Superwettability of Gas Bubbles and Its Application: From Bioinspiration to Advanced Materials

Enhancing electrochemical water-splitting efficiency with superaerophobic nickel-coated catalysts on Chinese rice paper

The quest for efficient hydrogen production highlights the need for cost-effective and high-performance catalysts to enhance the electrochemical water-splitting process. A significant challenge in developing self-supporting catalysts lies in the high cost and complex modification of traditional substrates. In this study, we developed catalysts featuring superaerophobic microstructures engineered on microspherical nickel-coated Chinese rice paper (Ni-RP), chosen for its affordability and exceptional ductility. These catalysts, due to their microspherical morphology and textured surface, exhibited significant superaerophobic properties, substantially reducing bubble adhesion. The nickel oxy-hydroxide (NiOxHy) and phosphorus-doped nickel (PNi) catalysts on Ni-RP demonstrated effective roles in oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), achieving overpotentials of 250 mV at 20 mA cm-2 and 87 mV at -10 mA cm-2 in 1 M KOH, respectively. Moreover, a custom water-splitting cell using PNi/Ni-RP and NiOxHy/Ni-RP electrodes reached an impressive average voltage of 1.55 V at 10 mA cm-2, with stable performance over 100 h in 1 M KOH. Our findings present a cost-effective, sustainable, and easily modifiable substrate that utilizes superaerophobic structures to create efficient and durable catalysts for water splitting. This work serves as a compelling example of designing high-performance self-supporting catalysts for electrocatalytic applications.

General Design of Aligned-Channel Porous Carbon Electrodes for Efficient High-Current-Density Gas-Evolving Electrocatalysis

Gas-evolving reactions (GERs) are important in many electrochemical energy conversion technologies and chemical industries. The operation of GERs at high current densities is critical for their industrial implementation but remains challenging as it poses stringent requirements on the electrodes in terms of reaction kinetics, mass transfer, and electron transport. Here the general and rational design of self-standing carbon electrodes with vertically aligned porous channels, appropriate pore size distribution, and high surface area as supports for loading a variety of catalytic species by facile electrodeposition are reported. These electrodes simultaneously possess high intrinsic activity, large numbers of active sites, and efficient transport highways for ions, gases, and electrons, resulting in significant performance improvements at high current densities in diverse GERs such as urea oxidation, hydrogen evolution, and oxygen evolution reactions, as well as overall urea/water electrolyzers. As an example, the carbon electrode decorated with Ni(OH)2 demonstrates a record-high current density of 1000 mA cm-2 at 1.360 V versus the reversible hydrogen electrode, largely outperforming the conventional nickel foam-based counterpart and the state-of-the-art electrodes.

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.

Self-Driven Gas Spreading on Mesh Surfaces for Regeneration of Underwater Superhydrophobicity

Underwater superhydrophobic surfaces stand as a promising frontier in technological applications such as drag reduction, antifouling, and anticorrosion. Unfortunately, the air film, known as the plastron, on these surfaces tends to be unstable. To address this problem, active approaches have been designed to preserve or restore plastrons. In this work, a self-driven gas spreading superhydrophobic mesh (SHM) surface is designed to facilitate recovery of the plastron. The immersed SHM can be "wetted" by gas, even when the plastron is removed. We demonstrate that the injected gas can spread spontaneously along the SHM over a large area, which greatly simplifies the plastron replenishment process. By incorporating a locally coated gas-producing layer, we achieve rapid in situ plastron recovery and long-term immersion stability, extending the plastron lifespan by at least 48 times. We also provide a framework for designing an SHM with suitable structural dimensions for gas spreading. Furthermore, an SHM with asymmetric structural dimensions enables unidirectional gas transport by the capillary pressure difference. This SHM surface shows excellent drag reduction properties (37.2%) and has a high slip recovery coefficient (73.4%) after plastron loss. This facile and scalable method is expected to broaden the range of potential applications involving nonwetting-related fields.

Hydrophobicity Promoted Efficient Hydroxyl Radical Generation in Visible-Light-Driven Photocatalytic Oxidation

Hydroxyl radical (•OH) with strong oxidation capability is one of the most important reactive oxygen species. The generation of •OH from superoxide radicals (•O2 -) is an important process in visible-light-driven photocatalysis, but the conversion generally suffers from slow reaction kinetics. Here, a hydrophobicity promoted efficient •OH generation in a visible-light-driven semiconductor-mediated photodegradation reaction is reported. Hydrophobic TiO2 that is synthesized by modifying the TiO2 surface with a thin polydimethylsiloxane (PDMS) layer and rhodamine B (RhB) are used as model semiconductors and dye molecules, respectively. The surface hydrophobicity resulted in the formation of a solid-liquid-air triphase interface microenvironment, which increased the local concentration of O2. In the meanwhile, the saturated adsorption quantity of RhB on hydrophobic TiO2 is improved by five-fold than that on untreated TiO2. These advantages increased the density of the conduction band photoelectrons and •O2 - generation, and stimulated the conversion of •O2 - to •OH. This consequently not only increased the kinetics of the photocatalytic reaction by an order of magnitude, but also altered the oxidation route from conventional decolorization to mineralization. This study highlights the importance of surface wettability modulation in boosting •OH generation in visible-light-driven photocatalysis.

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.

