Papers by Keyword: Photoelectrochemical

Abstract: Zinc oxide (ZnO) nanorods is widely investigated due to its high photoelectrochemical conversion performance. Further enhancement may be afforded by introducing a metal chalcogenide sensitization layer such as zinc selenide (ZnSe). In this study, ZnO nanorods were electrodeposited with ZnSe at potential range from -0.5 V to -0.9 V vs Ag/AgCl reference electrode. Structural, morphological and optical properties of ZnSe electrodeposited were investigated as a function applied potential by using X-ray diffractometry (XRD), field emission scanning electron microscopy (FESEM), and ultraviolet-visible spectroscopy (UV-Vis). ZnSe electrodeposited for 15 minutes at -0.7 V showed crystallite size of 20.13 nm with the lowest band gap energy of 2.97 eV. The existence of ZnSe particles with the size of 41.8 nm were proven by FESEM images, after ZnSe particles were electrodeposited onto ZnO nanorods that have an average diameter of 62.6 nm and length of 1.6 µm. The photocurrent density generated by samples were measured in a three-electrodes cell incorporated with halogen lamp. The photocurrent generated increased between -0.5 V to -0.7 V before dropped at higher applied potential due to hydrogen evolution process which affected the thin film quality, ultimately affecting photoconversion performance. The highest photocurrent density of 0.2621 mAcm^-2 was recorded for samples prepared at -0.7 V vs Ag/AgCl.

Abstract: Following successful growth of zinc oxide (ZnO) nanorods, a layer of zinc selenide (ZnSe) was electrodeposited onto the nanorods to further enhance its conversion efficiency in the photoelectrochemical (PEC) cell. The electrodeposited ZnSe layer onto the ZnO nanorods was subjected to heat treatment at 200, 250 and 300°C. The prepared films were characterized by X-ray diffractometry (XRD), field emission scanning electron microscopy (FESEM), and ultraviolet-visible spectroscopy (UV-Vis) to investigate the structural, morphological and compositional characteristics. Additionally, PEC conversion generated by the prepared thin films were tested with photocurrent measurements under calibrated visible illumination from a halogen lamp. Based on FESEM analysis, the thickness of ZnO thin film increased with temperature. However, the diameters of the ZnO nanorods were found to be in a decreasing trend upon heat treatment at higher temperature. The electrodeposited ZnSe layer at the potential of -0.7 V for 60 seconds (calcined at 200°C) possessed crystallite size of 20.1 nm. According to UV-Vis analysis, band gap energy measured was 2.8 eV, which is very close to standard ZnSe band gap value (2.7 eV). Additional layer of ZnSe electrodeposited enhanced thin film performance in terms of current density as much as 37.4% while having high photocurrent density of 0.2671 mAcm^-2.

Abstract: Hematite (Fe₂O₃) is one of the abundant magnetic materials in nature. Hematite has good absorption ability in the region visible light and good electrochemical stability, which make this material is potential as photoanode for photoelectrochemical (PEC) cells. However, Fe₂O₃ has some disadvantages such as short hole diffusion length and low hole mobility. Therfore, it is necessarily to combine Fe₂O₃ with photocatalyst material to improve photoelectrochemical performances. ZnO is ones of photocatalist material with good electron mobility, wide band gaps, cheap and are easily fabricated. The aim of this study is to investigate the performance of bilayer Fe₂O₃/ZnO as photoanode for photoelectrochemical cell. The bilayer Fe₂O₃/ZnO was prepared by spin-coating techniques and doctor blade methods. The samples were characterized by X-ray diffarction, and Scanning Electron Microscopy. The performance of photoelectrochemical cell was investigated by Cyclic Voltammetry (CV) under light illumination. The result indicate that bilayer Fe₂O₃/ZnO has good photoelectrochemical properties.

Abstract: Zinc oxide (ZnO) thin films were coated onto Indium Tin Oxide (ITO) glass substrate using spin coating technique as a function of annealing temperature. The thin film preparation was undertaken by utilising zinc acetate dihydrate, ethanol and diethanolamine as the precursors. The films were coated at room temperature prior to being annealed at temperatures ranging from 300 °C to 450 °C. The resulting crystalline structure and surface morphology of the thin films were then examined using X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). UV-visible spectrophotometer was also used to record the optical absorbance in wavelengths ranging from 200 to 800 nm. The findings revealed that the ZnO thin films showed a single phase of wurtzite with n-type semiconductor, with the lowest value of band gap energy of 3.28 eV for ZnO thin films annealed at 350 °C. FESEM results showed that the ZnO nanoparticles were very compact on the surface, whereby the average particle size was equivalent to 108.5, 115.3, 108.2 and 107.8 nm at the temperatures 300 °C, 350 °C, 400 °C, and 450 °C, respectively. Additionally, the highest photoconversion efficiency (0.11%) recorded for the sample was annealed at 350^◦C. Thus, annealing temperature was found to significantly affect the optical and electrical properties of ZnO nanoparticle seed layer, as well as its band gap energy and surface morphology.

