Abstract Photocatalysis provides a versatile approach to redox activation of various organic substrates for synthetic applications. To broaden the scope of photoredox catalysis, developing catalysts with strong photoredox power is imperative. Photoredox catalysts with excited-state properties that include cathodic oxidation potentials and long lifetimes are particularly demanded. In this research, we demonstrate the high-efficiency catalytic utility of two-coordinated Au(I) complex photocatalysts that exhibit an exclusive ligand-to-ligand charge-transfer (LLCT) transition in C-C cross-coupling reactions between N -heterocycles and (hetero)aryl halides, including redox-resistant (hetero)aryl chlorides. Our photocatalysis system can steer reactions under visible-light irradiation at a catalyst loading as low as 0.1 mol% and exhibits a broad substrate scope with high chemo- and regioselectivity. Our mechanistic investigations provide direct spectroscopic evidence for each step in the catalysis cycle and demonstrate that the LLCT-active Au(I) complex catalysts offer several benefits, including strong visible-light absorption, a 207 ns-long excited-state lifetime without short-lived components, and a 91% yield in the production of free-radical intermediates. Given the wide structural versatility of the proposed catalysts, we envision that our research will provide useful insights into the future utilization of the LLCT-active Au(I) complex for organic transformations.
Highly conductive and water-dispersible sheets of reduced graphene oxide (RGO) were produced by rapidly heating graphene oxide (GO) paper at a low temperature (300 °C) for a short processing time of 3 s. The GO paper was thermally treated during the rapid-heating reduction process and, consequently, the oxygen functional groups in the obtained RGO were highly reduced. The RGO film displays good thermal stability, crystallinity, low sheet resistance, and good dispersibility in water, which makes it an ideal candidate to be used in various carbon-based electronic devices. We finally demonstrate the suitability of RGO as an active channel material and as a source-drain electrode for graphene field-effect transistors, which bring the possibility of realizing all-carbon devices a step closer to reality.
This paper presents the analysis of the surface mounted permanent magnet (SMPM) machine for the sensorless control algorithm using the high frequency fluctuating voltage signal injection method. A simplified high frequency model of a SMPM machine in the estimated rotor reference frame is developed. Then, the impedances of a SMPM machine at high frequency are analyzed by finite element analysis (FEA) and is compared with impedance measurements using a pulse width modulation (PWM) inverter system under various injection conditions. The results of the FEA and high frequency impedance measurements are coincident with each other, and give physical insights in sensorless operation of the SMPM machine. The experimental results of speed control and position control using a commercial SMPM machine are presented based on the analysis of the SMPM machine for the sensorless control algorithm.
Abstract Visible light‐mediated photocatalytic trifluoromethylation, single electron transfer (SET) oxidation, and cycloaddition cascades of 2‐vinyl phenols with Umemoto's reagent and malononitrile were developed. This approach provided the multicomponent synthesis of trifluoromethylated 4 H ‐chromenes via the in situ generation of o ‐quinone methides, followed by sequential cyclization.
Methanol crossover is one of the largest problems in direct methanol fuel cells (DMFCs). Methanol passing from the anode to the cathode through the membrane is oxidized at the cathode, degrading the DMFC performance, and the intermediates of the methanol oxidation reaction (MOR) cause cathode catalyst poisoning. Therefore, it is essential to develop a cathode catalyst capable of inhibiting MOR while promoting the oxygen reduction reaction (ORR), which is a typical cathode reaction in DMFCs. In this study, a carbon-encapsulated Pt cathode catalyst was synthesized for this purpose. The catalyst was simply synthesized by heat treatment of Pt-aniline complex-coated carbon nanofibers. The carbon shell of the catalyst was effective in inhibiting methanol from accessing the Pt core, and this effect became more prominent as the graphitization degree of the carbon shell increased. Meanwhile, the carbon shell allowed O2 to permeate regardless of the graphitization degree, enabling the Pt core to participate in ORR. The synthesized catalyst showed higher performance and stability in single-cell tests under various conditions compared to commercial Pt/C.
Commercial batteries are typically charged with electrical power systems and consume electrical energy for recharging. Chemically self-charging batteries are a class of electrochemical devices that use chemical reactions to recharge batteries without electrical grids. Herein, we report the fabrication of a self-rechargeable zinc–air battery that is capable of simultaneously harnessing and storing energy based on biomass-derived functionalized graphene nanosheets (f-GNS). The chemical energy was harnessed into electric power by the spontaneous and reversible redox reactions between the f-GNS and atmospheric oxygen. This enables the fabrication of an energy storage device capable of self-charging without using any catalyst or organic dye. For the realization of integrated energy harvesting, conversion, and storage by a facile and sustainable approach, the f-GNS synthesized by the hydrothermal carbonization of pears followed by mild acid oxidation was used as the active material in an alkaline solution. The self-rechargeable zinc–air battery delivered an initial open circuit voltage of ∼1.15 V and a maximum instantaneous peak power density of ∼250 mW cm–2. The zinc–air batteries can charge themselves at rest in 15 min and exhibit high reversibility and excellent durability over prolonged charge and discharge cycles. When connected in series and parallel, the zinc–air batteries can offer the desired voltage and current, respectively, for practical applications. This work opens an avenue for further advancement in the design of self-sustainable, next-generation aqueous zinc–air batteries for practical applications.
This paper presents a design method for introducing a measurable saliency in the spatial impedances of structurally symmetrical AC machines without any periodic modulation and considerations in selection of AC machines for saliency-based sensorless control. In the structurally symmetrical AC machines such as surface mounted permanent magnet synchronous machine (SMPMM) and induction machine (IM), the saliency in the spatial impedances is built by the spatial saturation on the leakage flux paths. It is explained by the machine model considering the spatial saturation, analyzed by finite element method, and verified experimentally on the test machines. In the design or the selection of AC machines, the consideration of this phenomenon can make any saliency-based sensorless control for zero or low speed operation viable. The selection of AC machines and the control accuracy assessment for saliency-based sensorless control are discussed.
Abstract We report on the syntheses of core-shell Fe x @Pt ( x = 0.4–1.2) nanoparticles (NPs) with Pt-shell thickness systematically controlled while the overall particle size is constant. The syntheses were achieved via one-pot ultrasound-assisted polyol synthesis (UPS) reactions. Fe 1.2 @Pt showed a record-breaking high core-element content (55 at%) of core-shell NPs. Based on observations from a series of control experiments, we propose a mechanism of the NPs' formation that enables control of shell thickness in UPS reactions. Fe x @Pt NPs showed drastic enhancements in mass and specific activity for oxygen reduction reaction (ORR) and significantly enhanced durability compared to commercial Pt NPs. Fe x @Pt with a 1 (monolayer) ML Pt shell showed the highest activity. The ab initio density functional theory calculations on the binding energies of oxygen species on the surfaces of Fe x @Pt NPs showed that the 1 ML case is most favourable for the ORR and in good agreement with the experimental results.
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