Bioinspired Engineering of Fillable Gradient Structure into Flexible Capacitive Pressure Sensor Toward Ultra-High Sensitivity and Wide Working Range.

Tactile sensing is required for electronic skin and intelligent robots to function properly. However, the dielectric layer's poor structural compressibility in conventional pressure sensors results in a limited pressure sensing range and low sensitivity. To solve this issue, a flexible pressure sensor with a crocodile-inspired fillable gradient structure is provided. The fillable gradient structure and grooves in the pressure sensor accommodate the deformed microstructure that permits the enhancement of the media layer compressibility via COMSOL finite element simulation and optimization. The pressure sensor exhibits a high sensitivity of up to 0.97 k Pa-1 (0-4 kPa), a wide pressure detection range (7 Pa-380 kPa), and outstanding repeatability. The sensor can detect Morse code, robotic grabbing, and human motion monitoring. As a result, flexible sensors with a bionic fillable gradient structure pave the way for wearable devices and offer a novel method for achieving highly precise tactile perception.

Aurivillius-layered Bi2WO6 nanoplates with CoOx cocatalyst as high-performance piezocatalyst for hydrogen evolution.

Developing a high-performance piezocatalyst that directly transforms mechanical energy into hydrogen is highly desirable in the field of new energy. Herein, the Aurivillius-layered Bi2WO6 (BWO) nanoplates are prepared through a hydrothermal reaction at a moderate temperature of 160 °C, and exhibit strong piezoelectric properties, enabling them to catalyze water splitting through ultrasonic-induced piezocatalysis effect. The hydrogen evolution reaction (HER) and H2O2 generation efficiencies are measured to be 0.43 and 0.36 mmol g-1 h-1, respectively. To further boost piezocatalytic performance, cobalt oxide nanoparticles are intentionally photo-deposited onto these nanoplates as cocatalyst. This configuration results in a significantly boosted HER performance with an efficiency of 3.59 mmol g-1 h-1, which is 2.8 times higher than that of pristine nanoplates and demonstrates strong competitiveness compared to other reported piezocatalysts. The cobalt oxide cocatalyst plays a crucial role in facilitating efficient charge separation and migration, increasing the charge concentration, and ultimately enhancing piezocatalytic HER activity. Overall, this work highlights the potential of Aurivillius-layered bismuth oxide compounds as efficient piezocatalysts and provides valuable insights for designing high-performance piezocatalysts in the field of new energy.

An Emerging Family of Piezocatalysts: 2D Piezoelectric Materials.

Piezocatalysis is an emerging technique that holds great promise for the conversion of ubiquitous mechanical energy into electrochemical energy through piezoelectric effect. However, mechanical energies in natural environment (such as wind energy, water flow energy, and noise) are typically tiny, scattered, and featured with low frequency and low power. Therefore, a high response to these tiny mechanical energies is critical to achieving high piezocatalytic performance. In comparison to nanoparticles or 1D piezoelectric materials, 2D piezoelectric materials possess characteristics such as high flexibility, easy deformation, large surface area, and rich active sites, showing more promise in future for practical applications. In this review, state-of-the-art research progresses on 2D piezoelectric materials and their applications in piezocatalysis are provided. First, a detailed description of 2D piezoelectric materials are offered. Then a comprehensive summary of the piezocatalysis technique is presented and examines the piezocatalysis applications of 2D piezoelectric materials in various fields, including environmental remediation, small-molecule catalysis, and biomedicine. Finally, the main challenges and prospects of 2D piezoelectric materials and their applications in piezocatalysis are discussed. It is expected that this review can fuel the practical application of 2D piezoelectric materials in piezocatalysis.

Enhanced piezocatalytic hydrogen evolution performance of bismuth vanadate by the synergistic effect of facet engineering and cocatalyst engineering.

Developing piezocatalysts with excellent piezocatalytic hydrogen evolution reaction (HER) performance is highly desired but also challenging. Here, facet engineering and cocatalyst engineering are employed to synergistically improve the piezocatalytic HER efficiency of BiVO4 (BVO). Monoclinic BVO catalysts with distinct exposed facets are synthesized by adjusting pH of hydrothermal reaction. The BVO with highly exposed {110} facet exhibits a superior piezocatalytic HER performance (617.9 µmol g-1h-1) compared with that with {010} facet, owing to the strong piezoelectric property, high charge transfer efficiency, and excellent hydrogen adsorption/desorption capacity. The HER efficiency is enhanced by 44.7% by selectively depositing cocatalyst of Ag nanoparticles specifically on the reductive {010} facet of BVO, where the Ag-BVO interface provides the directional electron transport for high-efficiency charge separation. Under the collaboration between cocatalyst of CoOx on {110} facet and the hole sacrificial agent of methanol, the piezocatalytic HER efficiency is evidently enhanced by 2 times because CoOx and methanol can impede the water oxidation and improve the charge separation. This easy and simple strategy provides an alternative perspective on designing high-performance piezocatalysts.

