Low-temperature Reduction Method Research Articles

Intercalation Reaction Mechanism of Fluoride-Ions in (Ca, Sr)FeO2 Cathodes with Infinite Layer Structure for All-Solid-State Fluoride-Ion Batteries

Fluoride ion batteries, which use fluoride ions as carriers, are attracting attention as the next generation of storage batteries because of their theoretical high energy density. Conventional research has focused on metal/metal fluorides such as Cu/CuF2 as cathode materials.[1] However, these cathodes have disadvantages of the power density and cyclability due to the rapid decrease in electronic conductivity and large volume change during fluorination and defluorination. To solve these problems, cathode materials that utilize topotactic fluoride ion intercalation reactions, similar to electrode materials applied in lithium-ion secondary batteries, are being developed[2]. However, these materials have the disadvantage of relatively small capacity, compared to metal/metal fluorides.In this study, we focused on SrFeO2and Ca-doped SrFeO2 cathodes with infinite layer structure as new high-capacity intercalation cathodes, and evaluated its electrochemical properties and clarified the charge compensation mechanism.Ca1-xSrxFeO2 (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) was synthesized by a low-temperature reduction method using CaH2. Ca1-xSrxFeO2/La0.9Ba0.1F2.9/vapor grown carbon fiber (VGCF) was used as the composite cathode, La0.9Ba0.1F2.9 as the electrolyte and Pb/PbF2/ La0.9Ba0.1F2.9/VGCF as the composite anode to construct the electrochemical cell of the piezoelectric material. Charge-discharge measurements were carried out in the cut-off voltage range of -1.5 to 3.0 V at 140°C. X-ray absorption spectroscopy (XAS) measurements of Fe K-edge, O K-edge, and F K-edge and resonant inelastic X-ray scattering (RIXS) measurements of O K-edge were performed on the samples after charging and discharging.All the Ca1-xSrxFeO2 (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) cathode showed voltage plateaus around -0.5 V and 1.5 V during charging, and the maximum discharge capacity (580 mAh g-1) was obtained when x = 0.8, and the cathodes could be repeatedly charged and discharged. XAS of the Fe K-edge revealed that Fe compensated for the charge in the flat potential region around -0.5 V. XAS and RIXS measurements of the O K-edge revealed that the charge compensation was carried out by the formation of O2 molecules (oxidation of oxide ions), as which is observed in lithium-excess metal oxide on charge process[4], in the voltage plateau around 1.5 V. Using inexpensive Ca and Fe, we succeeded in developing an intercalation cathode material that significantly exceeds the capacity of conventional lithium-ion battery cathodes.

Highly efficient oxygen evolution reaction enabled by phosphorus-boron facilitating surface reconstruction of amorphous high-entropy materials

Efficient, cost-effective and durable electrocatalysts are highly required to overcome the slow kinetics and high overpotential of oxygen evolution reaction (OER). Here we report a series of novel amorphous high-entropy borophosphate catalysts FeCoNiMBPOx (M = Mg, Al, Cr, Mn) prepared by a low-temperature reduction method. The leaching of boron and phosphorus accelerates the surface self-reconstruction of FeCoNiMnBPOx, and the subsequently formed high-oxidation-state metal-OOH species is beneficial to improve the catalyst performance. Moreover, the unique amorphous structure with abundant defects provides more active sites for OER. As a return, all the samples exhibit excellent OER activity and stability. Among them, FeCoNiMnBPOx with the highest conductivity and the largest electrochemical active surface area (ECSA) exhibits the best electrocatalytic performance, requiring only low overpotentials of 248 mV and 294 mV to reach current densities of 10 mA cm−2 and 100 mA cm−2, respectively. This sample also shows an exceptional durability for 50 h without a significant increase in potential, which is superior to that of the benchmark RuO2 electrocatalyst. The combination of the adsorbate evolution mechanism (AEM) and the lattice oxygen-mediated mechanism (LOM) are responsible for the excellent catalyst performance. This work provides new ideas for designing high-activity multiple-element catalysts.

