Electronic Structure, Morphological Aspects, Optical and Electrochemical Properties of RuO2 Nanocrystals

Abstract

This letter reports the synthesis of RuO2 nanocrystals by the anionic surfactant-assisted hydrothermal method at 90 degrees C for 24 h followed by heat treatment at 500 degrees C for 1 h. These crystals were structurally characterized by means of X-ray diffraction (XRD) and Rietveld refinement analysis. Field emission scanning electron microscopy (FE-SEM) was employed to observe the morphological features these crystals. The optical behavior was investigated by ultraviolet-visible (UV-Vis) spectroscopy. First-principles quantum mechanical calculations based on the density functional theory at the B3LYP level were employed to obtain the electronic band structure and density of states. For electrochemical behavior, the supercapacitor properties of RuO2 crystals were investigated by cyclic voltammetry. XRD patterns and Rietveld refinement data indicate that RuO2 crystals have a rutile-type tetragonal structure. FE-SEM images showed the presence of sphere-like RuO2 crystals with an average crystal sized at around 19.13 nm. The experimental band gap energy (E-gap[exp]) was estimated at 2.60 eV by using UV-Vis spectroscopy, while the theoretical calculations indicate an E-gap[theo] at 1.92 eV. These calculations revealed a band structure predominantly composed of O 2p orbitals (valence band) and Ru 4d orbitals (conduction band). The specific capacitance measured for RuO2 film was 193 F g(-1) at 5 mV s(-1) in an electrode with 0.5 mg of electroactive material in 1 M Na2SO4 solution. Graphic For the first time, we report on the electronic structure, optical and electrochemical behavior of RuO2 nanocrystals/film synthesized by the anionic surfactant-assisted hydrothermal synthesis (90 degrees C for 24 h) followed by heat treatment (500 degrees C for 1 h).