High Hydrogen Production Activity Research Articles

One-step synthesis of the single crystal Ta2O5 nanowires with superior hydrogen production activity

We successfully synthesized the novel single crystal Ta2O5 nanowires for hydrogen production by facile one-step hydrolysis method. The as-prepared Ta2O5 photocatalysts displayed highly enhanced photocatalytic activities for hydrogen production, and the highest hydrogen production activity could reach up to ∼5.549mmol·g−1·h−1, which was 9.72-fold higher than that of the commercial Ta2O5. Besides, it was noticeable that the spectrum absorption edges of the Ta2O5 catalysts displayed an obvious red shift, and the single crystal Ta2O5 nanowires were also obtained with the increase of the hydrolysis temperatures. Besides, the estimated band gap of the as-prepared Ta2O5-160, Ta2O5-180, Ta2O5-200 and Ta2O5-220 catalysts were 4.20, 4.16, 4.09 and 3.83eV, respectively. And it could be concluded that the increase of the hydrolysis temperatures was contributing to improve the crystallinity and extend the spectrum response range of Ta2O5 catalyst in this experiment.

Highly stabilized Ag2O-loaded nano TiO2 for hydrogen production from glycerol: Water mixtures under solar light irradiation

Nano TiO2 prepared by a hydrothermal method and silver-loaded nano TiO2 prepared by impregnation were studied for the photocatalytic production of hydrogen from glycerol:water mixtures. The structural characteristics were revealed using XRD, EDAX, DRS, TEM, XPS, BET surface area and Raman techniques. The photocatalytic hydrogen production has been investigated under solar light irradiation. Effects of nano TiO2 calcination temperature, silver loading, photocatalyst content, light source and Ag oxidation state on hydrogen production have been systematically studied. Maximum hydrogen production of 200 μmol h−1 g−1 is observed on 4wt% silver-loaded nano TiO2 catalyst in pure water and the maximum hydrogen production of 7030 μmol h−1 g−1 is observed on 3wt% silver-loaded nano TiO2 catalyst in glycerol: water mixtures. Silver-loaded nano TiO2 reduced and photodeposited catalysts show similar hydrogen production activities in glycerol: water mixtures under solar irradiation. The optimum catalyst modified with conducting carbon materials (graphene oxide, graphene, carbon nanotubes) by a solid-state dispersion method were also studied for hydrogen production under solar light irradiation. Compared with pure nano TiO2, a 3wt% silver-loaded nano TiO2/graphene composite exhibited an approximately 17-fold enhancement of hydrogen production leading to hydrogen production rates of 12,100 μmol h−1 g−1. Based on the characterization results and hydrogen production activity on these catalysts, a structure–activity correlation has been proposed wherein the interacting Ag2OAg phases on the surface of nano TiO2 play an important role in maintaining a high hydrogen production activity under solar irradiation.

Extraordinarily Durable Graphdiyne-Supported Electrocatalyst with High Activity for Hydrogen Production at All Values of pH.

We have used a scalable and inexpensive method to prepare a catalyst comprising graphdiyne nanosheet-supported cobalt nanoparticles wrapped by N-doped carbon (CoNC/GD); this unprecedentedly durable electrocatalyst mediated the hydrogen evolution reaction (HER) with highly catalytic activity over all values of pH. The durability of the CoNC/GD structure was evidenced by the catalytic performance being preserved over 36 000, 38 000, and 9000 cycles under basic, acidic, and neutral conditions, respectively-behavior superior to that of commercial Pt/C (10 wt %) under respective conditions. Such long-term durability has rarely been reported previously for HER catalysts. In addition, this electrode displayed excellent catalytic activity because the improved physical/chemical properties facilitated electron transfer in the composite. The combination of high durability and high activity at all values of pH for this nonprecious metal catalyst suggests great suitability for practical water splitting.

Production of activated carbon materials from kenaf biomass to be used as catalyst support in aqueous-phase reforming process

In the present study, low value-added woody biomass, kenaf (Hibiscus cannabinus L.), was utilized for production of activated carbons (ACs) that can be used as catalyst support for deposition of metal particles such as Pt to produce highly active catalysts for gasification of biomass hydrolysates by aqueous-phase reforming (APR) process. H3PO4 was used as activating agent for production of AC materials. ACs produced from kenaf and non-hydrolyzed fraction of kenaf after dissolution in subcritical water were compared with the commercial one. The activated carbon material from kenaf had highest BET surface area and total pore volume among the materials tested including commercial AC. The catalyst prepared by Pt deposition on this material (kenaf AC-Pt) had also highest BET surface area and total pore volume. This catalyst exhibited very high activity and selectivity for hydrogen production (0.015molH2/g catalyst) in APR of biomass hydrolysate.

