Liquid Metal Nanoenergy Systems: Progress and Challenges

Abstract

The pursuit of advanced energy technologies has intensified the focus on innovative functional materials. Low-melting-point liquid metals (LMs), particularly Ga-based alloys, have emerged as a promising platform due to their unique combination of metallic conductivity, fluidity, and biocompatibility. Nanoscaling LMs to create nano-liquid metals (nano-LMs) further unlocks extraordinary properties, including electrical duality, enhanced surface reactivity, tunable plasmonics, and remarkable deformability, surpassing the limitations of their bulk counterparts. This review provides a comprehensive overview of the recent progress in nano-LM-based energy technology. We begin by delineating the fundamental properties of LMs and the novel characteristics imparted at the nanoscale. Subsequently, we critically analyze mainstream synthesis strategies, such as sonication, mechanical shearing, and microfluidics. The core of the review focuses on innovative applications in energy storage devices, energy harvesting system, and catalysis for energy conversion. Finally, we discuss persistent challenges in stability, scalable synthesis, and mechanistic understanding, while offering perspectives on future research directions aimed at realizing the full potential of nano-LMs in next-generation intelligent and sustainable energy systems.

1. Introduction

Against the backdrop of escalating global energy demands and increasingly severe environmental challenges, the pursuit of efficient, sustainable, and intelligent energy technologies has become a central theme in scientific research. Innovation in functional materials lies at the core of this transformation, offering pathways to advanced energy systems. Among various candidate materials, low-melting-point liquid metals (e.g., Ga and its alloys) have recently garnered significant attention as emerging functional materials, owing to their distinctive combination of properties. These materials not only exhibit characteristic metallic electrical, fluidic and thermal conductivity [1,2], but also display deformability [3,4], low volatility [5], and good biocompatibility [6], rendering them highly promising for applications in flexible energy devices [7,8,9], thermal management [10], wearable electronics [11,12], molecular scissor effects [13] and catalytic systems [14]. Their peculiar surface characteristics-such as autonomous reshaping [15], controllable oxidation [16], and unusual interfacial behavior across multiple scales [17] provide new avenues for designing high-performance and intelligent energy systems.

To transcend the limitations of conventional energy materials in terms of flexibility, interfacial transport, and multi-field coupling, and to enable energy systems with superior efficiency, adaptability, and intelligence, researchers are exploring new material platforms that allow precise regulation of energy capture, conversion, and storage at micro- and nanoscales. Nanomaterials have thus come into focus, with their distinctive nanoconfinement effects offering opportunities to surpass the performance boundaries of traditional bulk materials. Benefiting from extremely high specific surface areas, tunable quantum effects, and enhanced surface reactivities, nanomaterials exhibit exceptional capabilities [18,19]. These features make nanomaterials widely applicable in fields such as medical [20,21], electronics [22,23], energy [24,25], and other areas. It is within this context that the integration of liquid metals with nanotechnology-forming nano-liquid metal (nano-LM) systems with fluid metallic cores-has emerged as a particularly promising research direction. Current research on nano-LMs is advancing rapidly, with applications spanning energy generation, storage, conversion, and utilization. For instance, their high electrical conductivity and intrinsic self-healing capability make them attractive for energy storage devices [26]. Their plasmonic properties enable efficient light harvesting [27], and their deformability facilitates energy capture in flexible triboelectric nanogenerators (TENGs) [28]. Additionally, their highly active surfaces render them effective catalysts [29]. Despite these compelling demonstrations, key challenges remain in achieving long-term stability, scalable and controllable synthesis, mechanistic understanding, and system-level integration.

Given the highly interdisciplinary and rapidly evolving nature of nano-LM-based energy technology, this review provides a systematic overview of recent progress in the field, identifies critical scientific issues, and outlines future research directions. As illustrated in Figure 1, we begin with a discussion of the fundamental properties of liquid metals and their nanomaterials, followed by a summary of synthesis strategies for nano-LMs. We then critically review innovative applications and underlying mechanisms in energy storage, photoconversion, triboelectric generation, and catalysis. Finally, we discuss core challenges and offer perspectives on future developments. It is hoped that this review will inform future research in chemistry, materials science, and energy engineering, thereby supporting the ongoing development of nano-LM-based energy systems.

2. Fundamental Properties of Liquid Metals and Nano-Liquid Metals

2.1. Fundamental Properties of Liquid Metals

LMs derive their unique value from the combination of excellent intrinsic metallic properties and fluid-like deformability at room temperature - a traditionally paradoxical blend that endows them with unprecedented functional design flexibility and application diversity. The fundamental properties of LMs are interconnected and synergistic, forming a physicochemical basis for exploring their functionalities and applications.

One of the most distinctive and critical features of LMs is the instantaneous formation of an ultra-thin surface oxide layer when exposed to ambient air [30]. Ga and its alloys rapidly react with oxygen to form an extremely thin (typically 1–3 nm), dense, and self-limiting gallium oxide (Ga₂O₃) film (Figure 2a). The formation of this oxide layer is highly spontaneous thermodynamically, as evidenced by the strongly negative standard Gibbs free energy change (ΔG_f) for Ga₂O₃ compared to other metal oxides (Figure 2b), indicating a powerful driving force and extreme ease of reaction [31]. Remarkably, this oxide film is not a defect; rather, it is key to many of the extraordinary properties of LMs. A major function of this layer is to significantly stabilize the morphology of LMs. Without it, LMs would minimize surface energy by forming perfect spheres, making it difficult to fix shapes. The oxide skin provides a solid-like “skin” effect that effectively counteracts surface tension, enabling stable non-spherical configurations [32,33]. In addition to the counteracting effect of spontaneously formed oxide layers on surface tension, dynamic modulation of surface tension can be achieved through electrochemical oxide deposition techniques, thereby enabling controlled flow and precise manipulation of liquid metals [34,35]. For instance, Zhang et al. [36] employed a synergistic electrochemical mechanism to regulate the deformation of liquid metals. Their study demonstrated that in acidic or alkaline electrolytes, the application of voltage enables controlled formation and dissolution of oxide layers on the liquid metal surface. This process induces substantial variations in surface tension, successfully driving large-scale reversible deformation, directional movement, splitting, and coalescence of liquid metals. This trait underpins the patterning and micro-structuring of LMs, greatly expanding their potential in flexible electronics and deformable devices.

