Structural, Optical, Photoelectrochemical, and Electronic Properties of the Photocathode CuS and the Efficient CuS/CdS Heterojunction
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ABSTRACT:
SUBMITTER: Shaikh G
PROVIDER: S-EPMC9434620 | biostudies-literature | 2022 Aug
REPOSITORIES: biostudies-literature
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Project description:The ITO (indium tin oxide) conductive glass-matrix CuS-GeO2-TiO2 composite coating was generated via EPD (electrophoretic deposition) and followed by a sintering treatment at 450°C for 40 minutes. Characterizations of the CuS-GeO2-TiO2 composite coating were taken by SEM (scanning electron microscope), XRD (X-ray diffraction), EDX (energy dispersive X-ray), UV-Vis DRS (ultraviolet-visible diffuse reflection spectrum), and FT-IR (Fourier transform infrared spectroscopy). Results showed that CuS and GeO2 had dispersed in this CuS-GeO2-TiO2 composite coating (mass percentages for CuS and GeO2 were 1.23% and 2.79%, respectively). The electrochemical studies (cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and Tafel polarization) of this CuS-GeO2-TiO2 composite coating electrode were performed in pH = 9.51 Na2CO3-NaHCO3 buffer solution containing 0.50 mol/L CH3OH under the conditions of visible light, ultraviolet light (λ = 365 nm), and dark (without light irradiation as control), respectively. Electrochemical studies indicated that this CuS-GeO2-TiO2 composite coating electrode had better photoelectrocatalytic activity than the pure TiO2 electrode in the electrocatalysis of methanol under visible light.
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Project description:Solar energy conversion through photoelectrochemical water splitting (PEC) is an upcoming promising technique. MoS2/CoTe heterostructures were successfully prepared and utilized for PEC studies. MoS2 and CoTe were prepared by a hydrothermal method which were then ultrasonicated with wt. % ratios of 1:3, 1:1 and 3:1 to prepare MoS2/CoTe (1:3), MoS2/CoTe (1:1) and MoS2/CoTe (3:1) heterostructure, respectively. The pure materials and heterostructures were characterized by XRD, UV-vis-DRS, SEM, XPS, PL and Raman spectroscopy. Photoelectrochemical measurements were carried out by linear sweep voltammetry and electrochemical impedance spectroscopic measurements. A maximum photocurrent density of 2.791 mA/cm2 was observed for the MoS2/CoTe (1:1) heterojunction which is about 11 times higher than the pristine MoS2. This current density was obtained at an applied bias of 0.62 V vs. Ag/AgCl (1.23 V vs. RHE) under the light intensity of 100 mW/cm2 of AM 1.5G illumination. The enhanced photocurrent density may be attributed to the efficient electron-hole pair separation. The solar to hydrogen conversion efficiency was found to be 0.84% for 1:1 MoS2/CoTe, signifying the efficient formation of the p-n junction. This study offers a novel heterojunction photocatalyst, for PEC water splitting.
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Project description:Photoelectrochemical (PEC) water splitting is an appealing approach for "green" hydrogen generation. The natural p-type semiconductor of Cu2O is one of the most promising photocathode candidates for direct hydrogen generation. However, the Cu2O-based photocathodes still suffer severe self-photo-corrosion and fast surface electron-hole recombination issues. Herein, we propose a facile in-situ encapsulation strategy to protect Cu2O with hydrogen-substituted graphdiyne (HsGDY) and promote water reduction performance. The HsGDY encapsulated Cu2O nanowires (HsGDY@Cu2O NWs) photocathode demonstrates a high photocurrent density of -12.88 mA cm-2 at 0 V versus the reversible hydrogen electrode under 1 sun illumination, approaching to the theoretical value of Cu2O. The HsGDY@Cu2O NWs photocathode as well as presents excellent stability and contributes an impressive hydrogen generation rate of 218.2 ± 11.3 μmol h-1cm-2, which value has been further magnified to 861.1 ± 24.8 μmol h-1cm-2 under illumination of concentrated solar light. The in-situ encapsulation strategy opens an avenue for rational design photocathodes for efficient and stable PEC water reduction.
