The effect of the exposed crystal plane on the antioxidant activity of nanoceria

Previous reports have noted that exposed crystal planes could affect the antioxidant activity of nanocerias, although the synthesized nanocerias used in those studies had different exposed crystal planes, as well as different sizes and morphologies. In order to better understand the effect of the crystal planes on the antioxidant activity of the materials, two types of nanocerias with similar morphology and size distribution but different crystal planes were synthesized using the hydrothermal method (CeO₂–H) and the ultrasonic template method (CeO₂–U). The antioxidant activities of the nanocerias were further explored within different ·OH concentrations in the reaction system. The experimental results showed that there is an obvious difference in the antioxidant activity of the two types of nanocerias in the lower free radical concentration system due to the effects of exposed crystal planes. CeO₂–U, with more active crystal planes (100), had stronger antioxidant activity. However, with the increase in the ·OH concentration in the reaction system, the difference in the antioxidant activity of the two nanocerias decreased. This research will increase our understanding of the antioxidant activity of the exposed crystal planes on nanocerias.     

非晶Fe粉掺杂Al-12Si合金的高温压缩变形行为

为提高Al-12Si合金的热变形抗力,并探索非晶Fe粉掺杂对Al-12Si合金热压缩行为的影响和掺杂非晶Fe粉热压缩中的晶化温度等,采用连续挤压技术制备了掺杂10wt%非晶Fe粉与不掺杂非晶Fe粉的Al-12Si合金试样,对试样进行了不同温度和应变速率下的热压缩试验,分析了试样在热压缩中的组织转变,以及采用双曲正弦关系构建了试样的热流变应力方程。结果表明:非晶Fe掺杂试样在450 ℃及以下的热压缩时,Fe维持非晶态,500 ℃时,则已发生晶化;掺杂10wt%非晶Fe粉使Al-12Si合金的热抗变形能力显著提高,其热压缩激活能Q=211.29 kJ/mol,比未掺杂非晶Fe粉的Al-12Si合金试样高40.78 kJ/mol,且热压缩过程中存在动态回复和动态再结晶;利用双曲正弦关系构建试样的热流变应力方程为ε·=4.42×10¹⁴[sinh(0.016 6σ)]^6.13exp(-211 290/RT),线性回归系数高达0.99,即可为非晶Fe粉掺杂试样的热加工提供一定的理论指导。     

Impact of ZrO2 alloying on thermo-mechanical properties of Gd3NbO7

The ZrO₂ alloying effect is widely used to optimize the thermo-mechanical properties of potential thermal barrier coatings. In this study, dense x mol% ZrO₂-Gd₃NbO₇ with C222₁ space group were manufactured via a solid-state reaction. The crystalline structure was determined through X-ray diffraction and Raman spectroscopy, when the surface morphology was observed by scanning electron microscopy. ZrO₂-Gd₃NbO₇ had identical orthorhombic crystal structures, and there was no second phase. The crystalline structure of ZrO₂-Gd₃NbO₇ shrunk with the increasing ZrO₂ content as indicated by XRD and Raman results. The heat capacity and thermal diffusivity of ZrO₂-Gd₃NbO₇ were 0.31–0.43 J g⁻¹ K⁻¹ (25–900 °C) and 0.25–0.70 mm²/s (25–900 °C), respectively. It was found that ZrO₂-Gd₃NbO₇ had much lower thermal conductivity (1.21–1.82 W m⁻¹ K⁻¹, 25–900 °C) than YSZ (2.50–3.00 W m⁻¹ K⁻¹) and La₂Zr₂O₇ (1.50–2.00 W m⁻¹ K⁻¹). The thermal expansion coefficients (TECs) were higher than 10.60 × 10⁻⁶ K⁻¹ (1200 °C), which were better than that of YSZ (10.00 × 10⁻⁶ K⁻¹) and La₂Zr₂O₇ (9.00 × 10⁻⁶ K⁻¹). The mechanical properties of Gd₃NbO₇ change little with the increasing ZrO₂ content, Vickers hardness was about 10 GPa, and Young's modulus was about 190 GPa, which was lower than YSZ (240 GPa). Compared with previous work about alloying effects, much lower thermal conductivity was obtained. Due to the high melting point, high hardness, low Young's modulus, ultralow thermal conductivity and high TECs, it is believed that ZrO₂-Gd₃NbO₇ is promising TBCs candidate.     

