Progress in Preparation and Research of Water Electrolysis Catalyst for Transition Metal Phosphide

Confronted with growing energy crisis and environmental challenges, water electrolysis for hydrogen production can provide high-density, clean and renewable energy, but limited by sluggish kinetics of two half reaction, anodic oxygen evolution reaction (OER) and cathodic hydrogen evolution reaction(HER). Noble-metal-based electrocatalysts can decrease overpotential and accelerate kinetics dramatically, but limited by its scarcity and high cost. Transitional metal catalysts are abundant, low cost and have potential to become excellent catalyst due to unique electronic structure. Beginning from basic principle of electrocatalysis, this paper focuses on the synthesis method of transitional metal phosphide (TMP), and further discusses modification methods of TMP, including phase tuning, element doping/alloying, interfacial/structural engineering and three-dimensional architecture. Finally, the challenges of TMP are analyzed and future research focuses are prospected.

Phase-Change Metasurface by U-Shaped Atoms for Photonic Switch with High Contrast Ratio

Currently, diverse metasurfaces act as exotic platforms enabling versatile wave regulations in deep-subwavelength level for ultracompact integration. To address the existing issues of passive nature and low-efficiency in wave controls, one type of metasurface for active phase tuning is proposed in this paper by integrating the phase-change dielectric of Ge2Sb2Te5 into the of U-shaped meta-atoms. Specifically, the phase-change-based hybrid design of Ge2Sb2Te5-integrated metalens switch is demonstrated and numerically confirmed with switchable focusing. The well-defined metal-insulator-metal (MIM) setup is used to enable high-efficiency reflective wavefront tunig and practical Ge2Sb2Te5 phase transition. Upon the phase transition between the amorphous and crystalline states of Ge2Sb2Te5, the cross-polarized component of reflected waves in the given wavelength range is switched “on” (maximized) for as-designed geometric phase plus meta-lensing or “off” (minimized) for no lensing with ultra-high contrast ratio of ~36:1. As a result, such hybrid design of phase-change metasurface may provide a promising route for active photonic device with compact integration.

Electrochemical Performance of Delafossite, AgFeO2: A Pseudo-Capacitive Electrode in Neutral Aqueous Na2SO4 Electrolyte

Layered delafossite AgFeO2 with open channel structure is envisaged as a pseudo capacitor electrode using Fe2+/ Fe3+ redox couple. A simple co-precipitation method was employed for the phase formation of delafossite AgFeO2 resulting in a mixture of 2H and 3R-phase. Phase tuning of 2H phase was done by controlling the calcination conditions and characterizing by powder XRD, FT-IR, and Raman methods. 2H AgFeO2 was used to synthesize as a majority phase because it have the larger inter layer spacing than 3R phase shown. HRTEM study confirms the formation 2H phase in majority. All of the synthesized samples exhibit predominantly faradic battery-type redox behavior along with surface charge storage. Flower like microarchitectures of AgFeO2 show outstanding electrochemical performance with high specific capacity of 110.4 F/g at 1 A/g current density, that retained up to 89% after 2000th times charge/discharge in 1M Na2SO4 electrolyte. In an asymmetric device mode, AFO-400//AC full cell exhibits superior electrochemical performance by delivering high energy density (33.5 Wh/kg) and high power density (454.3 W/kg) with excellent cycling stability (86% retention after 2000th cycles). The results clearly demonstrate that the synthesized delafossite AgFeO2 containing mixture of 2H and 3R-phases have remarkable potential to be used as a negative electrode material for supercapacitor and other energy storage technologies

MoTe2 Field-Effect Transistors with Low Contact Resistance through Phase Tuning by Laser Irradiation

Due to their extraordinary electrical and physical properties, two-dimensional (2D) transition metal dichalcogenides (TMDs) are considered promising for use in next-generation electrical devices. However, the application of TMD-based devices is limited because of the Schottky barrier interface resulting from the absence of dangling bonds on the TMDs’ surface. Here, we introduce a facile phase-tuning approach for forming a homogenous interface between semiconducting hexagonal (2H) and semi-metallic monoclinic (1T’) molybdenum ditelluride (MoTe2). The formation of ohmic contacts increases the charge carrier mobility of MoTe2 field-effect transistor devices to 16.1 cm2 V−1s−1 with high reproducibility, while maintaining a high on/off current ratio by efficiently improving charge injection at the interface. The proposed method enables a simple fabrication process, local patterning, and large-area scaling for the creation of high-performance 2D electronic devices.

RADIO COMMUNICATION CHANNEL WITH FREQUENCY MODULATED SIGNAL BASED ON PROGRAMMABLE LOGICAL INTEGRATED CIRCUIT

This paper presents the results of an experimental study of a radio communication channel (RF) with a frequency-modulated signal based on a programmable logic integrated circuit (FPGA). The work highlights the features of hardware and software implementation of algorithms for the synthesis of frequency-modulated signal and demodulation of this signal using FPGA in real time. The software part is made in the development environment of ISE WebPack 14.7 in Verilog language with the ability to visualize the results of GTKWave. Hardware implementation is performed on the basis of FPGA (Spartan-6) using a debug board from Alinx AX309. The experimental study consists of two stages of the study of the FM oscillator modulator and the synchronous FM oscillator demodulator. In the course of research, the amplitude spectral characteristics of the signals (amplitude spectra) were obtained: at the output of the modulator and demodulator of the frequency-modulated signal, which have good agreement with the simulation results. The quality of the hardware synchronous demodulation of the FM signal based on the phase tuning system was confirmed by the result of the obtained spectrum of the restored information signal, in which the ratio between the first harmonic and the second is 51.87 dBm. When obtaining the results of experimental studies of the RH system, it was found necessary to take into account the peculiarities of the arithmetic of integers, which make errors in the hardware implementation of DSP algorithms. Thus, the use of programmable logic integrated circuits at the present stage of development of telecommunications and radio engineering opens wide opportunities for the construction of high-speed digital RH systems with parallel signal processing in real time.