Abstract: In this study, we can fabricate Cu₂O on F-doped SnO₂ coated glass (FTO) substrates as photocathode for hydrogen evolution reaction by electro-deposition techniques. Cyclic voltammetry as a new deposition method was studied to fabricate Cu₂O photocathode in a mixed solution of Cu (NO₃)₂ and KNO₃ under a condition of low temperature and without pH value adjustment. Amperometry as a previous method was used to compare for Cu₂O electrode fabrication under the situation of pH adjustment and higher temperature condition. A photocurrent from hydrogen evolution reaction was performed by keep potential at-0.2 V in 0.1 M Na₂SO₄ under visible irradiation comparing with both fabricated method. The Cu₂O photocathode from cyclic voltammetry deposition method presents photoelectrocatalytic activity higher than that of amperometry deposition method with the optimum conditions. This electro-deposition technique represents the excellent method with simple, fast and low cost of Cu₂O photocathode fabrication for photoelectrochemical hydrogen evolution reaction.

Abstract: Natural dyes were extracted from the plant species Etlingera elatior, Duranta erecta and Amaranthus spp. that were collected from Keningau and Tambunan, Sabah, Malaysia. The possibility of photon-electron conversion was then assessed based on their absorption ability in the region of wavelength between 400-900nm. In addition, FT-IR analysis was carried out to determine if functional groups exists in their extracts. Finally, the DSSCs were assembled and their efficiency measured. It shows the successful conversion from visible sunlight to electricity by using extracts from Etlingera elatior, Duranta erecta and Amaranthus spp. as raw natural dye sensitizers in Dye Sensitized Solar Cells (DSSCs) with efficiency of 0.1% ,0.06% and 0.04%, respectively. This result shows that local natural dyes can be used as sensitizer in DSSCs. However, further investigations are required to improve the efficiency.

Abstract: This article presents a simple method for fabrication of Au-CdS composite thin films onto indium-tin-oxide (ITO) coated glass substrates. The method starts with electrodeposition of CdS thin films onto ITO substrates and followed by spontaneous growth of Au nanoparticles onto the CdS surface in solutions containing AuCl₄^- ions. X-ray diffraction (XRD) and UV-vis spectroscopy were used to investigate the Au-CdS thin films. The photoelectrochemical property and sensing for Hg²⁺ ions of the Au-CdS/ITO were studied. The electrode exhibits a low limit of detection of 2.5 μM and a high selectivity for Hg²⁺ ions, even in the presence of a large excess (1000-fold) of other metal (Na⁺, K⁺, Ca²⁺, Mg²⁺, Cd²⁺, Pb²⁺, and Zn²⁺) ions.

Abstract: The differences in structural, compositional and photoelectrochemical properties for SnSe films annealed at different temperatures, under nitrogen atmosphere, were studied. Annealing the film electrode significantly improved its crystallinity but lowered its photoresponse. The photoresponse lowering was thus attributed to lowering in the defect concentrations.

Abstract: Hematite is one of the most promising photoanodes for water splitting, but its photoelectrochemical (PEC) efficiency is still low. This work proved that the PEC efficiency of hematite can be improved by Ce doping. The Ce doped hematite was successfully prepared by co-sputtering CeO₂ and Fe₂O₃, and followed by thermal oxidation treatment. The results of J-V test showed that the photocurrent of 5 at.% Ce doped α-Fe₂O₃ film can reached 1.35mA/cm² in 1 M NaOH (pH=13.6) at 1.23V vs. NHE, which is nearly 15 times higher than the undoped one. The enhancement of PEC efficiency was proved by the enhancement of absorbance of visible light, as well as increased carrier density after Ce doping.

Abstract: Development of efficient photoanodes for water splitting under solar light is desirable to surmount the possible fuel crisis in future. Ferrite systems, with their excellent visible light absorption capability, stability, non-toxicity, cost-effectiveness and abundance, are being preferred to titanates, niobates and sulfides. The present work briefly reviews the modified form of ferrites. Additionally, ZnFe₂O₄ an n-type semiconductor with the low band gap (~1.9eV) has been considered as special case of visible light PEC application. The work further emphasizes on the utilization of solution processed techniques to develop the ferrite photoanodes. The tuning of photoanode properties by virtue of electrode fabrication parameters say deposition parameters viz., precursor concentration, pH, stoichiometry has been reviewed and discussed.