Comparison on the immersion corrosion and electrochemical corrosion resistance of WC–Al2O3 composites and WC–Co cemented carbide in NaCl solution

WC–15 wt% Al₂O₃ composites were prepared via hot pressing sintering technology. The corrosion behaviors of WC–Al₂O₃ composites and traditional WC–Co cemented carbide in NaCl solution were studied by immersion corrosion and electrochemical technique. The impedance value of the WC–Al₂O₃ composite increased more rapidly than WC–Co cemented carbide during the 24 hours, which indicated that WC–Al₂O₃ composites had a more compact passivation film than WC–Co cemented carbide. The results confirmed that the corrosion resistance of WC–Al₂O₃ composites was higher than that of WC–Co cemented carbide in NaCl solution. The corrosion mechanisms of WC–Al₂O₃ composites and WC–Co cemented carbide in NaCl solution were also revealed by SEM, EDS, XPS and Raman. The corrosion products of WC–Al₂O₃ composites mainly contain WO₃, while for WC–Co cemented carbide they are Co(OH)₂, Co₃O₄ and WO₃. The different corrosion mechanism of the two materials is attributed to the Al₂O₃ phase instead of the Co binder, which avoids the galvanic corrosion between the WC phase and the Co binder.

WC–Al₂O₃ composites possess higher corrosion resistance compared with WC–Co cemented carbide. The main corrosion mechanism for WC–Al₂O₃ composites is the oxidation of the WC phase.     

Characterization and analysis of the aspect ratio of carbide grains in WC–Co composites

To study the aspect ratio distribution of carbide grains in WC–Co composites, two novel approaches, namely grain shape ellipse calculation and five parameter analysis (FPA) methods, are reported in this work. According to grain shape ellipse calculation, carbide grains that have a grain shape aspect ratio of 0.62 demarcate the more anisotropic grains with a larger size and the less anisotropic grains with a smaller size. Moreover, these grains remained predominantly populous under different cases of structural parameters and processing factors. According to five parameter analysis, the interface area aspect ratio can be derived from the relative area of prevalent (0001) basal planes and (10−10) prismatic planes, and can then be set relevance with the measured mechanical properties. The present work therefore offers new alternatives to establish the connection between the aspect ratio measurement and the property optimization of WC–Co composites.

To study the aspect ratio distribution of carbide grains in WC–Co composites, two novel approaches, namely grain shape ellipse calculation and five parameter analysis (FPA) methods, are reported in this work.     

A mesoporous tungsten carbide nanostructure as a promising cathode catalyst decreases overpotential in Li–O2 batteries

Lithium–oxygen (Li–O₂) batteries as promising energy storage devices possess high gravimetric energy density and low emission. However, poor reversibility of electrochemical reactions at the cathode significantly affects the electrochemical properties of nonaqueous Li–O₂ batteries, and low charge–discharge efficiency also results in short cycle-life. In this work, functional air cathodes containing mesoporous tungsten carbide nanoparticles for improving the reversibility of positive reactions in Li–O₂ cells are designed. Mesoporous tungsten carbides are synthesized with mesoporous carbon nitride as the reactive template and carbon source. And mesoporous tungsten carbides in cathode materials display better electrochemical performance in Li–O₂ cells in comparison with mesoporous carbon nitride and hard carbon. Tungsten carbide-1 (WC-1) with larger specific surface area promotes reversible formation and decomposition of Li₂O₂ at the cathode and lower charge overpotential (about 0.93 V) at 100 mA g⁻¹, which allows the Li–O₂ cell to run up to 100 cycles. In addition, synergistic interaction between WC-1 and LiI could further decrease the charging overpotentials of Li–O₂ cells and improve the charge–discharge performances of the Li–O₂ cells. These results indicate that mesoporous electrocatalysts can be utilized as promising functional materials for Li–O₂ cells to decrease overpotentials.

Tungsten carbide with large specific surface area catalyzes reversible formation/decomposition of Li₂O₂ with low overpotential in a Li–O₂ cell.     

