Cocatalyst For Hydrogen Evolution Research Articles

Heterostructure of Si and CoSe₂: A Promising Photocathode Based on a Non-noble Metal Catalyst for Photoelectrochemical Hydrogen Evolution.

Development of a solar water splitting device requires design of a low-cost, efficient, and non-noble metal compound as alternative to noble metals. For the first time, we showed that CoSe2 can function as co-catalyst in phototoelectrochemical hydrogen production. We designed a heterostructure of p-Si and marcasite-type CoSe2 for solar-driven hydrogen production. CoSe2 successively coupled with p-Si can act as a superior photocathode in the solar-driven water splitting reaction. Photocurrents up to 9 mA cm(-2) were achieved at 0 V vs. reversible hydrogen electrode. Electrochemical impedance spectroscopy showed that the high photocurrents can be attributed to low charge transfer resistance between the Si and CoSe2 interfaces and that between the CoSe2 and electrolyte interfaces. Our results suggest that this CoSe2 is a promising alternative co-catalyst for hydrogen evolution.

Titanate nanotube modified with different nickel precursors for enhanced Eosin Y-sensitized photocatalytic hydrogen evolution

Nickel species were loaded on titanate nanotubes (TNT) as a hydrogen evolution cocatalyst by an impregnation–calcination method. Nickel chloride, nickel nitrate and nickel acetate were used as the precursors. More Ni2+ ions intercalate into the interlayer of TNT when nickel chloride is used as the precursor. In the calcination process, the titanate transforms into anatase TiO2, and Ni2+ ions are reduced and doped partly in TiO2 and titanate. The Ni2+ ions intercalated into TNT inner can promote the phase transformation, growth of metal Ni particles and the Ni2+ doping. The formed Ni particles can be oxidized in air to form core/shell Ni@NiO structure. The Ni2+ doping promotes the formation of oxygen defects and increases the conductivity of TNT. The photocatalytic activity of Eosin Y-sensitized nickel-modified TNT for hydrogen evolution was investigated. The TNT modified with nickel chloride exhibit higher activity, which can be attributed to the higher conductivity and more effective formation of Ni@NiO structure.

Progress in Visible-Light Photocatalytic Hydrogen Production by Dye Sensitization

Dye sensitization is an important strategy for broadening the excitation wavelength range of wide- band-gap photocatalysts to use visible light from the sun. In this paper, the primary principle of dye-sensitized water splitting for hydrogen production was introduced, and the research progress in dye sensitizers, sensitized matrixes or supporters, the interaction between dyes and matrixes, co-catalysts for hydrogen evolution, and sacrificial electron donors were all reviewed. Moreover, the pathways of charge transmission and stability issues in dye-sensitized systems were discussed.

Photocatalytic hydrogen evolution over Erythrosin B-sensitized graphitic carbon nitride with in situ grown molybdenum sulfide cocatalyst

Erythrosin B (EB) sensitized graphitic carbon nitride (g-C3N4) for photocatalytic hydrogen evolution was investigated using triethanolamine (TEOA) as an electron donor under visible light irradiation (λ > 420 nm). MoSx was loaded on g-C3N4 as a cocatalyst by an in situ photoreduction method during the photocatalytic reaction employing (NH4)2MoS4 as a precursor. EB-sensitized MoSx-g-C3N4 (EB-MoSx-g-C3N4) exhibits the higher activity and stability than both EB-sensitized g-C3N4 (EB-g-C3N4) and EB-sensitized MoSx (EB-MoSx). With deposition of 0.5 wt% MoSx, the photoactivity of EB-MoSx-g-C3N4 increases by more than 160 times after 2 h irradiation compared with that of EB-g-C3N4. The activity of EB-MoSx-g-C3N4 is 19.3 times as high as that of EB-MoSx after 10 h irradiation, and the former is much more stable than the latter. The highest apparent quantum yield for hydrogen evolution reaches 8.3% at 545 nm. The improved photoactivity and stability is owing to MoSx as an excellent hydrogen evolution cocatalyst and the efficient electron transfer among photoexcited EB, g-C3N4 and MoSx. The possible mechanism was discussed.

