Hydrogen Reduction Method Research Articles

Preparation and electrochemical properties of Li4Ti5O12/Ti4O7 composite for lithium-ion batteries

In order to improve the rate capability of Li4Ti5O12, Ti4O7 powder was successfully fabricated by improved hydrogen reduction method, then a dual-phase composite Li4Ti5O12/Ti4O7 has been synthesized as anode material for lithium-ion batteries. It is found that the Li4Ti5O12/Ti4O7 composite shows higher reversible capacity and better rate capability compared to Li4Ti5O12. According to the charge-discharge tests, the Li4Ti5O12/Ti4O7 composite exhibits excellent rate capability of 172.3 mAh g−1 at 0.2 C, which is close to the theoretical value of the spinel Li4Ti5O12. More impressively, the reversible capacity of Li4Ti5O12/Ti4O7 composite is 103.1 mAh g−1 at the current density of 20 C after 100th cycles, and it maintains 84.8% of the initial discharge capacity, whereas that of the bare spinel Li4Ti5O12 is only 22.3 mAh g−1 with a capacity retention of 31.1%. The results indicate that Li4Ti5O12/Ti4O7 composite could be a promising anode material with relative high capacity and good rate capability for lithium-ion batteries.

Highly efficient Z-scheme WO3–x quantum dots/TiO2 for photocatalytic hydrogen generation

Z-scheme semiconductors are a promising class of photocatalysts for hydrogen generation. In this work, Z-scheme semiconductors composed of WO 3– x quantum dots supported on TiO 2 (WO 3– x QDs/TiO 2 ) were fabricated by solvothermal and hydrogen-reduction methods. Characterization by transmission electron microscopy and X-ray diffraction indicated that the amount and size of the WO 3– x QDs could be tuned by modulating the addition of the W precursor. Evidence from X-ray photoelectron spectroscopy and photoluminescence spectroscopy suggested that the hydrogen reduction of the composite induced the formation of oxygen vacancy (W 5+ /V O ) defects in WO 3 . These defects led to ohmic contact between WO 3- x and TiO 2 , which altered the charge-transfer pathway from type II heterojunction to Z-scheme, and maintained the highly reductive and oxidative ability of TiO 2 and WO 3– x , respectively. Therefore, the Z-scheme sample showed 1.3-fold higher photoactivity than pure TiO 2 in hydrogen generation. These results suggest that the formation of W 5+ /V O defects at the interface is highly beneficial for the fabrication of Z-scheme photocatalysts. Z-scheme WO 3– x quantum dots (QDs) supported on TiO 2 , fabricated by solvothermal and reduction methods, exhibit highly efficient charge separation and enhanced photocatalytic H 2 generation.

Graphene promoted oxygen vacancies in perovskite for enhanced thermoelectric properties

Abstract Oxygen vacancy plays an important role in optimizing the thermoelectric properties for achieving high figure of merit in perovskite oxides. However, it remains very challenging to find a facile and effective method for creating oxygen vacancy in bulk perovskite material. Using undoped strontium titanate (STO) as a model for perovskite, it is demonstrated here that incorporating graphene into STO can promote the formation of oxygen vacancy in perovskite far more effectively than the time and energy consuming hydrogen reduction method. With only 0.64 vol% of graphene content, reduced graphene oxide (RGO)/STO composite shows highly increased electrical conductivity and power factor compared to hydrogen reduced STO. Electron energy loss spectrum confirms the high concentration of oxygen vacancy in the area close to RGO in RGO/STO composite, which suggests a mild reaction between RGO and STO during sintering. In addition, the thermal conductivity is also depressed due to greatly restricted grain growth via adding RGO. Therefore, this study provides a fast, green and effective way of preparing oxygen deficient perovskite towards improved thermoelectric properties.

