A Multi-Bioinspired Dual-Gradient Electrode for Microbubble Manipulation toward Controllable Water Splitting

Emerging transparent conductive superhydrophobic surfaces

Transparent conductive superhydrophobic surfaces (TCSHSs) represent a novel class of multifunctional materials that concurrently exhibit high transparency, excellent electrical conductivity, and robust superhydrophobicity. These three desirable properties are synergistically combined to provide a wide variety of advantages for various optoelectronic applications with water-repelling capabilities, including solar cells, smart windows, touch screens, and automobile windshields, all of which benefit from self-cleaning, anti-icing, anti-fouling, and anti-corrosion properties. This review aims to provide an overview of recent advancements in the field of TCSHSs. It begins by revisiting the fundamental principles governing superhydrophobic behavior and delving into the underlying mechanisms of various wetting phenomena. The review also highlights the intricate balance among transparency, conductivity, and superhydrophobicity, along with the associated physical principles. Furthermore, it introduces emerging TCSHSs in terms of material types, preparation methods, evaluation criteria, and cutting-edge applications. Finally, it summarizes the critical challenges and promising future prospects for TCSHSs, which will facilitate further development in this field.

Erasable and Programmable Unidirectional Liquid Transport on Multiple Asymmetric Slippery Microstructures

Unidirectional fluid delivery on an asymmetric microstructure has garnered significant attention due to its advantages, such as being pumpless, multifunctional, and easy to integrate. However, the precise design of continuous flow in unidirectional transport and on-surface recyclable manipulation remains challenging. Here, we present a 3D-printed array of multiple asymmetric microstructures decorated with a nanoparticle-based sprayable slippery coating that can achieve promising liquid control for both droplets and flow. Inspired by two biological modes, lizard skin and butterfly wings, we designed two types of asymmetric microstructures, i.e., triangular protrusions and tilted microcones. Both asymmetric microstructures exhibit unidirectional wettability, such as directional droplet sliding and liquid spreading. Benefiting from the improved water repellency of the slippery surface, asymmetric microstructures can unlock more functions compared to previous examples, such as erasable liquid channels, programmable flow control, and modular fluidics. By tuning the motion resistance of the asymmetric microstructure, a complex and diverse pathway for the unidirectional channel is achieved, such as ordered flow transport and flow-based logic circuits for LED lighting. This contribution unifies two types of asymmetric microstructures in one system, providing a deeper analysis of resistance tuning in unidirectional fluid transport. We envision that these slippery asymmetric microstructures will diversify liquid-manipulating interfaces for the development of advanced fluidic devices.

Rice leaves microstructure-inspired high-efficiency electrodes for green hydrogen production

Hydrogen production via water electrolysis is deemed a prime candidate for large-scale commercial green hydrogen generation. However, during the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), bubble accumulation on the electrode surface substantially elevates the required voltage and diminishes electrolysis efficiency. In this work, we demonstrated a rice leaves-inspired anisotropic microstructured gas conduction electrode (Ni-conduction) that can rapidly detach bubbles from the anisotropic microstructure. The microstructured grooves on the electrode surface lower the interface energy and modify bubble detachment dynamics, enabling swift bubble release and directed bubble flow along the microstructured channels. As a result, the Ni-conduction achieves a reduction in HER/OER overpotential, reaching values of 92/123 mV at 10 mA cm-2. This performance significantly surpasses the performance of a flat nickel electrode (Ni-smooth), necessitating an overpotential of 183/176 mV under identical conditions. Furthermore, the assembled Ni-conduction||Ni-conduction overall water-splitting device only needs a cell voltage of 1.53 V to reach 10 mA cm-2. Our research emphasizes the significance of wettability design in electrode microstructure to enhance mass transfer and optimize water splitting efficiency, presenting novel strategies for the development of superior gas-evolution electrodes.

Interfacial fluid manipulation with bioinspired strategies: special wettability and asymmetric structures

The inspirations from nature always enlighten us to develop advanced science and technology. To survive in complicated and harsh environments, plants and animals have evolved remarkable capabilities to control fluid transfer via sophisticated designs such as wettability contrast, oriented micro-/nano-structures, and geometry gradients. Based on the bioinspired structures, the on-surface fluid manipulation exhibits spontaneous, continuous, smart, and integrated performances, which can promote the applications in the fields of heat transfer, microfluidics, heterogeneous catalysis, water harvesting, etc. Although fluid manipulating interfaces (FMIs) have provided plenty of ideas to optimize the current systems, a comprehensive review of history, classification, fabrication, and integration focusing on their interfacial chemistry and asymmetric structure is highly required. In this review, we systematically introduce development and highlight the state-of-the-art progress of bioinspired FMIs. Firstly, the biological prototype and development timeline are presented, and the underlying mechanism of on-surface fluid control on versatile structures is analyzed. Secondly, the definition and classification of FMIs as well as the strategy for controlling fluid/interface interaction are discussed. Thirdly, emergent applications of FMIs in practical scenarios including fog/vapor collection, fluid diodes, interfacial catalysis, etc. are presented. Furthermore, the challenges and prospects of interfacial liquid manipulation are concluded. We envision that this review should provide guidance for the incorporation of FMIs into suitable situations, which enlightens interdisciplinary research and practical applications in the fields of interface chemistry, materials design, bionic science, fluid dynamics, etc.

Biomimetic Janus Particles Induced In Situ Interfacial Remineralization for Dentin Hypersensitivity

Dentin hypersensitivity (DH), caused by the exposure of dentin tubules, is a common complaint of dental patients. Although occlusion of the exposed tubules is the primary treatment approach, the complex oral environment, and multiple simultaneous requirements often hinder its implementation. In this study, strawberry‐shaped hemispheric Janus particles (JPs) are synthesized, and their use in the treatment of DH is evaluated in vitro and in an animal model. The hemispheric side of the JPs is modified with polymers of quaternary ammonium salts (QASs) to form a superhydrophobic coating with antibiofilm properties, while the flat side is modified with catechol groups able to form strong bonds with dentin. Even after 1 h of ultrasonication or 1000 rounds of thermal cycling, the dentin tubules are completely occluded by the JPs. Moreover, biofilm formation is not observed, and the area of living bacteria is less than 1% compared to the blank control and sodium fluoride (NaF)‐treated groups. In a rat model, the dentin tubules in the fixed specimens are completely occluded at day 3, much earlier than the occlusion obtained with commonly used NaF. These results demonstrate that JPs can provide a novel approach to the treatment of DH.