Effect of the coexistence of albumin and H2O2 on the corrosion of biomedical cobalt alloys in physiological saline

The corrosion of Co–28Cr–6Mo and Co–35Ni–20Cr–10Mo, as biomedical alloys, has been investigated for effects of typical species (albumin and H₂O₂) in physiological saline, with their coexistence explored for the first time. Electrochemical and long term immersion tests were carried out. It was found that Co alloys were not sensitive to the presence of albumin alone, which slightly promoted anodic dissolution of Co–35Ni–20Cr–10Mo without noticeably affecting Co–28Cr–6Mo and facilitated oxide film dissolution on both alloys. H₂O₂ led to a clear drop in corrosion resistance, favouring metal release and surface oxide formation and inducing much thicker but less compact oxide films for both alloys. The coexistence of both species resulted in the worst corrosion resistance and most metal release, while the amount and composition of surface oxide remained at a similar level as in the absence of both. The effect of H₂O₂ inducing low compactness of surface oxides should prevail on deciding the poor corrosion protection ability of passive film, while albumin simultaneously promoted dissolution or inhibited formation of oxides due to H₂O₂. Corrosion resistance was consistently lower for Co–35Ni–20Cr–10Mo under each condition, the only alloy where the synergistic effect of both species was clearly demonstrated. This work suggests that the complexity of the environment must be considered for corrosion resistance evaluation of biomedical alloys.

Corrosion of biomedical Co alloys were firstly studied in the presence of both albumin and H₂O₂.     

Study of the electrochemical recovery of cobalt from spent cemented carbide

The massive accumulation of spent cemented carbide not only produces environmental pollution but also wastes resources such as tungsten and cobalt. To solve the problem, a low-temperature acid aqueous electrochemical method was used; cobalt was recycled on a stainless steel cathode, and at the same time, tungstic acid was enriched at a spent cemented carbide anode, achieving a high efficiency, low energy consumption, and low pollution separation and recovering spent cemented carbide. The transient electrochemical test results show the following: the reduction mechanism of cobalt is Co²⁺_(aq) + 2e⁻ → Co_(s). The nucleation mechanism is close to instantaneous nucleation. The electrodeposition is irreversible and controlled by the diffusion step. The average diffusion coefficient of Co(ii) is 2.16589 × 10⁻⁷ cm² s⁻¹. Electrodeposition experiments show that cobalt enters the electrolyte in the form of Co(ii) and is reduced to elemental cobalt on the stainless steel electrode, and tungsten carbide (WC) is oxidized to tungstic acid (H₂WO₄) under the oxidizing atmosphere of the anode and enriched in the anode area. The investigation provides favorable electrochemical conditions for the recovery and separation of other valuable metals from spent alloys.

Cobalt is recovered at the cathode, while tungstic acid is enriched at the anode, thereby successfully achieving efficient short-flow recovery of spent cemented carbide.     

Catalytic activity of Co-nanocrystal-doped tungsten carbide arising from an internal magnetic field

Pt is an excellent and widely used hydrogen evolution reaction (HER) catalyst. However, it is a rare and expensive metal, and alternative catalysts are being sought to facilitate the hydrogen economy. As tungsten carbide (WC) has a Pt-like occupied density of states, it is expected to exhibit catalytic activity. However, unlike Pt, excellent catalytic activity has not yet been observed for mono WC. One of the intrinsic differences between WC and Pt is in their magnetic properties; WC is non-magnetic, whereas Pt exhibits high magnetic susceptibility. In this study, the WC lattice was doped with ferromagnetic Co nanocrystals to introduce an ordered-spin atomic configuration. The catalytic activity of the Co-doped WC was ∼30% higher than that of Pt nanoparticles for the HER during the hydrolysis of ammonia borane (NH₃BH₃), which is currently attracting attention as a hydrogen fuel source. Measurements of the magnetisation, enthalpy of adsorption, and activation energy indicated that the synergistic effect of the WC matrix promoting hydrolytic cleavage of NH₃BH₃ and the ferromagnetic Co crystals interacting with the nucleus spin of the protons was responsible for the enhanced catalytic activity. This study presents a new catalyst design strategy based on the concept of an internal magnetic field. The WC–Co material presented here is expected to have a wide range of applications as an HER catalyst.

The catalytic activity of the Co-doped WC is 30% higher than that of Pt nanoparticles for the hydrogen evolution reaction arising from an internal magnetic field.     