Photocatalytic H2 evolution from NADH with carbon quantum dots/Pt and 2-phenyl-4-(1-naphthyl)quinolinium ion

Carbon quantum dots (CQDs) were simply blended with platinum salts (K2PtCl4 and K2PtCl6) and converted into a hydrogen-evolution co-catalyst in situ, wherein Pt salts were dispersed on the surface of CQDs under photoirradiation of an aqueous solution of NADH (an electron and proton source) and 2-phenyl-4-(1-naphthyl)quinolinium ion (QuPh+−NA) employed as an organic photocatalyst. The co-catalyst (CQDs/Pt) exhibits similar catalytic reactivity in H2 evolution as that of pure Pt nanoparticles (PtNPs) although the Pt amount of CQDs/Pt was only 1/200 that of PtNPs previously reported. CQDs were able to capture the Pt salt acting as Pt supports. Meanwhile, CQDs act as electron reservoir, playing an important role to enhance electron transfer from QuPh+−NA to the Pt salt, which was confirmed by kinetic studies, XPS and HRTEM.

Surface modification-a novel way of attaching cocatalysts on CdS semiconductors for photocatalytic hydrogen evolution

Noble metals as cocatalysts for hydrogen evolution are widely investigated for semiconductor photocatalytic water splitting. In this paper, we present a novel way to attach not only noble metals, but also transitional metals onto CdS nanocrystals as cocatalysts for hydrogen evolution. The hydrogen evolution performances for each metal were compared and result shows that Pd attached CdS gives the highest hydrogen evolution rate of 250 μmol/h. The amounts of metal ions attached on the surface were measured by inductively coupled plasma optical emission spectrometry (ICP-OES). This work confirms that surface modification is a promising way of attaching cocatalysts onto semiconductor photocatalysts.

Enhanced visible light-driven hydrogen production from water by a noble-metal-free system containing organic dye-sensitized titanium dioxide loaded with nickel hydroxide as the cocatalyst

Platinum is an excellent catalyst for hydrogen production but its application is limited by the high cost. In this present paper, a series of noble-metal-free nickel hydroxide/titanium dioxide (Ni(OH)2/TiO2) nanocomposites have been synthesized and characterized. Photocatalytic hydrogen production was observed in a system containing Eosin Y-sensitized Ni(OH)2/TiO2 photocatalysts in the presence of triethanolamine (TEOA) as a sacrificial reagent under visible light (λ>420nm). The resulting photocatalysts were well characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–vis spectroscopy (UV–vis), and X-ray photoelectron spectroscopy (XPS). The results revealed that dye-sensitized Ni(OH)2/TiO2 material has much higher photocatalytic activity than dye-sensitized TiO2 sample, indicating the important catalytic role of Ni(OH)2. The amount of the loaded cocatalyst significantly affected the photocatalytic activity and the optimal mole ratio of Ni(OH)2 in Ni(OH)2/TiO2 composite was determined to be 1.0%. The optimal rate of H2 evolution is about 15.76μmolh−1, which is about 90 times higher than pure TiO2 under the same condition. After 5h of irradiation, the photocatalytic activity of Ni(OH)2 as the cocatalyst for hydrogen evolution is much higher than other first-row transition metal based oxide/hydroxide materials, such as cobalt oxide (CoOx), cobalt hydroxide (Co(OH)2), nickel oxide (NiOx), ferric hydroxide (Fe(OH)3) and copper hydroxide (Cu(OH)2) on the surface of TiO2 semiconductor.