Carbon supported IrM (M = Fe, Ni, Co) alloy nanoparticles for the catalysis of hydrogen oxidation in acidic and alkaline medium

We studied the alloying effect in Ir-based alloys on the catalysis of the hydrogen oxidation reaction (HOR) in both acidic and alkaline medium. IrFe, IrNi and IrCo alloy catalysts with nanoparticle size of <5 nm were obtained by our solvent-vaporization plus hydrogen reduction method. The second metal played an important role in tuning the crystal structure and surface electronic structure of the Ir-based alloy catalyst. Among the IrFe, IrCo and IrNi alloy catalysts, Ni induced a mid-sized contraction of the Ir lattice, and gave the best HOR activity in both acidic and alkaline medium. In acidic medium, the weakening of the Ir–H ad interaction caused by the electronic effect of M (M = Fe, Ni, Co) alloying is responsible for the enhancement of HOR activity. The oxophilic effect of the catalytic metal surface, which affects OH ad adsorption and desorption and surface H ad coverage, has a large impact on the HOR activity in the case of alkaline medium. Among IrFe, IrCo, and IrNi alloy catalysts, Ni induced a mid-sized contraction of the Ir lattice and gave the best hydrogen oxidation activity in both acidic and alkaline medium.

Synthesis and Characterization of High Purity Ruthenium Sponge

Ruthenium is widely used as catalyst, magnetic recording and electrode materials. In this study, high-purity (≥99.995 wt%) ruthenium sponge was synthesized from crude ruthenium (≤99.9 wt%) by chemical refining technique. Initially, crude Ru was transformed into H2RuCl6 by distilling treatment. The H2RuCl6 was, then, added with NH4Cl powder to precipitate (NH4)2RuCl6 powder. Afterward, the (NH4)2RuCl6 powder was ignited in air and transformed into RuO2. Finally, RuO2 was changed to Ru by hydrogen reduction method. Impurities included in the starting Ru powder were eliminated after distillation and precipitation treatments. As-obtained ruthenium particles were spherical-like agglomeration, the average size was about 6 μm and the powder density was 11.83 g/cm3. The details of chemical transforming mechanisms in the refining process were described.

Fabrication of Wide-Range-Visible Photocatalyst Bi2WO6-x nanoplates via Surface Oxygen Vacancies.

Bi2WO6 as a high visible-light-driven catalyst has been aroused broad interest. However, it can only be excitated by the light with λ < 450 nm and the solar energy utilization need to be improved. Here, the wide–range–visible photoresponse Bi2WO6−x nanoplates were fabricated by introducing surface oxygen vacancies through the controllable hydrogen reduction method. The visible photoresponse wavelength range is extended from 450 nm to more than 600 nm. In addition, the photocatalytic activity of Bi2WO6−x is also increased and is 2.1 times as high as that of pristine Bi2WO6. The extending of the photoresponse range and the enhancement of the photoactivity both can be attributed to the surface-oxygen-vacancy states. This is because surface-oxygen–vacancy states generated above and partly overlapping of with the valence band (VB) will result in the rising of valence band maximum (VBM), thus broadening the VB width. This approach is proposed to develop many types of wide–range–visible optical materials and to be applicable to many narrow and wide bandgap materials.

Mesoporous silica nanoparticle supported PdIr bimetal catalyst for selective hydrogenation, and the significant promotional effect of Ir

A mesoporous silica nanoparticle (MSN) supported bimetal catalyst, PdIr/MSN, was prepared by a facile impregnation and hydrogen reduction method. The strong promotional effect of Ir was observed and thoroughly investigated. At the optimal molar ratio of Ir to Pd (NIr/NPd = 0.1), the activity of PdIr0.1/MSN was up to eight times and 28 times higher than that of monometallic Pd/MSN and Ir/MSN, respectively. The catalysts were characterized comprehensively by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and hydrogen temperature programmed reduction, which revealed that the promotional effect of Ir may be due to the enhanced dispersion of active components on the MSN, and to the intensified Pd–Ir electronic interaction caused by the addition of Ir.

