Thermal Hydrogen Reduction Research Articles

Hollow Fe3O4/Fe@C nanocubes for broadband microwave absorption spanning low- and high-frequency bands

Rationally constructing hollow structures with heterogeneous interface is usually an effective strategy to regulate the electromagnetic response behavior for lightweight and strong absorption, but achieving low-frequency and broadband absorption is a major challenge. This work adopts a novel Fe(II)/Fe(III) ions regulation strategy to design and synthesize hollow Fe(OH)X (x = 2, 3) nanocubes, which addresses the disadvantages of time-consuming or using etchant. Subsequently, a unique hollow Fe3O4/Fe@C nanoboxes with adjustable magnetic composition and uniformly coated shell have been successfully synthesized by in-situ carbonization with the assistance of phenolic resin and hydrogen thermal reduction. Notably, the different magnetic components induce the magnetic coupling assembly and play a crucial role in determining its electromagnetic parameters, whereas Fe3O4 contributes to more dipole polarization and stronger low-frequency response characteristics. For Fe3O4@C hollow nanoboxes, the minimum reflection loss (RLmin) is as low as –119.9 dB at 2.3 mm, and extremely wide effective absorption bandwidth (EAB) of 11.4 GHz is achieved spanning low-frequency band of 2.8 ∼ 7.2 GHz and high-frequency band of 11.0 ∼ 18 GHz at 5.0 mm. Surprisingly, the Fe3O4@C also has satisfactory EAB20 (RL＜ –20 dB) reaching 7.1 GHz (14.9 ∼ 18 GHz) at a thin thickness of 1.8 mm. The RLmin of other hollow nanoboxes is also below –30 dB, and the EAB is greater than 9 GHz. This study provides a competitive candidate for efficient microwave absorption in complex frequency bands, especially low-frequency bands.

Facile Preparation of Gold Nanoparticles Silica Composite Film Embedded in Anodized Aluminium Oxide-Glass Substrate

Thin film based on gold nanoparticles or AuNPs is typically used as catalyst in the industrial processes due to their high stability and good reusability. In this work, a thin AuNPs-silica composite film was fabricated firstly from sol-gel method by mixing gold pyrazolate complex to a medium comprised of ethanol, deionized water, and hydrochloric acid followed by addition of tetrabutyl orthosilicate as silica source. Next, 70 microliters of the sol-gel solution were spin-coated on several type of substrates such as glass, anodized aluminium oxide or AAO, and combination of both to yield gold complex-silica composite film. It was found that gold complex-silica composite film fabricated on combination of both AAO-glass substrate gave the best quality based on its surface thickness, layer uniformity and film brittleness. Later, the film was selected and subjected to thermal hydrogen reduction at 210 degrees Celsius for 2 hours to facilitate the formation of gold nanoparticles to give AuNPs-silica in AAO-glass film. Before the heat treatment, the light-brownish colour of the original gold complex-silica in AAO-glass film in daylight will appear as a pinkish red film under UV light, suggesting the interaction between gold atoms and supported by its luminescence spectrum at 692 nm. Upon heat treatment, the resulting AuNPs-silica in AAO-glass film gave a deep-red colour indicating the successful formation of AuNPs. The presence of AuNPs in the film was further confirmed based on the absorption peak at 545 nm, X-ray diffraction pattern at 38.20 degrees for d111 plane in wide-angle region, transmission electron microscopy images showing a small and sphere shape particles as well as its elemental composition in energy dispersive X-ray analysis. Moreover, scanning electron microscope images also suggested that the AAO pores is fully filled with the composite and is in accordance with its surface roughness study via atomic force microscopy analysis.