Rose-Inspired Adhesive Surface Regulation for Enhanced Fog Water Collection Efficiency and Self-Cleaning

Inspired by the adhesion differences on the surfaces of fresh and dried rose petals, a rose bionic self-cleaning fog collector (RBSC) was designed and prepared to realize a self-driven fog harvesting function. The droplet detachment iteration rate was revealed by the regulating mechanism of the surface adhesion force of the RBSC and the influence of bionic texture parameters, as demonstrated through the fog harvesting experiment and droplet detachment failure analysis. Through the surface adhesion force regulation, the probability of droplet dissipation with the airflow is reduced by increasing the falling droplets' mass, and the single surface fog capture efficiency is up to 740 mg cm-2 h-1. With the adhesion gradient regulation, the composite hexagonal patterned surface achieves a water collection efficiency of 960 mg cm-2 h-1, which is a 243% improvement compared with that of a slippery surface and is superior to the efficiencies of both circular and 90° square patterns. This is due to the fact that the composite hexagonal patterned surface ensures that the water droplets converge at the center while increasing the distance between the droplets, improving the stability of droplet detachment. Compared to the stainless steel surface, the RBSC exhibits excellent self-cleaning performance, with the impurity deposition rate reduced by 91.2%. The multi-inspired strategy optimizes the entire harvesting process, offering a promising solution to the water crisis in arid regions.

Machine learning-guided discovery of gas evolving electrode bubble inactivation

The adverse effects of electrochemical bubbles on the performance of gas-evolving electrodes are well known, but studies on the degree of adhered bubble-caused inactivation, and how inactivation changes during bubble evolution are limited. We study electrode inactivation caused by oxygen evolution while using surface engineering to control bubble formation. We find that the inactivation of the entire projected area, as is currently believed, is a poor approximation which leads to non-physical results. Using a machine learning-based image-based bubble detection method to analyze large quantities of experimental data, we show that bubble impacts are small for surface engineered electrodes which promote high bubble projected areas while maintaining low direct bubble contact. We thus propose a simple methodology for more accurately estimating the true extent of bubble inactivation, which is closer to the area which is directly in contact with the bubbles.

Boosting Droplet Transport for Fog Harvest

Wedge-shaped superhydrophilic tracks have been considered as one of the most effective ways to transport droplets for diverse cutting-edge applications, e.g., energy harvesting and lab-on-a-chip devices. Although significant progress, such as serial wedge-shaped tracks with curved edges, has evolved to advance the liquid transport, the ultrafast and long-distance transporting of drop-shaped liquid remains challenging. Here, inspired by the cactus spine that enables fast droplet transport and the serial spindle knot of spider silk, which is capable of collecting condensate from a wide range of distances, we created serial wedge-shaped superhydrophilic patterns and optimized their side edges with a convex brachistochrone curve to boost the acceleration. The junctions of the serial patterns were meanwhile reformed into concave brachistochrone curves to lower the energy barrier for sustained transport. For transporting the liquid in drop shapes to the long distance at high velocity, the wedge-shaped tracks were slenderized to the greatest extent to suppress the liquid spreading and thus prevent the degradation of the Laplace driving force. Moreover, the junction that determines the energy barrier of droplet striding was carefully designed based on the principle of minimizing momentum loss. The exquisite architecture design pushed the droplet transport to a maximum instantaneous velocity of 207.7 mm·s-1 and an outermost transport distance of 120.5 mm, exceeding most wettability or geometric gradient based reports. The transported volume of the droplets can be readily regulated by simply scaling the created architectures. The enhanced droplet transport facilitates the motion and departure of the cohered droplets, enabling a 1.9-fold rise of the water collection rate and 12-fold increase of the heat transfer coefficient during the fog harvest test. This scalable, controllable, and easily fabricatable surface design provides an essential pathway in realizing high-performance manipulation of droplets and possibly pioneers substantial innovative applications in multidisciplinary fields. Those include but are not limited to energy harvesting, lab-on-a-chip devices, and MEMS systems.

Bubble-Guidance Breaking Gas Shield for Highly Efficient Overall Water Splitting

Overall water splitting is a promising technology for sustainable hydrogen production, but the primary challenge is removing bubbles from the electrode surface quickly to increase hydrogen production. Inspired by the directional fluid transport properties of natural biological surfaces like Nepenthes peristome and Morpho butterfly's wings, here a strategy is demonstrated to achieve highly efficient overall water splitting by a bubble-guidance electrode, that is, an anisotropic groove-micro/nanostructured porous electrode (GMPE). Gradient groove micro/nanostructures on the GMPE serve as high-speed bubble transmission channels and exhibit superior bubble-guidance capabilities. The synergistic effect of the asymmetric Laplace pressure generated between microscale porous structure and groove patterns and the buoyancy along the groove patterns pushes the produced bubbles directionally to spread, transport, and detach from the electrode surface in time. Moreover, the low adhesive nanosheet arrays are beneficial to reduce bubble size and increase bubble release frequency, which cooperatively improve mass transfer with the microscale structure. Notably, GMPE outperforms planar-micro/nanostructured porous electrode (PMPE) in hydrogen/oxygen evolution reactions, with GMPE||GMPE showing better water splitting performance than commercially available RuO2||20 wt.% Pt/C. This work improves electrodes for better mass transfer and kinetics in electrochemical reactions at solid-liquid-gas interfaces, offering insight for designing and preparing gas-involved photoelectrochemical electrodes.

Scaling-Free Cathodes: Enabling Electrochemical Extraction of High-Purity Nano-CaCO3 and -Mg(OH)2 in Seawater

For electrochemical application in seawater or brine, continuous scaling on cathodes will form insulation layers, making it nearly impossible to run an electrochemical reaction continuously. Herein, we report our discovery that a cathode consisting of conical nanobundle arrays with hydrophobic surfaces exhibits a unique scaling-free function. The hydrophobic surfaces will be covered with microbubbles created by electrolytic water splitting, which limits scale crystals from standing only on nanotips of conical nanobundles, and the bursting of large bubbles formed by the accumulation of microbubbles will cause a violent disturbance, removing scale crystals automatically from nanotips. Benefiting from the scaling-free properties of the cathode, high-purity nano-CaCO3 (98.9%) and nano-Mg(OH)2 (99.5%) were extracted from seawater. This novel scaling-free cathode is expected to eliminate the inherent limitations of electrochemical technology and open up a new route to seawater mining.

Fluid Unidirectional Transport Induced by Structure and Ambient Elements across Porous Materials: From Principles to Applications

Spontaneous or nonspontaneous unidirectional fluid transport across multidimension can occur under specific structural designs and ambient elements for porous materials. While existing reviews have extensively summarized unidirectional fluid transport on surfaces, there is an absence of literature summarizing fluid's unidirectional transport across porous materials. This review introduces wetting phenomena observed on natural biological surfaces or porous structures. Subsequently, it offers an overview of diverse principles and potential applications in this field, emphasizing various physical and chemical structural designs (surface energy, capillary size, topographic curvature) and ambient elements (underwater, under oil, pressure, and solar energy). Applications encompass moisture-wicking fabric, sensors, skincare, fog collection, oil-water separation, electrochemistry, liquid-based gating, and solar evaporators. Additionally, significant principles and formulas from various studies are compelled to offer readers valuable references. Simultaneously, potential advantages and challenges are critically assessed in these applications and the perspectives are presented.

