Ultrasensitive and ultrastretchable electrically self-healing conductors.

Self-healing is a bioinspired strategy to repair damaged conductors under repetitive wear and tear, thereby largely extending the life span of electronic devices. The self-healing process often demands external triggering conditions as the practical challenges for the widespread applications. Here, a compliant conductor with electrically self-healing capability is introduced by combining ultrahigh sensitivity to minor damages and reliable recovery from ultrahigh tensile deformations. Conductive features are created in a scalable and low-cost fabrication process comprising a copper layer on top of liquid metal microcapsules. The efficient rupture of microcapsules is triggered by structural damages in the copper layer under stress conditions as a result of the strong interfacial interactions. The liquid metal is selectively filled into the damaged site for the instantaneous restoration of the metallic conductivity. The unique healing mechanism is responsive to various structural degradations including microcracks under bending conditions and severe fractures upon large stretching. The compliant conductor demonstrates high conductivity of ∼12,000 S/cm, ultrahigh stretchability of up to 1,200% strain, an ultralow threshold to activate the healing actions, instantaneous electrical recovery in microseconds, and exceptional electromechanical durability. Successful implementations in a light emitting diode (LED) matrix display and a multifunctional electronic patch demonstrate the practical suitability of the electrically self-healing conductor in flexible and stretchable electronics. The developments provide a promising approach to improving the self-healing capability of compliant conductors.

Noncontact rotation, levitation, and acceleration of flowing liquid metal wires.

This paper reports the noncontact manipulation of free-falling cylindrical streams of liquid metals into unique shapes, such as levitated loops and squares. Such cylindrical streams form in aqueous media by electrochemically lowering the interfacial tension. The electrochemical reactions require an electrical current that flows through the streams, making them susceptible to the Lorentz force. Consequently, varying the position and shape of a magnetic field relative to the stream controls these forces. Moreover, the movement of the metal stream relative to the magnetic field induces significant forces arising from Lenz's law that cause the manipulated streams to levitate in unique shapes. The ability to control streams of liquid metals in a noncontact manner will enable strategies for shaping electronically conductive fluids for advanced manufacturing and dynamic electronic structures.

Ultrathin Ga2O3 Photodetector with Fast Response and Trajectory Tracking Capability Fabricated by Liquid Metal Oxidation.

Low-dimensional Ga2O3 demonstrates a unique ultraviolet photoresponse and could be used in various electronic and optical systems. However, the low-dimensional Ga2O3 photodetector is faced with the challenges of a complex preparation process and poor device performance. In this work, ultrathin Ga2O3 layers with ∼7 nm thickness are prepared on quartz rods by UV exposure to liquid gallium. Benefiting from low-density oxygen vacancy defects cured by UV exposure, the low-dimensional Ga2O3 photodetector exhibits a high response speed (rise: 64.7 µs; fall: 51.4 µs) and an exceptional linear dynamic range of 120 dB. Furthermore, the photodetector array based on these ultrathin Ga2O3 shows an effective trajectory tracking capability by monitoring UV source motion. This work develops a simple preparation method to construct a low-dimensional UV photodetector array with fast response and useful trajectory tracking capability, exhibiting the significance of ultrathin Ga2O3 in UV optoelectronics.

Liquid-Metal-Based Spin-Coating Exfoliation for Atomically Thin Metal Oxide Synthesis.

Two-dimensional (2D) semiconductors possess exceptional electronic, optical, and magnetic properties, making them highly desirable for widespread applications. However, conventional mechanical exfoliation and epitaxial growth methods are insufficient in meeting the demand for atomically thin films covering large areas while maintaining high quality. Herein, leveraging liquid metal oxidation reaction, we propose a motorized spin-coating exfoliation strategy to efficiently produce large-area 2D metal oxide (2DMO) semiconductors with high crystallinity, atomically thin thickness, and flat surfaces on diverse substrates. Moreover, we realized a 2D gallium oxide-based deep ultraviolet solar-blind photodetector featuring a metal-semiconductor-metal structure, showcasing high responsivity (8.24 A W-1) at 254 nm and excellent sensitivity (4.3 × 1012 cm Hz1/2 W-1). This novel liquid-metal-based spin-coating exfoliation strategy offers great potential for synthesizing atomically thin 2D semiconductors, opening new avenues for future functional electronic and optical applications.

Electrically Driven Deterministic Plasmon Light Sources Based on Arrays of Molecular Tunnel Junctions.