Flexible nanohybrid substrates utilizing gold nanocubes/nano mica platelets with 3D lightning-rod effect for highly efficient bacterial biosensors based on surface-enhanced Raman scattering

In this study, gold nanocubes (AuNCs) were quickly synthesized using the seed-mediated growth method and reduced onto the surface of two-dimensional (2D) delaminated nano mica platelets (NMPs), enabling the development of AuNCs/NMPs nanohybrids with a 3D lightning-rod effect. First, the growth-solution amount can be changed to easily adjust the AuNCs average-particle size within a range of 30-70 nm. The use of the cationic surfactant cetyltrimethylammonium chloride as a protective agent allowed the surface of AuNCs and nanohybrids to be positively charged. Positively charged nanohybrid surfaces presented a good adsorption effect for detecting molecules with negative charges on the surface. Additionally, the NMP surfaces were rich in ionic charges and provided a large specific surface area for stabilizing the growth of AuNCs. Delaminated AuNCs/NMPs nanohybrids can generate a 3D hotspot effect through self-assembly to enhance the Raman signal. Surface-enhanced Raman scattering (SERS) is highly sensitive in detecting adenine biomolecules. Its limit of detection (LOD) and Raman enhancement factor reached 10-9 M and 3.6 × 108, respectively. Excellent reproducibility was obtained owing to the relatively regular arrangement of AuNC particles, and the relative standard deviation (RSD) was 10.7%. Finally, the surface of NMPs was modified by adding the hydrophilic poly(oxyethylene)-diamine (POE2000) and amphiphilic PIB-POE-PIB copolymer at different weight ratios. The adjustment of the surface hydrophilicity and hydrophobicity of AuNCs/NMPs nanohybrids led to better adsorption and selectivity for bacteria. AuNCs/POE/NMPs and AuNCs/PIB-POE-PIB/NMPs were further applied to the SERS detection of hydrophilic Staphylococcus aureus and hydrophobic Escherichia coli, respectively. The SERS-detection results suggest that the LOD of hydrophilic Staphylococcus aureus and hydrophobic Escherichia coli reached 92 CFU mL-1 and 1.6 × 102 CFU mL-1, respectively. The AuNCs/POE/NMPs and AuNCs/PIB-POE-PIB/NMPs nanohybrids had different hydrophilic-hydrophobic affinities, which greatly improved the selectivity and sensitivity for detecting bacteria with different hydrophilicity and hydrophobicity. Therefore, fast, highly selective, and highly sensitive SERS biological-detection results were obtained.

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.

Multifunctional MnFe2O4/TiO2/Ti3C2Tx composites based on in-situ grown TiO2 for efficient microwave absorption, high hydrophobicity, and heat dissipation properties

Despite the fact that the 2D structure Ti3C2Tx with abundant defects and functional groups contributes to the high microwave absorption (MA) performance, it is difficulty to improve the strength and bandwidth by pursuing higher conductivity or loading more groups due to the limitation of intrinsic properties. Therefore, it is important to ingeniously design efficient Ti3C2Tx based MA composites assembling the features of abundant surface groups, good dispersibility, multiple composition, and precise structure. Inspired by the fact that Ti3C2Tx contains thermodynamically metastable marginal Ti atoms, TiO2 nanoparticles can be grown in-situ on Ti3C2Tx nanosheets uniformly and increase the spacing of Ti3C2Tx layers, and then MnFe2O4 nanoparticles are introduced into the layers of Ti3C2Tx by electrostatic self-assembly method for optimized impedance matching. This designed hierarchical MnFe2O4/TiO2/Ti3C2Tx composites shows excellent MA performance, and the minimum reflection loss (RLmin) reaches -46.91 dB with a thickness of 2.5 mm at frequency of 10.4 GHz. The high MA performance mainly comes from the enhanced interfacial polarization induced by edges location and interface region among TiO2, MnFe2O4, and Ti3C2Tx. In addition, the conduction loss existed in the interior untreated Ti3C2Tx, the dielectric loss generated by multiple composition, the multiple scattering from improved large surface specific area all contribute to the excellent MA performance. Meanwhile, the simple preparation process and good stability storage at room temperature under air atmosphere of the MnFe2O4/TiO2/Ti3C2Tx composites promote its exploration on practical use, and the lab-gown cloth coated with MnFe2O4/TiO2/Ti3C2Tx composites shows better electromagnetic shielding properties, hydrophobicity, and heat transfer ability than pure fabric, showing the potential for practical application.

Review on Bubble Dynamics in Proton Exchange Membrane Water Electrolysis: Towards Optimal Green Hydrogen Yield

Water electrolysis using a proton exchange membrane (PEM) holds substantial promise to produce green hydrogen with zero carbon discharge. Although various techniques are available to produce hydrogen gas, the water electrolysis process tends to be more cost-effective with greater advantages for energy storage devices. However, one of the challenges associated with PEM water electrolysis is the accumulation of gas bubbles, which can impair cell performance and result in lower hydrogen output. Achieving an in-depth knowledge of bubble dynamics during electrolysis is essential for optimal cell performance. This review paper discusses bubble behaviors, measuring techniques, and other aspects of bubble dynamics in PEM water electrolysis. It also examines bubble behavior under different operating conditions, as well as the system geometry. The current review paper will further improve the understanding of bubble dynamics in PEM water electrolysis, facilitating more competent, inexpensive, and feasible green hydrogen production.

Bioinspired Hydrophobicity for Enhancing Electrochemical CO2 Reduction

Electrochemical carbon dioxide reduction (CO2 R) is a promising pathway for converting greenhouse gasses into valuable fuels and chemicals using intermittent renewable energy. Enormous efforts have been invested in developing and designing CO2 R electrocatalysts suitable for industrial applications at accelerated reaction rates. The microenvironment, specifically the local CO2 concentration (local [CO2 ]) as well as the water and ion transport at the CO2 -electrolyte-catalyst interface, also significantly impacts the current density, Faradaic efficiency (FE), and operation stability. In nature, hydrophobic surfaces of aquatic arachnids trap appreciable amounts of gases due to the "plastron effect", which could inspire the reliable design of CO2 R catalysts and devices to enrich gaseous CO2 . In this review, starting from the wettability modulation, we summarize CO2 enrichment strategies to enhance CO2 R. To begin, superwettability systems in nature and their inspiration for concentrating CO2 in CO2 R are described and discussed. Moreover, other CO2 enrichment strategies, compatible with the hydrophobicity modulation, are explored from the perspectives of catalysts, electrolytes, and electrolyzers, respectively. Finally, a perspective on the future development of CO2 enrichment strategies is provided. We envision that this review could provide new guidance for further developments of CO2 R toward practical applications.

