GaOOH Crystallite Growth on Liquid Metal Microdroplets in Water: Influence of the Local Environment

Liquid Metal Amplified Charge Separation in Photocatalytic Micro/Nanomotors for Antibacterial Therapy

Photocatalytic micro/nanomotors (MNMs) driven by electrophoresis have attracted considerable attention by virtue of their active mobility and versatile functionality. However, the rapid recombination of photogenerated electron-hole pairs on light illumination severely compromises the involvement of charge species in the catalytic redox reactions of fuels, thus hindering both the propulsion and the application performance of photocatalytic MNMs. Herein, we report a facile strategy to amplify charge separation by incorporating liquid metal (LM) into the construction of photocatalytic MNMs, thereby strengthening the electrophoretic propulsion of MNMs and promoting the generation of reactive oxygen species (ROS) for antibacterial application. The MNMs are constructed with a gallium (Ga) LM core, coated with abundant graphite-phase carbon nitride (g-C3N4) nanosheets and half covered by a thin platinum layer. These MNMs exhibit self-propulsion in hydrogen peroxide (H2O2) solution, with their motion dynamics further enhanced by light irradiation. Theoretical calculations and simulations reveal that the composition between Ga and g-C3N4 forms an ohmic junction in the electronic energy band structure, which effectively improves the charge separation efficiency of electron-hole pairs. These results align well with the experimental electrochemical tests and consequently intensify the catalytic redox reactions of H2O2, as well as accelerate the charge migration across MNMs, contributing to the enhancement of their propulsion performance. Simultaneously, the amplified separation of electrons facilitates increased ROS generation, empowering the MNMs with motion-enhanced antibacterial activity against Escherichia coli. Finally, an in vivo wound healing experiment is conducted, verifying the superior antibacterial therapeutic performance of photocatalytic MNMs. This work not only provides insights into the role of charge species in phoretic motion of MNMs but also gives inspiration for developing photocatalytic MNMs with advanced biomedical applications.

A Durable Metalgel Maintaining 3×106 S∙M‒1 Conductivity under 1 000 000 Stretching Cycles

Conductive elastomers are in high demand for emerging fields such as wearable electronics and soft robotics. However, it remains unavailable to realize the desired metal-level conductivity after extensive stretching cycles, which is a necessity for the above promising application. Here, a new material is presented that employs an elastic, homogeneous, and dense waterborne polyurethane network to immobilize the liquid metal continuum via electrostatic interactions. This new design enables the liquid metal continuum to deform synchronously and reversibly with the polymer network, preserving its conductive structure and significantly enhancing durability. The resulting durable metalgel exhibits conductivity of 3 × 106 S∙m-1, which remains stable after 1 000 000 stretching cycles. This work overcomes the performance limitations of current conductive elastomers and unlocks new opportunities for cutting-edge applications in wearable technology and robotics.

Cellulose Nanocrystal Stabilized Liquid Metal Pickering Emulsion as Photothermal and Conductive Direct-Writing Ink

Gallium-based liquid metal (LM) has attracted great attention for constructing flexible electronic devices due to its excellent deformability and electrical conductivity. However, its large surface tension makes it difficult to be uniformly dispersed in polymers, which severely limits its wide applications. Hence, a surfactant-free approach is proposed to prepare stable LM microspheres against precipitation and coalesce by facile ultrasonication via cellulose nanocrystal (CNC) stabilized LM-in-water Pickering emulsion (PE), where CNCs are employed as Pickering emulsifiers due their partial wettability with both LM and water phases, strong electrostatic adsorption and hydrogen bonding interactions with LM. So far, reports about LM PE and CNC-stabilized inorganic material PE are still rare. CNC/LM PE is employed as direct-writing inks on various substrates for delicate patterns. The pristine CNC/LM patterns show excellent photothermal conversion due to localized surface plasma resonance effect of CNC/LM microspheres. After activation by friction sintering, the LM patterns are highly electric conductive (1666.7 S m-1) due to the formation of LM connection. The activated LM patterns also displayed excellent Joule heating (83.2 °C at 0.9 V) and electromagnetic interference (EMI) shielding ability (585.7 dB mm-1) in X-band range.