In addition to tunable morphological stability, LMs exhibit exceptionally high electrical conductivity, a core metallic attribute. As shown in Figure 2c, their conductivity is on the same order of magnitude as excellent solid conductors like copper and silver, far surpassing most flexible conductive materials, while maintaining fluidity and low viscosity [37]. This rare combination of metal-like conductivity and fluid deformability distinguishes LMs from conventional solid conductors and other soft materials, making them ideal for fabricating wires, electrodes, and interconnects in flexible and stretchable electronics. Recent innovative material designs have further unlocked the potential of LMs under high conductivity and large deformation conditions. For example, Gu et al. [38] developed an intrinsically conductive solid-liquid biphasic LM conductor by compositing EGaIn (74.5 wt % Ga, and 25.5 wt % In) with carboxymethyl chitosan via ultrasonic dispersion, forming a hydrogel-like conductive paste with a conductivity of 20,974 S/cm, which is 61.6% of pure EGaIn. Similarly, Liu et al. [39] designed a dynamically conformable electrode based on an LM and non-Newtonian fluid hybrid. By doping the LM with copper particles, they retained high conductivity while reducing fluidity, achieving a semi-liquid metal conductivity as high as 9.0 × 10⁶ S/m.

The fluid nature of LMs grants them infinite deformability, excellent flowability, and low viscosity, offering new avenues for intelligent bioinspired systems. Previous studies have shown that under external fields, LMs can readily deform, split, merge, and flow, stabilizing into new configurations via the surface oxide layer after the field is removed [40,41,42]. Recently, Ma et al. elevated this deformability to a level of biomimetic intelligence [15]. Inspired by the chemotactic behavior of leukocytes in vivo, they developed biomimetic liquid metal “leukocytes” (Figure 2d). By cleverly controlling the surface chemistry of LMs and chemical gradients in the environment, they achieved autonomous directional motion, shape-shifting, and task execution by LM droplets. This work goes beyond passive deformation, demonstrating active, intelligent transformation in response to environmental cues, opening new paths for microrobots for targeted drug delivery and environmental remediation.

The stretchability of LM devices is closely tied to their extreme deformability. This is reflected not only in the inherent fluidity and shape-changing ability of the material, but more importantly, in the unique advantage of maintaining functional integrity under large mechanical strain at the macroscopic device level [43]. A common strategy is to encapsulate LMs within microchannels made of elastomers (e.g., PDMS, Ecoflex) to form highly soft and stretchable wires [44,45]. It should be noted that the stretchability of such wires does not originate from the intrinsic elasticity of the LM itself, but rather from its fluidity: When stretched, the LM flows internally to adaptively fill the changing channel space, thereby maintaining both physical continuity of the conductive path and stability of electrical performance. In the aforementioned study, the solid-liquid phase metal conductor developed by Gu et al. also demonstrates remarkable mechanical tolerance: its resistance increased only 21-fold under a strain as high as 2200%, highlighting the great potential of such materials to maintain electrical stability under extreme deformation [38]. Bartlett et al. [46] further expanded the application of LMs in stretchable electronics. They innovatively used LMs not only as conductors but also as stretchable electrodes in dielectric elastomer actuators (DEAs). DEAs require soft dielectric materials with high permittivity and electrodes that remain conductive under large deformation. The team embedded EGaIn microparticles into a silicone rubber matrix, creating a new composite dielectric (Figure 2e). The LM particles significantly increased the composite’s dielectric constant and, thanks to their excellent fluidity, ensured the electrode maintained structural integrity and conductivity even under extreme area strains exceeding 1000% (Figure 2f).

Under repeated mechanical deformation, traditional metal conductors are prone to fatigue, cracking, and eventual failure [47]. In contrast, LMs exhibit an innate self-healing capability due to their room-temperature fluidity and unique physicochemical properties. If an LM conductive path is temporarily broken by external force, it can automatically fuse back together driven by surface tension once the fractured interfaces come back into contact, restoring the conductive pathway without significant degradation in electrical performance [48,49]. The self-healing property of LMs shows broad prospects in various cutting-edge fields. Guo et al. [50] utilized this property to develop an efficient pattern transfer technique: an LM pattern is first imprinted on a specific substrate leveraging the stability of the oxide skin, and then completely transferred to a target substrate via contact pressure. After transfer, the LM autonomously recovers from a discontinuous state to a continuous morphology, successfully establishing circuit connectivity (Figure 2g). This method is rapid and efficient, requiring no complex lithography or vacuum equipment. Hou et al. [51] constructed an LM-based electrocatalytic system where electric field-induced dynamic evolution of nanocatalysts enabled in situ self-repair of the electrocatalytic electrode after deactivation, significantly enhancing the stability of the CO₂ reduction reaction. Furthermore, Chen et al. developed a liquid-solid biphasic self-healing flexible circuit by combining LMs with low-melting-point solid alloys and embedding them in a microstructured elastic substrate. This circuit maintained stable conductivity under high voltage and large strain, with impact resistance and durability superior to traditional flexible circuits [52]. This innate self-healing capability greatly enhances the durability and reliability of flexible electronics in harsh mechanical environments, making LMs an ideal choice for building robust wearable devices and soft robots.