Sustainable formation of tricarballylic acid from citric acid over highly stable Pd/Nb2O5·nH2O catalysts

Recently, a reaction sequence was developed for the production of tricarballylic acid, an interesting plasticiser precursor, from citric acid by using a H-Beta zeolite and Pd/C catalyst. Although yields of 85% of tricarballylic acid were obtained, citric acid elicited Al leaching from the zeolite framework, resulting in loss of activity. In this work, Nb2O5·nH2O was found to be a stable and performant catalyst for this reaction, and a strong involvement of the hydroxyl group of citric acid with the Nb2O5·nH2O surface was observed by 13C MAS NMR. Next, Pd/Nb2O5·nH2O catalysts were synthesized via a low temperature reduction method to preserve the acidity of the Nb2O5·nH2O support; the nature of the Pd phase was examined by XAS. In presence of a 0.6 wt% Pd/Nb2O5·nH2O catalyst, yields over 90% of tricarballylic acid were obtained over multiple runs. Finally, this catalyst was also suitable for the dehydration-hydrogenation of other monohydroxy carboxylic acids.

Efficient Sn Recovery from SnO2 by Alkane (CxHy=2x+2, 0\u2009\u2264\u2009x\u2009\u2264\u20094) Reduction

We study the mechanism of alkane reduction of SnO2 for efficient low-temperature recovery of Sn from SnO2. Based on thermodynamic simulation results, we comparatively analyze the reduction behavior and the efficiency of SnO2 reduction by H2 and alkanes (CxHy=2x+2, 0 ≤ x ≤ 4). We found that alkanes (n·CxHy) with the higher nx generally complete the reduction of SnO2 (T100) at the lower temperature. Moreover, the T100 of the SnO2 reduction by alkanes (n·CxHy) was decreased from the T100 of pure hydrogen with the same amount of hydrogen atoms (n·Hy). We found that the concentration of a gas phase product mixture, the amount of the produced solid carbon, and the T100 complementary vary as a function of the nx and ny, the total amount of carbon and hydrogen atoms in the reducing gas phase molecules. Our results demonstrate a viability of the low temperature reduction method of SnO2 by alkanes for efficient recovery of Sn from SnO2, which can be applied for Sn recovery from Sn containing industrial wastes or Sn ores with economic value added that is held by the co-produced H2.

Reversible Control of the Mn Oxidation State in SrTiO3 Bulk Powders.

We demonstrate a low-temperature reduction method for exhibiting fine control over the oxidation state of substitutional Mn ions in strontium titanate (SrTiO3) bulk powder. We employ NaBH4 as the chemical reductant that causes significant changes in the oxidation state and oxygen vacancy complexation with Mn2+ dopants at temperatures <350°C where lattice reduction is negligible. At higher reduction temperatures, we also observe the formation of Ti3+ in the lattice by diffuse-reflectance and low-temperature electron paramagnetic resonance (EPR) spectroscopy. In addition to Mn2+, Mn4+, and the Mn2+ complex with an oxygen vacancy, we also observe a sharp resonance in the EPR spectrum of heavily reduced Mn-doped SrTiO3. This sharp signal is tentatively assigned to surface superoxide ion that is formed by the surface electron transfer reaction between Ti3+ and O2. The ability to control the relative amounts of various paramagnetic defects in SrTiO3 provides many possibilities to study in a model system the impact of tunable dopant-defect interactions for spin-based electronic applications or visible-light photocatalysis.

Plasmonic Ag coated Zn/Ti-LDH with excellent photocatalytic activity

Highlights Nowadays, two-dimensional (2D) nanosheets, such as layered double hydroxides (LDH), have received considerable attention for their potential to meeting clean energy demand and solving environmental problems. In this work, novel and efficient photocatalysts of plasmonic Ag nanoparticles coated Zn/Ti-LDH nanosheets have been synthesized through low-temperature reduction method. The structural characteristics of the as-prepared products were investigated by a series of characteristic methods The scanning electron microscopy (SEM) and transmission electron microscope (TEM) images showed that Ag nanoparticles were distributed on the surface of Zn/Ti-LDH uniformly. The UV–vis diffuse reflectance spectra (DRS) showed that the absorbance of Ag/LDH in visible-light region enhanced markedly and presented a broad band at 500–600 nm, which was resulted from the surface plasmon resonance (SPR) effect of Ag nanoparticles. The photocatalytic activities of Ag/LDH were evaluated by degradation of Rhodamine-B (RhB) and NO. The photocatalytic experiments showed that Ag/LDH had higher photocatalytic activity than that of pure LDH, and 2%Ag/LDH exhibited the highest photocatalytic activity. In addition, the 2%Ag/LDH exhibited high photochemical stability after multiple reaction runs. The obtained results from photoluminescence (PL) spectroscopic measurement and transient photocurrent (I–V) analysis both revealed the existence of Schottky barriers between LDH and Ag nanoparticles. The electron spin resonance (ESR) showed that radical dotOH were the dominant active species in the photo-degradation process. The enhanced photocatalytic performance of the composite should be ascribed to both the SPR effect of Ag nanoparticles in visible light and the Schottky barriers between LDH and Ag nanoparticles.