Bias-Induced Ga-O-Ir Interface Breaks the Limits of Adsorption-Energy Scaling Relationships for High-Performing Proton Exchange Membrane Electrolyzers

Rationally manipulating the in situ formed catalytically active surface of catalysts remains a significant challenge for achieving highly efficient water electrolysis. Herein, we present a bias-induced activation strategy to modulate in situ Ga leaching and trigger the dynamic surface restructuring of lamellar Ir@Ga2O3 for the electrochemical oxygen evolution reaction. The in situ reconstructed Ga-O-Ir interface sustains high water oxidation rates at oxygen evolution reaction (OER) overpotentials. We found that OER at the Ga-O-Ir interface follows a bi-nuclear adsorbate evolution mechanism with unsaturated IrOx as the active sites, while GaOx atoms play an indirect role in promoting water dissociation to form OH* and transferring OH* to Ir sites. This breaks the scaling relationship of the adsorption energies between OH* and OOH*, significantly lowering the energy barrier of the rate-limiting step and greatly increasing reactivity. The Ir@Ga2O3 catalyst achieves lower overpotentials, a current density of 2 A cm-2 at 1.76 V, and stable operation up to 1 A cm-2 in scalable proton exchange membrane water electrolyzer (PEMWE) at 1.63 V, maintaining stable operation at 1 A cm-2 over 1000 hours with a degradation rate of 11.5 μV h-1. This work prompted us to jointly address substrate-catalyst interactions and catalyst reconstruction, an underexplored path, to improve activity and stability in Ir PEMWE anodes.

Ultrasonically Activated Liquid Metal Catalysts in Water for Enhanced Hydrogenation Efficiency

Hydride (H-) species on oxides have been extensively studied over the past few decades because of their critical role in various catalytic processes. Their syntheses require high temperatures and the presence of hydrogen, which involves complex equipment, high energy costs, and strict safety protocols. Hydride species tend to decompose in the presence of atmospheric oxygen and water, which reduces their catalytic activities. These challenges highlight the need for further research to improve the stability and efficiency of catalytic processes and develop safer and cost-effective synthesis methods. This paper introduces an ultrasonic fabrication method for gallium hydride species on liquid metal (LM) nanoparticles (Ga-H@LM NPs) in water and describes the evaluation of their catalytic properties. The Ga-H@LM NPs were synthesized by dispersing liquid metals of eutectic gallium-indium in water using a two-step ultrasonication process in an ice bath. The presence of Ga-H species was confirmed by Fourier-transform infrared spectroscopy. The Ga-H@LM NPs demonstrated the rapid catalytic hydrogenation of 4-nitrophenol and reductive degradation of azo dyes within minutes without the need for external reducing agents like NaBH4. The proposed mechanism involves high-energy ultrasonic cavitation at the interface between LM NPs and water, which promotes the formation of H2 from water and its activation to form Ga-H on particles surface during ultrasonication. This study has significant implications for advancing the field of catalysis because it provides a novel and efficient catalytic method for the synthesis of stable hydride species on gallium oxides.

The Liquid Metal Age: A Transition From Hg to Ga

This review offers an illuminating journey through the historical evolution and modern-day applications of liquid metals, presenting a comprehensive view of their significance in diverse fields. Tracing the trajectory from mercury applications to contemporary innovations, the paper explores their pivotal role in industry and research. The analysis spans electrical switches, mechanical applications, electrodes, chemical synthesis, energy storage, thermal transport, electronics, and biomedicine. Each section examines the intricacies of liquid metal integration, elucidating their contributions to technological advancements and societal progress. Moreover, the review critically appraises the challenges and prospects inherent in liquid metal applications, addressing issues of recycling, corrosion management, device stability, economic feasibility, translational hurdles, and market dynamics. By delving into these complexities, the paper advances scholarly understanding and offers actionable insights for researchers, engineers, and policymakers. It aims to catalyze innovation, foster interdisciplinary collaboration, and promote liquid metal-enabled solutions for societal needs. Through its comprehensive analysis and forward-looking perspective, this review serves as a guide for navigating the landscape of liquid metal applications, bridging historical legacies with contemporary challenges, and highlighting the transformative potential of liquid metals in shaping future technologies.

