2 ALD cycles were 97.5 and 135 F/g, respectively, at 1 A/g. The pseudocapacitance of the TiO2 ALD films greatly exceeded the electric double layer capacitance of the uncoated G and CNT samples. The galvanostatic charge/discharge ex...