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Exploring and controlling surface tension‐driven phenomena in liquid metals may lead to unprecedented possibilities for next‐generation microfluidics, electronics, catalysis, and materials synthesis. In pursuit of these goals, the impact of minor constituents within liquid alloys is largely overlooked. Herein, it is showed that the presence of a fraction of solute metals such as tin, bismuth, and zinc in liquid gallium can significantly influence their electrocapillarity and electrochemistry. The instability‐driven fractal formation of liquid alloy droplets is investigated with different solutes and reveals the formation of distinctive non‐branched droplets, unstable fractals, and stable fractal modes under controlled voltage and alkaline solution conditions. In their individually unique fractal morphology diagrams, different liquid alloys demonstrate significantly shifted voltage thresholds in transition between the three fractal modes, depending on the choice of the solute metal. Surface tension measurements, cycle voltammetry and surface compositional characterizations provide strong evidence that the minor alloy components drastically alter the surface tension, surface electrochemical oxidation, and oxide dissolution processes that govern the droplet deformation and instability dynamics. The findings that minor components are able to regulate liquid alloys' surface tensions, surface element distributions and electrochemical activities offer great promises for harnessing the tunability and functionality of liquid metals. [ABSTRACT FROM AUTHOR]

Liquid metals provide new dimensions for controlling and governing of reactions. The concept of freely moving metal solutes in liquid metals can be potentially used for enhancing and tuning interfacial reactions. In this work, zinc (Zn), as the solute metal is shown that, can move to the interface, enriching the interfacial area for the efficient synthesis of highly crystalline and porous zeolitic imidazolate framework‐8 (ZIF‐8). The highest rate of reaction is illustrated, and the best quality ZIF‐8, are obtained when a eutectic liquid metal system of Zn with gallium (Ga), containing 3.6 wt.% of Zn, is implemented. It is computationally shown that a combination of Ga activation and freely moving Zn leads to the highest reaction rate and better coordination with organic linkers. The comparisons with solid samples and non‐eutectic systems of Ga liquid demonstrate the advantages of eutectic mix. The work can be expanded to a variety of future interfacial reactions of zeolite imidazole frameworks for commercial scale up. [ABSTRACT FROM AUTHOR]

Nano‐/microparticles of gallium (Ga), as a low‐melting‐point metal, are extensively used in the fields of soft electronics and sensors to provide thermal and electrical conductivity. However, a passivating oxide layer can be formed on the surface of Ga nano‐/microparticles during the synthesis process. This oxide layer is removed by a secondary sintering step, especially mechanical sintering, which is generally not a controllable process, and compromises the integrity of the system. Herein, thiol molecules, 1‐butanethiol, thiophenol, and 4‐mercaptopyridine, that can functionalize the surface of Ga via sonication to reduce the oxidation of Ga surface are used. The resulting particles exhibit electrical conductivity based on metal–molecule junctions without the requirement for a sintering step. In particular, 4‐mercaptopyridine functionalized, thiolated Ga particles exhibit higher electrical conductivity compared to the other three thiolated Ga systems as the organic material conjugation provides conductive pathways for the mix. Subsequently, using these particle systems, soft devices are developed that can be used for gas, exhalation, and flex sensing. This study provides insights into the possibility of creating combinations of organic molecules with liquid metal‐based nano‐/microparticles to generate electrically conductive mixes and the prospects of fabricating multifunctional sensors. [ABSTRACT FROM AUTHOR]

Liquid metal droplets of gallium (Ga) and Ga‐based alloys are traditionally incorporated as deformable additives into soft elastomers to make them conductive. However, such a strategy has not been implemented to develop conductive sponges with real sponge‐like characteristics. Herein, polyurethane‐based sponges with Ga microdroplets embedded inside the polyurethane walls are developed. The liquid phase (at 45 °C) and solid phase (at room temperature) transition of the Ga fillers shows the temperature‐dependent functional variations in the mechanical, thermal, and electrical properties on the prepared composite sponges, which are investigated in detail. Unlike elastomers, the sponge possesses excellent elastic recovery, at ≈90%, and conductivity durability without sacrificing structural integrity. The reversible change of resistivity range is remarkable. When the Ga fillers account for 18% of the total sponge volume, the electrical resistivity varies from infinite values (insulator) under no applied pressure to 39.0 Ω m for the solid phase and 3.8 Ω m for the liquid phase under 386.8 kPa. New opportunities in developing flexible electrically conductive composite sponges with tunable mechanical and electrical properties that can be implemented for a variety of future applications are proposed. [ABSTRACT FROM AUTHOR]