Manipulation of bubble collapse patterns near the wall of an adherent gas layer

This paper aims to apply experimental methods to investigate the effect of the thickness of gas layers on the wall on the collapse direction of spark-induced bubbles. In the experiment, two high-speed cameras synchronously record the time evolution of the bubbles and the corresponding parameters such as the normalized collapse position and bubble collapse time. Experiments yielded results for individual bubbles over a range of normalized distances from 0 to 4.0 for different air layer thicknesses. Based on the morphology of the bubbles, the experimental jets were visualized into six different modes, namely, forward jet (FJ), merging jet (MJ), bidirectional jet (BJ), reversing jet (RJ), forward followed by reversing jet (FRJ), and non-directional jet (NDJ). The height of the air layer on the wall is affected by the fluctuation of the bubble volume and shows the opposite trend to the change of the bubble volume. The air film reaches its maximum height when the bubble collapses, which affects the final jet pattern. In addition, as the thickness of the air layer increases, the center of the bubble gradually migrates away from the wall. The different collapse modes and the migration of the bubble centers have positive significance for reducing cavitation erosion in engineering.

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.

The Secret of Nanoarrays toward Efficient Electrochemical Water Splitting: A Vision of Self-Dynamic Electrolyte

Nanoarray electrocatalysts with unique advantage of facilitating gas bubble detachment have garnered significant interest in gas evolution reactions (GERs). Existing research is largely based on a static hypothesis, assuming that buoyancy is the only driving force for the release of bubbles during GERs. However, this hypothesis overlooks the effect of the self-dynamic electrolyte flow, which is induced by the release of mature bubbles and helps destabilize and release the smaller, immature bubbles nearby. Herein, the enhancing effect of self-dynamic electrolyte flow on nanoarray structures is examined. Phase-field simulations demonstrate that the flow field of electrode with arrayed surface focuses shear force directly onto the gas bubble for efficient detachment, due to the flow could pass through voids and channels to bypass the shielding effect. The flow field therefore has a more substantial impact on the arrayed surface than the nanoscale smooth surface in terms of reducing the critical bubble size. To validate this, superaerophobic ferrous-nickel sulfide nanoarrays are fabricated and employed for water splitting, which display improved efficiency for GERs. This study contributes to understanding the influence of self-dynamic electrolyte on GERs and emphasizes that it should be considered when designing and evaluating nanoarray electrocatalysts.

Long-term stability of aerophilic metallic surfaces underwater

Aerophilic surfaces immersed underwater trap films of air known as plastrons. Plastrons have typically been considered impractical for underwater engineering applications due to their metastable performance. Here, we describe aerophilic titanium alloy (Ti) surfaces with extended plastron lifetimes that are conserved for months underwater. Long-term stability is achieved by the formation of highly rough hierarchically structured surfaces via electrochemical anodization combined with a low-surface-energy coating produced by a fluorinated surfactant. Aerophilic Ti surfaces drastically reduce blood adhesion and, when submerged in water, prevent adhesion of bacteria and marine organisms such as barnacles and mussels. Overall, we demonstrate a general strategy to achieve the long-term stability of plastrons on aerophilic surfaces for previously unattainable underwater applications.

Engineering hydrophobic-aerophilic interfaces to boost N2 diffusion and reduction through functionalization of fluorine in second coordination spheres

Ammonia is a crucial biochemical raw material for nitrogen containing fertilizers and a hydrogen energy carrier obtained from renewable energy sources. Electrocatalytic ammonia synthesis is a renewable and less-energy intensive way as compared to the conventional Haber-Bosch process. The electrochemical nitrogen reduction reaction (eNRR) is sluggish, primarily due to the deceleration by slow N2 diffusion, giving rise to competitive hydrogen evolution reaction (HER). Herein, we have engineered a catalyst to have hydrophobic and aerophilic nature via fluorinated copper phthalocyanine (F-CuPc) grafted with graphene to form a hybrid electrocatalyst, F-CuPc-G. The chemically functionalized fluorine moieties are present in the second coordination sphere, where it forms a three-phase interface. The hydrophobic layer of the catalyst fosters the diffusion of N2 molecules and the aerophilic characteristic helps N2 adsorption, which can effectively suppress the HER. The active metal center is present in the primary sphere available for the NRR with a viable amount of H+ to achieve a substantially high faradaic efficiency (FE) of 49.3% at -0.3 V vs. RHE. DFT calculations were performed to find out the rate determining step and to explore the full energy pathway. A DFT study indicates that the NRR process follows an alternating pathway, which was further supported by an in situ FTIR study by isolating the intermediates. This work provides insights into designing a catalyst with hydrophobic moieties in the second coordination sphere together with the aerophilic nature of the catalyst that helps to improve the overall FE of the NRR by eliminating the HER.

Bioinspired Hydrophobicity Coupled with Single Fe-N4 Sites Promotes Oxygen Diffusion for Efficient Zinc-Air Batteries

The poor oxygen diffusion and sluggish oxygen reduction reaction (ORR) kinetics at multiphase interfaces in the cathode suppress the practical application of zinc-air batteries. Developing effective strategies to tackle the issue is of great significance for overcoming the performance bottleneck but remains challenging. Here, a multiscale hydrophobic surface is designed on the iron single-atom catalyst via a gas-phase fluorination-assisted method inspired by the structure of gas-trapping mastoids on lotus leaves. The hydrophobic Fe-FNC attains a higher peak power density of up to 226 mW cm^-2 , a long durability of up close to 140 h, and better cyclic durability of up to 300 cycles compared to the corresponding Pt/C-based Zn-air battery. Experiments and theoretical calculations indicate that the formed more triple-phase interfaces and exposed isolated Fe-N₄ sites are proposed as the governing factors in boosting electrocatalytic ORR activity and remarkable cycling durability for Zn-air batteries.