Self-assembled graphene oxide thin films deposited by atmospheric pressure plasma and their hydrogen thermal reduction

This work uses an atmosphere-pressure plasma jet to obtain thin, homogeneous graphene oxide coatings. The films consisted of self-assembled graphene oxide (GO) layers, which were reduced by heat treatment under a reductive hydrogen atmosphere to obtain a reduced graphene oxide film. The electrochemical and photoelectrochemical analyses show that electrical conductivity increases after the reduction process; meanwhile, this process eliminates the p-type photoactivity of the graphene oxide film. The reduced graphene oxide X-ray diffraction pattern revealed the elimination of the signal at 2θ = 11° initially found in the graphene oxide film. The C1s and O1s high-resolution XPS analyses of the reduced graphene oxide film reveal a pronounced increase in the graphitic-like carbon (sp2), whereas a decrease in the organic-like carbon (sp3) and oxygenated species, such as C-OH, C-O-C, CO, and OCOH, initially found in the graphene oxide film.

Engineering Detrimental Functional Groups in Conductive Additives Toward High-Performance All-Solid-State Batteries.

Conductive additives are of great importance for the adequate utilization of active materials in all-solid-state lithium batteries by establishing conductive networks in the composite cathode. However, it usually causes severe interfacial side reactions with solid electrolytes, especially sulfide electrolytes, leading to sluggish ion transportation and accelerated performance degradation. Herein, a simple hydrogen thermal reduction process is proposed on a commonly used conductive additive Super P, which effectively removes the surface oxygen functional groups and weakens the interfacial side reactions with sulfide. With a small amount of 1 wt % reduced Super P, ASSLBs demonstrates a competitive capacity of 180.2 mAh g-1 , which is much higher than the 130.8 mAh g-1 of untreated Super P. Impressively, reduced Super P based ASSLBs also exhibit a higher capacity retention of 81.8 % than 64.6 % of untreated Super P. The cathode interfacial chemical evolutions reveal that reduced Super P could effectively alleviate the side reactions of sulfide. Reduced Super P shows better reversible capacity compared to reduced carbon nanofiber with almost no loss of capacity retention, due to its more complete conductive network. Our results highlight the importance of oxygen-containing functional groups for conductive additives, lightening the prospect of low-cost 0D conductive additives for practical ASSLBs.

Structural and electronic properties of Ce‐doped Ti4O7 based on experiments and first‐principles calculations

AbstractA series of Ti4O7 powders with different Ce‐cation doping concentrations were successfully prepared through a new strategy combining the wet chemical method and hydrogen thermal reduction. It is shown that Ce, entering the lattice of Ti4O7 during the reduction process, only occurs in the form of Ce3+, and the solubility of Ce is equal to 8.93 at.%. Furthermore, the electrical conductivity of Ce‐doped Ti4O7 powders was tested for the first time and theoretically explained by the first‐principles calculations. It was revealed that Ce provides a negative effect on the electrical conductivity of Ti4O7 powders, which is due to the decrease in the number of electronic states near the Fermi energy level caused by the introduction of Ce.

Correction: Synthesis and structural characterizations of CrCoFeNiMnx (0 ≤ x ≤ 1) high-entropy-alloy thin films by thermal reduction in hydrogen

Correction: Synthesis and structural characterizations of CrCoFeNiMnx (0 ≤ x ≤ 1) high-entropy-alloy thin films by thermal reduction in hydrogen

Hollow porous magnetic/magnetic heterostructured CoFe/defective spinel microspheres template-free synthesis and effective modulation of microwave absorption performance

To create a spinel ferrite with excellent performance for electromagnetic (EM) wave absorption in the low frequency range of 4–6 GHz, compositions based on Co0.75Zn0.125Fe0.125Fe2O4 (CZF–1) and Co0.5Zn0.25Fe0.25Fe2O4 (CZF–2) with multiple elements substituted for A sites were synthesized by using solvothermal method. Hollow porous magnetic/magnetic heterostructure microspheres (HHMs) of CZF–A1 and CZF–A2 with multiple interfaces were prepared by hydrogen–thermal reduction of CZF–1 and CZF–2, and their unique structure and EM absorption properties were investigated in detail. The widest effective absorption bandwidth (EAB) of CZF–A1 and CZF–A2 was 4.1 GHz (13.6–17.7 GHz) and 3.7 GHz (8.0–11.7 GHz) for a corresponding thickness of 1.4 mm and 2.0 mm, respectively. In addition, the minimum reflection loss (R.Lmin) of CZF–A1 and CZF–A2 reached –49.1 dB (at fm = 13.4 GHz) and –45.0 dB (at fm = 4.2 GHz) at a thicknesses of 1.6 mm and 3.7 mm, respectively. More specifically, in the low frequency region of 4–6 GHz, CZF–A1 and CZF–A2 exhibited excellent EM wave absorption due to the effective regulation of their natural resonance frequency. The EM wave absorption frequency band of CZF–A1 and CZF–A2 samples was able to completely cover the 4–6 GHz frequency region for at coating thickness of CZF–A1 and CZF–A2 was only 3.5 mm and 3.3 mm respectively, and their R.Lmin reached –36.5 dB and –22.6 dB. Moreover, the absorption mechanisms of CZF–A1 and CZF–A2 including magnetic resonance, eddy current loss, interfacial polarization and dipole polarization were also investigated in detail. This research provides new insights and guidance for the development of spinel ferrite-based EM absorbers for high efficiency EM wave absorption in the low frequency (4–6 GHz) region.