Liquid–liquid interfaces of liquid alloys with electrolytic solutions present fertile platforms for realizing exciting interfacial phenomena that can be devised to process alloys and produce nanomaterials. Here, such an interface is established by immersing a gallium–bismuth binary liquid alloy into aqueous electrolytes. It is shown that the application of a negative voltage to this interface results in a rapid and complete liberation of bismuth nanostructures from liquid gallium. The set of conditions that govern the chemistry of the interface can be adjusted to control the oxidation state, morphology, and crystal structure of the expelled bismuth. By changing the conditions; nanotubular, atomically thin plates, and sea‐urchin‐shaped bismuth oxide morphologies are obtained. The process can also control the crystal phase of bismuth oxide as monoclinic (α), tetragonal (β), or body‐centered cubic (γ). The addition of ascorbic acid to the electrolyte is observed to prevent the oxidation of the expelled entities, resulting in bismuth metal nanoparticles. Ab initio molecular dynamics and computational fluid dynamics simulations are performed to elucidate this rapid phase separation at the interface. This knowledge will potentially lead to new pathways for using alloys as reaction media to refine metals while simultaneously producing nanomaterials for various applications. [ABSTRACT FROM AUTHOR]

Heavy metal ions contamination is an ever‐growing threat to human health and ecosystems. Analytic sensing of heavy metal ions is a prerequisite step toward addressing this challenge. Electroanalytical technique is an effective and convenient way to detect heavy metal ions. Especially, stripping voltammetry techniques have been utilized for sensing metal ions at trace levels in different sample matrices. The choice of the working electrode materials plays a decisive role in the precision and sensitivity of stripping voltammetry. Post‐transition metals (including elements in group 12) are elements with low melting points, demonstrating unique properties including amalgamation with heavy metal ions that enhance the performance of stripping voltammetry during the pre‐concentration step, which make them particularly suitable for heavy metal ion sensing. Here, for better understanding the features and advantages of post‐transition metals in stripping voltammetry, eight classes of working electrodes based on zinc (Zn), mercury (Hg), gallium (Ga), indium (In), tin (Sn), lead (Pb), antimony (Sb), and bismuth (Bi), are reviewed, with their efficiency and effectiveness compared and recent progresses discussed. Additionally, liquid metal electrodes based on post‐transition metals and alloys are also presented. This review provides viable directions for future development of heavy metal ion sensors based on post‐transition metals. [ABSTRACT FROM AUTHOR]

Liquid metal (LM) catalysts have been demonstrated to accelerate chemical reactions, providing an intriguing route to fine chemical synthesis with immense technological implications. Herein, we explore gallium-based LMs as catalysts to promote the oxidative self-polymerization of natural polyphenols, an emerging class of natural building blocks for surface functionalization with diverse biochemical properties. The oxidative polymerization of polyphenols, triggered by eutectic alloy of gallium and indium, results in nanocoatings with remarkably high reaction kinetics. The oxidative polymerization occurs in a wide pH range including an acidic environmenta condition previously unexplored for the deposition of phenolic coatings. The LM triggers the generation of highly active radical species from the oxidant causing the rapid oxidation of the polyphenols and their subsequent deposition on a range of different substrates. We further show that the LM-based catalytic system addresses several other limitations of existing coating methods including a narrow pH range, substrate specificity (precursor–dependent), and low coating uniformity. Finally, we demonstrate that the phenolic nanocoatings obtained from the acidic pH environment have excellent antioxidant and antibacterial properties without requiring any post-functionalization step. This process for creating phenolic nanocoatings may find applications in a wide range of industries, food science, and biomedicine. [ABSTRACT FROM AUTHOR]