Effect of Ni/Co mass ratio and NiO–Co3O4 loading on catalytic performance of NiO–Co3O4/Nb2O5–TiO2 for direct synthesis of 2-propylheptanol from n-valeraldehyde

In the direct synthesis of 2-propylheptanol (2-PH) from n-valeraldehyde, a second-metal oxide component Co₃O₄ was introduced into NiO/Nb₂O₅–TiO₂ catalyst to assist in the reduction of NiO. In order to optimize the catalytic performance of NiO–Co₃O₄/Nb₂O₅–TiO₂ catalyst, the effects of the Ni/Co mass ratio and NiO–Co₃O₄ loading were investigated. A series of NiO–Co₃O₄/Nb₂O₅–TiO₂ catalysts with different Ni/Co mass ratios were prepared by the co-precipitation method and their catalytic performances were evaluated. The result showed that NiO–Co₃O₄/Nb₂O₅–TiO₂ with a Ni/Co mass ratio of 8/3 demonstrated the best catalytic performance because the number of d-band holes in this catalyst was nearly equal to the number of electrons transferred in hydrogenation reaction. Subsequently, the NiO–Co₃O₄/Nb₂O₅–TiO₂ catalysts with different Ni/Co mass ratios were characterized by XRD and XPS and the results indicated that both an interaction of Ni with Co and formation of a Ni–Co alloy were the main reasons for the reduction of NiO–Co₃O₄/Nb₂O₅–TiO₂ catalyst in the reaction process. A higher NiO–Co₃O₄ loading could increase the catalytic activity but too high a loading resulted in incomplete reduction of NiO–Co₃O₄ in the reaction process. Thus the NiO–Co₃O₄/Nb₂O₅–TiO₂ catalyst with a Ni/Co mass ratio of 8/3 and a NiO–Co₃O₄ loading of 14 wt% showed the best catalytic performance; a 2-PH selectivity of 80.4% was achieved with complete conversion of n-valeraldehyde. Furthermore, the NiO–Co₃O₄/Nb₂O₅–TiO₂ catalyst showed good stability. This was ascribed to the interaction of Ni with Co, the formation of the Ni–Co alloy and further reservation of both in the process of reuse.

NiO–Co₃O₄/Nb₂O₅–TiO₂ catalyst with a Ni/Co mass ratio of 8/3 and NiO–Co₃O₄ loading of 14% shows the best catalytic performance.     

Effect of cobalt addition on the structure and properties of Ni–MCM-41 for the partial oxidation of methane to syngas

A one-step hydrothermal crystallization method was used to synthesize Co–Ni–MCM-41 catalysts for the partial oxidation of methane to syngas reaction. Co was added as an assistant in the synthesis process. The formation of a Ni–Co alloy decreased the damage of Ni ions to the framework of MCM-41. The Ni–Co alloy introduced more Ni into the channel exposing more active sites. The properties of the synthesized catalysts were characterized by XRD, N₂ adsorption–desorption, TEM, ICP, FT-IR, H₂-TPR, XPS and TGA techniques. Co–Ni–MCM-41 catalysts showed superior catalytic performance and sintering resistance than Ni–MCM-41 catalyst without Co. The Ni–Co alloy inhibited the formation of the NiO, thus reducing the sintering of the catalyst. The result was attributed to higher metal dispersion and more regular pore structure of the Co–Ni–MCM-41 catalysts. When the Co content was 1%, a conversion of 88% and selectivity of 87% was achieved.

The Ni–Co alloy confined within MCM-41 improved dispersibility and the stability of Ni.     

Synthesis of multifunctional CuFe2O4–reduced graphene oxide nanocomposite: an efficient magnetically separable catalyst as well as high performance supercapacitor and first-principles calculations of its electronic structures