Figure 2. Fundamental properties of liquid metals. (a) Schematic diagram of liquid metal and its oxide film. (b) Gibbs free energy (ΔG_f) of the formation of different metal oxides. (a,b) Reproduced with permission from Ref. [31], copyright 2021, Wiley. (c) Volumetric conductivity versus mechanical rigidity for various materials. Reproduced with permission from Ref. [37], copyright 2015, Wiley (d) Transformable chemotaxic biomimetic LM leukocytes. Reproduced with permission from Ref. [15], copyright 2025, Elsevier. (e) Material schematic showing the dispersion of liquid-metal drops in a flexible and stretchable elastomer matrix. (f) Plot of tensile modulus as a function of the volume fraction loading of liquid metal. (e,f) Reproduced with permission from Ref. [46], copyright 2016, Wiley. (g) Self-healing ability of the liquid metal lines. Reproduced with permission from Ref. [50], copyright 2018, Wiley.

Figure 2. Fundamental properties of liquid metals. (a) Schematic diagram of liquid metal and its oxide film. (b) Gibbs free energy (ΔG_f) of the formation of different metal oxides. (a,b) Reproduced with permission from Ref. [31], copyright 2021, Wiley. (c) Volumetric conductivity versus mechanical rigidity for various materials. Reproduced with permission from Ref. [37], copyright 2015, Wiley (d) Transformable chemotaxic biomimetic LM leukocytes. Reproduced with permission from Ref. [15], copyright 2025, Elsevier. (e) Material schematic showing the dispersion of liquid-metal drops in a flexible and stretchable elastomer matrix. (f) Plot of tensile modulus as a function of the volume fraction loading of liquid metal. (e,f) Reproduced with permission from Ref. [46], copyright 2016, Wiley. (g) Self-healing ability of the liquid metal lines. Reproduced with permission from Ref. [50], copyright 2018, Wiley.

In summary, LMs, by combining fluidic properties with metallic characteristics, exhibit multi-scale and multi-form functional designability and application diversity, showing significant promise particularly in the energy sector. The spontaneously formed ultra-thin surface oxide layer not only provides excellent morphological stability and patterning capability, forming the basis for highly adaptive electrodes and conductors, but also, when coupled with high electrical conductivity and fluid deformability, enables stable electrochemical performance under large deformation, suitable for flexible energy storage, electrocatalysis, and stretchable thermoelectric systems. Furthermore, their outstanding fluidity, stretchability, and self-healing properties significantly improve device reliability and service life under mechanical stress, overcoming the limitations of traditional rigid conductors in flexible energy devices. However, current LM-based energy devices mostly rely on macroscopic or micron-scale material forms. Their relatively large size limits specific surface area and interfacial reactivity, presenting challenges in energy density and efficiency for applications highly dependent on surface and interface reactions, such as electrocatalysis and battery electrodes. To overcome this limitation, nanosizing liquid metals has become a crucial pathway for pushing performance boundaries. Liquid metal nanoparticles can significantly increase specific surface area, active sites, and modulate physical and electrochemical behaviors through size and surface effects.

2.2. Novel Properties of Liquid Metals Imparted by the Nanoscale

When the dimensions of liquid metals are reduced to the nanoscale, their physical and chemical properties exhibit distinct behaviors that significantly differ from those of their bulk counterparts, giving rise to a spectrum of novel characteristics [53,54,55]. These changes span multiple aspects, including electronic transport, thermal conduction mechanisms, deformability, biocompatibility, and optical responses, demonstrating broad multidisciplinary application prospects.

At the macroscopic scale, liquid metals exhibit high electrical conductivity approaching their intrinsic metallic values-for instance, EGaIn achieves a conductivity of up to 3.4 × 10⁶ S/m. However, when their size is reduced to the nanoscale, a fundamental transition in the conduction mechanism occurs. While bulk conduction arises from the continuous transport of free electrons, nanoscale liquid metal nanoparticles (LMNPs) develop an ultrathin (approx. 0.7–3 nm) native Ga₂O₃ due to their high specific surface area, rendering them insulating in the absence of external stimuli [56]. Liu et al. [57] systematically investigated the mechanical behavior of the oxide shell of LMNPs through experiments and simulations, revealing an inverse relationship between fracture stress and particle size: larger particles fracture more readily under tension, whereas smaller particles maintain structural integrity owing to enhanced shell stability. Leveraging this insight, the same study demonstrated the realization of both stretchable conductors with a conductivity of 24,130 S/cm at 500% strain and stretchable dielectrics that remain insulating even at 580% strain, highlighting the electrical duality of nanoscale liquid metals. As illustrated in Figure 3a, freestanding liquid metal structures (FS-Galn) can be fabricated via laser patterning on a silver nanowire (AgNW) composite film [58]. This strategy effectively integrates the intrinsic high conductivity of macroscopic liquid metals with the insulating behavior of nanoparticles resulting from interfacial barriers. The AgNW network serves as a conductive pathway that compensates for the limited conductivity of the nanoparticles, while laser processing enables precise control over conductive regions, offering a new approach for developing highly stretchable and complex three-dimensional electrodes.