Directly Printable Flexible Optoelectronics through Surface Atomic Modification of Liquid Metals at Room Temperature

Flexible optoelectronics have fully demonstrated their transformative roles in various fields, but their fabrication and application have been limited by complex processes. Liquid metals (LMs) are promising to be ideal raw materials for making flexible optoelectronics due to their extraordinary fluidity and printability. Herein, we propose a painting-modifying strategy based on solution processability for directly printing out fluorescent flexible optoelectronics from LMs via surface modification. The LMs of eGaIn, which were obtained by the mixing of gallium with indium metal spheres, were used as ink to paint high-finesse patterns on flexible substrates. Through introducing surface modification of LMs, the gallium atom on the surface of the LMs was directly transformed into the composite fluorescent functional layers of GaO(OH) and GaN after being modified with an ammonia aqueous solution. Owing to painting, this strategy is not limited by any curved surfaces, shapes, or facilities and has excellent adaptability. Particularly, the fluorescent layers were obtained through a spontaneous, instantaneous, and solution-processable process that is environmentally friendly, easy to administrate, recyclable, and adjustable. The present finding breaks through the limitations of LMs in making flexible optoelectronics and provides strategies for addressing severe challenges facing existing materials and flexible optoelectronics. This method is expected to be very useful for fabricating flexible lights, transformable displays, intelligent anticounterfeiting devices, skin-inspired optoelectronics, and chameleon-biomimetic soft robots in the coming time.

Assembled MXene-Liquid Metal Cages on Silicon Microparticles as Self-Healing Battery Anodes

In pursuit of higher energy density in lithium-ion batteries, silicon (Si) has been recognized as a promising candidate to replace commercial graphite due to its high theoretical capacity. However, the pulverization issue of Si microparticles during lithiation/delithiation results in electrical contact loss and increased side reactions, significantly limiting its practical applications. Herein, we propose to utilize liquid metal (LM) particles as the bridging agent, which assemble conductive MXene (Ti3C2Tx) sheets via coordination chemistry, forming cage-like structures encapsulating mSi particles as self-healing high-energy anodes. Due to the integration of robust Ti3C2Tx sheets and deformable LM particles as conductive buffering cages, simultaneously high-rate capability and cyclability can be realized. Post-mortem analysis revealed the cage structural integrity and the maintained electrical percolating network after cycling. This work introduces an effective approach to accommodate structural change via a resilient encapsulating cage and offers useful interface design considerations for versatile battery electrodes.

Long-Term Corrosion of Eutectic Gallium, Indium, and Tin (EGaInSn) Interfacing with Diamond

Thermal transport is of grave importance in many high-value applications. Heat dissipation can be improved by utilizing liquid metals as thermal interface materials. Yet, liquid metals exhibit corrosivity towards many metals used for heat sinks, such as aluminum, and other electrical devices (i.e., copper). The compatibility of the liquid metal with the heat sink or device material as well as its long-term stability are important performance variables for thermal management systems. Herein, the compatibility of the liquid metal Galinstan, a eutectic alloy of gallium, indium, and tin, with diamond coatings and the stability of the liquid metal in this environment are scrutinized. The liquid metal did not penetrate the diamond coating nor corrode it. However, the liquid metal solidified with the progression of time, starting from the second year. After 4 years of aging, the liquid metal on all samples solidified, which cannot be explained by the dissolution of aluminum from the titanium alloy. In contrast, the solidification arose from oxidation by oxygen, followed by hydrolysis to GaOOH due to the humidity in the air. The hydrolysis led to dealloying, where In and Sn remained an alloy while Ga separated as GaOOH. This hydrolysis has implications for many devices based on gallium alloys and should be considered during the design phase of liquid metal-enabled products.