Synthesis and structural characterizations of CrCoFeNiMnx (0 ≤ x ≤ 1) high-entropy-alloy thin films by thermal reduction in hydrogen

Synthesis and structural characterizations of CrCoFeNiMnx (0 ≤ x ≤ 1) high-entropy-alloy thin films by thermal reduction in hydrogen

Fe/Fe3O4@mSiO2 Core–Shell Nanostructures for Broad-Band Microwave Absorption

Fe/Fe3O4 composite particles with mesoporous silica (mSiO2) shells were successfully prepared via solvothermal reaction combined with hydrogen-thermal reduction. The introduction of mSiO2 on the surfaces of Fe3O4 constructs a ventilated frame and thereafter sustains the dispersion of the fine Fe particles that emerge from the reduction reaction. The conversion of Fe3O4 to Fe nanoparticles enhances the ferromagnetic loss, while the Fe3O4/Fe/mSiO2 interfaces induce an intensified dielectric loss. Fe/Fe3O4@mSiO2-500 (FFm-500) presents excellent electromagnetic wave-absorbing performances. The coating using FFm-500 as fillers presents a minimum reflection loss of −26.81 dB, together with an effective absorption bandwidth of 6.66 GHz. The results revealed the key role of mSiO2 in the synthesis of Fe/Fe3O4 nanostructures and the unique potential of Fe/Fe3O4@mSiO2 as broad-band EMA fillers.

Construction of MoO2/MoS2 heterojunctions on carbon nanotubes as high-efficiency electrocatalysts for H2 production

MoO2/MoS2 heterojunction was prepared on carbon nanotubes via an evaporation crystallization combined with hydrogen thermal reduction method and exhibited excellent catalytic activity for hydrogen evolution reaction.

Mordenite-Supported Ag+-Cu2+-Zn2+ Trimetallic System: A Variety of Nanospecies Obtained via Thermal Reduction in Hydrogen Followed by Cooling in an Air or Hydrogen Atmosphere.

Multimetallic systems, instead of monometallic systems, have been used to develop materials with diverse supported species to improve their catalytic, antimicrobial activity, etc., properties. The changes in the types of nanospecies obtained through the thermal reduction of ternary Ag+-Cu2+-Zn2+/mordenite systems in hydrogen, followed by their cooling in an air or hydrogen atmosphere, were studied. Such combinations of trimetallic systems with different metal content, variable ratios (between them), and alternating atmosphere types (during the cooling after reducing the samples in hydrogen at 350 °C) lead to diversity in the obtained copper and silver nanospecies. No reduction of Zn2+ was evidenced. A low silver content leads to the formation of reduced silver clusters, while the formation of nanoparticles of a bigger size takes place in the trimetallic samples with high silver content. The cooling of the reduced trimetallic samples in the air causes the oxidation of the obtained metallic clusters and silver and copper nanoparticles. In the case of copper, such conditions lead to the formation of mainly copper (II) oxide, while the silver nanospecies are converted mainly into clusters and nanoparticles. The zinc cations provoked changes in the mordenite matrix, which was associated with the formation of point oxygen defects in the mordenite structure and the formation of surface zinc oxide sub-nanoparticles in the samples cooled in the air.