In terms of thermal properties, liquid metals at the nanoscale exhibit unconventional behaviors, primarily attributable to their extremely high specific surface area and quantum confinement effects [59]. Although bulk liquid metals are widely used as thermal interface materials and cooling media [60], heat transfer mechanisms at the nanoscale differ markedly: confinement effects enhance phonon boundary scattering, leading to a reduction in intrinsic thermal conductivity. Nevertheless, their exceptionally large specific surface area significantly improves heat exchange efficiency [61], making them particularly suitable for efficient thermal management in microelectronic devices. A study has indicated that the high coalescence barrier of nanoscale liquid metal particles contributes to the long-term stability of insulating thermal interface materials [62]; other work has reported a printable liquid metal nanocomposite with an interfacial thermal resistance below 1 mm²·K/W, outperforming current commercial chip cooling materials [63]. Furthermore, a liquid metal/diamond sandwich-structured thermal interface material achieved a high thermal conductivity of 237.9 W/(m·K) and an ultralow interfacial thermal resistance of 2.53 K·mm²/W [64], providing a reliable solution for thermal management in high-power-density integrated circuits. More remarkably, Losurdo et al. [65] discovered that Ga nanoparticles can exhibit thermally stable coexistence of liquid and solid phases at room temperature. This anomalous behavior stems from a balance between surface and interfacial energies, not only expanding the fundamental understanding of phase transition theory at the nanoscale but also enabling the design of novel phase-change materials and thermal regulation devices (Figure 3b). As shown in Figure 3c, nanoscale Ga (~35 nm) exhibits significantly depressed melting and freezing points (−14.2 °C and −128.3 °C, respectively), far below the bulk melting point of 29.8 °C, underscoring the critical role of size effects in modulating thermal properties [66].

In the biomedical field, liquid metal nanoparticles offer considerable advantages due to their low toxicity, good biodegradability, and ease of functionalization [67,68]. As illustrated in Figure 3d, one study developed a tumor-microenvironment-responsive drug release system based on galvanic replacement reactions [69]. This approach utilizes the low pH and high glutathione levels in tumor regions to trigger the activation of liquid metal nanoparticles and subsequent drug release, enhancing targeting specificity while significantly reducing systemic toxicity, thereby providing a new strategy for precision cancer therapy. Wang et al. [70] developed a liquid metal-loaded microneedle patch, which showed no cytotoxicity at nanoparticle concentrations below 0.3 mg/mL and exhibited excellent antibacterial efficacy and wound-healing capacity in a methicillin-resistant Staphylococcus aureus infected mouse model. Treated animals showed no abnormalities in body weight, liver and kidney function, or tissue morphology, indicating good biocompatibility and therapeutic safety.

Another prominent feature of nanoscale liquid metals is their exceptional deformability and fluidic behavior, which governed by surface effects, endow them with morphological diversity beyond that of bulk forms [71]. Although macroscopic liquid metals are fluid, their high surface tension limits their patterning capabilities in practical applications. At the nanoscale, however, the high surface-area-to-volume ratio and dynamically reconfigurable surface oxide shell enable liquid metal particles to undergo substantial structural deformation and morphological transformation. Jeon et al. systematically investigated the shape evolution mechanisms of Ga-In alloy nanoparticles (Figure 3e), demonstrating that morphological transitions from spherical to fibrous, sheet-like, and even hollow structures can be achieved by controlling the oxidation degree and environmental pH [72]. This deformability arises from a dynamic balance between the fluidity of the liquid core and the mechanical stability of the surface oxide shell, offering a new pathway for developing intelligent shape-morphing materials and reconfigurable micro/nano devices.

Moreover, nanoscale liquid metals exhibit tunable plasmonic resonance characteristics and remarkable optical responses, originating from the collective oscillation of free electrons in the optical field within their core-shell structure [73]. By adjusting alloy composition, particle size, and morphology, their plasmonic absorption can be tuned broadly from the visible to the near-infrared region [74]. For instance, varying the Ga-In ratio allows continuous adjustment of the plasmon resonance peak, while external stimuli can induce shape changes, enabling dynamic modulation of their optical response [75]. In the core-shell structure, the liquid core provides a high concentration of free electrons, while the surface oxide shell modulates the local electromagnetic field distribution, collectively governing the optical properties [76]. Compared to traditional Au and Ag nanoparticles, liquid metal nanoparticles exhibit higher stability under high-temperature and oxidative environments, along with a broader tuning range, offering significant advantages in plasmonic photonics, sensing, and photothermal therapy [77].

Figure 3. Novel properties of liquid metals imparted by the nanoscale. (a) Schematic illustration of the LM-AgNW thin-film conductor process. Reproduced with permission from Ref. [58], copyright 2022, Springer Nature. (b) Energy-filtered image of Ga nanoparticles deposited on the sapphire substrates. Reproduced with permission from Ref. [65], copyright 2016, Springer Nature. (c) DSC curves of Ga nanoparticles and of bulk Ga (dashed black line). Reproduced with permission from Ref. [66], copyright 2015, Wiley. (d) Biocompatibility of nano-LM. Reproduced with permission from Ref. [69], copyright 2023, Wiley. (e) Shape transformation mechanism of EGaIn nanoparticles in water. Reproduced with permission from Ref. [72], copyright 2021, Wiley.

Figure 3. Novel properties of liquid metals imparted by the nanoscale. (a) Schematic illustration of the LM-AgNW thin-film conductor process. Reproduced with permission from Ref. [58], copyright 2022, Springer Nature. (b) Energy-filtered image of Ga nanoparticles deposited on the sapphire substrates. Reproduced with permission from Ref. [65], copyright 2016, Springer Nature. (c) DSC curves of Ga nanoparticles and of bulk Ga (dashed black line). Reproduced with permission from Ref. [66], copyright 2015, Wiley. (d) Biocompatibility of nano-LM. Reproduced with permission from Ref. [69], copyright 2023, Wiley. (e) Shape transformation mechanism of EGaIn nanoparticles in water. Reproduced with permission from Ref. [72], copyright 2021, Wiley.

Owing to their unique size effects and surface/interface characteristics, LMs at the nanoscale display distinct physicochemical behaviors divergent from those of bulk materials, showing great potential in flexible electronics, thermal management, biomedicine, and photonics. Their electrical duality, size-dependent thermal behavior, rich deformability, good biocompatibility, and dynamic plasmonic effects collectively constitute the core advantages of this material system. Future research may focus on their dynamic response mechanisms under multi-field coupling conditions, precise control of surface modifications, and cross-scale integration strategies, facilitating the transition of nanoscale liquid metals from fundamental concepts toward functional, integrated, and industrial applications. This material system not only expands the interdisciplinary frontier of nanoscience and liquid metal research but also provides a new perspective and platform for the design of next-generation intelligent materials and devices.

