Abstract
Although anodic tungsten oxide has attracted increasing attention in recent years, there is still a lack of detailed studies on the photoelectrochemical (PEC) properties of such kind of materials grown in different electrolytes under various sets of conditions. In addition, the morphology of photoanode is not a single factor responsible for its PEC performance. Therefore, the attempt was to correlate different anodizing conditions (especially electrolyte composition) with the surface morphology, oxide thickness, semiconducting, and photoelectrochemical properties of anodized oxide layers. As expected, the surface morphology of WO3 depends strongly on anodizing conditions. Annealing of as-synthesized tungsten oxide layers at 500 °C for 2 h leads to obtaining a monoclinic WO3 phase in all cases. From the Mott-Schottky analysis, it has been confirmed that all as prepared anodic oxide samples are n-type semiconductors. Band gap energy values estimated from incident photon−to−current efficiency (IPCE) measurements neither differ significantly for as−synthesized WO3 layers nor depend on anodizing conditions such as electrolyte composition, time and applied potential. Although the estimated band gaps are similar, photoelectrochemical properties are different because of many different reasons, including the layer morphology (homogeneity, porosity, pore size, active surface area), oxide layer thickness, and semiconducting properties of the material, which depend on the electrolyte composition used for anodization.
Highlights
Tungsten oxide (WO3 ) is an n-type semiconductor that has been considered so far as one of the most promising materials for photoanodes for photoelectrochemical (PEC) water splitting due to its superior charge transport properties, moderate hole diffusion length and, mostly, a relatively narrow band gap (2.5–2.8 eV)
We propose a detailed investigation of the morphology, photoelectrochemical, and optical properties of anodic WO3 layers grown in different electrolytes under various operation conditions
The estimated band gaps do not differ significantly within the their photoelectrochemical properties can be very different. It is related with a combination of samples, their photoelectrochemical properties can be very different. It is related with a combination several important factors such as the morphology of anodic oxide (homogeneity, porosity, pore size, of several important factors such as the morphology of anodic oxide, oxide layer thickness, and mostly, properties of the semiconductor itself, oxide layer thickness, and mostly, properties of the semiconductor itself density of charge carriers), which in turn depend on anodizing conditions, including electrolyte, which in turn depend on anodizing conditions, including electrolyte composition
Summary
Tungsten oxide (WO3 ) is an n-type semiconductor that has been considered so far as one of the most promising materials for photoanodes for photoelectrochemical (PEC) water splitting due to its superior charge transport properties, moderate hole diffusion length and, mostly, a relatively narrow band gap (2.5–2.8 eV). Many different methods have been employed for the synthesis of WO3 nanomaterials, including chemical vapor deposition (CVD) [1], hydrothermal methods [2,3], sol−gel processes [4], electrodeposition [5], anodic oxidation (anodization) [6,7,8], and many others [9] Among these techniques, electrochemical oxidation of metallic tungsten has received considerable attention since it can be applied to synthesize nanostructured WO3 with various morphologies such as nanoporous [6,8,10,11,12,13,14,15] or nanotubular layers [10,16], compact films [8,12,14], nanoplates [17,18], nanowires [11], and others [11,14]. The type of the received morphology and geometrical features of the Molecules 2020, 25, 2916; doi:10.3390/molecules25122916 www.mdpi.com/journal/molecules
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