Self-Driving Underwater "Aerofluidics"

Here, the concept of "aerofluidics," in which a system uses microchannels to transport and manipulate trace gases at the microscopic scale to build a highly versatile integrated system based on gas-gas or gas-liquid microinteractions is proposed. A kind of underwater aerofluidic architecture is designed using superhydrophobic surface microgrooves written by a femtosecond laser. In the aqueous medium, a hollow microchannel is formed between the superhydrophobic microgrooves and the water environment, which allows gas to flow freely underwater for aerofluidic devices. Driven by Laplace pressure, gas can be self-transported along various complex patterned paths, curved surfaces, and even across different aerofluidic devices, with an ultralong transportation distance of more than 1 m. The width of the superhydrophobic microchannels of the designed aerofluidic devices is only ≈42.1 µm, enabling the aerofluidic system to achieve accurate gas transportation and control. With the advantages of flexible self-driving gas transportation and ultralong transportation distance, the underwater aerofluidic devices can realize a series of gas control functions, such as gas merging, gas aggregation, gas splitting, gas arrays, gas-gas microreactions, and gas-liquid microreactions. It is believed that underwater aerofluidic technology can have significant applications in gas-involved microanalysis, microdetection, biomedical engineering, sensors, and environmental protection.

Unraveling the hydrophobic interaction mechanisms of hydrocarbon and fluorinated surfaces

HYPOTHESIS

Numerous hydrocarbon and fluorine-based hydrophobic surfaces have been widely applied in various engineering and bioengineering fields. It is hypothesized that the hydrophobic interactions of hydrocarbon and fluorinated surfaces in aqueous media would show some differences.

EXPERIMENTS

The hydrophobic interactions of hydrocarbon and fluorinated surfaces with air bubbles in aqueous solutions have been systematically and quantitatively measured using a bubble probe atomic force microscopy (AFM) technique. Ethanol was introduced to water for modulating the solution polarity. The experimental force profiles were analyzed using a theoretical model combining the Reynolds lubrication theory and augmented Young-Laplace equation by including disjoining pressure arisen from the Derjarguin-Landau-Verwey-Overbeek (DLVO) and non-DLVO interactions (i.e., hydrophobic interactions).

FINDINGS

The experiment results show that the hydrophobic interactions were firstly weakened and then strengthened by increasing ethanol content in the aqueous media, mainly due to the variation in interfacial hydrogen bonding network. The fluorinated surface exhibited less sensitivity to ethanol than hydrocarbon surface, which is attributed to the presence of ordered interfacial water layer. Our work reveals the different hydrophobic effects of hydrocarbon and fluorinated surfaces, with useful implications on modulating the interfacial interactions of relevant materials in various engineering and bioengineering applications.

Water Spider-Inspired Nanofiber Coating with Sustainable Scale Repellency via Air-Replenishing Strategy

To survive underwater even in severely hypoxic water for a long period, the water spider has to periodically collect and replenish air into the diving bell. Inspired by this natural air-replenishing strategy, a water spider-inspired nanofiber (WSN) coating with underwater superaerophilicity displaying excellent and sustainable scalephobic capability is prepared. Air film on the WSN coating can be well-kept and further employed as the barrier layer for scale repellence. Significantly, scalephobic capability of the WSN coating mainly originates from two aspects: inhibiting interfacial nucleation and reducing interfacial adhesion of scale. Compared with previous studies, this WSN coating achieves excellent and sustainable scale repellence (≈ 98% reduction in scale deposition) even after a one-month dynamic scaling test. Thus, this air-replenishing strategy may raise a new avenue for advanced long-term scalephobic materials.

Bioinspired and Bioderived Aqueous Electrocatalysis

The development of efficient and sustainable electrochemical systems able to provide clean-energy fuels and chemicals is one of the main current challenges of materials science and engineering. Over the last decades, significant advances have been made in the development of robust electrocatalysts for different reactions, with fundamental insights from both computational and experimental work. Some of the most promising systems in the literature are based on expensive and scarce platinum-group metals; however, natural enzymes show the highest per-site catalytic activities, while their active sites are based exclusively on earth-abundant metals. Additionally, natural biomass provides a valuable feedstock for producing advanced carbonaceous materials with porous hierarchical structures. Utilizing resources and design inspiration from nature can help create more sustainable and cost-effective strategies for manufacturing cost-effective, sustainable, and robust electrochemical materials and devices. This review spans from materials to device engineering; we initially discuss the design of carbon-based materials with bioinspired features (such as enzyme active sites), the utilization of biomass resources to construct tailored carbon materials, and their activity in aqueous electrocatalysis for water splitting, oxygen reduction, and CO2 reduction. We then delve in the applicability of bioinspired features in electrochemical devices, such as the engineering of bioinspired mass transport and electrode interfaces. Finally, we address remaining challenges, such as the stability of bioinspired active sites or the activity of metal-free carbon materials, and discuss new potential research directions that can open the gates to the implementation of bioinspired sustainable materials in electrochemical devices.

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.

Fast Capture, Collection, and Targeted Transfer of Underwater Gas Bubbles Using Janus-Faced Carbon Cloth Prepared by a Novel and Simple Strategy

Transportation of bubbles in liquids in a controlled fashion is a challenging task and an important subject in numerous industrial processes, including elimination of corrosive gas bubbles in fluid transportation pipes, water electrolysis, reactions between gases, heat transfer, etc. Using superaerophilic surfaces represents a promising solution for bubble movement in a programmed way. Here, a novel and low-cost method is introduced for the preparation of Janus-faced carbon cloth (Janus-CC) using poly(dimethylsiloxane) (PDMS) coating and then burning one side of the carbon cloth/PDMS on an alcoholic burner. The results show that the superhydrophobic face behaves as a superaerophilic surface, while the superhydrophilic side is aerophobic underwater. Subsequently, the Janus-CC is applied for pumpless transport of underwater gas bubbles even under harsh conditions. The movement of gas bubbles on the surface of the Janus-CC is interpreted based on the formed gaseous film on the aerophilic side of the Janus-CC. Various applications of the prepared Janus-CC for underwater bubble transportation, such as underwater gas distributor, gas collector membrane, gas transport for chemical reactions, unidirectional gas membrane, and elimination of gas bubbles in transport pipe, are presented.

