In-situ spectroscopic studies of electrochromic hydrated nickel oxide films

Abstract

In this investigation, in-situ spectroscopic studies of anodically deposited electrochromic hydrated nickel oxide electrodes were performed by visible/near-infrared spectroscopy and Fourier-Transform Infrared (FTIR) spectroscopy. All measurements were taken while the nickel oxide thin films were switching between the bleached and colored states, where the electrodes were not removed from the electrochemical cell. Optical transmittance measurements of the nickel oxide film relative to tin oxide coated glass varied during coloring from the integrated solar spectral transmittance, T.=1010/0-54%, and average near-infrared transmittance, T ni , = 1010/0-83%. The photopic transmission was Tp = 101 -31%. Transmittance" measurements versus time were also performed at selected wavelength values, ranging from 315 to llOO nm. Also diffe"rent scan rates (10-100 mV/s) were investigated at each of these wavelengths, where optimum switching rates could be determined. All changes in optical density were achieved by continuously cycling between a potential range ot.-5oo to +800 mY. Coloration occurs at a faster rate than bleaching of the films at every switching rate selected. Also, maximum and minimum transmission measurements at 420 nm do not to correspond to the cathodic and anodic peak current densities. Instead these transmission measurements correspond to the regions past the peak current densities. From these optical experiments, plots of transmission (%) versus voltage (mV) and transmission (%) versus total extracted charge (mC) were obtained. For FTIR spectroscopic experiments, chemical identification of the 10-20 nm thick films showed that the films exhibit different bonding environments for both the colored and bleached states. There exist surface hydroxyl groups associated with nickel oxide in the region of 3600-3800 cm-1 wave numbers. Fundamental water vibrations are also found at 3200-3500 cm-1 and at 1600-1700 cm-1 wave numbers. The nickel oxygen vibration region is at 400-525 cm-1 for both states. The coinparison of bleached and colored states exhibits distinctive molecular vibrational states, which correspond to Ni(OHh and NiOOH respectively.

Correlation between Chemical and Electronic Properties of Solution-Processed Nickel Oxide

“…α-Ni(OH) 2 can be identified by a broad absorption band between 3200 and 3700 cm −1 and several vibrational modes between 1300 and 1750 cm −1 . 45,46,49 These modes exhibit a clear temperature dependency: the higher T a the smaller their intensities, most probably because of the reduction of the α-Ni(OH) 2 concentration in the layers (we note that all films exhibit similar thicknesses; see Figure S4). This is a reasonable result since it is known that α-Ni(OH) 2 has the tendency to dehydrate, especially under thermal treatment, 50,51 and confirms that the degree of precursor transformation is dependent on T a .…”

“…When T a is reduced, these peaks become broader, indicating a less ordered structure. Possible overlapping contributions from Ni(OH) 2 , which also exhibit modes in this spectral range, 45,46 might slightly modify the FIR spectra.…”

Nickel oxide thin film from electrodeposited nickel sulfide thin film: peroxide sensing and photo-decomposition of phenol

“…The stability and the performances of the modified electrodes were tested over a wide range of pH (2)(3)(4)(5)(6)(7)(8)(9)(10)(11) and temperature (10-80 °C). It was determined that the maximum electrocatalytic decomposition of H 2 O 2 took place at pH 9 (Fig.…”

“…3 Nickel oxide (NiO), an electrochromic material (band gap energy from 3.6 to 4.0 eV) with high electron transport property, has received a great deal of interest because of its versatile application in modern science and technology. Thin films of NiO are widely used as gas sensors, 4 electrochemical display devices, 5 p-type transparent conducting electrodes, 6 organic light emitting diodes (OLEDs), 7 smart windows, 8 variable reflectance mirrors and non-emissive information displays. 9 Several deposition techniques, such as metal evaporation, 10 sputtering, 11 sol gel, 12 electrochemical and chemical 13 techniques, are employed to synthesize NiO thin films.…”

In Situ Optical Absorption Studies of Point Defect Kinetics and Thermodynamics in Oxide Thin Films

“…Each of these is discussed below. Extension of In Situ Optical Technique to New Compositions In situ optical absorption approaches have so far been applied to a limited set of compositions among oxides, including oxidation layers forming on metal/semiconductor films217 and nanoparticles,218 hydrated NiO x219 and IrO x ,220 (Zr,Y)O 2-d ,180 VO x ,161,162,163,164,166,167,168 TiO 2 , 136,145 MoO 3 , 74,139 WO 3 , 93 CoAl 2 O 4 , NiAl 2 O 4+,…”