Robust Superhydrophobic Composite Fabric with Self-Healing and Chemical Durability

Superhydrophobic fabrics with multiple functions have become a research hotspot. However, it is challenging to make self-healing mechanically robust and eco-friendly superhydrophobic fabrics, which are limited by complex fabrication processes and excessive use of environmentally unfriendly solvents during fabrication. Herein, inspired by the secretion of a waxy substance from the surface of lotus leaves to restore water repellency, self-healing superhydrophobic composite fabrics (as-synthesized PA66/6-PET@Tico) are obtained by constructing a papillary TiO2 and tentacle-like fluorinated acrylate polymer (FCB015) coating on polyester-nylon composite fabrics using two-step hydrothermal method. The result indicates that PA66/6-PET@Tico with hierarchical micro/nanostructure exhibits excellent superhydrophobic and self-healing properties. Compared with FCB015 coated fabric, the contact angles (CA) of water and soybean oil rise to 172.2° and 166.8° from 137.4° and 98.8°, respectively. After mechanical abrasion, PA66/6-PET@Tico recovers a water contact angle (WCA) of 165.6° at room temperature. The WCA remains higher than 155° after 18 h of chemical corrosion. Furthermore, the bacterial inhibition rates of PA66/6-PET@Tico for Staphylococcus Aureus and Escherichia Coli are 99.90 and 98.38%, respectively. In this work, a new idea is proposed for designing a simple and effective self-healing superhydrophobic coating, expecting to promote the large-scale industrial production and application of functional surfaces.

Rapid Defect Engineering in FeCoNi/FeAl2O4 Hybrid for Enhanced Oxygen Evolution Catalysis: A Pathway to High-Performance Electrocatalysts

Rational modulation of surface reconstruction in the oxygen evolution reaction (OER) utilizing defect engineering to form efficient catalytic activity centers is a topical interest in the field of catalysis. The introduction of point defects has been demonstrated to be an effective strategy to regulate the electronic configuration of electrocatalysts, but the influence of more complex planar defects (e.g., twins and stacking faults), on their intrinsic activity is still not fully understood. This study harnesses ultrasonic cavitation for rapid and controlled introduction of different types of defects in the FeCoNi/FeAl2O4 hybrid coating, optimizing OER catalytic activity. Theoretical calculations and experiments demonstrate that the different defects optimize the coordination environment and facilitate the activation of surface reconstruction into true catalytic activity centers at lower potentials. Moreover, it demonstrates exceptional durability, maintaining stable oxygen production at a high current density of 300 mA cm-2 for over 120 hours. This work not only presents a novel pathway for designing advanced electrocatalysts but also deepens our understanding of defect-engineered catalytic mechanisms, showcasing the potential for rapid and efficient enhancement of electrocatalytic performance.

Roles of Wettability and Wickability on Enhanced Hydrogen Evolution Reactions

Bubble dynamics significantly impact mass transfer and energy conversion in electrochemical gas evolution reactions. Micro-/nanostructured surfaces with extreme wettability have been employed as gas-evolving electrodes to promote bubble departure and decrease the bubble-induced overpotential. However, effects of the electrodes' wickability on the electrochemical reaction performances remain elusive. In this work, hydrogen evolution reaction (HER) performances are experimentally investigated using micropillar array electrodes with varying interpillar spacings, and effects of the electrodes' wettability, wickability as well as bubble adhesion are discussed. A deep learning-based object detection model was used to obtain bubble counts and bubble departure size distributions. We show that microstructures on the electrode have little effect on the total bubble counts and bubble size distribution characteristics at low current densities. At high current densities, however, micropillar array electrodes have much higher total bubble counts and smaller bubble departure sizes compared with the flat electrode. We also demonstrate that surface wettability is a critical factor influencing HER performances under low current densities, where bubbles exist in an isolated regime. Under high current densities, where bubbles are in an interacting regime, the wickability of the micropillar array electrodes emerges as a determining factor. This work elucidates the roles of surface wettability and wickability on enhancing electrochemical performances, providing guidelines for the optimal design of micro-/nanostructured electrodes in various gas evolution reactions.

Bioinspired Gas Manipulation for Regulating Multiphase Interactions in Electrochemistry

The manipulation of gas in multiphase interactions plays a crucial role in various electrochemical processes. Inspired by nature, researchers have explored bioinspired strategies for regulating these interactions, leading to remarkable advancements in design, mechanism, and applications. This paper provides a comprehensive overview of bioinspired gas manipulation in electrochemistry. It traces the evolution of gas manipulation in gas-involving electrochemical reactions, highlighting the key milestones and breakthroughs achieved thus far. The paper then delves into the design principles and underlying mechanisms of superaerophobic and (super)aerophilic electrodes, as well as asymmetric electrodes. Furthermore, the applications of bioinspired gas manipulation in hydrogen evolution reaction (HER), carbon dioxide reduction reaction (CO2RR), and other gas-involving electrochemical reactions are summarized. The promising prospects and future directions in advancing multiphase interactions through gas manipulation are also discussed.

Bubble Unidirectional Transportation on Multipath Aerophilic Surfaces by Adjusting the Surface Microstructure

Comprehending and controlling the behavior of bubbles on solid surfaces is of significant importance in various fields including catalysis and drag reduction, both industrially and scientifically. Herein, Inspired by the superaerophilic properties of the lotus leaf surface, a series of asymmetrically patterned aerophilic surfaces were prepared by utilizing a facile mask-spraying method for directional transport of underwater bubbles. The ability of bubbles to undergo self-driven transportation in an asymmetric pattern is attributed to the natural tendency of bubbles to move toward regions with lower surface energy. In this work, the microstructure of the aerophilic surface is demonstrated as a critical element that influences the self-driven transport of bubbles toward regions of lower surface energy. The microstructure characteristic affects the energy barrier of forming a continuous gas film on the final regions. We classify three distinct bubble behaviors on the aerophilic surface, which align with three different underwater gas film evolution states: Model I, Model II, and Model III. Furthermore, utilizing the energy difference between the energy barrier that forms a continuous gas film and the gas-gas merging, gas-liquid microreaction in a specific destination on the multiple paths can be easily realized by preinjecting a bubble in the final region. This work provides a new view of the microevolutionary process for the diffusion, transport, and merging behavior of bubbles upon contact with an aerophilic pattern surface.

Bioinspired Organic Porous Coupling Agent for Enhancement of Nanoparticle Dispersion and Interfacial Strength

Composite materials have significantly advanced with the integration of inorganic nanoparticles as fillers in polymers. Achieving fine dispersion of these nanoparticles within the composites, however, remains a challenge. This study presents a novel solution inspired by the natural structure of Xanthium. We have developed a polymer of intrinsic microporosity (PIM)-based porous coupling agent, named PCA. PCA's rigid backbone structure enhances interfacial interactions through a unique intermolecular interlocking mechanism. This approach notably improves the dispersion of SiO2 nanoparticles in various organic solvents and low-polarity polymers. Significantly, PCA-modified SiO2 nanoparticles embedded in polyisoprene rubber showed enhanced mechanical properties. The Young's modulus increases to 30.7 MPa, compared to 5.4 MPa in hexadecyltrimethoxysilane-modified nanoparticles. Further analysis shows that PCA-modified composites not only become stiffer but also gain strength and ductility. This research demonstrates a novel biomimetic strategy for enhancing interfacial interactions in composites, potentially leading to stronger, more versatile composite materials.