Controlled synthesis of CaTiO3:Ln3+ nanocrystals for luminescence and photocatalytic hydrogen production

Bifunctional CaTiO3:Ln3+ nanocrystals not only can show very stable luminescence properties and a much higher quenching concentration due to the scheelite related structure of CaTiO3, but also can exhibit a higher activity for hydrogen production.

Efficient photocatalytic hydrogen evolution system by assembling earth abundant NixOy nanoclusters in cubic MCM-48 mesoporous materials

A MCM-48 mesoporous support containing NiO and Ni2O3 nanoclusters exhibit high activity for photocatalytic hydrogen production in comparison to NiO.

Hydrothermal synthesis of a uniform sub-micrometer-spherical Zn0.83Cd0.17S photocatalyst with high activity for photocatalytic hydrogen production

A series of Zn0.83Cd0.17S with high photocatalytic activity was hydrothermally synthesized, the best hydrogen production rate of 45.97 mmol h−1 g−1 was obtained when the hydrothermal temperature was 160 °​C and the dosage was 0.03 g.

Novel Fe–Ni-Graphene composite electrode for hydrogen production

We have developed a novel, efficient and economical composite electrode for hydrogen production. The electrode has been formed by embedding graphene in the Fe–Ni matrix via room temperature electrodeposition. The obtained active coatings have been tested for their efficiency and performance as electrode surfaces for hydrogen evolution reaction (HER) in 6 M KOH by cyclic voltammetry and chronopotentiometry techniques. The coating obtained at 60 mA cm−2 exhibited approximately 3 times higher activity for hydrogen production than that of binary Fe–Ni alloy. Addition of graphene to electrolyte bath resulted in porous 3D projections of nano-sized spheres of Fe–Ni on the surface of graphene, which effectively increased the electrochemically active surface area. XPS analysis results showed the equal distribution of both Ni metal and NiO active sites on the composite. The addition of graphene favoured the deposition of metallic nickel, which accelerated the rate determining proton discharge reaction. All these factors remarkably enhanced the HER activity of Fe–Ni-Graphene (Fe–Ni-G) composite electrode. The Tafel slope analysis showed that the HER follows Volmer-Tafel mechanism. The structure–property relationship of Fe–Ni-G coating has been discussed by interpreting field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analysis results.

Structural and textural properties of Fe2O3/γ-Al2O3 catalysts and their importance in the catalytic reforming of CH4 with H2S for hydrogen production

Newer catalysts for the methane reforming with H2S are designed, which are based on Fe2O3/γ-Al2O3, nanocrystalline γ-Al2O3 supports, and 1.0 to 6.0 wt% Fe. The main phases are identified as hematite and γ-Al2O3, with sizes of about 2–4 nm. The structural features are characterized by X-ray diffraction, Rietveld's Refinement and Radial Distribution Function analysis. The textural properties of these catalysts are determined by N2 sorption and surface fractal dimension calculations. Also, the electronic states are inferred by Mössbauer and UV–Vis (diffuse reflectance) spectroscopies. The activity of Fe2O3/γ-Al2O3 catalysts in the methane reforming is tested in a fixed bed type reactor. Further calculations indicate that Fe2O3/γ-Al2O3 catalysts go through a charge transfer decrease, which depends on the iron content, i.e., from 1.08 to 0.88 eV; Mössbauer spectroscopy reveals that Fe3+ ions adopt a tetrahedral coordination, which coincides with their higher activity for hydrogen production, with respect to catalysts having octahedral coordination. The specific surface area of these catalysts is about 84 m2 g−1, with a mean pore diameter of 2.5 nm. A mechanism for the methane reforming with H2S is proposed herein.

Enhancement of hydrogen production by optimization of biofilm growth in a photobioreactor

To improve biofilm activity and obtain a high hydrogen production performance of biofilm photobioreactor (BPBR), the biofilm growth on the fiber-optic surface was optimized by using a multi-sensor measurement system, plus biofilm thickness automatic control device. The proposed measurement system consisted of three types of sensors, i.e. biofilm thickness sensors, biomass concentration sensor and fiber Bragg grating temperature sensors, respectively, to monitor biofilm growth and distribution, cell adsorption/detachment rates, cell metabolic heat production and distribution in time-dependent tests. The biofilm thickness was controlled in real time using the designed biofilm control device and the information obtained from the biofilm sensors. The biofilm, in the improved BPBR, showed a loose structure and high hydrogen production activity. The H2 concentration and H2 production rate reached a high level of 45 μg/mL and 2.72 mmol/L/h, respectively, for the improved BPBR; these values were 1.73 times and 1.49 times those of the unimproved BPBR, respectively.