3. Synthesis Strategies for Nano-Liquid Metals

The inherently high surface tension and facile oxidation of liquid metals pose significant challenges for their processing into nanomaterials suitable for functional devices. Consequently, the development of controllable and efficient nanofabrication strategies has become a critical prerequisite for unlocking their application potential. Current mainstream preparation methods primarily include sonication, mechanical shearing, and microfluidics. This chapter will systematically review the principles, characteristics, and research progress of these three core technologies.

Sonication has become one of the most widely adopted methods for preparing LMNPs due to its operational simplicity, scalability, and high efficiency in achieving nanoscale fragmentation. This method induces cavitation effects in the liquid medium via high-intensity sound waves. The localized high-intensity shear forces generated by the collapse of cavitation bubbles overcome the surface tension of the liquid metal, leading to its fragmentation into nanodroplets. This process can be conducted in various solvents, often supplemented with surfactants to enhance colloidal stability and prevent agglomeration [78]. Syed et al. [79] showed that during sonication, liquid Ga is not only fragmented into micro-nano droplets but also undergoes rupture and exfoliation of its surface oxide layer. Subsequent annealing can transform these into porous α-Ga₂O₃ nanosheets and nanorods with high specific surface area (Figure 4a). Li et al. [80] improved this method by introducing chitosan as a stabilizer, successfully preparing core-shell nanoparticles (Figure 4b) which were used as water-based lubricant additives, demonstrating excellent tribological performance. Such functionalization strategies significantly expand the practical application scope of LMNPs. Recently, sonication has been further applied to construct complex hybrid structures. Li et al. [81] found that sonication enables the encapsulation of LMNPs within metal-organic frameworks (MOFs) (Figure 4c), yielding multifunctional nanocomposites applicable in advanced biomedical field. This strategy ingeniously combines the unique properties of liquid metals with the high surface area and tunable porosity of MOFs, indicating that sonication is not only useful for size reduction but also facilitates the construction of complex material architectures. Multiple studies further indicate that ultrasonic parameters critically influence the final product properties. For instance, research has confirmed that by controlling oxidation conditions during sonication, unique semiconductor properties can be introduced into the Ga₂O₃ shell, thereby expanding its potential applications in photocatalysis [82,83]. Additionally, the type of stabilizer (e.g., polymer or surfactant) decisively affects colloidal stability and functional performance, as supported by numerous studies [84,85].

Mechanical shearing relies on applying controlled mechanical forces to bulk liquid metal, causing its deformation and fragmentation into micro- to nano-scale droplets. Unlike sonication, which depends on cavitation effects, this method achieves droplet fragmentation through direct application of shear stress, offering good scalability and continuous production capability, making it particularly suitable for industrial-scale applications [86,87]. Nor-Azman et al. [88] systematically revealed a “dual-pathway” mechanism for LMNP generation during mechanical stirring using high-speed imaging. One is “surface eruption”, where cavitation bubble collapse at the liquid-gas interface causes interfacial wave disturbances and releases particles; the other is “internal eruption”, where cavitation bubbles coalesce, grow, and burst within the metal, forming crater-like structures and releasing particles (Figure 4d). This study first correlated vortex ring formation with particle release behavior. The Shearing Liquids Into Complex Particles (SLICE) technique developed by Tevis et al. [89], applying shear force to liquid metal within an acidic carrier fluid, enabled the controlled preparation of particles ranging from simple droplets to complex structures (Figure 4e). The method can not only be used to prepare core-shell nanoparticles with a liquid metal core and an oxide/organic shell, exhibiting a tunable particle size range from 6.4 nm to 10 μm, but also non-spherical solid particles with patchy surface chemistry or special morphologies by tuning shear conditions and the phase separation behavior of multi-component melts. The mechanism involves fluid shear-induced Rayleigh-Plateau instability and interface tension-driven phase segregation. Lebon et al. [90] noted that mechanical shearing is particularly suitable for high-viscosity systems, as sonication efficiency decreases significantly in such media. Furthermore, since it does not rely on cavitation, the mechanical method can avoid unnecessary surface oxidation, yielding cleaner interfaces applicable in scenarios requiring stringent surface state control [91].

Microfluidics enables precise independent control over the size, morphology, and composition of LMNPs, representing the highest precision level among current preparation strategies. This technology utilizes microfabricated channel structures and precisely controlled flow conditions to generate monodisperse droplets via shear-dominated or geometrically constrained fragmentation mechanisms. Its laminar flow characteristics ensure high reproducibility, typically with a coefficient of variation (CV) below 5% and excellent batch-to-batch consistency [92,93,94]. Tang et al. [95] demonstrated the capability of microfluidics for large-scale production of stabilized LMNPs, achieving fine-tuning of particle size from submicron to several microns by adjusting flow rate ratios, channel geometry, and interfacial tension (Figure 4f). This method integrates in-situ stabilization steps during droplet generation, yielding high colloidal stability without post-processing and avoiding particle coalescence common in conventional batch methods. Hutter et al. [96] employed a flow-focusing microfluidic device to generate droplets within different carrier fluids, such as an aqueous surfactant solution and silicone oil, by precisely controlling the phase flow rate ratio (Qc/Qd) and the nozzle size (e.g., 40 μm and 80 μm) to successfully produce monodisperse EGaIn droplets (Figure 4g). They found that in oxygenated silicone oil, a Ga₂O₃ shell instantly forms on the liquid metal surface, stabilizing non-spherical “microrice” structures with high aspect ratios up to 2.0, whereas in deoxygenated silicone oil or aqueous environments, droplets retract into spheres to minimize surface energy due to the lack of an oxide layer. Microfluidics also offers the capability to construct multi-component complex particles, such as core-shell structures via sequential droplet generation or encapsulation strategies. Research by Yu et al. [97], for example, demonstrated the successful preparation of core-shell particles with a liquid metal core and a polymer shell in a single microfluidic device. Such complex structures are difficult to achieve via batch methods, highlighting the unique advantage of microfluidics in constructing multifunctional particles.