Flexible Platform Composed of T-Shaped Micropyramid Patterns toward a Waterproof Sensing Interface

Antifouling is essential to guaranteeing the sensitivity and precision of flexible sensing interfaces. Materials and structures are the two primary strategies. However, optimizing the inherent microstructures to integrate waterproofing and sensing is rarely reported. To improve the liquid repellency of micropyramid structures, this work presents a study of the design and fabrication of T-shaped micropyramid structures. These structures are patterned uniformly and largely on polydimethylsiloxane (PDMS) skin by the new process of two-step magnetic induction. The waterproofing is related to the breakthrough pressure and the liquid repellency, both of which are a function of structural characteristics, D, and material properties, θY. At the breakthrough transition, two failure models distinguished by θY appear: the depinning transition and the sagging transition. Meanwhile, when considering D in practice, some models will shift and occur early. The D value regulates the transition of the material's wettability to the liquid repellency. The influence of the material's inherent nonwettability on liquid repellency diminishes as D decreases, and the transition from completely wetting liquids to super-repellents can be achieved. Experiments demonstrate that for D = 0.3 under water the resistance is approximately 142 times larger than the depth of the structure, considerably facilitating the waterproofing of conventional micropyramid arrays. This work provides a novel method for fabricating flexible T-shaped micropyramid array structures and opens a new window on flexible sensing interfaces with excellent waterproofing.

Bubble Management for Electrolytic Water Splitting by Surface Engineering: A Review

During electrocatalytic water splitting, the management of bubbles possesses great importance to reduce the overpotential and improve the stability of the electrode. Bubble evolution is accomplished by nucleation, growth, and detachment. The expanding nucleation sites, decreasing bubble size, and timely detachment of bubbles from the electrode surface are key factors in bubble management. Recently, the surface engineering of electrodes has emerged as a promising strategy for bubble management in practical water splitting due to its reliability and efficiency. In this review, we start with a discussion of the bubble behavior on the electrodes during water splitting. Then we summarize recent progress in the management of bubbles from the perspective of surface physical (electrocatalytic surface morphology) and surface chemical (surface composition) considerations, focusing on the surface texture design, three-dimensional construction, wettability coating technology, and functional group modification. Finally, we present the principles of bubble management, followed by an insightful perspective and critical challenges for further development.

High-Performance Liquid-Repellent and Thermal-Wet Comfortable Membranes Using Triboelectric Nanostructured Nanofiber/Meshes

Skin-like functional membranes with liquid resistance and moisture permeability are in growing demand in various applications. However, the membranes have been facing a long-term dilemma in balancing waterproofness and breathability, as well as resisting internal liquid sweat transport, resulting in poor thermal-wet comfort. Herein, a novel electromeshing technique, based on manipulating the ejection and phase separation of charged liquids, is developed to create triboelectric nanostructured nano-mesh consisting of hydrophobic ferroelectric nanofiber/meshes and hydrophilic nanofiber/meshes. By combining the true nanoscale diameter (≈22 nm), small pore size, and high porosity, high waterproofness (129 kPa) and breathability (3736 g m-2 per day) for the membranes are achieved. Moreover, the membranes can break large water clusters into small water molecules to promote sweat absorption and release by coupling hydrophilic wicking and triboelectric field polarization, exhibiting a satisfactory water evaporation rate (0.64 g h-1 ) and thermal-wet comfort (0.7 °C cooler than the cutting-edge poly(tetrafluoroethylene) protective membranes). This work may shed new light on the design and development of advanced protective textiles.

Bubble Engineering on Micro-/Nanostructured Electrodes for Water Splitting

Bubble behaviors play crucial roles in mass transfer and energy efficiency in gas evolution reactions. Combining multiscale structures and surface chemical compositions, micro-/nanostructured electrodes have drawn increasing attention. With the aim to identify the exciting opportunities and rationalize the electrode designs, in this review, we present our current comprehension of bubble engineering on micro-/nanostructured electrodes, focusing on water splitting. We first provide a brief introduction of gas wettability on micro-/nanostructured electrodes. Then we discuss the advantages of micro-/nanostructured electrodes for mass transfer (detailing the lowered overpotential, promoted supply of electrolyte, and faster bubble growth kinetics), localized electric field intensity, and electrode stability. Following that, we outline strategies for promoting bubble detachment and directional transportation. Finally, we offer our perspectives on this emerging field for future research directions.

Designing a slippery/superaerophobic hierarchical open channel for reliable and versatile underwater gas delivery

Achieving long-term and stable gas manipulation in an aqueous environment is necessary to improve multiphase systems relating to gas/liquid interaction. Inspired by the Pitcher plant and the hummingbird beak, we report a slippery/superaerophobic (SLSO) hierarchical fluid channel for continuous, durable, and flexible gas transport. The immiscible lubricant layer inside the SLSO channel promotes one-year stability of gas transport, and the maximum flux of this open channel can reach 3000 mL h-1. Further integration of a CO2 capturing microchip demonstrates the availability and potential of this gas-manipulating interface, which should provide a valuable platform to develop advanced materials and devices.

Unidirectional Moisture Delivery via a Janus Photothermal Interface for Indoor Dehumidification: A Smart Roof

Rational control of the humidity in specific environments plays an important role in green building, equipment protection, etc. A smart apparatus that can actively expel inner moisture and largely prevent outer liquid penetration can be highly desirable. Through the integration of the Janus interface with unidirectional liquid manipulation and the solar evaporating layer, here, a Janus solar dehumidifying interface (JSDI) is designed for the switchable moisture management of an indoor environment. By covering with the JSDI roof, the continuous elimination of inner water is achieved via outward condensate delivery and solar evaporation on sunny days. On rainy days, JSDI with a hydrophobic lower surface can largely hamper inward liquid leakage and then spontaneously drain the accumulated water via a siphoning structure. The real-world water evaporation rate via the JSDI is ≈0.38 kg m^-2 h^-1 on an autumn day, showing a promising function of in situ moisture expelling. In addition, the JSDI is made of natural materials that are easy to scale up with a cost of four dollars per square meter. It is envisioned that the JSDI may meet the wide requirements of indoor dehumidification and update the understanding of the integration of Janus interfaces and solar steam generation.

Designing Versatile Superhydrophilic Structures via an Alginate-Based Hydrophilic Plasticene

The rational design of superhydrophilic materials with a controllable structure is a critical component in various applications, including solar steam generation, liquid spontaneous transport, etc. The arbitrary manipulation of the 2D, 3D, and hierarchical structures of superhydrophilic substrates is highly desirable for smart liquid manipulation in both research and application fields. To design versatile superhydrophilic interfaces with various structures, here we introduce a hydrophilic plasticene that possesses high flexibility, deformability, water absorption, and crosslinking capabilities. Through a pattern-pressing process with a specific template, 2D prior fast spreading of liquids at speeds up to 600 mm/s was achieved on the superhydrophilic surface with designed channels. Additionally, 3D superhydrophilic structures can be facilely designed by combining the hydrophilic plasticene with a 3D-printed template. The assembly of 3D superhydrophilic microstructure arrays were explored, providing a promising route to facilitate the continuous and spontaneous liquid transport. The further modification of superhydrophilic 3D structures with pyrrole can promote the applications of solar steam generation. The optimal evaporation rate of an as-prepared superhydrophilic evaporator reached ~1.60 kg·m^-2·h^-1 with a conversion efficiency of approximately 92.96%. Overall, we envision that the hydrophilic plasticene should satisfy a wide range of requirements for superhydrophilic structures and update our understanding of superhydrophilic materials in both fabrication and application.