Effect of elemental molar ratio on the synthesis of higher alcohols over Co-promoted alkali-modified Mo2C catalysts supported on CNTs

Abstract A series of molybdenum carbide catalysts promoted by potassium and cobalt, supported on carbon nanotubes (CNTs) were prepared by carbothermal hydrogen reduction method using CNTs as a carbon precursor. Firstly, molybdenum and cobalt were loaded by co-precipitation method, and then potassium and additional molybdenum were impregnated to previous resultant. Different Mo/Co and K/Co molar ratio were used in catalyst synthesis. All the catalysts were characterized by ICP, BET, TEM, TPR, XRD and XPS, and the catalysts performances for higher alcohols synthesis (HAS) were investigated in a fixed-bed micro-reactor. The maximum selectivity to higher alcohols (C 2+ OH) was obtained at Mo/Co and K/Mo molar ratios of 1.66 and 0.6, respectively. XRD results confirmed the formation of K-Mo-C site and Co 3 Mo 3 C phase that might play important role in producing C 2+ OH.

A simple plasma reduction for synthesis of Au and Pd nanoparticles at room temperature

Abstract A simple and fast plasma reduction method is developed for synthesis of Au and Pd metal nanoparticles. The scanning electron microscopy (SEM) analysis indicates a formation of aggregates of Au and Pd nanoparticles with branched structure. The transmission electron microscopy (TEM) image shows that the inclusive nanoparticles are all about 5 nm in size. Compared to conventional hydrogen reduction method, plasma method inhibits the agglomeration of metal particles. The room temperature operation is very helpful to limit the nanoparticle size. Most interestingly, plasma reduction produces more flattened metal particles. This plasma reduction does not require the use of any hazardous reducing chemicals, showing the great potential for the fabrication of noble metal nanoparticles.

Hierarchically Designed Germanium Microcubes with High Initial Coulombic Efficiency toward Highly Reversible Lithium Storage

Germanium has been investigated intensively for its high specific capacity and tough nature, which make it a promising candidate anode for high energy lithium-ion batteries. However, the rational design of a germanium electrode with enhanced electrochemical performances is still a big challenge. Herein, we designed and synthesized germanium microcubes with a hierarchical structure directly on titanium foil via a simple hydrogen reduction method. An ultrahigh initial Coulombic efficiency of 91.8% was acquired due to the high crystallinity of germanium for reversible lithium insertion and extraction, less adverse side reaction for irreversible lithium loss, and unique hierarchical structure for easier electrolyte penetration. In addition, the Li2CO3-predominated solid electrolyte interface contributes significantly to the excellent cycling and rate performances of the anode. Both half and full cell performances demonstrate that germanium has potential applications in high-performance lithium-ion batteries.

Magnetic iron oxides in the cementation technology of the boron-containing radioactive waste

Two ways of synthesis of non-detachable dispersed particles of magnetic materials useful for the boron-containing waste cementation process regulation were developed. Powder XRD showed that the method of carbothermic recovery of nanoscale iron hydroxide allows obtaining a mixture of iron oxides with content of the magnetic phase up to 70%. Method of low-temperature hydrogen reduction of the raw materials allows obtaining various compositions of a-iron and iron oxides with the possibility to change the size of the final particles in a wide range. The possibility of using composites of magnetic iron oxides and metal oxide compositions instead of ferromagnetic rods with VEP of boron-containing liquid radioactive waste in the fluidized field was studied. It was shown that the use of fine and nano particles of the iron oxides in the pre-treatment of the boron-containing LRW increases the strength of the final compounds and accelerates the cement setting compounds from 13 to 5-9 days.

Hydrodeoxygenation of methyl stearate as a model compound over Mo2C supported on mesoporous carbon

Molybdenum carbide (Mo2C) catalysts supported on mesoporous carbon (MC) were prepared by the carbothermal hydrogen reduction method. Their properties were characterized by N2 adsorption, XRD and TEM. The Mo2C formation procedure was investigated by TPR and XPS. Methyl stearate was employed as a model compound containing oxygen to investigate the hydrodeoxygenation (HDO) activity of Mo2C/MC catalyst. The results showed Mo2C was formed on MC at the reduction temperature up to 660 °C. The HDO of methyl stearate on Mo2C/MC catalyst occurred through two parallel routes to give the main product octadecane and the by-product heptadecane. 10 wt% Mo2C/MC catalyst exhibited high activity for HDO of methyl stearate with almost 100 % conversion of methyl stearate and high selectivity of 93.6 % toward octadecane, indicating that it is an excellent catalyst to convert vegetable oils into hydrocarbons.