Controllable Fabrication of Durable, Underliquid Superlyophobic Surfaces Based on the Lyophilic-Lyophobic Balance

Surfaces possessing desirable underliquid special wettability, particularly underliquid dual superlyophobicity, have a high potential for extensive applications. However, there is still a lack of controllable preparation strategies to regulate the underliquid wettability via balancing the underliquid lyophilicity-lyophobicity. Herein, we develop a nanocomposite coating system comprising silica nanoparticles (NPs), glycerol propoxylate triglycidyl ether (GPTE), and fluorinated alkyl silane (FAS) to obtain controllable underliquid special wettability surfaces. FAS is the vital factor in guiding the preparation of the surface coating with expected underliquid superwettability. Increasing the FAS content results in a tendency toward underwater superoleophobicity/underoil hydrophilicity to underwater oleophilicity/underoil superhydrophobicity. Significantly, the underliquid dual superlyophobic surface can be achieved when an appropriate FAS content is located. After the coating treatment, the fabric exhibits superamphiphilicity in air and superlyophobicity in liquid (i.e., exhibiting both underwater superoleophobicity and underoil superhydrophobicity). The coating also exhibits an adaptable antioil fouling ability and high durability against harsh environments. Furthermore, oil/water separation based on the underliquid dual superlyophobicity of coated fabrics is successfully demonstrated. Our work proposes a new fabrication principle for the design of underliquid special wettability surfaces and offers broad applications, such as switchable oil/water separation, antibiofouling, liquid manipulation, and smart textiles.

Constructing Unique Mesoporous Carbon Superstructures via Monomicelle Interface Confined Assembly

Constructing hierarchical three-dimensional (3D) mesostructures with unique pore structure, controllable morphology, highly accessible surface area, and appealing functionality remains a great challenge in materials science. Here, we report a monomicelle interface confined assembly approach to fabricate an unprecedented type of 3D mesoporous N-doped carbon superstructure for the first time. In this hierarchical structure, a large hollow locates in the center (∼300 nm in diameter), and an ultrathin monolayer of spherical mesopores (∼22 nm) uniformly distributes on the hollow shells. Meanwhile, a small hole (4.0-4.5 nm) is also created on the interior surface of each small spherical mesopore, enabling the superstructure to be totally interconnected. Vitally, such interconnected porous supraparticles exhibit ultrahigh accessible surface area (685 m² g^-1) and good underwater aerophilicity due to the abundant spherical mesopores. Additionally, the number (70-150) of spherical mesopores, particle size (22 and 42 nm), and shell thickness (4.0-26 nm) of the supraparticles can all be accurately manipulated. Besides this spherical morphology, other configurations involving 3D hollow nanovesicles and 2D nanosheets were also obtained. Finally, we manifest the mesoporous carbon superstructure as an advanced electrocatalytic material with a half-wave potential of 0.82 V (vs RHE), equivalent to the value of the commercial Pt/C electrode, and notable durability for oxygen reduction reaction (ORR).

Myriophyllum spicatum Leaves: Aerophily for Gas Collection and Transportation in Water

The unique living environment of aquatic plants makes them produce many fantastic properties different from land ones. For instance, the leaves of Myriophyllum spicatum show excellent hydrophobicity and aerophily characteristics. In this paper, the abundant morphological structure, composition, and aerophily properties of Myriophyllum spicatum leaves are revealed. The contact angle of the leaf surface can reach 122° in air, exhibiting wonderful gas collection ability under water. The results showed that the aerophily of the leaves is attributed to the multistage micro-nanostructure and waxy layer on the surface. The gas transportation toward the tips of leaves is based on the void gradient formed by the nanoscale morphology at different growth stages and the buoyancy as well. These features provide bionic experience for gas collection, bubble transportation, and liquid resistance reduction in water environments.

Hydrophobization Engineering of the Air-Cathode Catalyst for Improved Oxygen Diffusion towards Efficient Zinc-Air Batteries

Poor oxygen diffusion at multiphase interfaces in an air cathode suppresses the energy densities of zinc-air batteries (ZABs). Developing effective strategies to tackle the issue is of great significance for overcoming the performance bottleneck. Herein, inspired by the bionics of diving flies, a polytetrafluoroethylene layer was coated on the surfaces of Co₃ O₄ nanosheets (NSs) grown on carbon cloth (CC) to create a hydrophobic surface to enable the formation of more three-phase reaction interfaces and promoted oxygen diffusion, rendering the hydrophobic-Co₃ O₄ NSs/CC electrode a higher limiting current density (214 mA cm^-2 at 0.3 V) than that (10 mA cm^-2 ) of untreated-Co₃ O₄ NSs/CC electrode. Consequently, the assembled ZAB employing hydrophobic-Co₃ O₄ NSs/CC cathode acquired a higher power density (171 mW cm^-2 ) than that (102 mW cm^-2 ) utilizing untreated-Co₃ O₄ NSs/CC cathode, proving the enhanced interfacial reaction kinetics on air cathode benefiting from the hydrophobization engineering.

Synergistically active piezoelectrical H2O2 production composite film achieved from catalytically inert PVDF-HFP matrix and SiO2 fillers

Local and decentralized H 2 O 2 production via piezoelectrical process promise smart biological utilization as well as environmental benefits. However, stable, bio/environmental- safe, and easily applied H 2 O 2 generation materials are still lacking. Here we report a novel flexible H 2 O 2 generation polymeric film composed of catalytically inert PVDF-HFP (Poly(vinylidene fluoride-co-hexafluoropropylene)) matrix and SiO 2 nanoparticle fillers. The film is bio-/environmentally benign at resting states, but effectively produces H 2 O 2 upon ultrasonic motivation at a production rate of 492 μmol [[EQUATION]] in one hour. Experimental and simulation methods in combination indicate that the effective H 2 O 2 generation capabilities stem from the synergistic existence of piezoelectrical fields and the air-liquid-solid three-phase regions around the porous film. The chemical conversions are motivated by the adsorbed charges. The silicon hydroxyl groups properly stabilize the *OOH intermediate and facilitate the chemical conversions of 2e - ORR of ambient O 2 . We expect the report to inspire H 2 O 2 piezoelectrical generation materials and promote the novel production strategies of H 2 O 2 as well as piezoelectrical functional materials.

