Dye-sensitized Hydrogen Evolution Research Articles

Is platinum-loaded titania the best material for dye-sensitized hydrogen evolution under visible light?

Is platinum-loaded titania the best material for dye-sensitized hydrogen evolution under visible light?

Noble metal-free ternary cobalt-nickel phosphides for enhanced photocatalytic dye-sensitized hydrogen evolution and catalytic mechanism investigation.

Transition metal phosphides have emerged as compelling alternatives to noble metal catalysts for photocatalytic hydrogen evolution, owing to their high efficiency, stability, ease of preparation, and low-cost-effectiveness. This study investigates a series of binary and ternary phosphides predominantly composed of cobalt and nickel employed for photocatalytic dye-sensitized hydrogen evolution. Under the optimal dye-to-catalyst mass ratio, CoNiP exhibited the highest hydrogen evolution activity (12.96 mmol g-1 h-1), demonstrating more significant and satisfactory performance than a variety of other reported materials. This can be attributed to the high conductivity and low hydrogen evolution overpotential of phosphides, which result from their metallic characteristics and the presence of free electrons, which promote efficient electron transfer between the catalyst and sensitizer. Density functional theory calculations revealed that the cobalt incorporation into the binary phosphides causes a negative shift in the average d-band center for CoNiP, weakening the adsorption affinity of the catalyst towards H2 molecules, thus effectively improving the hydrogen evolution rate compared to the pure binary phosphides. This work provides valuable insights for the development of low-cost and high-performance ternary phosphide photocatalysts.

One-step synthesis of nickel oxide/nickel carbide/graphene composite for efficient dye-sensitized photocatalytic H2 evolution

To resolve the energy crisis and environment pollution, it is urgent to explore highly efficient and inexpensive catalysts for hydrogen evolution reaction (HER). In this work, we fabricate nickel oxide/nickel carbide/graphene (labeled as NNG) composite via one-step thermal treatment of NiCl2/graphene oxide (GO) as the precursor at relatively low temperature. GO plays a role of the carbon source to form nickel carbide and increases the distribution of the nickel species. The formed nickel carbide acts as the active sites for hydrogen atoms adsorption (Hads). The NiO contacted with the nickel carbide promotes the Volmer reaction: H2O+e→Hads+OH-. The two different adsorption sites (nickel carbide for Hads, NiO for OH−) jointly lead to the HER synergistic effect in basic solution. The obtained composites exhibit much higher dye-sensitized photocatalytic and electrocatalytic HER activities than nickel carbide, NiO and RGO alone. The highest apparent quantum yield (AQY) of dye-sensitized hydrogen evolution for NNG12 at 420 nm reaches 39.4%. And the electrocatalytic HER overpotential is -0.28 V at the current density of 10 mA cm-2 in 1.0 mol L-1 KOH. To the best of our knowledge, it is the first time to report nickel oxide/nickel carbide as an efficient HER catalyst in alkaline media. This work paves a way for facile and green fabrication of the efficient HER cocatalysts.

Near-infrared absorption carboxylated chlorophyll-a derivatives for biocompatible dye-sensitized hydrogen evolution

Chlorophylls (Chls) are naturally occurring photosensitizers having an excellent visible and near-infrared light absorption property. Herein, we employ three Chl a derivatives as sensitizers in a TiO2-based photocatalytic system for H2 evolution with ascorbic acid as the sacrificial reagent under visible light (λ > 400 nm). The H2-evolution activity of these Chl a derivatives depends on a carboxy group in the C3- and/or C17-substituent(s). The concentration of 1 mg/ml dye/Pt/TiO2 powder suspended in an aqueous solution with ascorbic acid as the sacrificial reagent gives the highest H2-evolution rate. The fact that Chl-2 with a carboxy group on the C3 position of the chlorin macrocycle gives the highest H2-evolution rate of 0.79 μmol h−1 is ascribed to the lowest charge recombination rate between Chl-2 and TiO2 among all Chls investigated. This work provides us with important information in synthesizing more favorable molecular structure of Chl derivatives for the highly efficient photocatalytic H2 evolution from water splitting.

Visible-light-induced hydrogen evolution reaction with WS x Se2−x

WS2 is a promising catalyst for the hydrogen evolution reaction. We have explored photocatalytic properties of ternary sulphoselenides of tungsten (WS x Se 2−x ) by the dye-sensitized hydrogen evolution. WS x Se 2−x solid solutions are found to exhibit high activity reaching 2339 μmol h−1 g−1 for WSSe, which is three times higher than that of WS2 alone (866 μmol h−1 g−1 ). The turnover frequency is also high (0.7 h−1 ). Such synergistic effect of selenium substitution in WS2 is noteworthy.

Hybrids of a Ruthenium(II) Polypyridyl Complex and a Metal Oxide Nanosheet for Dye-Sensitized Hydrogen Evolution with Visible Light: Effects of the Energy Structure on Photocatalytic Activity

Hybrid materials consisting of a ruthenium(II) polypyridyl complex and a Dion–Jacobson type perovskite oxide nanosheet were studied as photocatalysts for dye-sensitized H2 evolution under visible light with respect to the energy structure of the hybrids. Three Ru(II) complexes, RuII{(4,4′-X2-bpy)2(4,4′-(CH2PO3H2)2-bpy)} (X = H, CH3, CF3; bpy = 2,2′-bipyridine), were used as redox photosensitizers. HCa2–xSrxNb3O10 (0 ≤ x ≤ 2) and HCa2Nb3–yTayO10 (0 ≤ y ≤ 1.5) nanosheet aggregates, having a tunable conduction band potential (ECB), were employed as the building block. Nanosheets that possess more negative ECB value were found to be preferable for the dye-sensitized H2 evolution, unless electron injection from the excited-state sensitizer to the conduction band of a nanosheet is hindered. Among the combinations tested, the highest activity was obtained when an HCa2Nb3O10 nanosheet was sensitized by RuII{(4,4′-(CH3)2-bpy)2(4,4′-(CH2PO3H2)2-bpy)}, exhibiting a maximum apparent quantum yield of ca. 10% at 460 nm...

Dye sensitized hydrogen evolution from water

Photochemically stable catalysts for continuous production of dihydrogen from water in the presence of visible light are yet to be developed. Most of the proposed systems suffer from loss of activity with use, at varying extent. In the present investigation, the photoactivity of Pt/TiO 2 system in the visible region is improved by the addition of the sensitizer ([Ru(dcbpy) 2(dpq)] 2+) [where dcbpy=4,4′-dicarboxy 2,2′-bipyridine and dpq=2,3-bis-(2′-pyridyl)-quinoxaline] leading to efficient water reduction. This system is relatively inexpensive, reproducible, extremely stable and efficient in conversion of light into dihydrogen in aqueous solution. In order to obtain maximum information about the performance of TiO 2–Pt catalysts, we varied the components and conditions of the system for water reduction. The dependence of the dihydrogen evolution rate on the amount of catalysts, concentration of the sensitizer and percentage of platinum on TiO 2 has been studied. In addition to the above, a comparative study on the photocatalytic activities of Pt/TiO 2 and Pt/ZnO in the presence of the above sensitizer for the production of hydrogen was also made.