Effect of catalyst structure on steam reforming of toluene over Ni/La0.7Sr0.3AlO3−δ catalyst

We investigated steam reforming of toluene as a biomass tar model on Ni/La0.7Sr0.3AlO3−δ, which has high activity and low carbon deposition for hydrogen production. Carbon deposition was suppressed by the oxidation of surface carbon species with lattice oxygen on support. The effects of Ni particle size and support surface area on catalytic features were evaluated by varying the calcination temperature of supported Ni and perovskite support independently. Activity tests, isotopic transient response tests, and characterization were performed to ascertain how interaction between Ni and support contributes to this reaction. Additionally, we evaluated the catalytic activity and carbon deposition per unit of Ni surface and perimeter. The lattice oxygen release rate depends on the specific surface area of the support, Ni-support interface, and catalyst structure. High surface area of the support accelerates the exchange of lattice oxygen through the redox cycle during steam reforming. Furthermore, the larger interface between Ni and support enables rapid lattice oxygen release. When the lattice oxygen release rate was higher, the catalytic activity was higher and carbon deposition was lower for each catalyst. These results confirm that lattice oxygen plays an important role in the activation of toluene and removal of carbon deposition on supported Ni.

Direct Imaging of Light Emission Centers in Two‐Dimensional Crystals and Their Luminescence and Photocatalytic Properties

AbstractTo fully understand the fundamental properties of light‐energy‐converting materials, it is important to determine the local atomic configuration of photofunctional centers. In this study, direct imaging of one‐ and two‐Tb‐atom emission centers in a two‐dimensional Tb‐doped Ca2Ta3O10 nanocrystal was carried. The emission centers were located at the Ca sites in the perovskite structure, and no concentration‐based quenching was observed even when the emission centers were in close proximity to each other. The relative photoluminescence efficiency for green emission of the nanosheet suspension was 38.1 %. Furthermore, the Tb‐doped Ca2Ta3O10 nanocrystal deposited co‐catalyst showed high photocatalytic activity for hydrogen production from water (quantum efficiency: 71 % at 270 nm). Tb3+ dopants in the two‐dimensional crystal might have the potential to stabilize the charge separation state.

Direct imaging of light emission centers in two-dimensional crystals and their luminescence and photocatalytic properties.

To fully understand the fundamental properties of light-energy-converting materials, it is important to determine the local atomic configuration of photofunctional centers. In this study, direct imaging of one- and two-Tb-atom emission centers in a two-dimensional Tb-doped Ca2Ta3O10 nanocrystal was carried. The emission centers were located at the Ca sites in the perovskite structure, and no concentration-based quenching was observed even when the emission centers were in close proximity to each other. The relative photoluminescence efficiency for green emission of the nanosheet suspension was 38.1%. Furthermore, the Tb-doped Ca2Ta3O10 nanocrystal deposited co-catalyst showed high photocatalytic activity for hydrogen production from water (quantum efficiency: 71% at 270 nm). Tb(3+) dopants in the two-dimensional crystal might have the potential to stabilize the charge separation state.

Hydrogen production from methane dry reforming over nickel-based nanocatalysts using surfactant-assisted or polyol method

In this study, two series of Ni-based nanocatalysts were synthesized successfully by the polyol and surfactant-assisted methods and subsequently tested for hydrogen production from CO2–CH4 reforming. Surfactant-assisted catalysts were prepared by using cetyl trimethyl ammonium bromide (CTAB) as a surfactant, whereas polyol catalysts were prepared in ethylene glycol (EG) medium with polyvinylpyrrolidone (PVP) as a nucleation-protective agent. The catalytic performance of each catalyst, in terms of H2 yield and selectivity, was evaluated at different temperatures (500–800 °C). In order to clarify and explain the differences in catalytic activities of catalysts, the prepared samples were characterized by various techniques, such as BET, H2-TPR, CO2-TPD, XRD, TGA, SEM, HRTEM and CO pulse chemisorption. The results demonstrated that the method of preparation had a significant effect on the catalytic performance of tested catalysts. Overall, polyol catalysts showed high activity and selectivity for hydrogen production, while surfactant-assisted catalysts exhibited a fairly high resistance towards carbon deposition under similar reaction conditions of dry reforming of methane. Moreover, due to the reverse water gas shift reaction (RWGS), surfactant-assisted catalysts always produced smaller values of H2/CO product ratio than their corresponding polyol catalysts.

