A cobalt catalyst has been developed for the acceptorless dehydrogenation of alcohols and applied to synthesize imines from alcohols and amines. Deuterium labeling studies suggest that the reaction ...proceeds by an initial reversible alcohol dehydrogenation step involving a cobalt hydride intermediate.
2D and nanostructured metal sulfide materials are promising in the advancement of several gas sensing applications due to the abundant choice of materials with easily tunable electronic, optical, ...physical, and chemical properties. These applications are particularly attractive for gas sensing in environmental monitoring and breath analysis. This review gives a systematic description of various gas sensors based on 2D and nanostructured metal sulfide materials. Firstly, the crystal structures of metal sulfides are introduced. Secondly, the gas sensing mechanisms of different metal sulfides based on density functional theory analysis are summarised. Various gas-sensing concepts of metal sulfide-based devices, including chemiresistors, functionalized metal sulfides, Schottky junctions, heterojunctions, field-effect transistors, and optical and surface acoustic wave sensors, are compared and presented. It then discusses the extensive applications of metal sulfide-based sensors for different gas molecules, including volatile organic compounds (
i.e.
, acetone, benzene, methane, formaldehyde, ethanol, and liquefied petroleum gas) and inorganic gas (
i.e.
, CO
2
, O
2
, NH
3
, H
2
S, SO
2
, NO
x
, CH
4
, H
2
, and humidity). Finally, a strengths-weaknesses-opportunities-threats (SWOT) analysis is proposed for future development and commercialization in this field.
This review provides perspectives on metal sulfide-based gas sensors, including the crystal structure, gas sensing mechanisms, applications, and strengths-weaknesses-opportunities-threats (SWOT) analysis.
•Small heat pipes are the preferred cooling solutions for electronics.•The wicks from micro to nano sizes are under development for the ability to enhance the efficiency.•Because silicon is widely ...used in electronics, it is a favoured material for small heat pipes.•Polymer-based small heat pies are attractive for their easy fabrication and low cost.
Heat pipes (HPs) have received considerable attention in recent decades, especially in the field of cooling electronics, which requires the removal of added heat from an area of limited volume to the environment. Small HPs are widely used in electronic applications, which are normally limited by the compact structure and dimensions of the electronic device. Among small HPs, mini/micro HPs and two-phase loops (TPLs) with mini/micro wicks, including loop HPs (LHPs) and capillary pumped loops (CPLs), are preferred for their high efficiency, small dimensions, and compatible process with semiconductor devices. Particularly, TPLs possess all of the main advantages of traditional HPs with the addition of special properties that enable the transfer of heat for distances up to several metres at any orientation in the gravity field. Further, small vapour chambers (VCs), also referred to as flat HPs, are excellent candidates for electronic heat spreaders due to their light weight, geometric flexibility, and extremely high thermal conductivities. Because silicon is widely used in electronics, it is a preferred material for mini/micro HPs along with TPLs. Moreover, polymer-based small HPs are highly attractive for further development as they are inexpensive and easy to fabricate. Because the smaller wicks supply a greater capillary force, nano wicks, such as carbon nanotubes (CNTs), may represent the future of HPs due to their potentially outstanding characteristics. In this work, a review of small HPs, including their design, analysis, and fabrication, is presented.
The replacement of precious metals with inexpensive, less toxic, and earth-abundant elements in typical noble-metal-mediated organic transformations is a major goal in current synthetic chemistry and ...industries. The metal-catalyzed N-alkylation of amines with other amines through a “hydrogen-borrowing” principle represents a green and atom-economical reaction for the synthesis of secondary amines. However, catalysts developed thus far that are effective for this process remain quite scarce and are only limited to a few ruthenium and iridium complexes. In this work, we present a cobalt-catalyzed selective alkylation of amines with amines to synthesize a large variety of secondary amines. A range of amine substrates have been converted to the corresponding products through hetero- or homocoupling between amines. Cyclic sec-amines are also achieved from diamine precursors as rare examples.
The temperature of electrolytic capacitor in light-emitting diode (LED) drivers continuously increases under operation conditions, thus the capacitors degrade faster than that with constant ...temperature assumption. In this paper, a physics-of-failure (PoF)-based reliability prediction methodology is developed for LED drivers to consider the temperature change of electrolytic capacitor. SPICE simulation, compact thermal modeling, and Monte Carlo simulation are integrated to predict the failure rate distribution of an electrolytic capacitor of given LED driver systems. The simulation results agree well with the accelerated test results for an RC linear AC-DC converter. Furthermore, a single inductor buck-boost DC-DC converter is simulated to understand the degradation behavior of electrolytic capacitor. It has been found that the temperature of an output stage capacitor increases significantly during operation time. The capacitor's performance without taking temperature change into account results in an overestimated driver lifetime by more than 38% for the selected case study.
In order to solve issues of air pollution, to monitor human health, and to promote agricultural production, gas sensors have been used widely. Metal oxide semiconductor (MOS) gas sensors have become ...an important area of research in the field of gas sensing due to their high sensitivity, quick response time, and short recovery time for NO2, CO2, acetone, etc. In our article, we mainly focus on the gas-sensing properties of MOS gas sensors and summarize the methods that are based on the interface effect of MOS materials and micro–nanostructures to improve their performance. These methods include noble metal modification, doping, and core-shell (C-S) nanostructure. Moreover, we also describe the mechanism of these methods to analyze the advantages and disadvantages of energy barrier modulation and electron transfer for gas adsorption. Finally, we put forward a variety of research ideas based on the above methods to improve the gas-sensing properties. Some perspectives for the development of MOS gas sensors are also discussed.
