Two step novel chemical synthesis of polypyrrole nanoplates for supercapacitor application

Simple and inexpensive two step novel chemical method for the synthesis of polypyrrole (PPy) nanoplates has been reported. These PPy nanoplates are characterized with X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Polypyrrole nanoplates exhibit amorphous nature as confirmed from XRD study. Based on SEM and TEM analysis, the formation of the spherical bunches of PPy nanoplates with average size of about 20 nm are inferred. The electrochemical performance of PPy electrode was evaluated by cyclic voltammetry (CV) and galvanostatic charge-discharge measurement. A high specific capacitance of 533 F g⁻¹ was obtained within the potential range of −0.4 to 0.6 V in 0.5 M H₂SO₄ solution. Moreover, PPy electrode exhibited high discharge/charge efficiency of 93% and the capacitance retention of 83% at a current density of 10 mA cm⁻² indicating good electrochemical reversibility and rate capability.     

Nonlinear free vibration of skew nanoplates with surface and small scale effects

The nonlinear free flexural vibration of skew nanoplates is studied by considering the influences of free surface energy and size effect (small scale) simultaneously. The formulations are derived based on classical plate theory (CPT) in conjunction with nonlocal and surface elasticity theories using Hamilton's principle. Green's strain tensor together with von Kármán assumptions is employed to model the geometrical nonlinearity. The free surfaces are modeled as two-dimensional membranes adhering to the underlying bulk material without slipping. The solution algorithm is based on the transformation of the governing differential equation from the physical domain to a rectangular computational one, and discretization of the spatial derivatives by employing the differential quadrature method (DQM) as an efficient and accurate numerical tool. The effect of small scale parameter and surface effect together with the geometrical parameters and boundary conditions on the nonlinear frequency parameters of the skew nanoplates are studied.     

Ultraviolet-Visible-Short-Wavelength Infrared Broadband and Fast-Response Photodetectors Enabled by Individual Monocrystalline Perovskite Nanoplate

Perovskite-based photodetectors exhibit potential applications in communication, neuromorphic chips, and biomedical imaging due to their outstanding photoelectric properties and facile manufacturability. However, few of perovskite-based photodetectors focus on ultraviolet-visible-short-wavelength infrared (UV–Vis–SWIR) broadband photodetection because of the relatively large bandgap. Moreover, such broadband photodetectors with individual nanocrystal channel featuring monolithic integration with functional electronic/optical components have hardly been explored. Herein, an individual monocrystalline MAPbBr₃ nanoplate-based photodetector is demonstrated that simultaneously achieves efficient UV–Vis–SWIR detection and fast-response. Nanoplate photodetectors (NPDs) are prepared by assembling single nanoplate on adjacent gold electrodes. NPDs exhibit high external quantum efficiency (EQE) and detectivity of 1200% and 5.37 × 10¹² Jones, as well as fast response with rise time of 80 µs. Notably, NPDs simultaneously achieve high EQE and fast response, exceeding most perovskite devices with multi-nanocrystal channel. Benefiting from the high specific surface area of nanoplate with surface-trap-assisted absorption, NPDs achieve high performance in the near-infrared and SWIR spectral region of 850–1450 nm. Unencapsulated devices show outstanding UV-laser-irradiation endurance and decent periodicity and repeatability after 29-day-storage in atmospheric environment. Finally, imaging applications are demonstrated. This work verifies the potential of perovskite-based broadband photodetection, and stimulates the monolithic integration of various perovskite-based devices.     

Construction of WS2 triangular nanoplates array for hydrogen evolution reaction over a wide pH range

As a classic transition metal dichalcogenide, WS₂ has been synthesized by a variety of methods towards different applications. However, few of them are vertically grown self-templated structures, besides, all the reported WS₂ for hydrogen evolution reaction (HER) are in acidic media. Herein, we use a simple method to synthesize a new morphological WS₂ triangular nanoplates array through the sulfuration of hydrothermally obtained WO₃ nanowires on carbon cloth (WS₂TN/CC). The WS₂TNs are equilateral triangle with large surface area that grown vertically on carbon fiber. The WS₂TN/CC exhibits good catalytic activity and stability as electrocatalyst for HER in acidic media and firstly in both neutral and alkaline media. The overpotential of 196, 150 and 193 mV are needed to afford current density of 10 mA cm⁻² in acidic, neutral and alkaline media, respectively.     