Surface plasmons excited via inelastic tunnelling have led to plasmon light sources with small footprints and ultrafast response speeds, which are favored by integrated optical circuits. Self-assembled monolayers of organic molecules function as highly tunable tunnel barriers with novel functions. However, limited by the low effective contact between the liquid metal electrode and the self-assembled monolayers, it is quite challenging to obtain molecular plasmon light sources with high density and uniform emission. Here, by combining lithographic patterning with a solvent treatment method, we have demonstrated electrically driven deterministic plasmon emission from arrays of molecular tunnel junctions. The solvent treatment could largely improve the effective contact from 9.6% to 48% and simultaneously allow the liquid metal to fill into lithographically patterned micropore structures toward deterministic plasmon emission with desired patterns. Our findings open up new possibilities for tunnel junction-based plasmon light sources, laying the foundation for electrically driven light-emitting metasurfaces.

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.

Improving Wettability at Positive Electrodes to Enhance the Cycling Stability of Bi-Based Liquid Metal Batteries.

Liquid metal batteries (LMBs) are promising candidates for grid-scale energy storage due to their exceptional kinetics, scalability, and long lifespan derived from the distinctive three-liquid-layer structure. However, the positive electrode (such as Bi) suffers from insufficient wettability on the current collector, resulting in excess electrical resistance and uneven current distribution, thus deteriorating the cycling stability. Here the incorporation of 4 mol% Se into Bi-based metal is proposed producing an interface layer with highly surface-active property that decreases the electrode's contact angle with the 304 stainless-steel (SUS304) from 144.7° to 74.3°, so as to improve the wettability. The as-prepared 20 Ah Li || Bi-Se4 (the content of Se is 4 mol% of Bi) cell cycled 1200 times with capacity fade rate of merely 0.00174% per cycle. This facile and effective approach provides a pathway toward the production of stable cells with an extended lifespan and boosts the practical implementation of LMBs.

A Room-Temperature Self-Healing Liquid Metal-Infilled Microcapsule Driven by Coaxial Flow Focusing for High-Performance Lithium-Ion Battery Anode.

Liquid metals have attracted a lot of attention as self-healing materials in many fields. However, their applications in secondary batteries are challenged by electrode failure and side reactions due to the drastic volume changes during the "liquid-solid-liquid" transition. Herein, a simple encapsulated, mass-producible method is developed to prepare room-temperature liquid metal-infilled microcapsules (LMMs) with highly conductive carbon shells as anodes for lithium-ion batteries. Due to the reasonably designed voids in the microcapsule, the liquid metal particles (LMPs) can expand freely without damaging the electrode structure. The LMMs-based anodes exhibit superior capacity of rete-performance and ultra-long cycling stability remaining 413 mAh g-1 after 5000 cycles at 5.0 A g-1. Ex situ X-ray powder diffraction (XRD) patterns and electrochemical impedance spectroscopy (EIS) reveal that the LMMs anode displays a stable alloying/de-alloying mechanism. DFT calculations validate the electronic structure and stability of the room-temperature LMMs system. These findings will bring some new opportunities to develop high-performance battery systems.

Deterministic Fabrication of Liquid Metal Nanopatterns for Nanophotonics Applications.

Gallium-based liquid metals (LMs) are widely used for stretchable and reconfigurable electronics thanks to their fluidic nature and excellent conductivity. These LMs possess attractive optical properties for photonics applications as well. However, due to the high surface tension of the LMs, it is challenging to form LM nanostructures with arbitrary shapes using conventional nanofabrication techniques. As a result, LM-based nanophotonics has not been extensively explored. Here, a simple yet effective technique is demonstrated to deterministically fabricate LM nanopatterns with high yield over a large area. This technique demonstrates for the first time the capability to fabricate LM nanophotonic structures of various precisely defined shapes and sizes using two different LMs, that is, liquid gallium and liquid eutectic gallium-indium alloy. High-density arrays of LM nanopatterns with critical feature sizes down to ≈100 nm and inter-pattern spacings down to ≈100 nm are achieved, corresponding to the highest resolution of any LM fabrication technique developed to date. Additionally, the LM nanopatterns demonstrate excellent long-term stability under ambient conditions. This work paves the way toward further development of a wide range of LM nanophotonics technologies and applications.

Liquid Metal Doping Induced Asymmetry in Two-Dimensional Metal Oxides.