The synthesis strategies for liquid metal nanoparticles have evolved from early simple physical fragmentation to a diverse technological system capable of precise control over size, structure, and surface chemistry. Sonication, mechanical shearing, and microfluidics are suitable for different application scenarios: sonication dominates laboratory research and preliminary applications due to its simplicity, high efficiency, and versatile functionalization; mechanical shearing demonstrates significant potential for industrial-scale applications owing to its excellent scalability and continuous production capability; microfluidics, with its unparalleled precision and reproducibility, has become the preferred method for achieving complex structures and high monodispersity in high-end applications. Future research should focus on the convergence and complementarity of different methods. For instance, integrating the precise control of microfluidics with the large-scale production capacity of mechanical strategies, or incorporating external fields such as electric or magnetic fields to enable in situ manipulation and online monitoring. Such advances are expected to bridge the gap from controlled synthesis to precise structuring of liquid metal nanomaterials, ultimately accelerating their broad application in cutting-edge fields such as flexible electronics, biomedicine, and energy catalysis.

Figure 4. Synthesis strategies for nano-LM. (a) Step-by-step schematic of the synthesis process converting Ga metal into Ga₂O₃ nanoparticles during sonication, kept in DI water. Reproduced with permission from Ref. [79], copyright 2017, Wiley. (b) The schematic presentation of the preparation process of nanoscale liquid metal wrapped by chitosan. Reproduced with permission from Ref. [80], copyright 2020, Elsevier. (c) Two-step assembly of LMNPs@MOFs supraparticles. Reproduced with permission from Ref. [81], copyright 2023, Elsevier. (d) Size distribution comparison of Ga and HSGaBi for liquid metals sonicated in Milli-Q water and in 0.1 M NaOH. Reproduced with permission from Ref. [88], copyright 2024, American Chemical Society. (e) Schematic illustration of the SLICE process showing transformation of liquid metal, EGaIn, into micro- and nanoparticles. Reproduced with permission from Ref. [89], copyright 2014, American Chemical Society. (f) Schematic representation of the working mechanism. Reproduced with permission from Ref. [95], copyright 2018, Wiley. (g) Liquid-metal droplet formation in aqueous PEG solution using a device with 40 μm nozzle geometry. Reproduced with permission from Ref. [96], copyright 2012, Wiley.

Figure 4. Synthesis strategies for nano-LM. (a) Step-by-step schematic of the synthesis process converting Ga metal into Ga₂O₃ nanoparticles during sonication, kept in DI water. Reproduced with permission from Ref. [79], copyright 2017, Wiley. (b) The schematic presentation of the preparation process of nanoscale liquid metal wrapped by chitosan. Reproduced with permission from Ref. [80], copyright 2020, Elsevier. (c) Two-step assembly of LMNPs@MOFs supraparticles. Reproduced with permission from Ref. [81], copyright 2023, Elsevier. (d) Size distribution comparison of Ga and HSGaBi for liquid metals sonicated in Milli-Q water and in 0.1 M NaOH. Reproduced with permission from Ref. [88], copyright 2024, American Chemical Society. (e) Schematic illustration of the SLICE process showing transformation of liquid metal, EGaIn, into micro- and nanoparticles. Reproduced with permission from Ref. [89], copyright 2014, American Chemical Society. (f) Schematic representation of the working mechanism. Reproduced with permission from Ref. [95], copyright 2018, Wiley. (g) Liquid-metal droplet formation in aqueous PEG solution using a device with 40 μm nozzle geometry. Reproduced with permission from Ref. [96], copyright 2012, Wiley.

4. The Applications of Nano-Liquid Metals

4.1. Nano-Liquid Metals for Energy Storage Devices

Liquid metals have demonstrated remarkable application potential in the field of energy storage. Their unique physical and chemical properties offer innovative solutions to critical challenges in conventional batteries, such as electrode volume expansion, dendrite growth, and interfacial instability, making them a leading research focus in high-performance energy storage systems. As illustrated in

Table 1. The advantages of liquid metal over conventional energy storage devices.

Properties	Liquid Metal Energy Storage Device	Conventional Energy Storage Device	Ref.
Thermal conductivity	7~10 W/mK	Organic PCM: 0.1~0.3 W/mK	[98]
Volumetric latent heat	217.8 MJ/m3	Organic PCM: 214.3 MJ/m3
Electrical conductivity	Strain > 100%, conductivity remains stable	Graphene: strains > 10%, conductivity drastically decreases	[99]
Energy density	1989 Wh/kg	Zinc-air battery: 1361 Wh/kg	[100]
Capacity retention rate	91.3% (1500 cycles)	Graphite anode: <80% (500 cycles)	[101]
Safety	Flame-retardant	Flammable and prone to thermal runaway	[102]

, the advantages of liquid metal over conventional energy storage devices have been reported in several studies. With continuous advances in nanotechnology and composite materials, nano-liquid metal-based energy storage devices are rapidly transitioning from laboratory-scale proof-of-concept toward practical application.

