Improved Efficiency and Stability of Cadmium Chalcogenide Nanoparticles by Photodeposition of Co-Catalysts
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Improved Efficiency and Stability of Cadmium Chalcogenide Nanoparticles by Photodeposition of Co-Catalysts Philip Kalisman1 and Lilac Amirav1 1 Technion - Israel Institute of Technology, Department of Chemistry Haifa, 32000, Israel ABSTRACT The production of hydrogen by photocatalytic water splitting is a potentially clean and renewable source for hydrogen fuel. Cadmium chalcogenides are attractive photocatalysts because they have the potential to convert water into hydrogen and oxygen using photons in the visible spectrum. Cadmium sulfide rods with embedded cadmium selenide quantum dots (CdSe@CdS) are particularly attractive because of their high molar absorptivity in the UV-blue spectral region, and their energy bands can be tuned; however, two crucial drawbacks hinder the implementation of these materials in wide spread use: poor charge transfer and photochemical instability. Utilizing photochemical deposition of co-catalysts onto CdSe@CdS substrates we can address each of these weaknesses. We report how novel co-catalyst morphologies can greatly increase efficiency for the water reduction half-reaction. We also report photostability for CdSe@CdS under high intensity 455nm light (a wavelength at which photocatalytic water splitting by CdSe@CdS is possible) by growing metal oxide co-catalysts on the surface of our rods. INTRODUCTION There has been much interest in the use of cadmium chalcogenide based photocatalysts for solar light driven water splitting due to favorable optoelectronic properties which these materials possess.1,2 Cadmium chalcogenides absorb light well in the visible and ultra-violet spectra (ε ~ 105-106);2 furthermore, heterostructures of cadmium selenide and cadmium sulfide in particular can be synthesized such that they create a type-II heterojunction, which is desirable for separating photo-generated electrons and holes. Despite these optoelectronic properties, cadmium chalcogenide photocatalysts suffer from poor charge transfer to solution, and more importantly poor photostability. Co-catalysts have previously been grown on cadmium chalcogenide substrates, allowing for increased photocatalytic activity.3 In the present study, we show how photochemical deposition can be used to grow thermodynamically unstable reductive co-catalysts, and novel combinations of oxidative co-catalysts on cadmium chalcogenide substrates. EXPERIMENTAL DETAILS Substrates of cadmium selenide quantum dots asymmetrically embedded in cadmium sulfide nanorods (CdSe@CdS) were synthesized using methods based upon well documented methods from the literature.4 Photodeposition of co-catalysts was done by irradiation of
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precursors in a cuvette, using a Thorlabs 455nm (Royal Blue) LED at 50-200mW for the desired time. For the growth of gold tipped rods, 600μL of a gold(III) chloride (2m
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