Here, we report an ‘in situ’ co-precipitation reduction based synthetic methodology to prepare CuFe₂O₄ nanoparticle–reduced graphene oxide (CuFe₂O₄–RGO) nanocomposites. First principles calculations based on Density Functional Theory (DFT) were performed to obtain the electronic structures and properties of CuFe₂O₄, graphene and CuFe₂O₄–graphene composites, and to understand the interfacial interaction between CuFe₂O₄ and graphene in the composite. The synergistic effect, which resulted from the combination of the unique properties of RGO and CuFe₂O₄ nanoparticles, was exploited to design a magnetically separable catalyst and high performance supercapacitor. It has been demonstrated that the incorporation of RGO in the composite enhanced its catalytic properties as well as supercapacitance performance compared with pure CuFe₂O₄. The nanocomposite with 96 wt% CuFe₂O₄ and 4 wt% RGO (96CuFe₂O₄–4RGO) exhibited high catalytic efficiency towards (i) reduction of 4-nitrophenol to 4-aminophenol, and (ii) epoxidation of styrene to styrene oxide. For both of these reactions, the catalytic efficiency of 96CuFe₂O₄–4RGO was significantly higher than that of pure CuFe₂O₄. The easy magnetic separation of 96CuFe₂O₄–4RGO from the reaction mixture and good reusability of the recovered catalyst also showed here. 96CuFe₂O₄–4RGO also demonstrated better supercapacitance performance than pure CuFe₂O₄. 96CuFe₂O₄–4RGO showed specific capacitance of 797 F g⁻¹ at a current density of 2 A g⁻¹, along with ∼92% retention for up to 2000 cycles. To the best of our knowledge, this is the first investigation on the catalytic properties of CuFe₂O₄–RGO towards the reduction of 4-nitrophenol and the epoxidation reaction, and DFT calculations on the CuFe₂O₄–graphene composite have been reported.

Here, we report an ‘in situ’ co-precipitation reduction based synthetic methodology to prepare CuFe₂O₄ nanoparticle–reduced graphene oxide (CuFe₂O₄–RGO) nanocomposites.     

3D web freestanding RuO2–Co3O4 nanowires on Ni foam as highly efficient cathode catalysts for Li–O2 batteries

The mechanism of Li–O₂ batteries is based on the reactions of lithium ions and oxygen, which hold a theoretical higher energy density of approximately 3500 W h kg⁻¹. In order to improve the practical specific capacity and cycling performance of Li–O₂ batteries, a catalytically active mechanically robust air cathode is required. In this work, we synthesized a freestanding catalytic cathode with RuO₂ decorated 3D web Co₃O₄ nanowires on nickel foam. When the specific capacity was limited at 500 mA h g⁻¹, the RuO₂–Co₃O₄/NiF had a stable cycling life of up to 122 times. The outstanding performance can be primarily attributed to the robust freestanding Co₃O₄ nanowires with RuO₂ loading. The unique 3D web nanowire structure provides a large surface for Li₂O₂ growth and RuO₂ nanoparticle loading, and the RuO₂ nanoparticles help to promote the round trip deposition and decomposition of Li₂O₂, therefore enhancing the cycling behavior. This result indicates the superiority of RuO₂–Co₃O₄/NiF as a freestanding highly efficient catalytic cathode for Li–O₂ batteries.

Freestanding RuO₂–Co₃O₄ nanowires on Ni foam were synthesized and applied as a cathode in Li–O₂ battery. This cathode can deliver a high capacity of 9620 mA h g⁻¹ and stable long-term operation exceeding 122 cycles at 100 mA g⁻¹.     

Microwave dielectric properties of low-temperature-fired MgNb2O6 ceramics for LTCC applications

MgNb₂O₆ ceramics doped with (Li₂O–MgO–ZnO–B₂O₃–SiO₂) glass were synthesized by the traditional solid phase reaction route. The effects of LMZBS addition on microwave dielectric properties, grain growth, phase composition and morphology of MgNb₂O₆ ceramics were studied. The SEM results show dense and homogeneous microstructure with grain size of 1.72 μm. Raman spectra and XRD patterns indicate the pure phase MgNb₂O₆ ceramic. The experimental results show that LMZBS glass can markedly decrease the sintering temperature from 1300 °C to 925 °C. Higher density and lower porosity make ceramics have better dielectric properties. The MgNb₂O₆ ceramic doped with 1 wt% LMZBS glass sintered at 925 °C for 5 h, possessed excellent dielectric properties: ε_r = 19.7, Q·f = 67 839 GHz, τ_f = −41.01 ppm °C⁻¹. Moreover, the favorable chemical compatibility of the MgNb₂O₆ ceramic with silver electrodes makes it as promising material for low temperature co-fired ceramic (LTCC) applications.