Pt–Au alloy nanoparticles synthesized by glow discharge plasma for enhanced methanol oxidation reaction performance

AbstractPt–Au alloy is greatly important to direct methanol fuel cells as electrocatalysts given its stability and anti‐COads poisoning ability. Herein, Pt and Au ions are successfully prepared into Pt–Au alloy nanoparticles by glow discharge plasma without a reducing agent at room temperature. The high electrons from plasma accelerate to form intermetallic compounds. The low operating temperature of plasma inhibits the agglomeration of particles. Compared with the samples by traditional hydrogen thermal reduction, the catalytic activity and stability of samples in the methanol oxidation reaction (MOR) by plasma are improved due to the stronger metal–metal interaction and smaller size of nanoparticles. The optimal proportion of Pt15Au5/C showed the highest mass activity and specific activity of 1.52 and 6.59 times those of commercial JM Pt/C in electrocatalytic methanol oxidation.

Fe-Cu-Rh ternary alloy nanofibers as an outstanding pH-universal electrocatalyst for hydrogen evolution reaction: The catalytic roles of Fe depending on pH

Fe-Cu-Rh ternary alloy nanofibers having various elemental compositions (x-Fe@Cu-Rh) were synthesized through the thermal hydrogen reduction of Fe-substituted CuRh2O4 nanofibers, which were prepared by electrospinning of a solution containing Cu and Rh precursors at a constant molar ratio (Cu:Rh = 1:2) with varying Fe precursor wt% (x = 6, 12, 24, 48 and 80). A series of x-Fe@Cu-Rh nanofibers were composed of the phases of metallic (fcc) and/or spinel CuRh2O4 where Fe ion substitutes primarily Rh ion in the octahedral site. x-Fe@Cu-Rh ternary alloy nanofibers showed higher pH-universal HER activity than pure Rh and Cu-Rh binary counterparts; and particularly, 12-Fe@Cu-Rh composed of 7.3, 27.2 and 65.5 atomic % of Fe, Cu and Rh, respectively, presented a superb activity (e.g., the most positive onset potential and the smallest Tafel slope) along with reasonable stability, even outperforming commercial Pt. The addition of Fe to Cu-Rh binary system improved alkaline HER activity substantially, proposing the crucial role of Fe-Cu-Rh interfaces for facilitating water molecule adsorption/dissociation. In acidic condition, Fe served as an excellent diluent reducing noble Rh content without deteriorating the acidic HER activity. Surprisingly, 80-Fe@Cu-Rh having only 18.5 atomic % of noble Rh exhibited decent HER activity during 24 h, demonstrating its potential as a stable and economic catalyst particularly for acidic HER.

Suppression of secondary electron emission on oxygen-free copper surface of reduced graphene oxide coatings prepared by electrophoretic deposition

We proposed a new carbon coating to inhibit secondary electron emission. Graphene oxide(GO) coatings were prepared on the surface of oxygen-free copper by DC electrophoretic deposition, and reduced graphene oxide(rGO) coatings were obtained by hydrogen thermal reduction. The X-ray photoelectron spectroscopy (XPS) analysis shows that the oxygen content of the coating reduced from 26.37 at.% to 9.89 at.% after thermal reduction, The XPS and Raman analysis shows that rGO still maintained the sp2 hybrid structure. The inhibitory effect of rGO coatings on secondary electron emission was tested. It was found that the maximum total secondary electron yield (δmax) of the oxygen-free copper surface reduced from 1.38 to 1.09 after the preparation of rGO coating. The total secondary electron yield did not decrease further with the film thickness increasing when the rGO coating reached a certain thickness. Our research provides a new perspective on the preparation of carbon coatings to reduce the secondary electron yield.

Bismuth Nanoparticles Anchored on Ti3 C2 Tx MXene Nanosheets for High-Performance Sodium-Ion Batteries.

