Electrochromic Properties Of Nickel Oxide Film Prepared by Successive Ionic Layer Adsorption and Reaction Method
ELECTROCHROMIC PROPERTIES OF NICKEL OXIDE FILM PREPARED BY SUCCESSIVE IONIC LAYER ADSORPTION AND REACTION METHOD
1,2TURAN TAŞKÖPRÜ, 1 EVREN TURAN
1Department of Physics, Faculty of Science, Anadolu University, Eskişehir, Turkey
2Department of Physics, Çankırı Karatekin University, Çankırı, Turkey
E-mail :
Abstract: Nickel oxide film was deposited on FTO coated glass substrate using the successive ionic layer adsorption and reaction (SILAR) method. Structural and electrochemical features of the NiO film were investigated. XRD studies reveal that the films is polycrystalline with faced centered cubic structure with (200) preferential orientation. The electrochemical behavior of the film was studied by means of cyclic voltammetry in 0.3 M KOH solution. The reversibility of the film found to be in the range of 87 and 79% .
Keywords: Nickel oxide; Electrochromism; SILAR
3
Electrochromic Properties Of Nickel Oxide Film Prepared by Successive Ionic Layer Adsorption and Reaction Method
1. INTRODUCTION
Nickel oxide is one of the most popular transition metal oxides with p-type semiconductivity and having wide band gap in the range of 3.6 - 4.0 eV [1]. NiO has been extensively studied as optically active material in electrochromic devices, gas sensors, magnetic materials and fuel cell electrodes [2].
Different techniques are being currently used in order to produce nickel oxide films such as RF sputtering, electron beam evaporation, spray pyrolysis, sol-gel technique, chemical bath deposition and SILAR method [3]. Among them SILAR method has various advantages such as low cost, low deposition temperature, high feasibility for large area deposition, layer-by-layer growing feature, good control over the deposition process and film thickness.
In this study, the structural and electrochemical features of the NiO film have been discussed.
2. DETAILS EXPERIMENTAL
NiO film was prepared on ultrasonically cleaned FTO coated conductive glass substrate by SILAR method. For the deposition of film, 0. 1 M nickel nitrate solution in double distilled water is used as cationic precursor. As an oxidizing agent diluted KOH is used which acts as anionic precursor. The deposition was carried out at room temperature. A SILAR cycle involves two following steps: (1) immersing the substrate in cationic precursor Ni(NO3)2.6H2O solution for 5 s so that the nickel ions were adsorbed on the surface of the substrate, (2) immersing the substrate in anionic precursor KOH solution for 10 s for nickel ions to react with the adsorbed OH- ions on the glass substrate resulting in the formation of nickel hydroxide. Nickel hydroxide film has produced for 5 SILAR cycles. The as-deposited films were annealed at 400ºC for two hours in air.
X-ray diffractometer (Bruker D8 Advance XRD) with Cu Kα line wavelength 1.5406 Å was used to analyze the crystal structure. The optical transmission measurements recorded using Solid Spec-3700 DUV spectrophotometer in the wavelength range 200–1000 nm. Raman spectrum was obtained with a Bruker Senterra Dispersive Raman Microscope. A 3B diode laser (532 nm) having 3 - 5 cm−1 resolution was used as excitation source at a power of 20 mW. The electrochemical properties of the film was characterized by cyclic voltammetry in a three-electrode arrangement using Electrochemical Quartz Potentiometer. Ag/AgCl was used as a reference electrode, a platinum wire as the counter electrode and NiO films deposited on FTO substrate as the working electrode. The sample was cycled at 100 mV/s in 0.3 M KOH solution. The current density data were recorded during 50 cycles under the conditions described above.
3. RESULTS AND DISCUSSION
XRD pattern exhibits a face centered cubic crystal structure having a preferential growth along (200) plane. The other lower intensity peaks (111), (220) and (311) have also been assigned to NiO face centered cubic phase (Bunsenite, JCSPD 47-1049)(Fig.1.). Other peaks in XRD pattern belong to FTO.
Fig.2. shows the Raman spectrum for NiO film. Raman peaks located around 518 cm-1 and 1100 cm-1 could be assigned to LO and 2LO phonon modes of NiO, respectively. The LO mode at 518 cm-1 showed that the NiO film is almost stoichiometric [4].
Fig.1. XRD pattern of NiO (Other peaks belong to FTO)
Fig.2. Raman spectra of NiO film at room temperature
The electrochemical properties of the NiO film was characterized by cyclic voltammetry. The film has been cycled from -0.6 V to 1.4 V at a sweep rate of 100 mV/s in 0.3 M KOH solution. The cyclic voltammetric curves [1st, 25th and 50th cycles] for the NiO film are shown in Fig.3. The peaks associated with each cycle correspond to the oxidation (Ox.) and the reduction (Rx.) process during the electrochemical experiment. During anodic potential scan, oxidation of Ni2+ to Ni3+ takes place and causes brown coloration. During cathodic scan, bleaching of the film (Ni3+ to Ni2+) takes place. Coloration and bleaching of NiO film is associated with insertion and deinsertion of OH- ions and electrons in the film. The better-defined reduction peak and the more rapid increase in current as a function of potential indicate a larger and faster ion deintercalation from the NiO.
Fig. 3. Voltamograms of NiO in 0.3 M KOH at scan speed of 100 mV/s
From values of the amount of charges intercalated (Qa) during anodic scan and amount of charges de-intercalated (Qc) during cathodic scan, electrochromic reversibility was estimated. Qa/Qc gives us the coulombic efficiency of the film. The estimated values for reversibility of the film was given in Table 1. The reversibility varies between 87 and 79%.
Table 1: Parameters obtained from cyclic voltammetry
Fig. 4. Optical transmittance spectra of NiO film at its colored and bleached states
The change in optical density (∆OD) was calculated using the measured transmittance of the film in the colored (Tc) and bleached (Tb) states by applying the equation ∆OD = Log10 Tb/Tc. The change in optical density at l= 630 nm was found to be 0.38.
Fig.5. Photograph of the NiO film in the colored state
CONCLUSIONS
Electrochromic NiO film was successfully deposited by SILAR method. The Raman spectrum showed that the film is almost stoichiometric. The film showed reversibility in 0.3M KOH. The reversibility varies between 87 and 79%. The change in optical density at l= 630 nm was found to be 0.38.
ACKNOWLEDGMENTS
This work has been supported by the Scientific Research Commission of Anadolu University (1210F159).
REFERENCES
[1] D. Adler, J. Feinleib, Electrical and optical properties of narrow-band Materials, Phy Rev B, 2 ( 1970) 3112- 3134.
[2] P.C. Yu, C.M. Lampert, In-situ spectroscopic studies of electrochromic hydrated nickel oxide films, Sol. Energy Mater. , 19 (1989) 1-16.
[3] Taskopru, T., Bayansal, F., Sahin, B., Zor, M. (2015). Structural and optical properties of Co-doped NiO films prepared by SILAR method. Philosophical Magazine, 95,32-40.
[4] Gary, H. (2003). Chemical solution deposition of semiconductor films. Marcel Dekker Inc.
3