The emergence of ferroelectricity in two-dimensional (2D) metal oxides is a topic of significant technological interest; however, many 2D metal oxides lack intrinsic ferroelectric properties. Therefore, introducing asymmetry provides access to a broader range of 2D materials within the ferroelectric family. Here, the generation of asymmetry in 2D SnO by doping the material with Hf0.5Zr0.5O2 (HZO) is demonstrated. A liquid metal process as a doping strategy for the preparation of 2D HZO-doped SnO with robust ferroelectric characteristics is implemented. This technology takes advantage of the selective interface enrichment of molten Sn with HZO crystallites. Molecular dynamics simulations indicate a strong tendency of Hf and Zr atoms to migrate toward the surface of liquid metal and embed themselves within the growing oxide layer in the form of HZO. Thus, the liquid metal-based harvesting/doping technique is a feasible approach devised for producing novel 2D metal oxides with induced ferroelectric properties, represents a significant development for the prospects of random-access memories.

Liquid Metal-Enabled Tunable Synthesis of Nanoporous Polycrystalline Copper for Selective CO2-to-Formate Electrochemical Conversion.

Copper-based catalysts exhibit high activity in electrochemical CO2 conversion to value-added chemicals. However, achieving precise control over catalysts design to generate narrowly distributed products remains challenging. Herein, a gallium (Ga) liquid metal-based approach is employed to synthesize hierarchical nanoporous copper (HNP Cu) catalysts with tailored ligament/pore and crystallite sizes. The nanoporosity and polycrystallinity are generated by dealloying intermetallic CuGa2 formed after immersing pristine Cu foil in liquid Ga in a basic or acidic solution. The liquid metal-based approach allows for the transformation of monocrystalline Cu to the polycrystalline HNP Cu with enhanced CO2 reduction reaction (CO2RR) performance. The dealloyed HNP Cu catalyst with suitable crystallite size (22.8 nm) and nanoporous structure (ligament/pore size of 45 nm) exhibits a high Faradaic efficiency of 91% toward formate production under an applied potential as low as -0.3 VRHE. The superior CO2RR performance can be ascribed to the enlarged electrochemical catalytic surface area, the generation of preferred Cu facets, and the rich grain boundaries by polycrystallinity. This work demonstrates the potential of liquid metal-based synthesis for improving catalysts performance based on structural design, without increasing compositional complexity.

Liquid Metal-Modified 3D Cu Foam for Dendrite-Free Sodium Plating.

Sodium metal is regarded as one of the most promising anode materials due to its high theoretical capacity (1166 mAh g-1) and low redox potential (-2.714 V vs standard hydrogen electrode). However, the practical application of sodium metal is hindered by the formation of dendrites during Na stripping and plating, which can degrade performance and cause potential safety hazards. To address this issue, previous work focuses on leveraging either 3D current collectors or liquid metal modification on current collectors. In this work, both strategies are simultaneously leveraged to design a 3D Cu foam with liquid metal modification (LM@Cu) for dendrite-free sodium plating. The 3D configuration of Cu effectively reduces local current density and evenly distributes electric fields, while the introduction of liquid metal enhances the sodiophilicity of Cu to lower the nucleation barrier for sodium, thereby promoting its uniform plating. As a result, symmetric cells of Na with LM@Cu maintain stable cycling for over 2800 h. Additionally, full cells comprising Na-LM@Cu and Na3V2(PO4)3 sustain 97.5% of the capacity upon 1000 cycles, underscoring the great potentiality of liquid metal-mediated 3D current collectors in energy storage.

Lignin-Stabilized Tough, Sticky, and Recyclable Liquid Metal/Protein Organogels for Multifunctional Epidermal Smart Materials.

Biomass-encapsulated liquid metals (LMs) composite gels have aroused tremendous attention as epidermal smart materials due to their biocompatibility and sustainability. However, they can still not simultaneously possess toughness, adhesion, and recoverability. In this work, the tough, sticky, and recyclable protein-encapsulated LMs organogels (GLMx) are fabricated through the micro-interfacial stabilization of LMs by lignin and the following preparation of food-making inspired gels. With the help of lignin modification, the LMs micro-drops demonstrated uniform dispersion in the protein matrix, as well as dense non-covalent interactions (e.g., H─bond and hydrophobic interaction) with amino acid residues in peptide chains, which endowed the GLMx with high conductivity (≈5.4 S m-1), toughness (≈738.2 kJ m-3), self-adhesiveness (a maximal lap-shear strength of ≈58.3 kPa), and recoverability. By tightly adhering onto human skin, the GLMx can act as epidermal sensors to detect drastic (e.g., joint bending) and subtle body movements (e.g., swallowing) and even recognize handwriting and speaking in real-time. Moreover, the organogels can also harvest solar energy and convert it into heat and electricity, which is promising in self-powered intelligent devices. Thus, this work paves a facile way to prepare protein/LMs composite organogels that are suitable for multiple applications like healthcare, human-robot interactions, and solar energy conversion.