Synthesizing BaTiO3 Nanostructures to Explore Morphological Influence, Kinetics, and Mechanism of Piezocatalytic Dye Degradation.

Piezocatalysts have attracted much attention due to their excellent degradation ability for organics. In this work, three types of BaTiO3 (BTO) nanostructures, including hydrothermally synthesized nanocubes (NCs), sol-gel calcined nanoparticles (NPs), and electrospun nanofibers (NFs), are prepared for catalyzing the dye degradation. Compared with the NCs and NPs, the NFs exhibit a higher piezocatalytic degradation performance due to the large specific surface area, fine crystal size, and easy deformation structure. Moreover, the kinetic factors, including initial dye concentration, ionic strength, ultrasonic power, and applied action, influencing the degradation performance of the BTO NFs are analyzed deeply. A high degradation rate constant of 0.0736 min-1 is achieved for rhodamine B, which is superior compared with the previous reports. The excellent stability of BTO NFs is demonstrated by the cycling tests, where a high degradation efficiency of 97.6% within 110 min is still obtained after the third cycle. Furthermore, the mechanism of piezocatalysis revealed that the hydroxyl and superoxide radicals are the main reactive species in the degradation process. This work is of importance for the development of high-performance piezocatalysts and highlights the potential of piezocatalysis for water remediation.

3D highly efficient photonic micro concave-pit arrays for enhanced solar water splitting.

The construction of three-dimensional (3D) photonic micro/nanostructures is regarded as one of the most promising approaches to develop highly efficient photoelectrodes for solar water splitting. Here, we report the design and fabrication of an indium tin oxide glass with 3D micro concave-pit arrays (MCPAs) as an effective photonic substrate for dramatically enhanced photoelectrochemical (PEC) water splitting. Compared with the planar counterpart, more than three-fold photocurrent density can be obtained for the 3D photoelectrodes with In2S3 nanosheet arrays grown on the inner surfaces of the MCPAs, mainly ascribable to their largely improved light trapping ability and increased surface area for charge separation and extraction. The PEC performance is further elevated by constructing an effective In2S3/ZnO heterojunction to accelerate the photocarrier separation. As a result, the 3D MCPA-based photoanodes demonstrate a maximum incident photon to current efficiency of 11.7% at 380 nm, which is about four times higher than that of the planar counterpart. The significant advancement demonstrated here provides a facile and low-cost route for the large-scale fabrication of 3D photonic electrodes aiming to achieve highly efficient PEC water splitting.

High-performance ultra-violet phototransistors based on CVT-grown high quality SnS2 flakes.

van der Waals layered two-dimensional (2D) metal dichalcogenides, such as SnS2, have garnered great interest owing to their new physics in the ultrathin limit, and become potential candidates for the next-generation electronics and/or optoelectronics fields. Herein, we report high-performance UV photodetectors established on high quality SnS2 flakes and address the relatively lower photodetection capability of the thinner flakes via a compatible gate-controlling strategy. SnS2 flakes with different thicknesses were mechanically exfoliated from CVT-grown high-quality 2H-SnS2 single crystals. The photodetectors fabricated using SnS2 flakes reveal a desired response performance (R λ ≈ 112 A W-1, EQE ≈ 3.7 × 104%, and D* ≈ 1.18 × 1011 Jones) under UV light with a very low power density (0.2 mW cm-2 @ 365 nm). Specifically, SnS2 flakes present a positive thickness-dependent photodetection behavior caused by the enhanced light absorption capacity of thicker samples. Fortunately, the responsivity of thin SnS2 flakes (e.g. ∼15 nm) could be indeed enhanced to ∼140 A W-1 under a gate bias of +20 V, reaching the performance level of thicker samples without gate bias (e.g. ∼144 A W-1 for a ∼60 nm flake). Our results offer an efficient way to choose 2D crystals with controllable thicknesses as optimal candidates for desirable optoelectronic devices.