Alkali metal anodes are regarded as ideal candidates for next-generation high-energy-density rechargeable batteries due to their exceptionally high theoretical specific capacity and low electrochemical potential. However, severe dendrite formation and significant volume variation during cycling limit their long-term cyclability and safety [103,104]. Guo et al. [105] developed a room-temperature liquid alloy that functions as a self-healing anode for alkali metal batteries. The ternary alloy reversibly reverts to a binary eutectic liquid phase upon ion extraction, enabling continuous structural repair. As illustrated in Figure 5a, bulk liquid metal exhibits poor self-healing due to slow ion diffusion, leading to irreversible volume changes and interfacial failure. In contrast, when formulated as nano-sized particles composited with carbon and binder, the liquid metal achieves rapid ion transport and full structural recovery after cycling (Figure 5b). The practical advantage was confirmed in full cells with an LFP cathode: the Ga-In liquid metal anode maintained superior cycling stability, capacity retention, and high Coulombic efficiency over 200 cycles compared to metallic lithium, even under differing C-rates (Figure 5d), underscoring its potential for durable battery applications. Similarly, to suppress crack formation in electrodes caused by repeated volume changes during cycling, Zhu et al. [101] fabricated a self-supporting anode consisting of core-shell structured fibers prepared by coaxial electrospinning followed by carbonization. The resulting electrode encapsulates LMNPs within hollow carbon fibers, whose cavity structure effectively accommodates volume variations during lithiation/delithiation. The LMNPs, remaining liquid at room temperature, function as high-capacity active materials while endowing the electrode with self-healing capability. This binder- and conductive-additive-free design enhances the overall energy density by eliminating inactive components. Moreover, the incorporation of multi-walled carbon nanotubes and reduced graphene oxide improves electronic conductivity and mitigates LMNP agglomeration (Figure 5c).

Figure 5. Various nano-LM for energy storage devices. Schematics of the anode design and working mechanism for bulk liquid metal (a) and LMNP system (b) in a full cell. (c) The carbonization steps and the electrochemical processes for the LMNPs@CS fibers [101]. (d) Galvanostatic cyclic tests with carbon coated LiFePO₄ (LFP) as cathode, Li metal or LMNP electrode as anode. (a,b,d) reproduced with permission from Ref. [105], copyright 2018, Wiley. (e) Schematics of the battery structures and optical images demonstrating the LED illumination across different substrates. Reproduced with permission from Ref. [106], copyright 2025, Wiley. (f) In situ conductivity test during uniaxial stretching. (g) Schematic of LM-based symmetric stretchable ESD, showing ionogel sandwiched between the electrodes. (h) Photo of the device powering a temperature humidity monitor. (f–h) reproduced with permission from Ref. [107], copyright 2025, Wiley.

Figure 5. Various nano-LM for energy storage devices. Schematics of the anode design and working mechanism for bulk liquid metal (a) and LMNP system (b) in a full cell. (c) The carbonization steps and the electrochemical processes for the LMNPs@CS fibers [101]. (d) Galvanostatic cyclic tests with carbon coated LiFePO₄ (LFP) as cathode, Li metal or LMNP electrode as anode. (a,b,d) reproduced with permission from Ref. [105], copyright 2018, Wiley. (e) Schematics of the battery structures and optical images demonstrating the LED illumination across different substrates. Reproduced with permission from Ref. [106], copyright 2025, Wiley. (f) In situ conductivity test during uniaxial stretching. (g) Schematic of LM-based symmetric stretchable ESD, showing ionogel sandwiched between the electrodes. (h) Photo of the device powering a temperature humidity monitor. (f–h) reproduced with permission from Ref. [107], copyright 2025, Wiley.

However, the natural oxide layer formed on the surface of LMNPs tends to be mechanically weak, prone to fracture under stress, and susceptible to dissolution in harsh chemical environments, limiting their practical applicability. To overcome this challenge, researchers developed a dry biphasic nano-powder consisting of graphene oxide (GO) encapsulated liquid metal [106]. This core-shell structure ingeniously combines the high electrical conductivity and deformability of liquid metal with the excellent mechanical strength and chemical stability of graphene. The GO shell not only provides effective mechanical protection and chemical shielding for the liquid metal core but also facilitates rapid ion transport through its porous structure, making the material suitable for applications in energy storage and electrochemical sensing. Studies have shown that anodes based on GO@EGaIn nanocomposites exhibit significant energy storage capacity in alkali metal-ion batteries. Figure 5e illustrates a battery schematic with a trilayer printed architecture fabricated from four functional inks, highlighting its customizable and integrable design.

Beyond liquid metal batteries, the rapid development of flexible electronics has created an urgent demand for intrinsically stretchable energy storage devices. A representative study embedded liquid metal particles into an elastic conductive matrix, creating electrodes that withstand ~900% strain [107]. Conductivity even increased at 250% strain and recovered fully at 500%, due to particle reorganization and conductive pathway reformation (Figure 5f). The elastic matrix and liquid metal showed strong synergy, with smooth strain increase and no fracture or hysteresis (Figure 5g). The device retained 100% capacity after 1400 cycles, with Coulombic efficiency > 90%, demonstrating excellent durability. These stretchable devices are promising for wearable electronics and soft robotics, providing conformal integration and stable power (Figure 5h).

Nano-LM materials, leveraging their unique dynamic self-healing capability, excellent electrical conductivity, and high deformability, open important avenues for a new generation of high-performance and high-safety energy storage systems. From self-healing alloy anodes to stretchable electrode architectures, liquid metal-based materials show great potential in addressing key challenges such as electrode-electrolyte interfacial stability, volume variation, and mechanical flexibility. Although challenges remain in scalable material synthesis, long-term chemical stability, and interface engineering, ongoing interdisciplinary innovations are expected to drive significant breakthroughs in areas such as flexible electronics, smart wearables, and energy systems for extreme environments. Future research should focus more on integrated material-structure-function design to facilitate the translation of these technologies from the laboratory to real-world applications.