Crystallization and spectroscopic properties in Er3+ doped oxyfluorogermanate glass ceramics containing Na

The Er³⁺ doped oxyfluorogermanate glasses, with a composition containing Na element, were synthesized by the conventional melting–quenching technique. When Na element was introduced into the composition of oxyfluorogermanate glass, the crystals behavior was investigated in details. Depending on the annealing procedure supplied, thermal annealing of precursor glasses in the system GeO₂/BaF₂/AlF₃/Na₂O/NaF/ZnO/GdF₃/ErF₃ led to the precipitation of different crystal phase nanocrystals. It was confirmed the nanocrystals in GC600 is orthorhombic NaBaAlF₆ which led to enhance obviously in the UC luminescence of Er³⁺. However, the nanocrystals in G585 led to decrease in the UC luminescence, which indicated few Er ions enter into the lattice of this nanocrystal phase. The reason of the decrease in UC emission intensity of GC585 was analyzed.     

Achieving Efficient Alkaline Hydrogen Evolution Reaction over a Ni5P4 Catalyst Incorporating Single-Atomic Ru Sites

Developing efficient electrocatalysts for alkaline water electrolysis is central to substantial progress of alkaline hydrogen production. Herein, a Ni₅P₄ electrocatalyst incorporating single-atom Ru (Ni₅P₄-Ru) is synthesized through the filling of Ru³⁺ species into the metal vacancies of nickel hydroxides and subsequent phosphorization treatment. Electron paramagnetic resonance spectroscopy, X-ray-based measurements, and electron microscopy observations confirm the strong interaction between the nickel-vacancy defect and Ru cation, resulting in more than 3.83 wt% single-atom Ru incorporation in the obtained Ni₅P₄-Ru. The Ni₅P₄-Ru as an alkaline hydrogen evolution reaction catalyst achieves low onset potential of 17 mV and an overpotential of 54 mV at a current density of 10 mA cm^-2 together with a small Tafel slope of 52.0 mV decade^-1 and long-term stability. Further spectroscopy analyses combined with density functional theory calculations reveal that the doped Ru sites can cause localized structure polarization, which brings the low energy barrier for water dissociation on Ru site and the optimized hydrogen adsorption free energy on the interstitial site, well rationalizing the experimental reactivity.     

锂-二氧化碳电池阴极催化剂的研究进展

锂-二氧化碳电池通过捕获、转化二氧化碳为储能物质，既可以减少二氧化碳排放量又可以作为创新的储能装置，引起了研究者们的广泛关注。本文简单介绍了锂-二氧化碳电池的工作机理、发展历程和目前研究存在的难题，通过对研究工作的总结、电池性能的对比，将不同类型的催化剂进行了系统的分类和简单的概括，综述了催化剂的设计理念和研究现状，提出了催化剂目前存在的难题与挑战，并展望了催化剂未来的发展方向。本文主要针对锂-二氧化碳电池阴极催化剂的最新研究进展进行了详细的阐述，指出高效的阴极催化剂是促进锂-二氧化碳电池电化学反应动力学、降低充电平台和过电势的关键所在。     

Effect of nanosilica with different interfacial structures on mechanical properties of polyimide/SiO2 composites

In this article, the effects of coupling agent, silica particle size, and particle shape on the mechanical properties of polyimide (PI) were studied by molecular dynamics (MD) simulations, and the effect of SiO₂ surface treated with coupling agent on the mechanical properties of PI was investigated by experiment. At the same doping volume fraction (5%), the simulation results show that the surface interaction energy between the matrix and particle gradually increases with the radius of the embedded nanoparticles. Meanwhile, the interface interaction energy and mechanical properties of the sphere-type were significantly higher than the ones of other shaped nanoparticles. Moreover, the simulations were compared with the experimental results; atomic force microscopy and scanning electron microscopy images can verify that after being treated with coupling agent, interface interaction between nanosilica and PI enhances quite a little. The mechanical experimental results show that the tensile strength and elasticity modulus of pure PI, unbonded (UB) PI/SiO₂, and bonded PI/SiO₂ films are 34.47 and 1.13, 36.46 and 1.32, and 66.20 MPa and 1.72 GPa, respectively. It is indicated that the coupling agent plays a crucial role in nanocomposites. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48595.     