Improved Liquid Collection on a Dual-Asymmetric Superhydrophilic Origami

Manipulating fluid with an open channel provides a promising strategy to simplify the current systems. Nevertheless, spontaneous on-surface fluid transport with large flux, high speed, and long distance remains challenging. Inspired by scallop shells, here a shell-like superhydrophilic origami (S-SLO) with multiple-paratactic and dual-asymmetric channels is presented to improve fluid collection. The origami channel can capture various types of liquids, including droplets, flow, and steam, and then transport collected liquid unidirectionally. The S-SLO with 2 mm depth can reach maximum flux of 450 mL h^-1 , which is five times the capacity of a flat patterned surface with similar dimension. To diversify the function of such interface, the SLO is further integrated with a superhydrophobic zirconium carbide/silicone coating for enhanced condensation via the collaboration of directional fluid manipulation and a radiative cooling layer. Compared with the unmodified parallel origami, the shell-like origami with a radiative cooling layer shows a 56% improvement in condensate efficiency as well as the directional liquid drainage. This work demonstrates a more accessible design for the optimization of on-surface fluid control, and the improved performance of liquid transport should extend the applications of bioinspired fluid-manipulating interfaces.

Non-Newtonian fluid gating membranes with acoustically responsive and self-protective gas transport control

Control of gas transport through porous media is desired in multifarious processes such as chemical reactions, interface absorption, and medical treatment. Liquid gating technology, based on dynamically adaptive interfaces, has been developed in recent years and has shown excellent control capability in gas manipulation-the reversible opening and closing of a liquid gate for gas transport as the applied pressure changes. Here, we report a new strategy to achieve self-protective gas transport control by regulating the dynamic porous interface in a non-Newtonian fluid gating membrane based on the shear thickening fluid. The gas transport process can be suspended and restored via modulation of the acoustic field, owing to the transition of particle-to-particle interactions in a confined geometry. Our experimental and theoretical results support the stability and tunability of the gas transport control. In addition, relying on the shear thickening behaviour of the gating fluid, the transient response can be achieved to resist high-impact pressure. This strategy could be utilized to design integrated smart materials used in complex and extreme environments such as hazardous and explosive gas transportation.

Engineered Switchable-Wettability Surfaces for Multi-Path Directional Transportation of Droplets and Subaqueous Bubbles

Conventional engineered surfaces for fluid manipulation are hindered by the set wettability, and thus they can only achieve spontaneous transport of single-phase fluid, namely liquid or gas. Moreover, fluid transport systems that are robust to path defects have yet to be fully explored. Here, unprecedentedly, a universal wettability switching strategy is developed for achieving programmable directional transport of both droplets and subaqueous bubbles on a dumbbell-patterned functional surface (DPFS), featuring in strong robustness, high efficiency, and effective cost. By tuning the superwettability of DPFS through octadecyltrichlorosilane treatment and ultraviolet-C selective irradiation, the transport fluid can alternate between liquid and gas. The material's switchable superwettability regulates the fluid directed dynamics within the confined pattern, in which the sustaining fluid propelling relies on the surface energy difference between the starting and terminal sites. This enables the construction of multiple channels, which works synergistically with ultralow-volume-loss transport to impart the fluidic system with strong robustness against path defects. Underlying the completion of complex microfluidics tasks, spatially-selective cooling devices and subaqueous gas microreactors are successfully demonstrated. This energy-consumption-free fluid transport system opens a new avenue for on-chip programmable fluid manipulation, promoting innovative applications requiring rational control of two-phase fluid transport.

Fluid manipulation via multifunctional lubricant infused slippery surfaces: principle, design and applications

Water-repellent interfaces with high performance have emerged as an indispensable platform for developing advanced materials and devices. Inspired by the pitcher plant, slippery liquid-infused porous surfaces (SLIPSs) with reliable hydrophobicity have proven to possess great potential for various applications in droplet and bubble manipulation, droplet energy harvesting, condensation, fog collection, anti-icing, and anti-biofouling due to their excellent properties such as persistent surface hydrophobicity, molecular smoothness, and fluidity. This review aims to introduce the development history of interaction between SLIPSs and fluids as well as the design principles, preparation methods, and various applications of some of the more typical SLIPSs. The fluid manipulation strategies of the slippery surfaces have been proposed including the wettability pattern, oriented micro-structure, and geometric gradient. At last, the application prospects of SLIPSs in various fields and the challenges in the design and fabrication of slippery surfaces are analyzed. We envision that this review can provide an overview of the fluid manipulating processes on slippery surfaces for researchers in both academic and industrial fields.

Ultrastable Super-Hydrophobic Surface with an Ordered Scaly Structure for Decompression and Guiding Liquid Manipulation

Directional droplet manipulation is very crucial in microfluidics, intelligent liquid management, etc. However, excessive liquid pressure tends to destroy the solid-gas-liquid (SAL) composite interface, creating a highly adhesive surface, which is not conducive to liquid transport. Herein, we propose a strategy to enhance the surface durability, in which the surface cannot withstand liquid pressure only by "blocking" but must instead guide liquid transport for "decompression". Learning from the water resistance of water strider legs and the drag reduction of shark skin, we present a continuous integrated system to obtain an ultrastable super-hydrophobic surface with a highly ordered scaly structure via a liquid flow-induced alignment method for lossless unidirectional liquid transport. The nonwetting scaly structure can both buffer liquid pressure and drive droplet motion to further reduce the vertical pressure of the liquid. Moreover, droplets can be manipulated unidirectionally using a voice. This work could aid in manufacturing scalable anisotropic micro-nanostructure surfaces, which inspires efforts in realizing lossless continuous liquid control on demand and related microfluidic applications.

Ultraviolet-Driven Janus Foams with Wetting Gradients: Unidirectional Penetration Control for Underwater Bubbles

Understanding the behavior of underwater bubbles and enabling their effective manipulation is important for bubble capture, collection, and transport. Here, to discuss the underwater permeation behavior of bubbles and critical influencing parameters in this process, the copper foams with tunable wettability were fabricated by utilizing the light-stimulated wettability response of TiO₂. The Janus copper foams had different wettability gradients from superhydrophobic/hydrophobic to superhydrophobic/hydrophilic after UV irradiation at different times, and the bubbles on the surfaces showed distinctly diverse penetration behaviors. In particular, the constructed superhydrophobic/hydrophilic surfaces showed more difficult to achieve bubble penetration than the fully superhydrophobic, superhydrophobic/hydrophobic surface. It was found that the wetting states of the foams exposed to different irradiation times underwater plays a crucial role in the bubble penetration behavior. In other words, the difficulty of bubble penetration depends on the difficulty of bubble transition from gas-liquid contact to gas-solid contact. This facile and low-cost fabrication approach for Janus foams provided a valuable approach to understand the penetration behaviors of underwater bubbles, which is significant for expanding potential applications in bubble capture, bubble transport, and control of unstable gas reactions in underwater conditions.