High-Performance Heterogeneous Thermocatalysis Caused by Catalyst Wettability Regulation

Catalyst wettability regulation has emerged as an attractive approach for high catalytic performance for the past few years. By introducing appropriate wettability, the molecule diffusion of reactants and products can be enhanced, leading to high activity. Besides this, undesired molecules are isolated for high selectivity of target products and long-term stability of catalyst. Herein, we summarize wettability-induced high-performance heterogeneous thermocatalysis in recent years, including hydrophilicity, hydrophobicity, hybrid hydrophilicity-hydrophobicity, amphiphilicity, and superaerophilicity. Relevant reactions are further classified and described according to the reason for the performance improvement. It should be pointed out that studies of utilizing superaerophilicity to improve heterogeneous thermocatalytic performance have been included for the first time, so this is a comparatively comprehensive review in this field as yet.

Bioinspired superwettable electrodes towards electrochemical biosensing

Superwettable materials have attracted much attention due to their fascinating properties and great promise in several fields. Recently, superwettable materials have injected new vitality into electrochemical biosensors. Superwettable electrodes exhibit unique advantages, including large electrochemical active areas, electrochemical dynamics acceleration, and optimized management of mass transfer. In this review, the electrochemical reaction process at electrode/electrolyte interfaces and some fundamental understanding of superwettable materials are discussed. Then progress in different electrodes has been summarized, including superhydrophilic, superhydrophobic, superaerophilic, superaerophobic, and superwettable micropatterned electrodes, electrodes with switchable wettabilities, and electrodes with Janus wettabilities. Moreover, we also discussed the development of superwettable materials for wearable electrochemical sensors. Finally, our perspective for future research is presented.

Biomimetic Janus photonic soft actuator with structural color self-reporting

Soft actuators with variable signal/color play an important role in the fields of targeted locomotion, artificial phototropism, drug screening, cargo transportation, and interactive sensing. The ability to achieve rapid response, large curvature, wide bending angle, and full-color display continues to be an unresolved challenge for artificial actuating materials. Inspired by the angle-dependent structural color of broad-tailed hummingbird and the Janus wettability of the lotus leaf, a Janus photonic soft actuator (JPSA) was fabricated by integrating an underwater super-oleophilic copper micro-nano array and oil-phobic inverse opal through a Laplace channel. The JPSA exhibits unidirectional permeability to underwater oil droplets. Attractively, with the combination of a swellable super-oleophilic surface and photonic crystals, JPSAs were endowed with oil-controlled reversible bending behavior with self-reporting angle-dependent color indication. We described for the first time the directional actuating mechanism induced by underwater oil unidirectional penetration and revealed the corresponding actuating kinetics and the inner-stress distribution/transfer by using structural color. As an extension of such theory, a rapid responsive JPSA with a wide bending angle and full-color self-reporting is further fabricated. This work provides an efficient strategy for oil directional transportation and separation in aqueous media and inspires the fabrication of a soft actuator/sensor with structural color self-reporting.

Optimization and Validation of a Custom-Designed Perfusion Bioreactor for Bone Tissue Engineering: Flow Assessment and Optimal Culture Environmental Conditions

Various perfusion bioreactor systems have been designed to improve cell culture with three-dimensional porous scaffolds, and there is some evidence that fluid force improves the osteogenic commitment of the progenitors. However, because of the unique design concept and operational configuration of each study, the experimental setups of perfusion bioreactor systems are not always compatible with other systems. To reconcile results from different systems, the thorough optimization and validation of experimental configuration are required in each system. In this study, optimal experimental conditions for a perfusion bioreactor were explored in three steps. First, an in silico modeling was performed using a scaffold geometry obtained by microCT and an expedient geometry parameterized with porosity and permeability to assess the accuracy of calculated fluid shear stress and computational time. Then, environmental factors for cell culture were optimized, including the volume of the medium, bubble suppression, and medium evaporation. Further, by combining the findings, it was possible to determine the optimal flow rate at which cell growth was supported while osteogenic differentiation was triggered. Here, we demonstrated that fluid shear stress up to 15 mPa was sufficient to induce osteogenesis, but cell growth was severely impacted by the volume of perfused medium, the presence of air bubbles, and medium evaporation, all of which are common concerns in perfusion bioreactor systems. This study emphasizes the necessity of optimization of experimental variables, which may often be underreported or overlooked, and indicates steps which can be taken to address issues common to perfusion bioreactors for bone tissue engineering.

Enhanced Phase-Change Heat Transfer by Surface Wettability Control

The phase-change heat-transfer coefficient can be improved by several orders of magnitude through the design of micro-nanostructures on typical surfaces. However, with the rapid development of intelligent and integrated devices, there is an increasing desire to regulate the heat exchange form of the surface to adapt to various environmental requirements. This study concerns the design of a carbon nanotube array-based phase-change heat-transfer surface, which can switch its wettability between superhydrophobicity and superhydrophilicity. By installing this surface on a device that integrates boiling heat transfer and condensation heat transfer, the device can independently adjust the surface wettability for different heat-transfer requirements. As a result, this surface can enhance condensation heat-transfer coefficient over 90 % in the superhydrophobic state and enhance the boiling heat-transfer coefficient over 41 % in the superhydrophilic state. Surfaces with controllable wettability can aid development of a new generation of smart control technologies to actively regulate system and device temperatures.

Fabrication of a Tool Electrode with Hydrophobic Features and Its Stray-Corrosion Suppression Performance for Micro-electrochemical Machining

Micro-electrochemical machining (micro-ECM) can machine microstructures with excellent surface integrity on difficult-to-cut alloys. During micro-ECM, stray corrosion results in tapered sidewalls of machined structures. To suppress the stray corrosion, a novel tool electrode with the sidewall insulation of a gas film is proposed by fabricating the metal tool sidewall into a hydrophobic surface. The sidewall surface is designed to be characterized with spherical array cavities (radius of 500 nm) acting as the hydrophobic features, enhancing the gas-shielding effect of the gas film under electrolysis. The fabrication process of the hydrophobic sidewall is described in detail, including the self-assembly procedure of a monolayer template of Φ_1 μm polystyrene microspheres, the copper-electroforming procedure for filling the microspheres' gaps, and the removal procedure for forming spherical array cavities. The fabricated tool electrode (Φ_500 μm) obtains the hydrophobic features of a contact angle of up to 138°. As a result, bubbles generated on the tool surface can form an air-electrolyte interface instead of a dispersed bubble cluster. Micro-ECM experiments of microstructures verify that the novel tool electrode can improve machining accuracy by suppressing sidewall stray corrosion.

