Bioinspired soft robots for deep-sea exploration.

The deep ocean, Earth's untouched expanse, presents immense challenges for exploration due to its extreme pressure, temperature, and darkness. Unlike traditional marine robots that require specialized metallic vessels for protection, deep-sea species thrive without such cumbersome pressure-resistant designs. Their pressure-adaptive forms, unique propulsion methods, and advanced senses have inspired innovation in designing lightweight, compact soft machines. This perspective addresses challenges, recent strides, and design strategies for bioinspired deep-sea soft robots. Drawing from abyssal life, it explores the actuation, sensing, power, and pressure resilience of multifunctional deep-sea soft robots, offering game-changing solutions for profound exploration and operation in harsh conditions.

Breaking through Barriers: Ultrafast Microbullet Based on Cavitation Bubble.

Micromotors hold great promise for extensive practical applications such as those in biomedical domains and reservoir exploration. However, insufficient propulsion of the micromotor limits its application in crossing biological barriers and breaking reservoir boundaries. In this study, an ultrafast microbullet based on laser cavitation that can utilize the energy of a cavitation bubble and realize its own hurtling motion is reported. The experiments are performed using high-speed photography. A boundary integral method is adopted to reveal the motion mechanism of a polystyrene (PS)/magnetic nanoparticle (MNP) microbullet under the action of laser cavitation. Furthermore, the influence of certain factors (including laser intensity, microbullet size, and ambient temperature) on the motion of the microbullet was explored. For the PS/MNP microbullet driven by laser cavitation, the instantaneous velocity obtained can reach 5.23 m s-1 . This strategy of driving the PS/MNP microbullet provides strong penetration ability and targeted motion. It is believed that the reported propulsion mechanism opens up new possibilities for micromotors in a wide range of engineering applications.

Nonlinear dynamics of a cavitation bubble pair near a rigid boundary in a standing ultrasonic wave field.

The dynamics of a micrometer-sized bubble pair in water near a rigid boundary under standing ultrasonic wave excitation is investigated in this study. The viscous effect in the boundary layer at the air-water interface is considered following the viscous correction model. The evolution of the bubble surface at the collapsing stage of the bubble pair is presented for different parameter sets. The field pressure near the rigid boundary, which is induced by the oscillating bubble pair, and the high-speed water jet at the collapse stage, form the main focus of the analysis. This reveals that a horizontal configuration of the bubble pair retards the strength of the bubble jet towards the boundary, whilst a vertical configuration, especially with differently-sized bubbles, can enhance the bubble collapse. This study may help to understand the interaction of multiple bubbles in an acoustic field and its application to surface cleaning.

Polyoxometalate-Based Metal-Organic Frameworks with Conductive Polypyrrole for Supercapacitors.

Metal-organic frameworks (MOFs) with high porosity could act as an ideal substitute for supercapacitors, but their poor electrical conductivities limit their electrochemical performances. In order to overcome this problem, conductive polypyrrole (PPy) has been introduced and a novel nanocomposite resulting from polyoxometalate (POM)-based MOFs (NENU-5) and PPy has been reported. It comprises the merits of POMs, MOFs, and PPy. Finally, the highly conductive PPy covering the surfaces of NENU-5 nanocrystallines can effectively improve the electron/ion transfer among NENU-5 nanocrystallines. The optimized NENU-5/PPy nanocomposite (the volume of Py is 0.15 mL) exhibits high specific capacitance (5147 mF·cm-2), larger than that of pristine NENU-5 (432 mF·cm-2). Furthermore, a symmetric supercapacitor device based on a NENU-5/PPy-0.15 nanocomposite possesses an excellent areal capacitance of 1879 mF·cm-2, which is far above other MOF-based supercapacitors.

Polyoxometalate-Based Metal-Organic Framework on Carbon Cloth with a Hot-Pressing Method for High-Performance Lithium-Ion Batteries.