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Project description:Using many-body perturbation theory, we study the optical properties of phenylthiolate-capped cadmium sulfide nanoparticles to understand the origin of the experimentally observed blue shift in those properties with decreasing particle size. We show that the absorption spectra predicted by many-body perturbation theory agree well with the experimentally measured spectra. The results of our calculations demonstrate that all low-energy excited states correspond to a mixture of two fundamental types of excitations: intraligand and ligand-to-metal charge-transfer excitations. We find that for each excited state, the intraligand excitation contribution is dominant and that bright excited states, corresponding to the clear peaks in the absorption spectra, have a larger ligand-to-metal charge-transfer contribution. There are no low-energy bulk-like excitons, excited states for which both the hole and the excited electron components are predominantly delocalized over the inorganic core of the particles. Phenylthiolate-capped cadmium sulfide nanoparticles appear not to behave like the textbook cartoon picture of quantum dots. We speculate that the observed blue shift is the result of a combination of a Stark-like shift of the intraligand contribution, modulated by a change in the charge of the inorganic core and the confinement of the excited electron component of the ligand-to-metal charge-transfer contribution.
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Project description:Cadmium sulfide (CdS) as one of the most common visible-light-responsive photocatalysts has been widely investigated for hydrogen generation. However, its low solar-hydrogen conversion efficiency caused by fast carrier recombination and poor catalytic activity hinders its practical applications. To address this issue, we develop a novel and highly efficient nickel-cobalt phosphide and phosphate cocatalyst-modified CdS (NiCoP/CdS/NiCoPi) photocatalyst for hydrogen evolution. The dual-cocatalysts were simultaneously deposited on CdS during one phosphating step by using sodium hypophosphate as the phosphorus source. After the loading of the dual-cocatalysts, the photocurrent of CdS significantly increased, while its electrical impedance and photoluminescence emission dramatically decreased, which indicates the enhancement of charge carrier separation. It was proposed that the NiCoP cocatalyst accepts electrons and promotes hydrogen evolution, while the NiCoPi cocatalyst donates electrons and accelerates the oxidation of sacrificial agents (e.g., lactic acid). Consequently, the visible-light-driven hydrogen evolution of this composite photocatalyst greatly improved. The dual-cocatalyst-modified CdS with a loading content of 5 mol % showed a high hydrogen evolution rate of 80.8 mmol·g-1·h-1, which was 202 times higher than that of bare CdS (0.4 mmol·g-1·h-1). This is the highest enhancement factor for metal phosphide-modified CdS photocatalysts. It also exhibited remarkable stability in a continuous photocatalytic test with a total reaction time of 24 h.
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Project description:CdS decorated CuS structures have been controllably synthesized through a one-pot hydrothermal method. The morphologies and compositions of the as-prepared samples could be concurrently well controlled by simply tuning the amount of CdCl2 and thiourea. Using this strategy, the morphology of the products experienced from messy to flower-like morphologies with multiple porous densities, together with the phase evolution from pure CuS to the CdS/CuS composites. Serving as a photocatalyst, the samples synthesized with the addition of 1 mmol cadmium chloride and 3 mmol thiourea during synthetic process, showed the best photocatalytic activity, which could reach a maximum photocatalytic efficiency of 93% for methyl orange (MO) photodegradation after 150 min. The possible mechanism for the high photocatalytic efficiency of the sample was proposed by investigating the composition, surface area, structure, and morphology before and after photocatalytic reaction.
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Project description:Hydrogen production from water splitting using solar energy based on photoelectrochemical (PEC) cells has attracted increasing attention because it leaves less of a carbon footprint and has economic superiority of solar and hydrogen energy. Oxide semiconductors such as ZnO possessing high stability against photocorrosion in hole scavenger systems have been widely used to build photoanodes of PEC cells but under visible light their conversion efficiencies with respect to incident-photon-to-current conversion efficiency (IPCE) measured without external bias are still not satisfied. An innovative way is presented here to significantly improve the conversion efficiency of PEC cells by constructing a core-shell structure-based photoanode comprising Au@CdS core-shell nanoparticles on ZnO nanowires (Au@CdS-ZnO). The Au core offers strong electronic interactions with both CdS and ZnO resulting in a unique nanojunction to facilitate charge transfer. The Au@CdS-ZnO PEC cell under 400 nm light irradiation without any applied bias provides an IPCE of 14.8%. Under AM1.5 light illumination with a bias of 0.4 V, the Au@CdS-ZnO PEC cell produces H2 at a constant rate of 11.5 μmol h-1 as long as 10 h. This work provides a fundamental insight to improve the conversion efficiency for visible light in water splitting.
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