Synthesis of Pd nanoparticles decorated with graphene and their application in electrocatalytic degradation of 4-chlorophenol.

Pd/graphene catalysts were prepared in situ from graphite oxide and palladium salts by the hydrogen-reduction method and were then used for the construction of Pd/graphene gas-diffusion electrodes (GDE). The prepared catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and differential pulse voltammetry (DPV) techniques. In the Pd/graphene catalysts, Pd particles, with an average size of 3.6 nm and an amorphous structure, were highly dispersed in the graphene. The Pd/graphene catalysts accelerated the two-electron reduction of O2 to H2O2 by feeding air, which favors the production of hydroxyl radicals (HO*). In the electrolytic system, HO* was determined in the reaction mixture by the electron spin resonance spectrum (ESR). The dechlorination degree of 4-chlorophenol reached approximately 90.5% after 80 min, and the removal efficiency and the average removal efficiency of 4-chlorophenol, in terms of total organic carbon (TOC) after 120 min, reached approximately 93.3% and 85.1%, respectively. Furthermore, based on the analysis of electrolysis intermediates by high performance liquid chromatography (HPLC) and ion chromatography (IC), a reaction scheme was proposed for the Pd/grapheme GDE catalytic degradation of 4-chlorophenol.

Carbon‐Supported Molybdenum‐Based Catalysts for the Hydrodeoxygenation of Maize Oil

AbstractThe hydrodeoxygenation (HDO) of maize oil was performed in an autoclave with Mo‐based catalysts supported by different carbon materials, such as reduced graphene oxide, activated charcoal, graphite, and fullerene. Nanostructured Mo‐based catalysts with different phase compositions were prepared by using the carbothermal hydrogen reduction method at temperatures ranging from 500 to 700 °C and characterized by Raman spectroscopy, N2 adsorption isotherms, SEM, TEM, XRD, X‐ray photoelectron spectroscopy, and ammonia temperature‐programmed desorption. The highest total hydrocarbon yield of 90.32 % was obtained on the reduced graphene oxide‐supported molybdenum carbide catalyst at 700 °C. These results are subject to the complicated effect of different factors such as phase composition, defect concentration, and particle size on the catalytic behavior of the materials. Unique structures of different supports also play a significant role in the HDO reaction. On the basis of the results of comprehensive analysis of products and catalysts, an HDO mechanism was proposed. These Mo‐based catalysts are a promising system to prepare high‐quality diesel fuels from renewable resources.

High-performance PdRu bimetallic catalyst supported on mesoporous silica nanoparticles for phenol hydrogenation

A high-performance PdRu bimetallic catalyst supported on mesoporous silica nanoparticles (MSN), PdRu/MSN, was prepared by a facile impregnation–hydrogen reduction method. It was found that PdRu/MSN showed 5 times higher activity than that of Pd/MSN towards the liquid-phase hydrogenation of phenol. The catalysts were characterized comprehensively by multiple techniques, X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and hydrogen temperature program reduction (TPR). It was revealed that adding Ru could effectively improve the Pd dispersion and promote the electronic interaction between the Pd and Ru, both of which contribute to enhancing the catalytic activity.