Surface patterning of liquid metals (LMs) is a key processing step for LM‐based functional systems. Current patterning methods are substrate specific and largely suffer from undesired imperfections—restricting their widespread applications. Inspired by the universal catechol adhesion chemistry observed in nature, LM inks stabilized by the assembly of a naturally abundant polyphenol, tannic acid, has been developed. The intrinsic adhesive properties of tannic acid containing multiple catechol/gallol groups, allow the inks to be applied to a variety of substrates ranging from flexible to rigid, metallic to plastics and flat to curved, even using a ballpoint pen. This method can be further extended from hand‐written texts to complex conductive patterns using an automated setup. In addition, capacitive touch and hazardous heavy metal ion sensors have been patterned, leveraging from the synergistic combination of polyphenols and LMs. Overall, this strategy provides a unique platform to manipulate LMs from hand‐written pattern to complex designs onto the substrate of choice, that has remained challenging to achieve otherwise. [ABSTRACT FROM AUTHOR]

2D transition metal dichalcogenides (TMDs) play increasingly significant roles in research and future optoelectronics. However, the large‐scale deposition of 2D TMDs remains challenging due to sparse nucleation and substrate dependency. Liquid metals can offer effective solutions to meet these challenges due to their reactive, non‐polarized, and templating properties. Here, self‐deposition of 2D molybdenum sulfide is shown by introducing a molybdenum precursor onto the surface of a eutectic alloy of gallium and indium (EGaIn). EGaIn serves as an ultra‐smooth template and reducing agent for the precursor to form large‐scale planar molybdenum sulfides, which is transferrable to any substrate. The molybdenum sulfides form spontaneously on the surface of EGaIn, which has a sufficient potential to drive the cathodic reactions of the deposition process. A highly crystalline 2H‐MoS2 is obtained after a final annealing step. This work demonstrates a fundamentally new capability for the formation of large‐scale 2D TMDs. [ABSTRACT FROM AUTHOR]

Microcopper particles are introduced to trigger and trace persistent surface convection of eutectic gallium indium (eGaIn) when the liquid-metal is partially immersed in shallow alkaline solution. It is found that the surface convection, which further induces large-scale shape transformation of the liquid-metal body, is driven by the surface-tension imbalance originated from the numerous tiny copper-eGaIn galvanic couples through the electrocapillary mechanism. Meanwhile, the particular configuration of particles binding to the liquid-metal surface and surfing with the flow also enables one to capture the flow patterns and visualize the flow field with the assistance of particle imaging velocimetry technology. This overcomes the difficulties in directly observing and quantifying the dynamic surface-flow behaviors of such nontransparent yet highly reflective liquid-metals. Characteristic flow regimes of the liquid-metal surface convection are revealed and their indications regarding the flow beneath the surface are also made. [ABSTRACT FROM AUTHOR]

This study focuses on the influence of driving fluid properties on the mass transfer process of ejector apparatus. A liquid-actuated ejector system is firstly designed and three experimental cases working with different kinds of driving fluids, i.e., gallium-based liquid metal, aqueous NaI solution and water, are successively investigated. The results show that the ejector system working with liquid metal has high-vacuum ejecting capacity and good temperature stability. With a system power consumption of about 50 W, the liquid metal driving ejector obtains a no-entrainment vacuum pressure of 33 Pa which is three orders of magnitudes lower than that of the water driving case. When the gas-suction pressure exceeds 40 kPa, NaI solution driving case reveals the highest entrainment. The reasons for the differences in the ejector performance are later discussed. Based on the experimental results and theoretical analyses, the method of using high density, low viscosity and low vapor pressure working fluid to improve ejector performance is proposed. Other than conventional methods which focus on optimizing the geometrical design and operating parameters of ejectors, the method discussed here puts forward a new perspective to improve ejector performance. Moreover, the ejector system working with liquid metal demonstrates its advantages such as compact system design, oil-free vacuum pumping as well as high temperature operation. [ABSTRACT FROM AUTHOR]

