Understanding CO2 electrochemical reduction kinetics of mixed-conducting cathodes by the electrical conductivity relaxation method

Electrochemical reduction reaction is an important approach to utilize CO₂ and convert it into valuable products. Exceptional reaction kinetics at a high temperature of solid oxide electrolysis cells (SOECs) attracts particular attention. In this work, we propose to investigate CO₂-RR kinetics using a new theoretical method based on the electrical conductivity relaxation (ECR) technique on a typical mixed-conducting Sr₂Fe_1.5Mo_0.5O_6-δ (SFM) electrode. Three kinetic parameters that are commonly adopted in the typical electrochemical test experiments consisting of overpotential, current density and area-specific resistance (ASR) are derived. The overpotential resulted from the difference in the oxygen partial pressure is caused by the change of CO₂ partial pressure, while current density from the surface reaction rate constant. Accordingly, area-specific resistance, as well as overpotential-current density relationship, can be derived. We believe that this work brings a new method to study the kinetic process of CO₂ electrolysis and to evaluate the electrocatalyst activity of developed new electrode materials as well as to benefit the designing of novel electrode electrocatalysts for highly efficient solid oxide electrolysis cells.     

Perovskite materials for highly efficient catalytic CH4 fuel reforming in solid oxide fuel cell

SOFC (solid oxide fuel cell, SOFC) is recognized to be efficient green energy technology in the 21st century. However, when hydrocarbons are directly used as fuel, carbon deposition is easy to occur in Ni-based anode, thus losing electrochemical catalytic activity. Fuel pre-reforming is also called on-cell reforming of hydrocarbons, which has been a promising solution for alleviating the carbon deposition problem in cermet anodes to varying degrees. And the key factor is to find an efficient and stable fuel reforming catalyst. Perovskite oxides have stable structure, highly catalytic activity and adjustable thermal expansion coefficient for using on the cells, showing great potentials of application for fuel reforming. In this paper, we summarize the application of perovskite catalyst in CH₄ fuel reforming based on the research of our group and other scholars, and puts forward the corresponding views and perspective, especially in perovskite catalyst with Ni exsolution.     

Optimization of graphene-MoS2 barristor by 3-aminopropyltriethoxysilane (APTES)

We theoretically and experimentally investigated the influence of the Fermi level position of graphene relative to the Dirac point on the performance of a graphene/MoS₂ heterojunction barristor. A large Fermi level modulation (ΔE_F = 0.28 eV) of graphene, when the V_GS is changed between −20 V and +20 V, was theoretically predicted when the Fermi level is located at the Dirac point. For reference, ΔE_F = 0.11 eV when the Fermi level is far from the Dirac point. This prediction was experimentally proven using two kinds of barristors with pristine (strongly p-type) and 2.4% APTES-treated (intrinsic) graphene. The on/off-current ratio was improved by a factor of 32 (a 2.1-fold increase in the on-current density and a 15-fold increase in the off-current density) in the APTES-treated device, as compared to the control. Using a temperature-dependent current-voltage measurement, we quantitatively confirmed the larger modulation of the barrier height in the APTES-treated barristor (ΔE_F = 0.27 eV) compared to that of the control device (ΔE_F = 0.14 eV). This study can be used to guide the design and optimization of graphene-based heterojunction devices.     

Microstructural evidence for counter-diffusion of aluminum and oxygen during the growth of alumina scales

Abstract

A novel, two-stage oxidation experiment is described that enables the outward diffusion of cations in alumina scales during high-temperature oxidation to be analyzed on the basis of microstructural changes in the surface morphology of the scale. Using this technique, observations of aluminum out-diffusion along α-Al₂O₃ grain boundaries during oxidation of Fe–Cr–Al alloys, nickel aluminides and platinum-modified NiAl bond-coats are made. Although microstructural evidence for the inward grain boundary diffusion of oxygen is more difficult to obtain, it still can be demonstrated by the growth of the oxide above interface cavities on nickel aluminides and inside internal cracks in the alumina scales during cyclic oxidation of zirconia top-coated material. SEM examination of the crack surfaces after scale spallation provides a vivid illustration of two simultaneous processes, aluminum outward and oxygen inward diffusion along grain boundaries in the scale.     