Liquid-Repellent Surfaces

Surfaces are vibrant sites for various activities with environments, especially as the transfer station for mass and energy exchange. In nature, natural creatures exhibit special wetting and interfacial properties such as water repellency and water affinity to adapt to various environmental challenges by taking advantage of air or liquid infusion media. Inspired by natural surfaces, various engineered liquid-repellent surfaces have been developed with a wide range of applications in both open and closed underwater environments. In particular, underwater conditions are characterized by high viscosity, high pressure, and complex compositions, which pose more challenges for the design of robust and functional repellent surfaces. In this Perspective, we take a parallel approach to introduce two classical liquid-repellent surfaces: an air-infused repellent surface and a lubricated liquid-repellent surface. Then we highlight fundamental challenges and design configurations of robust liquid-repellent surfaces both in air and underwater. We summarize the advantages and drawbacks of two kinds of repellent surfaces and list several applications of liquid-repellent surfaces for use in the ocean, medical care, and energy harvesting. Finally, we provide an outlook of research directions for robust liquid-repellent surfaces.

An interfacial floating tumbler with a penetrable structure and Janus wettability inspired by Pistia stratiotes

Designing advanced interfacial materials is decisive to the improvement of multiphase systems. Inspired by the superior floatability of Pistia stratiotes, here we present a superhydrophobic/hydrophilic 3D Janus floater with a water managing ability. Its self-regulated floatation mechanism, as well as its water removal logic, should provide insight into the development of multifunctional interfacial carriers in the fields of micro-devices, solar evaporation, etc.

Bioinspired Anisotropic Slippery Cilia for Stiffness-Controllable Bubble Transport

Bubbles play a crucial role in multidisciplinary industrial applications, e.g., heat transfer and mass transfer. However, existing methods to manipulate bubbles still face many challenges, such as buoyancy inhibition, hydrostatic pressure, gas dissolving, easy deformability, and so on. To circumvent these constraints, here we develop a bioinspired anisotropic slippery cilia surface to achieve an elegant bubble transport by tuning its elastic modulus, which results from the different contacts of bubbles with cilia, i.e., soft cilia will be easily bent by the bubble motion, while hard cilia will pierce into the bubble, consequently leading to the asymmetric three-phase contact line and resistance force. Moreover, a real-time and arbitrarily directional bubble manipulation is also demonstrated by applying an external magnetic field, enabling the scalable operation of bubbles in a remote manner. Our work exhibits a strategy of regulating bubble behavior smartly, which will update a wide range of gas-related sciences or technologies including gas evolution reactions, heat transfer, microfluidics, and so on.

Bioinspired Robust Water Repellency in High Humidity by Micro-meter-Scaled Conical Fibers: Toward a Long-Time Underwater Aerobic Reaction

Superhydrophobic surfaces have suffered from being frequently penetrated by micro-/nano-droplets in high humidity, which severely deteriorates their water repellency. So far, various biological models for the high water repellency have been reported, which, however, focused mostly on the structural topology with less attention on the dimension character. Here, we revealed a common dimension character of the superhydrophobic fibrous structures of both Gerris legs and Argyroneta abdomens, featured as the conical topology and the micro-meter-scaled cylindrical diameter. In particular, it can be expressed by using a parameter of rp/l > 0.75 μm (r, l, and p are the radius, length, and apex spacing between fibers, respectively). Drawing inspiration, we developed a superhydrophobic micro-meter-scaled conical fiber array with a rather high rp/l value of 0.85 μm, which endows ultra-high water repellency even in high humidity. The micro-meter-scale asymmetric confined space between fibers enables generating a big difference in the Laplace pressure enough to propel the condensed dews away, while the tips help pin the air pocket underwater with a rather long life over 41 days. Taking advantage, we demonstrated a sustainable underwater aerobic reaction where oxygen was continuously supplied from the trapped air pocket by a gradually diffusing process. As a parameter describing both the dimension character and structural topology, the rp/l offers a new perspective for fabricating superhydrophobic fibrous materials with robust water repellency in high humidity, which inspires the innovative underwater devices with a robust anti-wetting performance.

Impact of Bubbles on Electrochemically Active Surface Area of Microtextured Gas-Evolving Electrodes

The adverse effects of electrochemical bubbles on the performance of gas-evolving electrodes have been extensively studied. However, the ways in which bubbles dynamically alter the electrochemically active surface area during bubble evolution are not well understood. Here, we study hydrogen evolution at industrially relevant current densities by using controlled microtexture to examine this fundamental relationship. Surprisingly, the most densely microtextured electrodes have the lowest performance on an active surface area basis. Using high-speed imaging, we show that the benefits of microtexture to release smaller bubbles more consistently are outweighed by the inactivation induced by bubbles growing within the denser microtexture, causing these performance limitations. Additionally, we show that the area beneath adhered bubbles is electrochemically active, contrary to currently held assumptions. Our study therefore has broad implications for electrode design to avoid ineffective use of precious catalyst materials, which is especially critical for porous electrodes and three-dimensional structures with high specific surface areas.

Magnetic-Actuated Robot Enables High-Performance Underwater Bubble Maneuvering on Laser-Textured Biomimetic Slippery Surfaces

Controllable underwater gas bubble (UGB) transport on a surface is realized by geography-/stimuli-induced wettability gradient force (F_wet-grad). Unfortunately, the high-speed maneuvering of UGBs along free routes on planar surfaces remains challenging. Herein, a regime of magnetism-actuated robot (MAR) mounting on biomimetic laser-ablated lubricant-impregnated slippery surfaces (LA-LISS) is reported. Leveraging on LA-LISS, MAR-entrained UGBs can move along arbitrary directions through the loading of a tracing magnetic trigger. The underlying hydrodynamics is that MAR-entrained UGBs would be actuated slipping upon a giant magnetic-induced towing force (F_M//). Once the magnetism stimuli is discharged, F_M// vanishes immediately to immobilize the UGBs on LA-LISS. Thanks to the MAR's robust bubble affinity, a typical UGB (20 μL) on the optimized LA-LISS can be accelerated at 500 mm/s² and gain an ultrafast velocity of over 205 mm/s that far exceeds previously reported figures. Moreover, fundamental physics renders MAR antibuoyancy, steering locomotive UGBs on the inclined LA-LISS. Significantly, an MAR propelling UGBs to configure desirable patterns, realize on-demand coalescence, remedy the cutoff switch, as well as facilitate a programmable light-control-light optical shutter is successfully deployed. Compared with previous smart surfaces, the current multifunctional regime is more competent for harnessing UGBs featuring an unparalleled transport velocity independent of the feeble F_wet-grad.