Metal foams are highly sought‐after porous structures for heterogeneous catalysis, which are fabricated by templating, injecting gas, or admixing blowing agents into a metallic melt at high temperatures. They also require additional catalytic material coating. Here, a low‐melting‐point liquid metal is devised for the single‐step formation of catalytic foams in mild aqueous environments. A hybrid catalytic foam fabrication process is presented via simultaneous chemical foaming, melting, and sintering reaction of liquid metal nanoparticles. As a model, nanoparticles of tertiary low‐melting‐point eutectic alloy of indium, bismuth, and tin (Field's metal) are processed with sodium hydrogen carbonate, an environmentally benign blowing agent. The competing endothermic foaming and exothermic sintering reactions are triggered by an aqueous acidic bath. The overall foaming process occurs at a localized temperature above 200 °C, producing submicron‐ to micron‐sized open‐cell pore foams with conductive cores and semiconducting surface decorations. The catalytic properties of the metal foams are explored for a range of applications including photo‐electrocatalysis, bacteria electrofiltration, and CO2 electroconversion. In particular, the Field's metal‐based foams show exceptional CO2 electrochemical conversion performance at low applied voltages. The facile process presented here can be extended to other low‐temperature post transition and transition metal alloys. [ABSTRACT FROM AUTHOR]

The nascent field of nanotechnology-enabled metallurgy has great potential. However, the role of eutectic alloys and the nature of alloy solidification in this field are still largely unknown. To demonstrate one of the promises of liquid metals in the field, we explore a model system of catalytically active Bi-Sn nano-alloys produced using a liquid-phase ultrasonication technique and investigate their phase separation, surface oxidation, and nucleation. The Bi-Sn ratio determines the grain boundary properties and the emergence of dislocations within the nano-alloys. The eutectic system gives rise to the smallest grain dimensions among all Bi-Sn ratios along with more pronounced dislocation formation within the nano-alloys. Using electrochemical CO2 reduction and photocatalysis, we demonstrate that the structural peculiarity of the eutectic nano-alloys offers the highest catalytic activity in comparison with their non-eutectic counterparts. The fundamentals of nano-alloy formation revealed here may establish the groundwork for creating bimetallic and multimetallic nano-alloys. The combination of metallurgy concepts and nanotechnology with liquid metal processing has been largely unexplored. Here the authors use liquid-phase ultrasonication to produce a model system of catalytically active nano-alloys, demonstrating electrocatalysis and photocatalysis. [ABSTRACT FROM AUTHOR]

Liquid metals offer unprecedented chemistry. Here it is shown that they can facilitate self‐limiting oxidation processes on their surfaces, which enables the growth of metal oxides that are atomically thin. This claim is exemplified by creating atomically thin hydrated MnO2 using a Galvanic replacement reaction between permanganate ions and a liquid gallium–indium alloy (EGaIn). The "liquid solution"–"liquid metal" process leads to the reduction of the permanganate ions, resulting in the formation of the oxide monolayer at the interface. It is presented that under mechanical agitation liquid metal droplets are established, and simultaneously, hydrated gallium oxides and manganese oxide sheets delaminate themselves from the interfacial boundaries. The produced nanosheets encapsulate a metallic core, which is found to consist of solid indium only, with the full migration of gallium out of the droplets. This process produces core/shell structures, where the shells are made of stacked atomically thin nanosheets. The obtained core/shell structures are found to be an efficient photocatalyst for the degradation of an organic dye under simulated solar irradiation. This study presents a new research direction toward the modification and functionalization of liquid metals through spontaneous interfacial redox reactions, which has implications for many applications beyond photocatalysis. [ABSTRACT FROM AUTHOR]

In article number 1800406, Jianbo Tang, Jing Liu and co‐workers propose a liquid‐metal‐enabled room‐temperature particle cross‐linking method which is able to "weld" discrete copper nanoparticles into thin, continuous yet porous networks through interfacial electrochemical processes. The authors also demonstrate remarkable mechanical and electrical properties of the materials caused by network formation. [ABSTRACT FROM AUTHOR]