Comparison of MPC based advanced hybrid controllers for STATCOM in medium scale PEM fuel cell systems

In this article is about off grid medium scale Proton Exchange Membrane (PEM) Fuel Cell (FC) Renewable Energy System (FCRES). It is aimed to investigate the elimination of reactive power on the loads fed from the FCRES by using PI-Model Predictive Control (PI-MPC), Fractional PI (PI^λ)-Model Predictive Control (PI^λ−MPC) and Two-Degree of Freedom PI (2DOFPI)-Model Predictive Controller (2DOFPI-MPC). The effectiveness of these controllers were examined and compared both when controlling reactive power and using different control techniques. The reactive power was attempted to be eliminated using Static Synchronous Compensator (STATCOM). An advanced controller structure has been introduced by controlling capacitor voltages by switching 24 IGBTs in the 5-level inverter within its structure. In this way, the efficiency of the system was increased. The system was simulated in MATLAB/Simulink environment. System consisted of FC, STATCOM, loads, filter, coupling inductance, measurement units and advanced hybrid controllers. In the study, system behavior was also examined in the case of compensation in the system consisting of FCs working off grid.     

Effects of Sn doping on the manufacturing,performance and carbon deposition of Ni/ScSZ cells in solid oxide fuel cells

This work demonstrates the effect of tin (Sn) doping on the manufacturing, electrochemical performance, and carbon deposition in dry biogas-fuelled solid oxide fuel cells (SOFCs). Sn doping via blending in technique alters the rheology of tape casting slurry and increases the Ni/ScSZ anode porosity. In contrast to the undoped Ni/ScSZ cells, where open-circuit voltage (OCV) drops in biogas, Sn–Ni/ScSZ SOFC OCV increases by 3%. The maximum power densities in biogas are 0.116, 0.211, 0.263, and 0.314 W/cm² for undoped Ni/ScSZ, undoped Ni/ScSZ with 3 wt% pore former, Sn–Ni/ScSZ and Sn–NiScSZ with 1 wt% pore former, respectively. Sn–Ni/ScSZ reduces the effect of the drop in the maximum power densities by 26%–36% with the fuel switch. A 1.28–2.24-fold higher amount of carbon is detected on the Sn–Ni/ScSZ samples despite the better electrochemical performance, which may reflect an enhanced methane decomposition reaction.     

Processing of orthotropic and isotropic superhard B4C composites reinforced with reduced graphene oxide

A fabrication route based on aqueous colloidal processing plus transient liquid-phase assisted spark-plasma-sintering (SPS) with Ti-Al additives is described for the environmentally friendly obtention of superhard B₄C composites reinforced with reduced graphene oxide (rGO) having orthotropic and isotropic microstructures. It is shown that the former, which have coarse rGO platelets preferentially aligned perpendicular to the SPS pressing direction, can be prepared from mixtures of B₄C and Ti-Al particles with a source of thick, large rGO nanoplatelets by imposing smooth co-dispersion conditions to avoid platelet re-exfoliation and fragmentation. The latter, which have fine rGO platelets randomly oriented, can be fabricated from mixtures of B₄C and Ti-Al particles with a source of thin, small rGO nanoplatelets by applying intensive sonication to promote platelet re-exfoliation and fragmentation during co-dispersion. Finally, it is shown that these orthotropic and isotropic B₄C/rGO composites are equally superhard, and that, as expected, their microstructures interact differently with the cracks. Finally, this processing route is simple, and easily adaptable/extensible to make other ceramic/rGO composites with orthotropic and isotropic microstructures.