Recently, development of a new type of anode material for lithium-ion batteries that possesses multielectron reaction, sufficient charge transfer, and restricted volume suppression has been considered a huge challenge. Herein, we find a simple hot-pressing method to incorporate polyoxometalate (POM)-based metal-organic frameworks (MOFs) onto three-dimensionally structured carbon cloth (CC), denoted as HP-NENU-5/CC, which immobilizes POMs into the MOFs avoiding the leaching of POMs and employs HP-NENU-5/CC as a flexible, conductive, and porous anode material. The HP-NENU-5/CC anode materials show outstanding electrochemical performance, exhibiting high reversible capacity (1723 mAh g-1 at 200 mA g-1), high rate capability (1072 mAh g-1 at 1000 mA g-1), and superior cycling stability (1072 mAh g-1 at 1000 mA g-1 after 400 cycles). Most importantly, the performance of HP-NENU-5/CC is the best among those of all reported POMs and MOF-based materials. In addition, we perform a comparative study for active materials coated on a two-dimensional current collector and CC, and our experimental results and analysis prove that the active material coated on CC does enhance the electrochemical performance.

Polyoxometalate precursors for precisely controlled synthesis of bimetallic sulfide heterostructure through nucleation-doping competition.

Molybdenum disulfide (MoS2)-based bimetallic sulfides have drawn increasing research attention because of their unique structures and properties. Herein, a one-pot hydrothermal synthesis method is proposed to grow a series of bimetallic sulfides on carbon cloth (M-Mo-S/CC, M = Co, Ni, Fe) using Anderson-type polyoxometalates (POMs) as bimetallic sources for the first time. An ideal model of M-Mo-S/CC was used to study the growth process through the nucleation-doping competition mechanism. It is proved for the first time that M-Mo-S/CC possess certain compositions of bimetallic sulfides rather than metal doped MoS2 structures because the nucleation reaction is predominant in the nucleation-doping competition. Moreover, the nucleation rates of different metals can be compared to study the different morphologies of M-Mo-S/CC because Anderson-type POMs have fixed bimetal proportions and precise structures. Co-Mo-S and Ni-Mo-S show spherical heterostructures with CoS2 or NiS mainly inside and interconnected MoS2 nanosheets outside, while Fe-Mo-S exhibits uniform nanosheet morphology without stacking. As electrodes for alkaline water electrolysis, M-Mo-S/CC with different compositions and morphologies exhibit a variety of activities. Particularly, among the M-Mo-S/CC samples, Co-Mo-S/CC achieves the best performance for hydrogen evolution reaction, oxygen evolution reaction and overall water splitting. This study presents a facile strategy of using POMs as bimetallic precursors for studying the growth mechanism as well as the water electrolysis performances of MoS2-based bimetallic sulfides.

Dynamic behaviour of a two-microbubble system under ultrasonic wave excitation.

Acoustic bubbles have wide and important applications in ultrasonic cleaning, sonochemistry and medical ultrasonics. A two-microbubble system (TMS) under ultrasonic wave excitation is explored in the present study, by using the boundary element method (BEM) based on the potential flow theory. A parametric study of the behaviour of a TMS has been carried out in terms of the amplitude and direction of ultrasound as well as the sizes and separation distance of the two bubbles. Three regimes of the dynamic behaviour of the TMS have been identified in terms of the pressure amplitude of the ultrasonic wave. When subject to a strong wave with the pressure amplitude of 1 atm or larger, the two microbubbles become non-spherical during the first cycle of oscillation, with two counter liquid jets formed. When subject to a weak wave with the pressure amplitude of less than 0.5 atm, two microbubbles may be attracted, repelled, or translate along the wave direction with periodic stable separation distance, depending on their size ratio. However, for the TMS under moderate waves, bubbles undergo both non-spherical oscillation and translation as well as liquid jet rebounding.

Polyoxomolybdate-Polypyrrole/Reduced Graphene Oxide Nanocomposite as High-Capacity Electrodes for Lithium Storage.

A nanocomposite polyoxomolybdate (PMo12)-polypyrrole (PPy)/reduced graphene oxide (RGO) is fabricated by using a simple one-pot hydrothermal method as an electrode material for lithium-ion batteries. This facile strategy skillfully ensures that individual polyoxometalate (POM) molecules are uniformly immobilized on the RGO surfaces because of the wrapping of polypyrrole (PPy), which avoids the desorption and dissolution of POMs during cycling. The unique architecture endows the PMo12-PPy/RGO with the lithium storage behavior of a hybrid battery-supercapacitor electrode: the nanocomposite with a lithium storage capacity delivers up to 1000 mAh g-1 at 100 mA g-1 after 50 cycles. Moreover, it still demonstrates an outstanding rate capability and a long cycle life (372.4 mAh g-1 at 2 A g-1 after 400 cycles). The reversible capacity of this nanocomposite has surpassed most pristine POMs and POMs-based electrode materials reported to date.