Manipulating particles using a fluid interface has both fundamental implications and technological promises. However, the stabilization of interfacial particle structures remains challenging. This study proposes a room‐temperature particle cross‐linking strategy achieved by introducing a surface transition process to metal particles confined at a liquid metal–electrolyte template, which is electrochemically reducing. The method enables cross‐linking Cu nanoparticles into nanoporous networks of micrometric thickness. It is shown that the particle networks possess remarkable mechanical strength and can be readily isolated and then be transferred onto desired substrates. The electrical properties of the material due to network formation are further highlighted, with a focus on an anomalous electric‐field‐induced resistance reduction effect. Such favorable mechanical property and intriguing conducting behavior forecast promising perspectives of the material for smart sensor applications or novel electronic devices. Meanwhile, the proposed particle cross‐linking method can provide general implications for particle‐based, interface‐assisted fabrication. A liquid‐metal‐enabled electrochemical welding phenomenon is discovered for room‐temperature, in‐solution cross‐linking of metal particles. Cu nanoparticles are "welded" together to form continuous, thin, porous, and conductive networks through interfacial electrochemical processes. The obtained materials reveal strong mechanical strength and anomalous electric‐field‐induced resistance drop as a result of network formation. [ABSTRACT FROM AUTHOR]

Gallium and many of its alloys remain in liquid phase across impressively wide temperature ranges. Here such liquid metals are proposed as reaction media for the carbonization of low thermal stability polymeric precursors at high temperatures. Plain and cross-linked polyvinyl alcohol are chosen as representatives of such polymers. We show that due to the immiscibility of organic carbons within the liquid metal phase, these polymers that would otherwise vaporize at elevated temperatures, can function as precursors for the formation of carbonaceous films. The thin polymeric films are placed in an intimate contact with the liquid metal surface before thermal processing and show amorphous to graphitic-like characteristics after carbonization. Graphitic-like properties were obtained when a high melting point graphitization catalyst, such as copper, was co-alloyed. The proposed work can be expanded to explore other metallic elements within the bulk of gallium-based alloys for the carbonization of polymeric precursors at large-scales. Image 1 • Polymers that do not carbonize otherwise can be 'capped' by liquid metals and thereby carbonized. • Gallium-based liquid metals exhibit selective miscibility to non-metallic elements. • Gallium, gallium-indium and gallium-copper were chosen as liquid metal reactors. • Carbon films with amorphous and graphitic characteristics were formed. • Inclusion of copper in liquid metal enhanced the graphitic characteristics of the films. [ABSTRACT FROM AUTHOR]

Giant electrohydrodynamic instability of a partially immersed liquid‐metal body is triggered by tiny copper particles, resulting in long‐term surface convection and large‐scale shape transformation of the liquid metal. In article number 1700939, Jianbo Tang, Jing Liu, and co‐workers describe how complex flow patterns of the particle‐driven surface convection are further captured by tracing the motions of the particles accompanying the flow. [ABSTRACT FROM AUTHOR]

Abstract Liquid metals (LM) such as eutectic gallium-indium and gallium-indium-tin are important functional liquid-state metal materials with many unique properties, which have attracted wide attentions especially from soft robot area. Recently the amoeba-like transformations of LM on the graphite surface are discovered, which present a promising future for the design and assemble of self-fueled actuators with dendritically deformable body. It appears that the surface tension of the LM can be significantly reduced when it contacts graphite surface in alkaline solution. Clearly, the specific surface should play a vital role in inducing these intriguing behaviors, which is valuable and inspiring in soft robot design. However, the information regarding varied materials functions underlying these behaviors remains unknown. To explore the generalized effects of surface materials in those intriguing behavior, several materials including glass, graphite, nickel and copper oxides (CuO) were comparatively investigated as substrate surfaces. Important results were obtained that only LM amoeba transformations were observed on graphite and CuO surfaces. In order to identify the proper surface condition for LM transformation, the intrinsic properties of substrate surfaces, such as the surface charge and roughness, as well as the specific interaction with LM like wetting behavior and mutual locomotion etc., were characterized. The integrated results revealed that LM droplet appears more likely to deform on surfaces with higher positive surface charge density, higher roughness and less bubble generation on them. In addition, another surface material, CuO x , is identified to own similar ability to graphite, which is valuable in achieving amoeba-like transformation. Moreover, this study offers a fundamental understanding of the surface properties in realizing LM amoeba transformations, which would shed light on packing and structure design of liquid metal-based soft device within multi-material system. [ABSTRACT FROM AUTHOR]