In this work, large size (i.e., diameter > 100 nm) graphene tubes with nitrogen‐doping are prepared through a high‐temperature graphitization process of dicyandiamide (DCDA) and Iron(II) acetate ...templated by a novel metal–organic framework (MIL‐100(Fe)). The nitrogen‐doped graphene tube (N‐GT)‐rich iron‐nitrogen‐carbon (Fe‐N‐C) catalysts exhibit inherently high activity towards the oxygen reduction reaction (ORR) in more challenging acidic media. Furthermore, aiming to improve the activity and stability of conventional Pt catalysts, the ORR active N‐GT is used as a matrix to disperse Pt nanoparticles in order to build a unique hybrid Pt cathode catalyst. This is the first demonstration of the integration of a highly active Fe‐N‐C catalyst with Pt nanoparticles. The synthesized 20% Pt/N‐GT composite catalysts demonstrate significantly enhanced ORR activity and H2‐air fuel cell performance relative to those of 20% Pt/C, which is mainly attributed to the intrinsically active N‐GT matrix along with possible synergistic effects between the non‐precious metal active sites and the Pt nanoparticles. Unlike traditional Pt/C, the hybrid catalysts exhibit excellent stability during the accelerated durability testing, likely due to the unique highly graphitized graphene tube morphologies, capable of providing strong interaction with Pt nanoparticles and then preventing their agglomeration.
An iron‐containing metal–organic framework, MIL‐100(Fe), is employed to prepare a new oxygen‐reduction non‐precious metal catalyst containing bamboo‐like nitrogen‐doped graphene tubes (diameter > 100 nm). The highly active graphene tubes are further integrated with Pt nanoparticles in order to build a hybrid electrocatalyst, exhibiting significantly improved activity and stability compared to conventional Pt/C catalysts in acid electrolyte.
Cobalt(II) alkyl complexes of aliphatic PNP pincer ligands have been synthesized and characterized. The cationic cobalt(II) alkyl complex (PNHPCy)Co(CH2SiMe3)BArF 4 (4) (PNHPCy = ...bis(2-dicyclohexylphosphino)ethylamine) is an active precatalyst for the hydrogenation of olefins and ketones and the acceptorless dehydrogenation of alcohols. To elucidate the possible involvement of the N–H group on the pincer ligand in the catalysis via a metal–ligand cooperative interaction, the reactivities of 4 and (PNMePCy)Co(CH2SiMe3)BArF 4 (7) were compared. Complex 7 was found to be an active precatalyst for the hydrogenation of olefins. In contrast, no catalytic activity was observed using 7 as a precatalyst for the hydrogenation of acetophenone under mild conditions. For the acceptorless dehydrogenation of 1-phenylethanol, complex 7 displayed similar activity to complex 4, affording acetophenone in high yield. When the acceptorless dehydrogenation of 1-phenylethanol with precatalyst 4 was monitored by NMR spectroscopy, the formation of the cobalt(III) acetylphenyl hydride complex (PNHPCy)CoIII(κ2-O,C-C6H4C(O)CH3)(H)BArF 4 (13) was detected. Isolated complex 13 was found to be an effective catalyst for the acceptorless dehydrogenation of alcohols, implicating 13 as a catalyst resting state during the alcohol dehydrogenation reaction. Complex 13 catalyzed the hydrogenation of styrene but showed no catalytic activity for the room temperature hydrogenation of acetophenone. These results support the involvement of metal–ligand cooperativity in the room temperature hydrogenation of ketones but not the hydrogenation of olefins or the acceptorless dehydrogenation of alcohols. Mechanisms consistent with these observations are presented for the cobalt-catalyzed hydrogenation of olefins and ketones and the acceptorless dehydrogenation of alcohols.
Nitrogen‐doped graphene/graphene‐tube nanocomposites are prepared by a hightemperature approach using a newly designed cage‐containing metal‐organic framework (MOF) to template nitrogen/carbon ...(dicyandiamide) and iron precursors. The resulting N‐Fe‐MOF catalysts universally exhibit high oxygen‐reduction activity in acidic, alkaline, and non‐aqueous electrolytes and superior cathode performance in Li‐O2 batteries.
As an increasing attention towards sustainable development of energy and environment, the power electronics (PEs) are gaining more and more attraction on various energy systems. The insulated gate ...bipolar transistor (IGBT), as one of the PEs with numerous advantages and potentials for development of higher voltage and current ratings, has been used in a board range of applications. However, the continuing miniaturization and rapid increasing power ratings of IGBTs have remarkable high heat flux, which requires complex thermal management. In this paper, studies of the thermal management on IGBTs are generally reviewed including analyzing, comparing, and classifying the results originating from these researches. The thermal models to accurately calculate the dynamic heat dissipation are divided into analytical models, numerical models, and thermal network models, respectively. The thermal resistances of current IGBT modules are also studied. According to the current products on a number of IGBTs, we observe that the junction-to-case thermal resistance generally decreases inversely in terms of the total thermal power. In addition, the cooling solutions of IGBTs are reviewed and the performance of the various solutions are studied and compared. At last, we have proposed a quick and efficient evaluation judgment for the thermal management of the IGBTs depended on the requirements on the junction-to-case thermal resistance and equivalent heat transfer coefficient of the test samples.
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