Sodium-ion batteries are promising energy-storage systems, but they are facing huge challenges for developing fast-charging anode materials. Bismuth (Bi)-based anode materials are considered as candidates for fast-charging anodes of sodium-ion batteries due to their excellent rate performance. Herein, we designed a two-dimensional Bi/MXene anode material based on a hydrogen thermal reduction strategy. Benefitting from microstructure advantages, Bi/MXene anodes exhibited an excellent rate capability and superior cycle performance in Na//Bi/MXene half-batteries and Na3 V2 (PO4 )3 /C//Bi/MXene full-batteries. Moreover, full-batteries can complete a charge/discharge cycle in 7 min and maintain an excellent cycle life (over 7000 cycles). The electrochemical test results showed that Bi/MXene is a promising anode material with fast charge/discharge capability for sodium-ion batteries.

A Robust Recovery of Ni From Laterite Ore Promoted by Sodium Thiosulfate Through Hydrogen-Thermal Reduction.

Laterite ore is one of the important sources of nickel (Ni). However, it is difficult to liberate Ni from ore structure during reduction roasting. This paper provided an effective way for a robust recovery of Ni from laterite ore by H2 reduction using sodium thiosulfate (Na2S2O3) as a promoter. . It was found that a Ni content of 9.97% and a Ni recovery of 99.24% were achieved with 20 wt% Na2S2O3 at 1,100°C. The promoting mechanism of Na2S2O3 in laterite ore reduction by H2 was also investigated. The thermogravimetric results suggested the formation of Na2Mg2SiO7, Na2SO3, Na2SO4, and S during the pyrolysis of laterite with Na2S2O3, among which the alkali metal salts could destroy the structures of nickel-bearing silicate minerals and hence release Ni, while S could participate in the formation of the low-melting-point eutectic phase of FeS-Fe. The formation of low-melting-point phases were further verified by the morphology analysis, which could improve the aggregation of Ni-Fe particles due to the capillary forces of FeS-Fe as well as the enhanced element migration by the liquid phase of sodium silicates during reduction.

Turning waste into wealth

Turning waste into wealth

Enhanced cyclic stability of NCM-622 cathode by Ti3+ doped TiO2 coating

The TiO2 coating on LiNi0.6Co0.2 Mn0.2O2 electrode can effectively improve its electrochemical properties, such as cyclic stability, ratio capacity and coulomb efficiency, etc. In this paper, Ti3+ was introduced into TiO2 coating by means of hydrogen thermal reduction. Compared with the original material and TiO2 coating material, Ti3+ doped TiO2 coating material has better electrochemical performance. After 150 cycles at 1 C, the capacity retention rates of the three materials were 79.9%, 92.8% and 95.1%, respectively. Our findings provide an effective approach for further enhancing the electrochemical performance of NCM cathode materials.

Towards High Efficacy of Pd-Au/C Catalyst for Tetrachloromethane Hydrodechlorination

We present an efficient strategy for synthesising the PdAu catalysts with a homogeneous PdAu alloy phase for environmentally important hydrodechlorination of tetrachloromethane in the gas phase. The synthesis of carbon-supported catalysts involved two major steps: (i) incorporation of palladium and gold nanoparticles into carbon support and (ii) activation of the catalysts. The critical part of this work was to find the optimal conditions for both steps. Thus, the incorporation of the nanoparticles was carried out in two ways, by impregnation and direct redox reaction method using acetone solutions of metal precursor salts. The activation was performed either by a conventional thermal reduction in hydrogen or flash irradiation in a microwave oven. The homogeneity and structure of the PdAu alloy were found to depend on the catalyst activation method critically. In all cases, we observed better homogeneity for catalysts that were subject to microwave irradiation. Moreover, the flash microwave irradiation of prepared catalysts provided catalysts of better stability and selectivity towards the desired products (hydrocarbons) in the hydrodechlorination of tetrachloromethane as compared to the catalyst obtained by conventional thermal activation in hydrogen.

CoFe2/BaTiO3 Hybrid Nanofibers for Microwave Absorption

CoFe2/BaTiO3 hybrid nanofibers (CoFe2/BTO HNFs) have been synthesized via a simple single-spinneret electrospinning followed by a calcination and hydrogen-thermal reduction process for microwave ab...