Wafer-Scale Fabrication of Self-Catalyzed 1.7 eV GaAsP Core–Shell Nanowire Photocathode on Silicon Substrates

We present the wafer-scale fabrication of self-catalyzed p-n homojunction 1.7 eV GaAsP core-shell nanowire photocathodes grown on silicon substrates by molecular beam epitaxy with the incorporation of Pt nanoparticles as hydrogen evolution cocatalysts. Under AM 1.5G illumination, the GaAsP nanowire photocathode yielded a photocurrent density of 4.5 mA/cm(2) at 0 V versus a reversible hydrogen electrode and a solar-to-hydrogen conversion efficiency of 0.5%, which are much higher than the values previously reported for wafer-scale III-V nanowire photocathodes. In addition, GaAsP has been found to be more resistant to photocorrosion than InGaP. These results open up a new approach to develop efficient tandem photoelectrochemical devices via fabricating GaAsP nanowires on a silicon platform.

Facile One-Pot Solvothermal Method to Synthesize Sheet-on-Sheet Reduced Graphene Oxide (RGO)/ZnIn2S4 Nanocomposites with Superior Photocatalytic Performance

Highly reductive RGO (reduced graphene oxide)/ZnIn2S4 nanocomposites with a sheet-on-sheet morphology have been prepared via a facile one-pot solvothermal method in a mixture of N,N-dimethylformamide (DMF) and ethylene glycol (EG) as solvent. A reduction of GO (graphene oxide) to RGO and the formation of ZnIn2S4 nanosheets on highly reductive RGO has been simultaneously achieved. The effect of the solvents on the morphology of final products has been investigated and the formation mechanism was proposed. The as-prepared RGO/ZnIn2S4 nanoscomposites were characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), N2-adsorption BET surface area, UV-vis diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM). The photocatalytic activity for hydrogen evolution under visible light irradiations over the as-prepared RGO/ZnIn2S4 nanocomposites has been investigated. The as-prepared RGO/ZnIn2S4 nanocomposites show enhanced photocatalytic activity for hydrogen evolution under visible light irradiations and an optimum photocatalytic activity is observed over 1.0 wt % RGO incorporated ZnIn2S4 nanocomposite. The superior photocatalytic performance observed over RGO/ZnIn2S4 nanocomposites can be ascribed to the existence of highly reductive RGO which has strong interactions with ZnIn2S4 nanosheets. The existence of the strong interaction between ZnIn2S4 nanosheets and RGO in the nancomposites facilitates the electron transfer from ZnIn2S4 to RGO, with the latter serving as a good electron acceptor, mediator as well as the co-catalyst for hydrogen evolution. This study can provide some guidance for us in the developing of RGO-incorporated nanocomposite photocatalysts.

Photocatalytic Water Splitting Using Oxynitride and Nitride Semiconductor Powders for Production of Solar Hydrogen

57 Water splitting using a photocatalyst for direct solar hydrogen production from sunlight and water, has been regarded as an important approach to artificial photosynthesis.1,2 Solar hydrogen, which is the simplest solar fuel, can then be converted to various energy carriers such as organic hydrides, methanol, methane, and ammonia for transportation and storage. Thus, energy systems based on solar hydrogen can lead to a stable, secure, and ecologically-friendly society. Although solar fuel production using electricity from photovoltaic cells and concentrated solar thermal power is an existing technology, direct synthesis of solar fuels by artificial photosynthesis has more scalability in terms of system cost. To split water into hydrogen and oxygen, 1.23 V of energy is required, corresponding to a 2 electron reaction. An energy of 1.23 V is equivalent to a photon energy of 1000 nm, so that the visible light (400-800 nm in wavelength) that represents half of the solar energy spectrum can be thermodynamically used for water splitting. The challenge is to obtain an efficient photocatalyst that has an absorption edge in longer wavelength and the ability to split water. Highly efficient oxide photocatalysts, such as La-doped NaTaO3, and Zn-doped Ga2O3, have been reported with quantum efficiencies of over 50%.3-5 However, these oxides only absorb ultraviolet (UV) light with wavelengths shorter than 300 nm. In the solar spectrum at the earth’s surface, such short UV light is not present, so that these oxides cannot operate efficiently under solar irradiation. Most oxides have band gaps wider than the UV energy because of the deeper O 2p potential of the valence band. The valence band of nitrides is composed of the shallower N 2p potential, and thus their band gaps are generally narrower than those of oxides. For photocatalytic water splitting, photoexcited electrons in the conduction band reduce water to evolve hydrogen, and photogenerated holes in the valence band oxidize water to evolve oxygen. Therefore, the potential of the conduction band should be shallower than the reversible hydrogen potential and the potential of the valence band should be deeper than the reversible oxygen potential. In this article, the properties of oxynitride and nitride photocatalysts for water splitting are described. Surface modification of semiconductor photocatalyst particles with hydrogenor oxygen-evolving cocatalysts is an indispensable technique in the study of photocatalytic water splitting. In fact, hydrogen-evolution cocatalysts are required Photocatalytic Water Splitting Using Oxynitride and Nitride Semiconductor Powders for Production of Solar Hydrogen

