Spectroelectrochemical and photoelectrochemical studies of electrodeposited tungsten trioxide films

Charge Separation, Band-Bending, and Recombination in WO3 Photoanodes

“…This feature, previously reported in photo-and electrochromic studies of WO3, arises from W 5+ states associated with oxygen vacancies, and therefore highlights that the occupancy of these states and the degree of band-bending in WO3 are directly correlated. 34,[36][37] The clear resemblance between the spectral signal observed when a greater number of these states are occupied (Figure 1b, cathodic potential) and the broad, red-NIR TA (Figure 1a, red) confirms our assignment of this signal to photogenerated electrons in W 5+ states, and thereby indicates their trapped nature. As such, this correlation suggests that changes in oxygenvacancy state occupancy as a result of band-bending may also manifest in changes in photogenerated populations that can be monitored transiently, with likely repercussions for performance.…”

Photochromism in transition-metal oxides

“…A longer irradiation time will result in a larger photochromic response [22]. This photochromic phenomenon is observed most prominently in thin films of tungsten oxide [8,, which can be prepared by thermal evaporation [8, 26-28, 44, 45, 47, 48, 68, 71], reactive evaporation [44,72] rf sputtering [22,29,37,44,71], dc sputtering [54], electron beam deposition [34,60], sol-gel-related techniques [24,38,55,73,74], spray pyrolysis [47], electrodeposition [63,64], laser-related deposition technique [51,52,58] and so on. Different techniques for the film preparation often lead to thin films with somewhat different properties.…”

“…The color remains quite stable in an inert atmosphere and there is a slight optical bleaching (5%) upon visible light irradiation. The color can be bleached by the introduction of oxidizing agent (such as O 2 , O 3 , H 2 O 2 and Fe 2 (SO 4 ) 3 ) [8,23,26,33,35,36,48], by application of anodic polarization [63,64], or by heating treatment in air [8]. In the case of bleaching by oxidizing agent or anodic polarization, the film can be colored again by UV light irradiation.…”

“…Besides the UV-Vis absorption spectra, the virgin and colored WO 3 films have been characterized widely by many other techniques, such as electron spin resonance (ESR) [73], Raman spectroscopy [17,60], Fourier transform infrared (FT-IR) absorption spectra [24,60,73], X-ray photoelectron spectroscopy (XPS) [45,50,58,63,64], extended X-ray absorption fine-structure spectroscopy (EX-AFS) [73], X-ray diffraction (XRD) [8,24], electron diffraction [8], electron microscopy [8,24,38,73], atomic force microscopy (AFM) [58], scanning tunneling microscopy (STM) [58], Auger electron spectroscopy (AES) [50], small-angle X-ray scattering (SAXS) [38,73], ellipsometry [54], electrical characterization [8,28,44,58], etc. These results indicate that the UV-light irradiation can lead to lots of changes in the properties of WO 3 as well as the coloration.…”

FABRICATION AND CHARACTERIZATION OF Fe-DOPED TUNGSTEN TRIOXIDE PHOTOELECTRODES IN AQUEOUS MEDIUM USING TUNGSTIC ACID AND FERROCENE AS STARTING MATERIALS

“…The narrow band gap of 2.20 -2.80 eV helps in absorption of ultraviolet region and blue region of visible light in solar spectrum [22][23][24][25]. Furthermore, WO 3 has been investigated with the aim of improving catalyst activity and stability in the irradiated aqueous environment [26][27][28][29]. Tungsten trioxide powders prepared from various W precursors has been studied by Bamwenda and Arakawa [30].…”