3D Network of Liquid Metal-Embedded Graphene via Surface Coating for Flexible Thermal Management.

The rapid growth of flexible electronics has led to significant demand for relevant accessories, particularly highly efficient flexible heat dissipators. The fluidity of liquid metal (LM) makes it a candidate for realizing flexible thermal interface materials (TIMs). However, it is still challenging to combine LM with a conductive thermal network to achieve the synchronous improvement of thermal conductivity and flexibility. In this work, highly conductive flexible LM@GN/ANF films are made by coating LM nano-droplets with graphene nanosheets (GN) via sonication, and then they are combined with aramid nanofibers (ANF). The LM@GN/ANF film is found to have a thermal conductivity of 5.67 W m-1 K-1 and a 24.5% reduction in Young's modulus, making it suitable for various flexible electronic applications such as wearable devices and biosensors.

Alveoli-Mimetic Synergistic Liquid and Solid Thermal Conductive Interface as a Novel Strategy for Designing High-Performance Thermal Interface Materials.

Thermal interface materials (TIMs) are in desperate desire with the development of the modern electronic industry. An excellent TIM needs desired comprehensive properties including but not limited to high thermal conductivity, low Yong's modulus, lightweight, as well as low price. However, as is typically the case, those properties are naturally contradictory. To tackle such dilemmas, a strategy of construction high-performance TIM inspired by alveoli is proposed. The material design includes the self-alignment of graphite into 3D interconnected thermally conductive networks by polydimethylsiloxane beads (PBs) -the alveoli; and a small amount of liquid metal (LM) - capillary networks bridging the PBs and graphite network. Through the delicate structural regulation and the synergistic effect of the LM and solid graphite filler, superb thermal conductivity (9.98 ± 0.34 W m-1 K-1) can be achieved. The light emitting diode (LED) application and their performance in the central processing unit (CPU) heat dispersion manifest the TIM developed in the work has stable thermal conductivity for long-term applications. The thermally conductive, soft, and lightweight composites are believed to be high-performance silicone bases TIMs for advanced electronics.

Versatile Patterning of Liquid Metal via Multiphase 3D Printing.

This paper presents a scalable and straightforward technique for the immediate patterning of liquid metal/polymer composites via multiphase 3D printing. Capitalizing on the polymer's capacity to confine liquid metal (LM) into diverse patterns. The interplay between distinctive fluidic properties of liquid metal and its self-passivating oxide layer within an oxidative environment ensures a resilient interface with the polymer matrix. This study introduces an inventive approach for achieving versatile patterns in eutectic gallium indium (EGaIn), a gallium alloy. The efficacy of pattern formation hinges on nozzle's design and internal geometry, which govern multiphase interaction. The interplay between EGaIn and polymer within the nozzle channels, regulated by variables such as traverse speed and material flow pressure, leads to periodic patterns. These patterns, when encapsulated within a dielectric polymer polyvinyl alcohol (PVA), exhibit an augmented inherent capacitance in capacitor assemblies. This discovery not only unveils the potential for cost-effective and highly sensitive capacitive pressure sensors but also underscores prospective applications of these novel patterns in precise motion detection, including heart rate monitoring, and comprehensive analysis of gait profiles. The amalgamation of advanced materials and intricate patterning techniques presents a transformative prospect in the domains of wearable sensing and comprehensive human motion analysis.

Electrochemical Nitrate-to-Ammonia Conversion Enabled by Carbon-Decoration of Ni─GaOOH Synthesized via Plasma-Assisted CO2 Reduction.