MgNb₂O₆ ceramics doped with (Li₂O–MgO–ZnO–B₂O₃–SiO₂) glass were synthesized by the traditional solid phase reaction route.     

Peculiarities of the microwave properties of hard–soft functional composites SrTb0.01Tm0.01Fe11.98O19–AFe2O4 (A = Co,Ni, Zn,Cu, or Mn)

Herein, we investigated the correlation between the chemical composition, microstructure, and microwave properties of composites based on lightly Tb/Tm-doped Sr-hexaferrites (SrTb_0.01Tm_0.01Fe_11.98O₁₉) and spinel ferrites (AFe₂O₄, A = Co, Ni, Zn, Cu, or Mn), which were fabricated by a one-pot citrate sol–gel method. Powder XRD patterns of products confirmed the presence of pure hexaferrite and spinel phases. Microstructural analysis was performed based on SEM images. The average grain size for each phase in the prepared composites was calculated. Comprehensive investigations of dielectric properties (real (ε′) and imaginary parts (ε′′) of permittivity, dielectric loss tangent (tan(δ)), and AC conductivity) were performed in the 1–3 × 10⁶ Hz frequency range at 20–120 °C. Frequency dependency of microwave properties were investigated using the coaxial method in frequency range of 2–18 GHz. The non-linear behavior of the main microwave properties with a change in composition may be due to the influence of the soft magnetic phase. It was found that Mn- and Ni-spinel ferrites achieved the strongest electromagnetic absorption. This may be due to differences in the structures of the electron shell and the radii of the A-site ions in the spinel phase. It was discovered that the ionic polarization transformed into the dipole polarization.

Paper presents the correlation between the composition, microstructure, and microwave properties of composites based on Tb/Tm-doped Sr-hexaferrites and spinel ferrites (AFe₂O₄), which were fabricated by a one-pot citrate sol–gel method.     

Metal–organic framework derived hollow porous CuO–CuCo2O4 dodecahedrons as a cathode catalyst for Li–O2 batteries

Herein, hollow porous CuO–CuCo₂O₄ dodecahedrons are synthesized by using a simple self-sacrificial metal–organic framework (MOF) template, which resulted in dodecahedron morphology with hierarchically porous architecture. When evaluated as a cathodic electrocatalyst in lithium–oxygen batteries, the CuO–CuCo₂O₄ composite exhibits a significantly enhanced electrochemical performance, delivering an initial capacity of 6844 mA h g⁻¹ with a remarkably decreased discharge/charge overpotential to 1.15 V (vs. Li/Li⁺) at a current density of 100 mA g⁻¹ and showing excellent cyclic stability up to 111 charge/discharge cycles under a cut-off capacity of 1000 mA h g⁻¹ at 400 mA g⁻¹. The outstanding electrochemical performance of CuO–CuCo₂O₄ composite can be owing to the intrinsic catalytic activity, unique porous structure and the presence of substantial electrocatalytic sites. The ex situ XRD and SEM are also carried out to reveal the charge/discharge behavior and demonstrate the excellent reversibility of the CuO–CuCo₂O₄ based electrode.

Metal–organic framework derived porous CuO–CuCo₂O₄ dodecahedrons as a cathode catalyst for Li–O₂ batteries with significantly enhanced rate and cyclic performance.     

Electrochemical preparation and properties of a Mg–Li–Y alloy via co-reduction of Mg(ii) and Y(iii) in chloride melts

Mg–Li based alloys have been widely used in various fields. However, the widespread use of Mg–Li based alloys were restricted by their poor properties. The addition of rare earth element in Mg–Li can significantly improve the properties of alloys. In the present work, different electrochemical methods were used to investigate the electrochemical behavior of Y(iii) on the W electrode in LiCl–KCl melts and LiCl–KCl–MgCl₂ melts. In LiCl–KCl melts, typical cyclic voltammetry was used to study the electrochemical mechanism and thermodynamic parameters for the reduction of Y(iii) to metallic Y. In LiCl–KCl–MgCl₂ melts, the formation mechanism of Mg–Y intermetallic compounds was investigated, and the results showed that only one kind of Mg–Y intermetallic compound was formed under our experimental conditions. Mg–Li–Y alloys were prepared via galvanostatic electrolysis, and XRD and SEM equipped with EDS analysis were used to analyze the samples. Because of the restrictions of EDS analysis, ICP-AES was used to analyze the Li content in Mg–Li–Y alloys. The microhardness and Young''s modulus of the Mg–Li–Y alloys were then evaluated.