Dry plasma reduction to prepare a high performance Pd/C catalyst at atmospheric pressure for CO oxidation

A high performance Pd/C catalyst (Pd/C-PC) was successfully prepared by simple incipient wetness impregnation followed by the process of dry plasma reduction and calcination. Oxygen-containing group surface-fuctionalized activated carbon was used to absorb the palladium precursor PdCl42−, and small sized (1.92 ± 0.75 nm) Pd nanoparticles were formed in Pd/C-PC, which were smaller than those prepared by low pressure cold plasma (4.0–4.5 nm). The results of XRD, XPS, TPR and TEM showed that dry plasma with calcination could completely remove the residual Cl− ions and obtain predominantly metallic Pd nanoparticles without aggregation. The dry plasma prepared Pd/C-PC catalyst gave excellent catalytic activity for CO oxidation, and the TOF value for 5 wt% Pd/C-PC was about 6.1 times as that for 6 wt% Pd/graphene prepared by the conventional impregnation and hydrogen reduction method. The high performance was attributed to the smaller size and predominantly metallic Pd nanoparticles.

A solvent evaporation plus hydrogen reduction method to synthesize IrNi/C catalysts for hydrogen oxidation

A novel solvent evaporation plus H2 reduction method is developed for the controllable synthesis of IrNi/C catalysts with high HOR activity.

Investigation of high temperature oxidation behavior and tribological performance on cold sprayed nickel–alumina composite coating

Abstract Cold spraying shows a great potential in the fabrication of metal matrix composites. In this study, a nickel-coated Al 2 O 3 powder produced with the hydrothermal hydrogen reduction method was employed aiming to increase the volume fraction of ceramic particles in the cold sprayed composites. The effect of oxidation temperatures on the microstructure and microhardness of as-cold-sprayed and vacuum heat-treated Ni/Al 2 O 3 composite coatings was characterized. In addition, the high temperature oxidation behaviors of as-sprayed and heat-treated coatings were compared and discussed. Eventually, the tribological performance of as-sprayed coating was examined at 25 °C and 400 °C. Results show that the oxidized coatings are denser compared with the as-sprayed coating. The oxide films morphologies of as-sprayed coatings are obviously different under different oxidizing temperatures. Moreover, the as-sprayed coating has a similar oxide film feature to the heat-treated coating when oxidized at 850 °C, which may suggest the direct use of coating after deposition without any heat-treatment. The microhardness values of the oxidized coatings are comparable with the as-sprayed coating and even the heat-treated coating. Finally, friction tests indicate that the as-sprayed coating shows a good tribological performance at elevated working temperatures.

Fabrication of porous Co/NiO core/shell nanowire arrays for electrochemical capacitor application

Abstract We report self-supported porous Co/NiO core/shell nanowire arrays via the combination of hydrogen reduction and chemical bath deposition methods. The Co nanowire acts as the backbone for the growth of NiO nanoflake shell forming hierarchically porous Co/NiO core/shell nanowire arrays. As electrode materials for pseudo-capacitors, the Co/NiO core/shell nanowire arrays exhibit a specific capacitance of 956 F g− 1 at 2 A g− 1 and 737 F g− 1 at 40 A g− 1, and good cycling stability, which is mainly due to the metal nanowire based core/shell nanowire architecture which provides good conductive network as well as fast ion/electron transfer and sufficient contact between active materials and electrolyte.

An effective Pd-promoted gold catalyst supported on mesoporous silica particles for the oxidation of benzyl alcohol

A bimetallic Pd-promoted gold catalyst with mesoporous silica nanoparticles (MSNs) as support, PdAu/MSN, was prepared by an impregnation–hydrogen reduction method, and its catalysis for the base-free oxidation of benzyl alcohol was investigated. It was found that adding a small amount of Pd, with a Pd/Au atomic ratio as low as 0.05/1, can significantly decrease the size of the gold particles and thereby remarkably enhance the catalyst's activity for aerobatic oxidation. At the optimal Pd/Au atomic ratio of 0.2/1, the catalyst Pd0.2Au/MSN showed 8 times and 3 times higher activity than the monometallic catalysts Au/MSN and Pd/MSN, respectively. The prepared catalysts were comprehensively characterized by XRD, DRUV-vis, TEM, XPS, and H2-TPR to correlate the enhanced activity with the promotional effect induced by adding Pd.