The release of nitrates into the environment leads to contaminated soil and water that poses a health risk to humans and animals. Due to the transition to renewable energy-based technologies, an electrochemical approach is an emerging option that can selectively produce valuable ammonia from nitrate sources. However, traditional metal-based electrocatalysts often suffer from low nitrate adsorption that reduces NH3 production rates. Here, a Ni-GaOOH-C/Ga electrocatalyst for electrochemical nitrate conversion into NH3 is synthesized via a low energy atmospheric-pressure plasma process that reduces CO2 into highly dispersed activated carbon on dispersed Ni─GaOOH particles produced from a liquid metal Ga─Ni alloy precursor. Nitrate conversion rates of up to 26.3 µg h-1 mg-1 cat are achieved with good stability of up to 20 h. Critically, the presence of carbon centers is central to improved performance where both Ni─C and NiO─C interfaces act as NO3- adsorption and reduction centers during the reaction. Density functional theory (DFT) calculations indicate that the NiO─C and Ni─C reaction sites reduce the Gibbs free energy required for NO3- reduction to NH3 compared to NiO and Ni. Importantly, catalysts without carbon centers do not produce NH3, emphasizing the unique effects of incorporating carbon nanoparticles into the electrocatalyst.

Liquid Metal Interlayer for Ultrastable Solid-State Sodium Metal Battery.

Solid-state sodium metal batteries have attracted wide attention due to their high energy density, remarkable safety, and abundant sodium resources. However, the growth of Na dendrites and poor interfacial contact between Na metal anode and Na3Zr2Si2PO12 (NZSP) solid-state electrolytes severely limit their practical application. Herein, a wettable liquid metal (GaIn) interlayer significantly reduces the interfacial resistance and avoids the formation of voids at the Na/NZSP interface. Moreover, the Ga4Na and NaIn alloys at the interface caused by the spontaneous reaction of GaIn with Na metal enhance the bond of NZSP with Na anode, which provides a continuous Na+ diffusion pathway and homogeneous Na+ flux to suppress Na dendrite growth. The symmetric cell can cycle stably for over 6500 h at 0.05 mA cm-2 and over 3000 h at 0.1 mA cm-2, with a critical current density of 0.8 mA cm-2 at 25 °C, and the interfacial resistance is significantly reduced to 21.6 Ω from 1095.1 Ω. The full cell coupled with NaNi1/3Fe1/3Mn1/3O2 also shows outstanding cycling performance, maintaining 85.1% capacity after 100 cycles at 0.5 C. This work demonstrates that the liquid metal interlayer has a large potential for the practical application of solid-state metal batteries.

Surface-Enriched Room-Temperature Liquid Bismuth for Catalytic CO2 Reduction.

Bismuth-based electrocatalysts are effective for carbon dioxide (CO2) reduction to formate. However, at room temperature, these materials are only available in solid state, which inevitably suffers from surface deactivation, declining current densities, and Faradaic efficiencies. Here, the formation of a liquid bismuth catalyst on the liquid gallium surface at ambient conditions is shown as its exceptional performance in the electrochemical reduction of CO2 (i.e., CO2RR). By doping a trace amount of bismuth (740 ppm atomic) in gallium liquid metal, a surface enrichment of bismuth by over 400 times (30 at%) in liquid state is obtained without atomic aggregation, achieving 98% Faradic efficiency for CO2 conversion to formate over 80 h. Ab initio molecular simulations and density functional theory calculations reveal that bismuth atoms in the liquid state are the most energetically favorable sites for the CO2RR intermediates, superior to solid Bi-sites, as well as joint GaBi-sites. This study opens an avenue for fabricating high-performing liquid-state metallic catalysts that cannot be reached by elementary metals under electrocatalytic conditions.

3D Printed Gallium Battery with Outstanding Energy Storage: Toward Fully Printed Battery-on-the-Board Soft Electronics.

The last decade observed rapid progress in soft electronics. Yet, the ultimate desired goal for many research fields is to fabricate fully integrated soft-matter electronics with sensors, interconnects, and batteries, at the ease of pushing a print button. In this work, an important step is taken toward this by demonstrating an ultra-stretchable thin-film Silver-Gallium (Ag-Ga) battery with an unprecedented combination of areal capacity and mechanical strain tolerance. The Biphasic Gallium-Carbon anode electrode demonstrates a record-breaking areal capacity of 78.7 mAh cm-2, and an exceptional stretchability of 170%, showing clear progress over state-of-the-art. The exceptional theoretical capacity of gallium, along with its natural liquid phase self-healing, and its dendrite-free operation permits excellent electromechanical cycling. All composites of the battery including liquid-metal-based current collectors, and electrodes are sinter-free and digitally printable at room temperature, enabling the use of a wide range of substrates, including heat-sensitive polymer films. Consequently, it is demonstrated for the first time multi-layer, and multi-material digital printing of complex battery-on-the-board stretchable devices that integrate printed sensor, multiple cells of printed battery, highly conductive interconnects, and silicone chips, and demonstrate a tailor-made patch for body-worn electrophysiological monitoring.