The roles of surface oxygen vacancy over Mg4Ta2O9-x photocatalyst in enhancing visible-light photocatalytic hydrogen evolution performance

Extending the light absorption range of wide-band-gap semiconductor oxides is crucial to the effective solar-hydrogen energy conversion. Here, we introduced surface oxygen vacancies into Mg4Ta2O9 and constructed a narrow band-gap Mg4Ta2O9-x photocatalyst by a simple low temperature reduction method. The as-synthesized Mg4Ta2O9-x exhibits a significantly extended absorption edge in visible light range, which originates from the intermediate defect level band and electronic states created by introducing surface oxygen vacancy. With the same Pt loaded content (0.5wt%), the Pt-loaded Mg4Ta2O9-x exhibits the excellent photocatalytic stability and higher hydrogen evolution activity (4.42μmol·h−1) than the Pt-loaded Mg4Ta2O9 (0.14μmol·h−1) under visible light irradiation.

Development of Cu-Ag pastes for high temperature sustainable bonding

The combination of excellent electrical conductivity and low cost makes copper a good selection for interconnect materials. However, rapid oxidation of Cu nanoparticles especially at high temperatures is a fatal demerit. To improve the oxidation resistance and realized mass production, Cu@Ag core-shell submicron particles were prepared using commercial copper oxide particles through a low temperature reduction method and subsequent electroless-plating to form Ag shells. Thermal analytical results suggest that Ag coated Cu particles show improved anti-oxidation ability. Mixed with Ag submicron particles obtained from thermal spray pyrolysis, the electrical resistivity of the sintered Cu-Ag composite pastes reaches 10.4μΩcm under a reductive atmosphere. Under the bonding pressure of 10MPa at 275°C for 30min, robust Cu to Cu bonding can be achieved with the Cu-Ag composite pastes, for which the shear strength of the joints reaches 32.7MPa, and it remains 28.2MPa as the bonding pressure is reduced to 5MPa. It was also demonstrated that the joints thus formed have superior elevated temperature strength, and excellent reliability subjected to high temperature storage at 250°C as well as thermal cycling ranged from −65°C to 150°C.

Solution-Processed Graphite Membrane from Reassembled Graphene Oxide

A new synthesis route of a solution-processed highly conductive self-standing graphite membrane from reassembled graphene oxide (GO) has become one of the intensive research focus, because of its immense application opportunities. Previously demonstrated techniques were limited by the unstable reduced graphene oxide (RGO) dispersion and agglomeration during chemical reduction without any surfactant. This results in poor packing morphology and low electrical conductivity of the RGO membrane. Here, we report a novel synthesis route of a highly concentrated RGO solution from exfoliated GO, which results highly conductive and self-standing RGO membrane without using any binders or organic solvents. Our low-temperature reduction method is significantly different from previous investigations in which controlling the reduction rate by lowering the reduction temperature of the GO solution and collision probability was the key factor in preventing random agglomeration. Further high-temperature reduction of the RGO membrane gave rise to a reassembled graphite structure containing negligible oxygen content (O 1s/C 1s = 0.005), and high electrical conductivity (up to 1.6 × 105 S/m) without disintegration of its self-standing feature. This result is better than any previously reported value. Developed RGO membrane could be mass-produced for various flexible device applications. The in-plane alignment and through-thickness consolidation of GO and RGO membranes using vacuum-filtration and thermal treatment successfully ensured the synthesis of highly conductive, mechanically robust RGO and graphite membranes.