Multi-walled carbon nanotubes reinforced nickel phosphide composite: As an efficient electrocatalyst for hydrogen evolution reaction by one-step powder sintering

Transition metal phosphides (TMPs) have been proven to be a high-performance non-noble metal electrocatalyst with high activity and nearly ~100% Faraday efficiency. However, their applications remain faces great challenging due to its unsatisfactory exposure to catalytic active sites and electronic conductivity. Here, powder sintering was used to prepare Ni–P-Multi-walled carbon nanotubes (Ni–P-MWCNTs) composite electrodes with a hierarchical flower-like structure with a large surface area, the composite electrodes were synthesized by phosphating mixed powder (porous nickel powder, red phosphorus and MWCNTs). Due to the flower-like nanoplate hierarchical structure, the fast vectorial electron transfer along the building block nanoplates was effectively induced and active sites were highly exposed. The resulting Ni_xP-43 wt%MWCNTs shows high activity and durability towards the Hydrogen evolution reaction (HER) under acidic conditions. It demands extremely low onset-potential of 29 mV, 96 mV to achieve a current density of 10 mA cm⁻². This work suggests an effective method to facilitate grain preferred orientation growth and exposure high activity active, experimental results demonstrate that the electrocatalytic performance of as-prepared Ni–P-MWCNTs were successfully optimized through the addition of MWCNTs, and might promote further study of the TMPs catalysts for HER.     

Electrochemical performance of ZnO nanoplates as anode materials for Ni/Zn secondary batteries

Plate-like ZnO with good crystallinity were prepared by a simple hydrothermal synthesis method in Zn(NO₃)₂·6H₂O and NaOH solution at 180 °C. The dimension of ZnO powder ranged from 200 to 500 nm and the average thickness was about 50 nm. The electrochemical performances of ZnO nanoplates as anode active materials for Ni/Zn cells were investigated by galvanostatic charge/discharge cycling and cyclic voltammogram (CV). The ZnO nanoplates showed better cycle stability than the conventional ZnO, and the discharge capacity maintained 420 mAh g⁻¹ throughout 80 cycling tests. At the same time, they also exhibited higher midpoint discharge voltage and lower midpoint charge voltage. The continual SEM examinations on the electrode found that the morphology of the plate-like ZnO active material did not change essentially and the zinc dendrite was suppressed effectively, which resulted in the improvement of cycle stability of Ni/Zn secondary cells.     

Small scale effect on the thermal buckling of orthotropic arbitrary straight-sided quadrilateral nanoplates embedded in an elastic medium

As a first endeavor, the small scale effect on the thermal buckling characteristic of orthotropic arbitrary straight-sided quadrilateral nanoplates embedded in an elastic medium is investigated. The surrounding elastic medium is modeled as the two-parameter elastic foundation. The formulation is derived using the classical plate theory (CPT) in conjunction with the nonlocal elasticity theory. The solution procedure is based on the transformation of the governing equations from physical domain to computational domain and then discretization of the spatial derivatives by employing the differential quadrature method (DQM) as an efficient and accurate numerical tool. The fast rate of convergence of the method is shown and the results are compared against existing results in literature. Then, the influence of small scale parameter in combination with the elastic medium parameters, geometrical shape and the boundary conditions on the thermal buckling load of the nanoplates is investigated.     

The Role of Etching in the Formation of Ag Nanoplates with Straight,Curved and Wavy Edges and Comparison of Their SERS Properties

We investigate the role of etching in the formation of Ag nanoplates with different morphologies. By examining the reduction of AgNO₃ with poly(vinyl pyrrolidone) in an aqueous solution under a hydrothermal condition, we confirm that etching plays an essential role in promoting the growth of Ag triangular nanoplates with straight edges at the expense of multiple twinned particles via Ostwald ripening. Once all the multiple twinned particles are gone, etching will continue at the corners of nanoplates, leading to the formation of enneahedral nanoplates with curved edges. When the nanoplates with straight edges are transferred into ethanol and subjected to a solvothermal treatment, we obtain nanoplates with wavy edges and sharp corners due to etching on the edges. A comparison study indicates that, at the same particle concentration, Ag nanoplates with wavy edges embraces a SERS enhancement factor at least 6 and 13 times stronger than those with straight and curved edges, respectively. The results from finite difference time domain calculations support our experimental observation that the sharp features on nanoplates with wavy edges are the most active sites for SERS.     

Preparation of triangular and hexagonal silver nanoplates on the surface of quartz substrate

In this paper, triangular and hexagonal silver nanoplates were prepared on the surface of quartz substrate using photoreduction of silver ions in the presence of silver seeds. The obtained silver nanoplates were characterized by atomic force microscopy and UV–vis spectroscopy. It was found that the silver seeds played an important role in the formation of triangular and hexagonal silver nanoplates. By varying the irradiation time, nanoplates with different sizes and shapes could be obtained. The growth mechanism for triangular and hexagonal nanoplates prepared on quartz substrate was discussed.