Mg–Li based alloys have been widely used in various fields.     

Structure and mechanical behavior of in situ developed Mg2Si phase in magnesium and aluminum alloys – a review

The demand for lightweight, high specific strength alloys has drastically increased in the last two decades. Magnesium and aluminum alloys are very suitable candidate materials. Research on alloys with an Mg₂Si phase started about three decades ago. The current scenario is that magnesium and aluminum alloys containing an Mg₂Si phase are very popular in the scientific community and extensively used in the automotive and aerospace industries. Mg₂Si is a very stable phase and exhibits excellent mechanical, thermal, electrochemical and tribological properties. This paper presents a brief review of Mg–Si binary alloys, and Mg–Si–Al and Al–Si–Mg alloys. Grain refinement methods and mechanical properties have been reported on lightweight alloys containing Mg and Si. The available results show that silicon reacts with magnesium and forms an intermetallic compound with the stoichiometric formula Mg₂Si. There is in situ formation of an Mg₂Si phase in Mg–Si, Mg–Si–Al and Al–Mg–Si alloys by the diffusion or precipitation process. The morphology and size of an in situ developed Mg₂Si phase depend on the synthesis route and base metal or matrix. In the liquid metallurgy process the precipitation sequence depends on the cooling rate. The morphology of the Mg₂Si phase depends on the precipitation sequence and the mechanical properties depend on the morphology and size of the Mg₂Si phase within the alloy matrix.

The demand for lightweight, high specific strength alloys has drastically increased in the last two decades.     

Study of Ag precipitation and mechanical properties of Ti–Ta–Ag ternary alloy

Ti–25Ta–xAg alloy samples with different content of Ag were prepared by spark plasma sintering method. X-ray diffraction, microscopic metallographic, scanning electron microscopy, and transmission electron microscopy were used to analyze the phase structure and morphology of the alloy samples. Ti–Ta–Ag can form a stable ternary alloy system. Furthermore, with the increase of Ag content and sintering temperature, Ag will be precipitated at the grain boundary. In order to explore the precipitation mechanism of Ag in the alloy and its influence on the mechanical properties, the crystal structure, electronic structure, and elastic constant under different Ag solid solubility were calculated systematically by using first-principles calculations. The results show that the critical temperature of Ag in Ti–Ta–Ag ternary alloy is about 2200 K, and the high temperature is favorable for the aging precipitation of Ag. The lattice constants and mechanical properties of (Ti_1−xAg_x)₃Ta solid solution suddenly change when the Ag solid solubility x value is equal to 0.8, and their changes will follow different rules. The internal mechanism of this phenomenon is that the 4d¹⁰ electronic states of Ag have changed from obvious local electronic states to mixed local and non-local electronic states. These results provide theoretical guidance for the application of Ti–Ta–Ag ternary alloys in biomedicine.

Precipitation of columnar Ag particles from Ti–Ta–Ag ternary alloys improves mechanical properties.     

One step synthesis of high-efficiency AgBr–Br–g-C3N4 composite catalysts for photocatalytic H2O2 production via two channel pathway

In this work, a two-component modified AgBr–Br–g-C₃N₄ composite catalyst with outstanding photocatalytic H₂O₂ production ability is synthesized. XRD, UV-Vis, N₂ adsorption, TEM, XPS, EPR and PL were used to characterize the obtained catalysts. The as-prepared AgBr–Br–g-C₃N₄ composite catalyst shows the highest H₂O₂ equilibrium concentration of 3.9 mmol L⁻¹, which is 7.8 and 19.5 times higher than that of GCN and AgBr. A “two channel pathway” is proposed for this reaction system which causes the remarkably promoted H₂O₂ production ability. In addition, compared with another two-component modified catalyst, Ag–AgBr–g-C₃N₄, AgBr–Br–g-C₃N₄ composite catalyst displays the higher photocatalytic H₂O₂ production ability and stability.