Room-Temperature Liquid Metals for Flexible Electronic Devices

Room-temperature gallium-based liquid metals (RT-GaLMs) have garnered significant interest recently owing to their extraordinary combination of fluidity, conductivity, stretchability, self-healing performance, and biocompatibility. They are ideal materials for the manufacture of flexible electronics. By changing the composition and oxidation of RT-GaLMs, physicochemical characteristics of the liquid metal can be adjusted, especially the regulation of rheological, wetting, and adhesion properties. This review highlights the advancements in the liquid metals used in flexible electronics. Meanwhile related characteristics of RT-GaLMs and underlying principles governing their processing and applications for flexible electronics are elucidated. Finally, the diverse applications of RT-GaLMs in self-healing circuits, flexible sensors, energy harvesting devices, and epidermal electronics, are explored. Additionally, the challenges hindering the progress of RT-GaLMs are discussed, while proposing future research directions and potential applications in this emerging field. By presenting a concise and critical analysis, this paper contributes to the advancement of RT-GaLMs as an advanced material applicable for the new generation of flexible electronics.

Liquid-Metal Molecular Scissors

Molecules are the smallest units of matter that can exist independently, relatively stable, maintaining their physical and chemical activities. The key factors that dominate the structures and properties of molecules include atomic species, alignment commands, and chemical bonds. Herein, we reported a generalized effect in which liquid metals can directly cut off oxygen-containing groups in molecular matter at room temperature, allowing the remaining groups to recombine to form functional materials. Thus, we propose basic liquid-metal scissors for molecular directional clipping and functional transformations. As a proof of concept, we demonstrate the capabilities of liquid-metal scissors and reveal that the gallium on the surface of liquid metals directly extracts oxygen atoms from H2O or CH3OH molecules to form oxides. After clipping, the remaining hydrogen atoms from the H2O molecules recombine to form H2, while the remaining fragments of CH3OH produce H2, carbon materials, and carboxylates. This finding refreshes our basic understanding of chemistry and should lead to the development of straightforward molecular weaving techniques, which can help to overcome the limitations of molecular substances with single purposes. It also opens a universal route for realizing future innovations in molecular chemical engineering, life sciences, energy and environment research, and biomedicine.

Self-healing and durable antifouling zwitterionic hydrogels based on functionalized liquid metal microgels

Hydrogels are a promising new class of antifouling materials. But their utility is constrained by low mechanical strength and unsatisfactory antifouling performance over the long term. Herein, we successfully prepared zwitterionic polymer PEIS cross-linked gallium-based liquid metal microgels-based (PEIS-Gel@PMPC-GLM) hydrogels via UV-curing and amidation reaction. The as-prepared hydrogels showed preferable mechanical properties and superior hydrophilicity to the original hydrogels. The PEIS-Gel@PMPC-GLM hydrogels could prevent the adhesion of more than 90 % of microalgae and nearly 100 % of bacteria in a short-term antifouling test. PEIS-Gel@PMPC-GLM hydrogels also performed exceptionally well in the high concentration antibacterial test and the long-term antifouling test (remove more than 90 % bacteria and 80 % microalgae). In addition to releasing a high concentration of gallium ions, as shown by the ICP-OES test, PEIS-Gel@PMPC-GLM hydrogels also exhibitedexcellent lubrication performance, as demonstrated by the friction test (coefficient of friction as low as 0.023). Therefore, the antifouling effect of gallium ions combined with the strong hydration ability of the surfaces endowed the hydrogels remarkable antibacterial and antifouling properties. As a result of the exposed gallium atoms inducing further crosslinking of residual vinyl monomer in hydrogels, PEIS-Gel@PMPC-GLM hydrogels revealed certain self-healing performance.

Coating of gallium-based liquid metal particles with molybdenum oxide and oxysulfide for electronic band structure modulation

Liquid metal (LM) droplets are now used in many applications including catalysis, sensing, and flexible electronics. Consequently, the introduction of methods for on-demand alternating electronic properties of LMs is necessary. The active surface of LMs provides a unique environment for spontaneous chemical reactions that enable the formation of thin layers of functional materials for such modulations. Here, we showed the deposition of n-type MoO_x and MoO_xS_y semiconductors on the surface of EGaIn LM droplets under mechanical agitation to successfully modulate their electronic structures. The "liquid solution"-"liquid metal" interaction resulted in the formation of oxide and oxysulfide layers on the surface of LM droplets. The comprehensive study of electronic and optical properties revealed a decrease in the band gap of the droplets after surface decoration with MoO_x and MoO_xS_y, leading to deeper n-type doping of the materials. This method provides a facile procedure for engineering the electronic band structure of LM-based composites when they are necessary for various applications.