ATR-SEIRAS Investigation of the Fermi Level of Pt Cocatalyst on a GaN Photocatalyst for Hydrogen Evolution under Irradiation

The interaction of photogenerated carries in GaN photocatalyst with Pt cocatalyst for hydrogen evolution under irradiation was investigated from in situ ATR-SEIRAS measurement by following the CO vibrational frequency. After irradiation, the CO frequency shifted higher, indicating that the Fermi level of Pt particles was positively shifted by the photogenerated holes. Thereafter, a lower frequency peak appeared, indicating that the Fermi level of some Pt particles was negatively shifted to the hydrogen evolution potential by photogenerated electrons, which is the essential function of cocatalysis for hydrogen evolution.

Role and Function of Noble-Metal/Cr-Layer Core/Shell Structure Cocatalysts for Photocatalytic Overall Water Splitting Studied by Model Electrodes

The mechanism of hydrogen evolution by a core/shell noble-metal/Cr2O3 particulate as a highly efficient cocatalyst for overall water splitting under visible light using the photocatalyst (Ga1−xZnx)(N1−xOx) is investigated by electrochemical and in situ spectroscopic measurements of model electrodes. The electrodes are prepared by electrochemical deposition of 1.8−3.5 nm thick Cr2O3 films on Rh and Pt plates and are evaluated as model systems of Rh/Cr2O3 and Pt/Cr2O3 core/shell particulates, which have previously been applied effectively as cocatalysts for hydrogen evolution in this system. Proton adsorption/desorption and H2 evolution currents are observed for both the Cr2O3-coated and the bare electrodes, and the infrared absorption band due to Pt−H stretching (2039 cm−1) is apparent for both the coated and the bare electrodes. These observations indicate that the Cr2O3 layer does not interfere with proton reduction or hydrogen evolution and that proton reduction takes place at the Cr2O3/Pt interface. However, the reduction of oxygen to water is suppressed only in the Cr2O3-coated samples. The Cr2O3 layer is thus permeable to protons and the evolved hydrogen molecules, but not to oxygen. Cocatalyst modification by thin films with this type of functionality thus appears to be a useful strategy for improving the efficiency of photocatalytic overall water splitting.

Effect of preparation method of colloidal platinum on performance of 12-tungstosilicate for photocatalytic hydrogen generation

Colloidal platinum nanoparticles, the co-catalyst for hydrogen evolution, were prepared using 12-tungstosilicate as photocatalyst by two methods in which photolysis and reduction reaction took place at the same time and at different time, respectively. For the former, H 2PtCl 6 was reduced directly to colloidal platinum under irradiation and 12-tungstosilicate would transfer into a new structure compound during the process. For the latter, 12-tungstosilicate was first photoreduced to heteropoly blue anion, and then the blue anion could reduce H 2PtCl 6 to colloidal platinum under no irradiation. The Pt particle size and reactivity of 12-tungstosilicate were characterized by UV–vis and cyclic voltammetry. Preparation methods affect markedly the Pt particle size and reactivity of 12-tungstosilicate so that the photocatalytic activity and stability for hydrogen evolution are different. The possible mechanism was discussed.