[Display omitted] • Liquid metals offer economic pathways for biomass conversion. • Hydrogen production induced by liquid metals was of high selectivity. • Only mild mechanical agitation is needed for the reformation. • Liquid metals enable structure reformation towards value-added products. Having showcased intriguing features in a vast range of catalytic applications, liquid metals (LMs) are continuously ticking boxes of pathways that are conventionally only associated with transitional metals. Herein, we report a gallium-ethylene glycol system where gallium is utilized to interact and break down organic bonds. Ethylene glycol is selected as a model organic compound, as it has been extensively studied for the reformation mechanisms and the potential to produce hydrogen gas. With mechanical agitation applied to the LM-based reaction system, we establish an in-situ monitoring approach for the gaseous products and also perform a series of characterizations on the post-reaction mixture. We reveal that the hydrogen gas production from the system is continuous and highly selective. Gaseous alkanes and alkenes are also observed in the output. Our analyses demonstrate that gallium induces structural reformations of ethylene glycol following a complex pathway. The process generates methyl, aldehyde, carbonyl, and other groups. We further reveal the formation of polymer products with repeating methylene groups in the system. The process for reforming ethylene glycol signifies the capability of LMs to efficiently break down organic bonds. As such, this study provides a platform to explore environment-friendly and alternative strategies for hydrogen production and organic transformation toward valuable products. [ABSTRACT FROM AUTHOR]

[Display omitted] • Liquid metals are super catalytic materials for hydrocarbons conversion. • Synergy between liquid metals and mechanical energy enabled mechano-catalytic reactions. • A series of biofuels (i.e. , renewable hydrocarbons) were converted at low temperatures. • Hydrogen and ethylene production achieved without involving harsh conditions. • Density functional theory calculations validated the reaction processes. Liquid metals are super catalysts that facilitate reactions at low temperatures while also providing new reaction pathways by the incorporation of co-catalysts. Synthesising H 2 and C 2 H 4 from renewable resources, with a low carbon footprint, is crucial for environmental sustainability. However, the high temperature requirement and over-reliance on fossil fuels restrict the sustainable production of H 2 and C 2 H 4. Here we demonstrate a hybrid catalytic system, which realises the conversion of renewable biofuels into mostly H 2 and C 2 H 4 at near room temperature, by employing mechanical energy as the stimulus and liquid metal gallium (Ga) together with nickel (Ni) particles as co-catalysts. During the collision of the suspended nano/micro-sized Ga/Ni co-catalysts, the biofuels, including canola oil and other liquid hydrocarbons, are converted at the interfaces of the catalytic materials. Density functional theory calculations show that C H and C C bond dissociation reactions on the Ga surface proceed under low energy conditions. These biofuels are converted into mainly H 2 and C 2 H 4 with CH 4 , CO, CO 2 , C 2 H 2 , C 3 H 6 and solid carbon as other by-products. With mild heating at ∼ 60 °C and the use of a 20 ml reactor, the process is capable of producing 2.15 cm3 of H 2 and 2.47 cm3 of C 2 H 4 per hour with canola oil as the feedstock. Meanwhile, the durability and potential practical applicability of the system are demonstrated with 10 days of continuous operation. This approach offers an alternative for H 2 and C 2 H 4 production without involving high reaction temperatures and fossil fuel hydrocarbons. [ABSTRACT FROM AUTHOR]