Facile synthesis of nanostructured reduced titanium oxides using borohydride toward the creation of oxide-based fuel cell electrodes

A facile, low-temperature reduction method using sodium borohydride to yield corundum-type Ti(2)O(3) nanorods from rutile-type TiO(2) nanorods with morphology retention is proposed. The electrochemical analyses confirmed their promising performance as electrodes and excellent stability to the environment of interest for fuel cell operation.

Synthesis, characterization and electromagnetic properties of Fe 1− xCo x alloy flower-like microparticles

Fe 1− x Co x alloy microparticles with size 3–5 μm and novel flower-like shapes were prepared by a simple low temperature reduction method. The electromagnetic properties for the paraffin matrix composites containing Fe 1− x Co x alloy microparticles were measured using a vector network analyzer in the 2–18 GHz frequency range. As a consequence of large surface- and shape-anisotropy energy for the flower-like shaped 3D microstructures, the strong natural resonance around 8–12 GHz and remarkable dielectric relaxation were observed in the complex permittivity and permeability spectrum, which are dominant in the enhanced electromagnetic wave absorption (EMA) performance. It was found that both the electromagnetic parameters of complex permittivity and permeability and the intensity and location of absorption band were remarkably dependent on the Co/Fe molar ratio. The enhanced EMA performance was obtained in these Fe 1− x Co x –paraffin ( x=0.4, 0.5, and 0.6) composites system. For the Fe 0.5Co 0.5 alloy, the reflection loss ( RL) exceeding −20 dB was obtained in the broad frequency range of 5.4–18 GHz with a thin sample thickness of between 1.0 and 2.9 mm. In particular, an optimal RL of −59 dB was obtained at 3.61 GHz with a thin thickness of 3.6 mm for the Fe 0.4Co 0.6 sample. The Fe 1− x Co x alloy microparticles may be attractive candidates for applications of microwave absorption materials with a wide frequency range and strong absorption in the high frequency region.

Microwave absorption properties of FeNi3 submicrometre spheres and SiO2@FeNi3 core–shell structures

Nearly monodispersed FeNi3 submicrometre spheres with an average diameter of 220 nm were synthesized by a simple low temperature reduction method. SiO2@FeNi3 core–shell structured submicrometre spheres with 25 nm thick SiO2 shell were then fabricated by a sol–gel process. A significant enhancement of electromagnetic absorption (EMA) performance was achieved by the silica coating over the 2–18 GHz. The reflection loss (RL) exceeding −20 dB of the composite was obtained over 6.7–15.1 GHz by choosing an appropriate sample thickness between 2.1 and 3.3 mm, and an optimal RL of −61.3 dB was obtained at 8.7 GHz with a thin absorber thickness of 2.9 mm. The coating of the dielectric silica shell significantly enhanced the EMA performance due to the enhancement of interface polarization at the alloys and dielectric interfaces.

Bimetallic Pt–Sn/γ-alumina catalyst for highly selective liquid phase hydrogenation of diethyl succinate to γ-butyrolactone

Platinum–tin bimetallic catalyst on γ-alumina support was prepared by impregnation method and was reduced by sodium borohydride at room temperature. XRD and XPS characterization revealed that platinum was reduced to Pt0 while, tin was probably partially reduced to Sn2+ due to the low temperature reduction method and Sn0 was completely absent, avoiding the formation of Pt–Sn alloy. Pt–Sn/γ-alumina (Pt 1%, Sn 9%) thus prepared was found to give almost complete selectivity to γ-butyrolactone in liquid phase hydrogenation of diethyl succinate. A plausible reaction pathway is proposed involving Pt–O–Sn state and high selectivity to GBL is due to the Lewis acidity of Sn2+/4+.

Spectroscopic and catalytic characterization of Ni nano-size catalyst for edible oil hydrogenation

Nano-size nickel catalysts were prepared by different methods including impregnation, co-precipitation, and precipitation-deposition techniques on different supports such as silica, alumina and zeolite, by a low temperature reduction method (160–230 °C). Characterization of nano-nickel using ESR technique proved to be very effective, by which the actual particle size was obtained. The estimated particle size was compared with that determined from XRD patterns of Ni and was found to be directly proportional to the degree of conversion of the hydrogenated edible oil with a regression factor r = −0.99. The particle size measured by XRD did not give this direct relation. The obtained results showed that, the catalytic conversion over the prepared samples followed the order impregnation > co-precipitation > precipitation-deposition method.