Automated Manipulation of Miniature Objects Underwater Using Air Capillary Bridges: Pick-and-Place, Surface Cleaning, and Underwater Origami

Various insects can entrap and stabilize air plastrons and bubbles underwater. When these bubbles interact with surfaces underwater, they create air capillary bridges that de-wet surfaces and even allow underwater reversible adhesion. In this study, a robotic arm with interchangeable three-dimensional (3D)-printed bubble-stabilizing units is used to create air capillary bridges underwater for manipulation of small objects. Particles of various sizes and shapes, thin sheets and substrates of diverse surface tensions, from hydrophilic to superhydrophobic, can be lifted, transported, placed, and oriented using one- or two-dimensional arrays of bubbles. Underwater adhesion, derived from the air capillary bridges, is quantified depending on the number, arrangement, and size of bubbles and the contact angle of the counter surface. This includes a variety of commercially available materials and chemically modified surfaces. Overall, it is possible to manipulate millimeter- to sub-millimeter-scale objects underwater. This includes cleaning submerged surfaces from colloids and arbitrary contaminations, folding thin sheets to create three-dimensional structures, and precisely placing and aligning objects of various geometries. The robotic underwater manipulator can be used for automation and control in cell culture experiments, lab-on-chip devices, and manipulation of objects underwater. It offers the ability to control the transport and release of small objects without the need for chemical adhesives, suction-based adhesion, anchoring devices, or grabbers.

Emerging Separation Applications of Surface Superwettability

Human beings are facing severe global environmental problems and sustainable development problems. Effective separation technology plays an essential role in solving these challenges. In the past decades, superwettability (e.g., superhydrophobicity and underwater superoleophobicity) has succeeded in achieving oil/water separation. The mixture of oil and water is just the tip of the iceberg of the mixtures that need to be separated, so the wettability-based separation strategy should be extended to treat other kinds of liquid/liquid or liquid/gas mixtures. This review aims at generalizing the approach of the well-developed oil/water separation to separate various multiphase mixtures based on the surface superwettability. Superhydrophobic and even superoleophobic surface microstructures have liquid-repellent properties, making different liquids keep away from them. Inspired by the process of oil/water separation, liquid polymers can be separated from water by using underwater superpolymphobic materials. Meanwhile, the underwater superaerophobic and superaerophilic porous materials are successfully used to collect or remove gas bubbles in a liquid, thus achieving liquid/gas separation. We believe that the diversified wettability-based separation methods can be potentially applied in industrial manufacture, energy use, environmental protection, agricultural production, and so on.

Electrically Induced Underwater Superaerophilicity/Superaerophobicity Switching on Polypyrrole-Coated Mesh Films for Selective Bubble Permeation

Recently, materials with controllable superwettability have attracted much attention. However, almost all studies focused on controlling wetting of water and oil; research on underwater gas bubble wetting control is still rare. Herein, we report a mesh film prepared by coating polypyrrole (PPy) film on Ti mesh. Briefly, the film mesh is underwater superaerophilic when PPy is doped with perfluorooctanesulfonate ions (PFOS^- ), and becomes underwater superaerophobic as the PFOS^- are removed. The transition of the wettability can be triggered by electrical stimuli, which is attributed to the cooperative effect between the rough structure and chemical components variation. The controllable wettability allows adjustable bubble permeation. It can be envisioned that the film will provide potential applications in the future, such as underwater bubble capture/release and microfluidic devices.

Precursor film formation on catalyst–electrolyte–gas boundaries during CO2 electroreduction with gas diffusion electrodes

Thin and long layers of catholyte precursor films spread near triple-phase boundaries on composite catalysts containing hydrophobic materials. Dissolved CO2 molecules in the precursor films reduce on the composite catalyst surface without depletion.

Oxygen Generation Using Catalytic Nano/Micromotors

Gaseous oxygen plays a vital role in driving the metabolism of living organisms and has multiple agricultural, medical, and technological applications. Different methods have been discovered to produce oxygen, including plants, oxygen concentrators and catalytic reactions. However, many such approaches are relatively expensive, involve challenges, complexities in post-production processes or generate undesired reaction products. Catalytic oxygen generation using hydrogen peroxide is one of the simplest and cleanest methods to produce oxygen in the required quantities. Chemically powered micro/nanomotors, capable of self-propulsion in liquid media, offer convenient and economic platforms for on-the-fly generation of gaseous oxygen on demand. Micromotors have opened up opportunities for controlled oxygen generation and transport under complex conditions, critical medical diagnostics and therapy. Mobile oxygen micro-carriers help better understand the energy transduction efficiencies of micro/nanoscopic active matter by careful selection of catalytic materials, fuel compositions and concentrations, catalyst surface curvatures and catalytic particle size, which opens avenues for controllable oxygen release on the level of a single catalytic microreactor. This review discusses various micro/nanomotor systems capable of functioning as mobile oxygen generators while highlighting their features, efficiencies and application potentials in different fields.

Electrochemical Visualization of Gas Bubbles on Superaerophobic Electrodes Using Scanning Electrochemical Cell Microscopy

Electrocatalytic gas evolution reactions, where gaseous molecules are electrogenerated by reduction or oxidation of a species, play a central role in many energy conversion systems. Superaerophobic electrodes, usually constructed by their surface microstructures, have demonstrated excellent performance for electrochemical gas evolution reactions due to their bubble-repellent properties. Understanding and quantification of the gas bubble behavior including nucleation and dynamics on such microstructured electrodes is an important but underexplored issue. In this study, we reported a scanning electrochemical cell microscopy (SECCM) investigation of individual gas bubble nucleation and dynamics on nanoscale electrodes. A classic Pt film and a nonconventional transition-metal dichalcogenide MoS₂ film with different surface topologies were employed as model substrates for both H₂ and N₂ bubble electrochemical studies. Interestingly, the nanostructured catalyst surface exhibit significantly less supersaturation for gas bubble nucleation and a notable increase of bubble detachment compared to its flat counterpart. Electrochemical mapping results reveal that there is no clear correlation between bubble nucleation and hydrogen evolution reaction (HER) activity, regardless of local electrode surface microstructures. Our results also indicate that while the hydrophobicity of the nanostructured MoS₂ surface promotes bubble nucleation, it has little effect on bubble dynamics. This work introduces a new method for nanobubble electrochemistry on broadly interesting catalysts and suggests that the deliberate microstructure on a catalyst surface is a promising strategy for improving electrocatalytic gas evolution both in terms of bubble nucleation and elimination.