Multi-Bioinspired Janus Copper Mesh for Improved Gravity-Irrelevant Directional Water Droplet and Flow Transport

A conceptually novel multi-bioinspired strategy based on structures and functions derived from the Namib desert beetle and lotus leaf is proposed in this paper. The proposed scheme synergistically combines the features of alternating wettability patterns and asymmetric wettability for improved directional water transport. Consequently, a Janus copper mesh, which substantially outperforms other single-bioinspired synthetic materials, is produced. The Janus copper mesh achieves directional self-transportation of tiny water droplets and continuous water flow in a gravity-irrelevant or an anti-gravity manner without energy consumption. This depends on the asymmetric wettability and alternating hydrophobic-hydrophilic wettability patterns on the hydrophobic surface of the mesh. In particular, Janus copper shows remarkable selective directional water transport in a water-oil system, rendering it a promising candidate for practical applications.

Environmentally Responsive Intelligent Dynamic Water Collector

Collecting water from fog flow is emerging as a promising solution to the water shortage problem. This work demonstrated a novel environmentally responsive water collector made from a self-prepared Janus polyvinyl alcohol sponge in combination with a two-way shape memory alloy spring, which transforms the traditional manner of static water collection into a dynamic one. The unidirectional water transport of the Janus structure together with the dynamic collection approach correspond to a 30.8% increase in the water-collection rate (WCR). The resultant WCR is up to 5.1 g/h, which ranks relatively high compared to similar studies. The light- and thermal-response capability, easy fabrication, and good cycling performance indicate that our devices could be utilized in a variety of applications. In this work, an efficient, intelligent adaptive, simple-preparation, precision-guided, and economical fog-collecting devices are recommended. Our work provides new insights on the design of high-efficient water collectors with practicability.

Ultrahigh-Current-Density and Long-Term-Durability Electrocatalysts for Water Splitting

Hydrogen economy is imagined where excess electric energy from renewable sources stored directly by electrochemical water splitting into hydrogen is later used as clean hydrogen fuel. Electrocatalysts with the superhigh current density (1000 mA cm^-2 -level) and long-term durability (over 1000 h), especially at low overpotentials (<300 mV), seem extremely critical for green hydrogen from experiment to industrialization. Along the way, numerous innovative ideas are proposed to design high efficiency electrocatalysts in line with industrial requirements, which also stimulates the understanding of the mass/charge transfer and mechanical stability during the electrochemical process. It is of great necessity to summarize and sort out the accumulating knowledge in time for the development of laboratory to commercial use in this promising field. This review begins with examining the theoretical principles of achieving high-efficiency electrocatalysts with high current densities and excellent durability. Special attention is paid to acquaint efficient strategies to design perfect electrocatalysts including atomic structure regulation for electrical conductivity and reaction energy barrier, array configuration constructing for mass transfer process, and multiscale coupling for high mechanical strength. Finally, the importance and the personal perspective on future opportunities and challenges, is highlighted.

Nanoarchitectonics for Electrospun Membranes with Asymmetric Wettability

Membranes with asymmetric wettability have attracted significant interest by virtue of their unique transport characteristics and functionalities arising from different wetting behaviors of each membrane surface. The cross-sectional wettability distinction enables a membrane to realize directional liquid transport or multifunction integration, resulting in rapid advance in applications, such as moisture management, fog collection, oil-water separation, and membrane distillation. Compared with traditional homogeneous membranes, these membranes possess enhanced transport performance and higher separation efficiency owing to the synergistic or individual effects of asymmetric wettability. This Review covers the recent progress in fabrication, transport mechanisms, and applications of electrospun membranes with asymmetric wettability and provides a perspective on future development in this important area.

Ultrafast Bubble Bursting by Superamphiphobic Coatings

Controlling bubble motion or passively bursting bubbles using solid interfaces is advantageous in numerous industrial applications including flotation, catalysis, electrochemical processes, and microfluidics. Current research has explored the formation, dissolution, pinning, and rupturing of bubbles on different surfaces. However, the ability to tune and control the rate of bubble bursting is not yet achieved. Scaling down surface-induced bubble bursting to just a few milliseconds is important for any application. In this work, the hierarchical structure of superamphiphobic surfaces is tuned in order to rapidly rupture contacting bubbles. Surfaces prepared using liquid flame spray show ultrafast bubble bursting (down to 2 ms) and superior durability. The coatings demonstrate excellent mechanical and chemical stability even in the presence of surface-active species. Air from the ruptured bubble is absorbed into the aerophilic Cassie-state. Long-term applicability is demonstrated by preventing the accumulation of air in the plastron via a connection of the plastron to the environment. The times recorded for bubble rupture and complete reorganization of air are reduced by approximately a factor of 3 compared to previously reported values. The concept is utilized to passively control surfactant-rich foam in froth flotation. Material collection efficiency increased by more than 60 times compared to controls.

Efficient Mesh Interface Engineering: Insights from Bubble Dynamics in Electrocatalysis

Electrochemical catalysis offers great potential in energy and mass conversion in academy and industry. However, bubble dynamics and its influence on gas-evolving electrode systems remain ambiguous. Detailed information on the local transport process between different phases and the underlying mechanism are required for the full understanding of two-phase flow evolution and distribution. Here, we construct a three-electrode water splitting reaction system to study the bubble dynamics and system efficiency of titanium electrodes with different morphologies. The dynamics of a gas bubble at an electrode with a plate and 100-mesh, 150-mesh, and 300-mesh structures is systematically investigated with respect to applied voltage conditions. Parameters and underlying mechanisms that influence the two-phase flow evolution and electrochemical reaction performance are carefully discussed. Finally, the underlying dynamic force balance on the gas bubble is analyzed to illustrate the mechanism and experimental observations. Our study provides insights in gas-evolving electrocatalysis and offers opportunities for the design and fabrication of high-performance electrocatalytic reactors.

Plasma-Induced Defect Engineering and Cation Refilling of NiMoO4 Parallel Arrays for Overall Water Splitting

Developing highly active water splitting electrocatalysts with ordered micro/nanostructures and uniformly distributed active sites can meet the increasing requirement for sustainable energy storage/utilization technologies. However, the stability of complicated structures and active sites during a long-term process is also a challenge. Herein, we fabricate a novel approach to create sufficient atomic defects via N₂ plasma treatment onto parallel aligned NiMoO₄ nanosheets, followed by refilling of these defects via heterocation dopants and stabilizing them by annealing. The parallel aligned nanosheet arrays with an open structure and quasi-two-dimensional long-range diffusion channels can accelerate the mass transfer at the electrolyte/gas interface, while the incorporation of Fe/Pt atoms into defect sites can modulate the local electronic environment and facilitate the adsorption/reaction kinetics. The optimized Pt-NP-NMC/CC-5 and Fe-NP-NMC/CC-10 electrodes exhibit low overpotentials of 71 and 241 mV at 10 mA cm^-2 for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), respectively, and the assembled device reveals a low voltage of 1.55 V for overall water splitting. This plasma-induced high-efficiency defect engineering and coupled active site stabilization strategy can be extended to large-scale fabrication of high-end electrocatalysts.