Core-shell structure of polypyrrole grown on W18O49 nanorods for high performance gas sensor operating at room temperature

In this work, uniform core-shell structure of polypyrrole wrapped on tungsten oxide nanorods (PPy@W₁₈O₄₉ core-shell nanorods) were synthesized via a two-step process for gas-sensing applications. The core-nanorods of W₁₈O₄₉ were first grown by solvothermal method with tungsten hexachloride (WCl₆) as precursor. The PPy-shell layer was then formed uniformly on the solvothermally synthesized W₁₈O₄₉ nanorods by in-situ chemical polymerization of pyrrole monomer (Py), with sodium dodecyl benzene sulfonic acid (DBSA) as dopant and ammonium persulfate (APS) as oxidant. High dispersion of Py achieving in ethanol is proved to be crucial to form the uniform PPy-shell layer, and the layer thickness of PPy-shell is highly controlled by adjusting the Py concentration in polymeric solution. The morphology and structure of the nanocomposite were characterized systematically; it shows that the composite exhibits perfect core-shell structure of one-dimensional (1D) nanorods with average diameter of around 70–90 nm. The NH₃-sensing properties of the sensors based on the PPy@W₁₈O₄₉ core-shell nanorods were investigated at operating temperature of 15–130 °C over NH₃ concentration ranging from 1 to 200 ppm. The response magnitude of the PPy@W₁₈O₄₉ sensor can be affected seriously by temperature fluctuation, even in room temperature range (15–30 °C), and meanwhile, a temperature-dependent p-n response characteristic reversal is observed for the heteronanorods sensor. At much low room temperature of 15 °C, the present PPy@W₁₈O₄₉ nanorods show quick and sensitive response to NH₃ gas mainly due to the ultrathin, uniform PPy shell and the special heterojunction effect between p-type PPy and n-type W₁₈O₄₉. The underlying gas-sensing mechanism is analyzed.     

S-Nitroso-N-acetyl-D-penicillamine covalently linked to polydimethylsiloxane (SNAP–PDMS) for use as a controlled photoinitiated nitric oxide release polymer

Abstract

Nitric oxide (NO) plays a critical role in the regulation of a wide variety of physiological processes. It is a potent inhibitor of platelet adhesion and aggregation, inhibits bacterial adhesion and proliferation, is implicated in mediating the inflammatory response toward implanted devices, plays a role in tumor growth and proliferation, and is a neurotransmitter. Herein, we describe the synthesis and NO-release properties of a modified polydimethylsiloxane that contains S-nitroso-N-acetyl-D-penicillamine covalently attached to the cross-linking agent (SNAP–DMS). Light from a C503B-BAN-CY0C0461 light-emitting diode (470 nm) was used as an external trigger to allow precise control over level and duration of NO release ranging from a surface flux of zero to approximately 3.5×10^?10 mol cm^-2 min^-1. SNAP–PDMS films stored in the dark released NO after 297 days, indicating the long-term stability of SNAP–PDMS.     

Kinetics,equilibrium and thermodynamics studies of arsenate adsorption from aqueous solutions onto iron hydroxide

This paper reports the equilibrium, kinetics and thermodynamic studies of arsenate adsorption onto freshly precipitated iron hydroxide. Adsorption of arsenate onto iron hydroxide depends on arsenate concentration, contact time and temperature. The intrapartical diffusion model indicates that both the film and intrapartical diffusion control arsenate adsorption on iron hydroxide. The values of activation energies (E_a) indicate the chemical nature of adsorption accompanied by diffusion controlled processes as the rate limiting step. The endothermic nature of the adsorption process suggests that adsorption reaction consumes energy. The negative values of ΔS^# can be assigned to decreased randomness at the solid liquid interface.     

提高韶冶烧结氧化物料处理能力的研究与应用

介绍韶冶在氧化物料对工厂生产经营和现场环境造成不利影响的条件下,通过设备、工艺两方面的研究,提高氧化物料处理能力,从而增强烧结工艺对原料的适应性,使干精矿含硫降低,烧结机产能大幅度提升,烧结块质量保持较高水平,年创效益约2 500万元。     

热轧加热炉内步进梁及立柱耐火材料粘渣原因分析

分析了热轧加热炉内步进梁与立柱粘渣的原因,认为所用耐火材料荷重软化温度低、变形大是主要原因之一。从侵蚀结构分析看,氧化铝溶解进入炉衬的粘接渣相中,增加了渣的黏度,可能导致炉衬的严重挂渣,不利于生产的正常顺行。常规的加热炉耐火材料控制标准没有荷重软化温度等指标,不利于控制炉衬实物质量。     

Magnetoresistance effect in a graphene modulated by magnetic-electrical barriers

We theoretically investigate the magnetoresistance (MR) effect in a monolayer graphene modulated by both magnetic and electrical barriers, which can be experimentally realized by depositing two parallel metallic ferromagnetic tripes under an applied voltage on the top and bottom of a graphene. The tremendous MR can be found due to the significant difference between the transmissions through the parallel and antiparallel magnetization configurations, and the MR ratio strongly depends on the strength of the magnetic field and the height of the electric barrier. Therefore, we can control the MR effect by changing either of the two magnetic fields or the electric barrier to make a MR device based on a graphene.