The effects of Pt addition to supported Ni catalysts on dry (CO2) reforming of methane to syngas

Ni/CeZrO2 and Ni/Al2O3 catalysts promoted by Pt were explored for dry reforming of methane at temperatures ranging from 100°C to 800°C. Temperature programmed reduction (TPR) and temperature programmed reaction studies showed that Pt increases the reducibility of Ni-based monometallic catalysts. TPR studies suggested an alloy formation between Pt and Ni. The induction period with the Pt is much lower than on the Ni alone especially on the Al2O3. At lower temperatures, the Pt–Ni bimetallic catalyst showed slightly higher activity for hydrogen production during dry reforming of methane. Reaction investigations over alumina supported catalysts demonstrated a higher H2:CO ratio than ceria supported catalysts. A mechanism involving more steam reforming due to more water consumption is proposed for the reaction on alumina supported catalysts.

Facile preparation of yttrium and aluminum co-doped ZnO via a sol–gel route for photocatalytic hydrogen production

Yttrium and aluminum co-doped ZnO were successfully synthesized by the sol–gel method. The obtained products showed high photocatalytic activity for hydrogen production (5.71 mmol h−1 g−1), and exhibited excellent stability and recyclability.

Microwave-assisted hydrothermal synthesis of graphene based Au–TiO2photocatalysts for efficient visible-light hydrogen production

Au–TiO2–graphene photocatalysts display high visible-light hydrogen production activity due to the load of Au nanoparticles and introduction of graphene.

Effect of Pt addition to Ni/La0.7Sr0.3AlO3−δ catalyst on steam reforming of toluene for hydrogen production

Pt/Ni/La0.7Sr0.3AlO3−δ (Pt/Ni/LSAO) catalyst showed high catalytic activity and low coke formation for hydrogen production by steam reforming of toluene, even without pre-reduction. STEM-EDX and XAFS analyses revealed that Pt and Ni formed adjacent or alloy structure. Electron donation from supported Pt to Ni was observed by XPS observation, and the improvement of reducibility of Ni by Pt addition was observed by H2-TPR. Catalytic activity of the reduced Ni was brought by the PtNi interaction. The impregnation order of Pt and Ni affected the catalytic activity and the amount of coke formation due to the difference of the structure of supported metals. Dilution effects of Pt on Ni metal and the contact between Ni and LSAO support apparently affect the suppression of coke formation.

Photocatalytic hydrogen production with visible light over Mo and Cr-doped BiNb(Ta)O4

In the present work, we prepared pure and Cr(III) and Mo(V)-doped BiNbO4 and BiTaO4 by the citrate method. Pure BiNbO4 and BiTaO4 were obtained in triclinic phase at 600 °C and 800 °C, respectively. The metal doping influenced strongly the crystal structure as well as the photocatalytic activity of the oxides. The XRD data could prove that the Mo(V) doping induces the orthorhombic phase, while the Cr(III) doping favors the triclinic phase for both oxides. Metal doping also modified the photosensitivity of the oxides, extending the absorption toward the visible light region. The photocatalytic activity in water splitting under visible light irradiation was evaluated by monitoring the H2, CO2 and CO evolution. The results showed that Cr(III)-doped BiTaO4 and BiNbO4, in general, are more selective for hydrogen production, while Mo(V)-doped materials are more selective for CO2 generation. Comparing the photocatalytic activity of BiTaO4 and BiNbO4, the former shows higher activity for hydrogen production as well as for CO2 generation, specially when the concentration was 2% in Cr(III) and Mo(V), respectively. Those results are in agreement with the computational study to access the effect of doping on the electronic structure. For Mo(V)-doped materials a negligible change of conduction band minimum potential was found, indicating that there might be no improvement on the reduction power of the material following the substitutional doping. In Cr(III)-doped BiNbO4 there is a slight shift of the CBM potential increasing a little bit the reduction power. However, the effect is much stronger in the Cr(III)-doped BiTaO4.

Fabrication of In2O3 modified ZnO for enhancing stability, optical behaviour, electronic properties and photocatalytic activity for hydrogen production under visible light

With the purpose of enhancing the stability, optical behaviour, electronic properties and photocatalytic activity for hydrogen production under visible light, ZnO has been modified by In2O3. The thriving modification of ZnO by In2O3 was confirmed from X-ray diffraction, DRUV-vis spectra, X-ray photoelectron spectroscopy, transmission electron microscopy, photoluminescence spectroscopy and photoelectrochemical measurement. DRUV-vis spectra showed that the optical absorption of ZnO was significantly enhanced to the visible region by modification with In2O3. TEM study confirmed that the particle size of ZnO was drastically reduced by the modification with In2O3 which helped to retard the recombination of charge carriers and enhanced the photocatalytic activity. Moreover, In2O3 modification greatly enhanced the stability of ZnO in aqueous medium which is a really challenging task in the photocatalytic chemistry of ZnO. All the In2O3 modified ZnO samples showed high photocatalytic activity for hydrogen production under visible light.