Wetting-regulated gas-involving (photo)electrocatalysis: biomimetics in energy conversion

(Photo)electrolysis of water or gases with water to species serving as industrial feedstocks and energy carriers, such as hydrogen, ammonia, ethylene, propanol, etc., has drawn tremendous attention. Moreover, these processes can often be driven by renewable energy under ambient conditions as a sustainable alternative to traditional high-temperature and high-pressure synthesis methods. In addition to the extensive studies on catalyst development, increasing attention has been paid to the regulation of gas transport/diffusion behaviors during gas-involving (photo)electrocatalytic reactions towards the goal of creating industrially viable catalytic systems with high reaction rates, excellent long-term stabilities and near-unity selectivities. Biomimetic surfaces and systems with special wetting capabilities and structural advantages can shed light on the future design of (photo)electrodes and address long-standing challenges. This article is dedicated to bridging the fields of wetting and catalysis by reviewing the cutting-edge design methodologies of both gas-evolving and gas-consuming (photo)electrocatalytic systems. We first introduce the fundamentals of various in-air/underwater wetting states and their corresponding bioinspired structural properties. The relationship amongst the bubble transport behavior, wettability, and porosity/tortuosity is also discussed. Next, the latest implementations of wetting-related design principles for gas-evolving reactions (i.e. the hydrogen evolution reaction and oxygen evolution reaction) and gas-consuming reactions (i.e. the oxygen reduction reaction and CO2 reduction reaction) are summarized. For photoelectrode designs, additional factors are taken into account, such as light absorption and the separation, transport and recombination of photoinduced electrons and holes. The influences of wettability and 3D structuring of (photo)electrodes on the catalytic activity, stability and selectivity are analyzed to reveal the underlying mechanisms. Finally, remaining questions and related future perspectives are outlined.

Integrated Bundle Electrode with Wettability-Gradient Copper Cones Inducing Continuous Generation, Directional Transport, and Efficient Collection of H2 Bubbles

The hydrogen evolution reaction (HER), as an efficient process of converting various energies into high-purity hydrogen, has attracted much attention from both scientific research studies and industrial productions. However, its wide applications still confront considerable difficulties, for example, bubble coverage on the electrode and bubble dispersion in the electrolyte, which will disturb current distribution and isolate active sites from reaction ions resulting in a high reaction overpotential and large Ohmic voltage drop. Consequently, timely removing the generated gas bubbles from the electrode as well as avoiding their direct release into the electrolyte can be an effective approach to address these issues. In this work, we have developed an elegant electrode, that is, the integrated bundle electrode with wettability-gradient copper cones, which is endowed with the multifunctions of continuous generation, direct transport, and efficient collection of hydrogen bubbles. All processes are proceeding on the electrode, which not only remove the generated hydrogen bubbles efficiently but also prevent the hydrogen bubbles from releasing into the electrolyte, which should greatly advance the development of water electrolysis and offer inspirations for people to fabricate more efficient HER devices.

Water/gas separation based on the selective bubble-passage effect of underwater superaerophobic and superaerophilic meshes processed by a femtosecond laser

To solve the problems caused by tiny bubbles in liquids and the difficulties involved in collecting useful gas underwater, this paper proposes a method to separate bubbles from water by integrating underwater superaerophobic and superaerophilic porous membranes, including bubble removal and collection methods. Inspired by fish scales and lotus leaves, underwater superaerophobic microstructures and underwater superaerophilic microstructures are prepared on a stainless steel (SS) mesh by femtosecond laser processing, respectively. The as-prepared underwater superaerophobic mesh has an anti-bubble ability, while the underwater superaerophilic mesh has a bubble-absorption ability in water. Based on the different dynamic behavior of bubbles on these two kinds of superwetting meshes, efficient water/bubble separation is achieved by using laser-induced superwetting meshes. Tiny bubbles can be completely removed from the water flow in a pipe or easily collected. Such water/gas separation methods based on underwater superaerophobic and superaerophilic porous membranes provide an effective way to prevent the damage caused by bubbles and to collect the available gas in liquids, which has great potential applications in energy utilization, environmental protection, medical and health care, microfluidic chips, chemical manufacturing, agricultural breeding, and so on.

High-Performance Ultrafine Bubble Aeration on Janus Aluminum Foil Prepared by Laser Microfabrication

Aeration is a mass transfer process, in which gas is dispersed into a liquid by utilizing air inflation or agitation. Typically, a microporous device is often used for aeration. Increasing the gas flow rate and decreasing the pore size reduce the bubble size, but the surface wettability of the gas/solid interface also has a significant impact on the bubble size, which is rarely studied. In this study, a superhydrophilic/superhydrophobic Janus aluminum foil (JAF) is fabricated by laser microstructuring and low surface energy modification. The gas-repelling superhydrophilic surface not only facilitates ultrafine bubble generation but also allows the bubbles to detach from the aerator surface quickly, while the superhydrophobic surface prevents water from infiltrating into the aeration chamber and reduces the mass transfer resistance. The micropores with different diameters are obtained by adjusting the laser processing parameters. The pore prepared by the laser is uniform, consequently leading to the uniform bubble size. When the pore diameter is set to 30 μm, the diameter of bubbles released from the superhydrophilic surface of the JAF is only 0.326 mm, and the gas dissolution rate is about six times that of the double-sided superhydrophobic aluminum foil. This simple, low-cost, and controllable method of the laser processing JAF has broad applications in wastewater treatment, energy production, and aquaculture.