Self-Stratified Versatile Coatings for Three-Dimensional Printed Underwater Physical Sensors Applications

A new strategy for developing versatile nanostructured surfaces utilizing the swelling of polymers in solvents is described. The self-stratified coating on 3D printed acrylonitrile-butadiene-styrene (ABS) copolymers with nanoparticles enables mechanically durable superhydrophobic characteristics. Unlike other methods, it was capable to produce superhydrophobicity on complex 3D structured surfaces. Mechanically durable superhydrophobic coatings that can withstand an abrasion cycle were obtained. Partial embedding of the nanoparticles into the ABS surface due to the swelling and self-stratification is considered as the reason for the increased mechanical strength of the coating. Utilizing this idea, the original concept of power-free physical sensors responding to changes in temperature, pressure, and surface tension was proposed.

Bioinspired Universal Approaches for Cavity Regulation during Cylinder Impact Processes for Drag Reduction in Aqueous Media: Macrogeometry Vanquishing Wettability

Stabilizing lubricating gas films at the solid-liquid interface is a promising strategy for underwater drag reduction. It has been restricted by the enormous extra energy input and the poor stability of superhydrophobic coatings. Cavity encapsulation is a valid method to improve and maintain the formation of the air layer on the solid surface, which is created by the rapidly impacting process on a water surface. The wettability of solid objects (the combination of the surface roughness and chemical component) and liquid properties played a key factor in determining the water impact process for cavity entrainment. However, inspired by the striking behavior of basilisk lizards and their toe's shape, we found that the geometric shape of solid objects plays an equally important role in cavity entrainment and stabilization, which is often ignored. Herein, we present a universal strategy to retain the air cavity on the cylinder surfaces. The cavity can be retained not only on the surface of superhydrophobic cylinders but also on the surface of hydrophobic, hydrophilic, and even superhydrophilic cylinders, without bursting at a depth of 70.0-90.0 cm underwater. The retaining cavity enfolds the profile and upper sides of the cylinder and changes its shape to a streamlined body to achieve underwater drag reduction. In addition, optimizing the cylinders' shapes by increasing the fillet radii significantly improved the drag reduction efficiency from 64.2 to 70.5%.

A membrane-less electrolyzer with porous walls for high throughput and pure hydrogen production

Membrane-less electrolyzers utilize fluidic forces instead of solid barriers for the separation of electrolysis gas products. These electrolyzers have low ionic resistance, a simple design, and the ability to work with electrolytes at different pH values. However, the interelectrode distance and the flow velocity should be large at high production rates to prevent gas cross over. This is not energetically favorable as the ionic resistance is higher at larger interelectrode distances and the required pumping power increases with the flow velocity. In this work, a new solution is introduced to increase the throughput of electrolyzers without the need for increasing these two parameters. The new microfluidic reactor has three channels separated by porous walls. The electrolyte enters the middle channel and flows into the outer channels through the wall pores. Gas products are being produced in the outer channels. Hydrogen cross over is 0.14% in this electrolyzer at flow rate = 80 mL h^-1 and current density (j) = 300 mA cm^-2. This cross over is 58 times lower than hydrogen cross over in an equivalent membrane-less electrolyzer with parallel electrodes under the same working conditions. Moreover, the addition of a surfactant to the electrolyte further reduces the hydrogen cross over by 21% and the overpotential by 1.9%. This is due to the positive effects of surfactants on the detachment and coalescence dynamics of bubbles. The addition of the passive additive and implementation of the porous walls result in twice the hydrogen production rate in the new reactor compared to parallel electrode electrolyzers with similar hydrogen cross over.

Light-driven Locomotion of Underwater Bubbles on Ultrarobust Paraffin-impregnated Laser-ablated Fe3O4-doped Slippery Surfaces

Manipulating underwater bubbles (UGBs) is realized on morphology-tailored or stimuli-responsive slippery lubricant-impregnated porous surface (SLIPS). Unfortunately, the volatile lubricants (e. g., silicone oil, ferrofluid) greatly decrease their using longevity. Designed is light-responsive paraffin-infused Fe₃O₄-doped slippery surface (LR-PISS) by incorporation of hybrid lubricants and superhydrophobic micropillar-arrayed elastometric membranes resulted from one-step femtosecond laser vertically scanning. Upon LR-PISS, the dynamic motion control bwteen pinning and sliding along free routes over UGB could be realized by alternately loading/discharging NIR-trigger. The underlying principle is that when the NIR was applied, UGB would be actuated to slide along the NIR trace because the irradiated domain melts for a slippery surface within 1.0 s. Once the NIR is removed, the liquefied paraffin would be reconfigured to solid phase for pinning a moving UGB within 0.5 s. Newly explored hydrokinetics imparts us with capability of steering UGBs to arrange any desirable patterns and switch light-path behaving as the light-control-light optical shutter. In comparison with previously reported SLIPS, current LR-PISS unfolds unparalleled ultrarobust antidisturbance ability even in flowing liquid ambient. More significantly, even subjected to physical damage, underwater LR-PISS is capable of in situ self-healing within 13 s under the assistance of remote NIR. The results here could inspire the design of robust bubble manipulator and further boost their applications in optofluidics and all-optical modulators.

Robust superhydrophobicity: mechanisms and strategies

Superhydrophobic surfaces hold great prospects for extremely diverse applications owing to their water repellence property. The essential feature of superhydrophobicity is micro-/nano-scopic roughness to reserve a large portion of air under a liquid drop. However, the vulnerability of the delicate surface textures significantly impedes the practical applications of superhydrophobic surfaces. Robust superhydrophobicity is a must to meet the rigorous industrial requirements and standards for commercial products. In recent years, major advancements have been made in elucidating the mechanisms of wetting transitions, design strategies and fabrication techniques of superhydrophobicity. This review will first introduce the mechanisms of wetting transitions, including the thermodynamic stability of the Cassie state and its breakdown conditions. Then we highlight the development, current status and future prospects of robust superhydrophobicity, including characterization, design strategies and fabrication techniques. In particular, design strategies, which are classified into passive resistance and active regeneration for the first time, are proposed and discussed extensively.

Recent advances in femtosecond laser-structured Janus membranes with asymmetric surface wettability

Janus wettability membranes have received much attention because of their asymmetric surface wettability. On the basis of this distinctiveness from traditional symmetrical membranes, relevant scholars have been inspired to pursue many innovations utilizing such membranes. Femtosecond laser microfabrication shows many advantages, such as precision, short time, and environmental friendliness, over traditional fabrication methods. Now this has been applied in structuring Janus membranes by researchers. This review covers recent advances in femtosecond laser-structured Janus membranes with asymmetric surface wettability. The background in femtosecond laser-structured Janus membranes is first discussed, focusing on the Janus wettability membrane and femtosecond laser microfabrication. Then the applications of Janus membranes are introduced, which are divided into unidirectional fluid transport, oil-water separation, fog harvesting, and seawater desalination. Finally, based on femtosecond laser-structured Janus membranes, some existing problems are pointed out and future perspectives proposed.