ORIGINAL PAPER Structural and electrochemical properties of spray deposited molybdenum trioxide ( α -MoO3) thin films S. A. Khalate 1 & R. S. Kate 1 & H. M. Pathan 2 & R. J. Deokate 1 Received: 20 December 2016 /Revised: 2 February 2017 /Accepted: 10 February 2017 # Springer-Verlag Berlin Heidelberg 2017 Abstract Nanostructured molybdenum trioxide ( α -MoO 3 ) thin films were deposited to investigate effect of substrate tem- perature on microstructural, morphological, optical, electrical, and electrochemical properties of the α -MoO 3 thin films. X-ray diffraction results indicated deposited α -MoO 3 thin films are polycrystalline, crystallizes in orthorhombic structure, and crys- talline quality improved with substrate temperature. Films show the optical band gap varied between 2.56 and 2.85 eV, the activation energy of the α -MoO 3 thin films were found to be in the range of 0.15 – 0.30 eV. The measured electrochemical properties of α -MoO 3 thin film electrode deposited at 673 K exhibits significantly improved supercapacitive performance in Na 2 SO 4 (0.5 M) electrolyte about 73.61 F/g at current density 0.6 mA/cm 2 than the other deposition temperatures. The max- imum energy density (11.13 Wh/kg) at the power density 10.54 kW/kg was observed. Keywords Orthorhombic phase . Nanorods . Optical properties . Electrochemical Introduction Recently, use of nanomaterial supercapacitor electrodes has been attracting great interest due to their high power and energy den- sities than the respective bulk materials [ 1 ]. According to the energy storage mechanism, supercapacitors are classified into two categories, namely, electrical double-layer capacitors (EDLC) with carbon materials as electrodes and pseudocapacitors with metal oxide or conducting polymers. Previous research has shown several important factors affecting the performance of EDLC: specific area, electrical conductivity, pore size, and distribution [ 2 ]. However, the low-energy density, especially the low volumetric energy density of EDLC materials is yet to be improved. The pseudocapacitors store energy through a Faradic process that involves fast and reversible redox reactions occurring at or near the electrode surface [ 3 – 5 ]. The most widely explored pseudocapacitive electrode materials include transition metal oxides or hydroxides (MnO 2 , V 2 O 5 , RuO 2 , Co 3 O 4 , NiO, MoO 3 , etc.) [ 6 – 11 ]; among these electrode materials for pseudocapacitors, MoO 3 has been extensively investigated due to its natural abundance, large theoretical capability, and low toxicity [ 12 ]. Moreover, MoO 3 have attracted much attention as pseudocapacitive electrode material due to its crystallographic structure, multiple oxidation states, n-type conductivity, etc. [ 13 – 15 ]. Different techniques like hydrothermal method [ 16 ], sputtering [ 17 ], atomic layer deposition [ 18 ], sol-gel [ 19 ], chemical vapor deposition [ 20 , 21 ], molecular beam epitaxy [ 22 ], and spray pyrolysis [ 23 – 26 ] have been used to prepare the α -MoO 3 thin films. Among them, spray pyrolysis coating is a simple and low-cost method for the preparation of thin films with large areas. This method is convenient for prepar-
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