In this work, a two-component modified AgBr–Br–g-C₃N₄ composite catalyst with outstanding photocatalytic H₂O₂ production ability is synthesized.     

Yttrium stabilization and Pt addition to Pd/ZrO2 catalyst for the oxidation of methane in the presence of ethylene and water

Catalytic oxidation is the most efficient method of minimizing the emissions of harmful pollutants and greenhouse gases. In this study, ZrO₂-supported Pd catalysts are investigated for the catalytic oxidation of methane and ethylene. Pd/Y₂O₃-stabilized ZrO₂ (Pd/YSZ) catalysts show attractive catalytic activity for methane and ethylene oxidation. The ZrO₂ support containing up to 8 mol% Y₂O₃ improves the water resistance and hydrothermal stability of the catalyst. All catalysts are characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), O₂-temperature-programmed desorption (O₂-TPD), and CO-chemisorption techniques. It shows that high Pd dispersion and Pd–PdO reciprocation on the Pd/YSZ catalyst results in relatively high stability. In situ diffuse reflectance infrared Fourier-transform (DRIFT) experiments are performed to study the reaction over the surface of the catalyst. Compared with bimetallic catalysts (Pd : Pt), the same amounts of Pd and Pt supported on ZrO₂ and Y₂O₃-stabilized ZrO₂ catalysts show enhanced activity for methane and ethylene oxidation, respectively. A mixed hydrocarbon feed, containing methane and ethylene, lowers the CH₄ light-off temperature by approximately 80 °C. This shows that ethylene addition has a promotional effect on the light-off temperature of methane.

Addition of 8.0% Yttrium (Y) to ZrO₂ substantially increased the activity and stability of Pd/ZrO₂.     

Bismuth trioxide-tailored sintering temperature,microstructure and NTCR characteristics of Mn1.1Co1.5Fe0.4O4 ceramics

Mn_1.1Co_1.5Fe_0.4O₄ ceramics with tailored sintering temperature, microstructure, and NTCR characteristics were prepared using Bi₂O₃ sintering additive by a solid-state reaction route. Densification and morphological characterization indicate that bismuth trioxide can play a critical role in the sintering process. The results reveal that the sintering temperature can be decreased significantly from 1200 °C to 1050 °C by using the appropriate content of Bi₂O₃ additive. The resistivity decreases first and then increases with increasing Bi₂O₃ content. The obtained B_25/50 value and ρ₂₅ ranges were 3647–3697 K, and 800–1075 Ω cm, respectively. Oxygen sorption theory can be used to illustrate the optimal thermal stability (ΔR/R₀ = 0.10%). Complex impedance analysis further elucidates that grain boundaries make a dominant contribution to the total resistance. The mechanisms of grain boundary conduction and relaxation behavior are systematically analyzed. These findings open up a window for the further advancement of NTC ceramics at lower sintering temperature.

The addition of bismuth trioxide hugely decreased the sintering temperature and improved aging stability.     

MOF-derived ZnCo2O4 porous micro-rice with enhanced electro-catalytic activity for the oxygen evolution reaction and glucose oxidation

A porous ZnCo₂O₄ micro-rice like microstructure was synthesized via calcination of a Zn–Co MOF precursor at an appropriate temperature. The as-prepared ZnCo₂O₄ sample presented good electrocatalytic oxygen evolution reaction performance with a small overpotential (η₁₀ = 389 mV) and high stability in basic electrolyte. Furthermore, in basic medium, the as-synthesized ZnCo₂O₄ micro-rice also showed good electrocatalytic activity for glucose oxidation. A ZnCo₂O₄ micro-rice modified glass carbon electrode may be used as a potential non-enzymatic glucose sensor. The excellent electrocatalytic OER and glucose oxidation performances of ZnCo₂O₄ might be attributed to the unique porous structure formed by the nanoparticles. The porous architecture of the micro-rice can provide a large number of electrocatalytically active sites and high electrochemical surface area (ECSA). The result may offer a new way to prepare low-cost and high performance oxygen evolution reaction and glucose oxidation electrocatalysts.

A porous ZnCo₂O₄ micro-rice like microstructure was synthesized via calcination of a Zn–Co MOF precursor at an appropriate temperature.