4.2. Nano-Liquid Metals for Energy Harvesting

The surface of liquid metals can generate unique plasmonic resonance effects, which can be tuned via deformation, alloying, or surface modification, offering a novel pathway for efficient light harvesting and mechanical-to-electrical energy conversion [108,109]. Nanoenergy technology focuses on harvesting minute ambient energy and converting it into electricity, thereby providing self-sustaining power solutions for low-consumption electronic devices. Among various energy harvesting approaches, liquid metal-based nanogenerators demonstrate remarkable application potential, primarily owing to their inherent rheological properties that maintain conductive pathways under large mechanical deformations, along with their tunable optical responses governed by surface oxide layers [110,111]. Furthermore, the self-healing capability of liquid metals significantly enhances the reliability and operational lifetime of energy harvesters, making them particularly suitable for flexible wearable devices and bio-integrated systems.

4.2.1. The Photothermal Effect of Nano-Liquid Metals

The photoelectric effect in liquid metals arises from their ability to generate or enhance electrical signals under illumination, primarily attributed to their unique optical properties and surface plasmon resonance effect [112]. Ga-based liquid metals such as EGaIn and Galinstan exhibit tunable optical responses across the visible to near-infrared spectrum, positioning them as promising material systems for high-performance photoelectric conversion devices [113]. Upon exposure to air, a self-limiting Ga₂O₃ forms spontaneously on their surface, which not only enhances stability but also significantly modulates light-matter interactions.

Recent research focuses on improving the photothermal conversion efficiency, structural stability, and functional integration of LMs for flexible electronics and energy harvesting. Qi et al. [114] developed a Ga³⁺/Ca²⁺ dual-ion chelation strategy, constructing a mechanically robust shell via a two-step coordination process that effectively addresses issues of oxidation and fusion. Owing to SPR, the resulting LM powder exhibits highly controllable photothermal behavior: under 808 nm NIR irradiation at 50–200 mW/cm², its temperature rises precisely to 30–64 °C within 120 s and remains stable (Figure 6a), outperforming the negligible response of bulk EGaIn. Integrated as a light-absorbing layer at the hot end of a solar thermoelectric generator (STEG), the powder establishes a stable temperature gradient of 25–40 °C under 60 s of sunlight, with uniform thermal distribution (Figure 6b,c). Another innovative design combines EGaIn nano-droplets with a 3D micro-pyramid grating array for broad-spectrum light trapping [115] (Figure 6d). Here, a polydopamine layer serves as both a thermal insulator and photothermal converter, while an rGO shell enhances broadband absorption, collectively suppressing heat dissipation. The pyramidal array boosts incident light coupling via multiple reflections and trapping, achieving absorptances of 94.9% and 97.3% along parallel and perpendicular grating orientations, with a total photothermal efficiency of 89.4%. Tuning PDA deposition time further optimizes performance; Figure 6e shows the short-circuit current (I_SC) of an integrated STEG under 1.5 G simulation, demonstrating rapid thermal response and structural reliability.

Figure 6. The photothermal effect of nano-LM. (a) Temperature-time curve of LM powders under NIR irradiation with various power densities. (b) Schematic illustration of the integrated STEG system. (c) Visualized light-to-heat conversion collected by IR imager and corresponding temperature distribution images of absorber upon solar light irradiation; (a–c) reproduced with permission from Ref. [114], copyright 2024, Wiley. (d) Schematic of the setup to measure the solar-thermal-electric properties. (e) I_SC yielded from the integrated STEG device upon the irradiation of simulated one sun illumination; (d,e) reproduced with permission from Ref. [115], copyright 2022, American Chemical Society. (f) Schematic illustration showing the transformable LM nanobots for antibacterial photothermal therapy. (g) Applications in ultrasound-assisted motion tracking and bioimaging, enabling real-time monitoring; (f,g) reproduced with permission from Ref. [116], copyright 2021, American Chemical Society. (h) Schematic illustration of the preparation process and light-induced shape transformation of PDA-coated LM nanodroplets. Reproduced with permission from Ref. [117], copyright 2019, Wiley.

Figure 6. The photothermal effect of nano-LM. (a) Temperature-time curve of LM powders under NIR irradiation with various power densities. (b) Schematic illustration of the integrated STEG system. (c) Visualized light-to-heat conversion collected by IR imager and corresponding temperature distribution images of absorber upon solar light irradiation; (a–c) reproduced with permission from Ref. [114], copyright 2024, Wiley. (d) Schematic of the setup to measure the solar-thermal-electric properties. (e) I_SC yielded from the integrated STEG device upon the irradiation of simulated one sun illumination; (d,e) reproduced with permission from Ref. [115], copyright 2022, American Chemical Society. (f) Schematic illustration showing the transformable LM nanobots for antibacterial photothermal therapy. (g) Applications in ultrasound-assisted motion tracking and bioimaging, enabling real-time monitoring; (f,g) reproduced with permission from Ref. [116], copyright 2021, American Chemical Society. (h) Schematic illustration of the preparation process and light-induced shape transformation of PDA-coated LM nanodroplets. Reproduced with permission from Ref. [117], copyright 2019, Wiley.

Advances in LM photoelectric technology have also enabled biomedical applications. NIR laser irradiation induces controllable morphological transitions in photo-responsive LM nanoparticles, accompanied by significant photothermal heating (19.7–29.5 °C increase, Figure 6f). This light-mediated reshaping and heating synergy allows for high-penetration antibacterial therapy and supports the development of theranostic nanoplatforms. Figure 6g illustrates applications in ultrasound-assisted motion tracking and bioimaging, enabling real-time monitoring [116]. Additionally, PDA-coated LM droplets offer a route to reconfigurable photodetectors (Figure 6h) [117]. Ultrasonication disperses bulk LM into stable nano-droplets, which are encapsulated via dopamine self-polymerization in Tris buffer. The PDA shell exhibits strong photothermal conversion, driving droplet shape change from spherical to ellipsoidal under laser exposure. This enables adaptive optimization of the light-absorbing interface, laying a foundation for dynamically tunable photoresponse.

Despite these advantages, the path forward is faced with core challenges rooted in material properties and fabrication limits. The inherent high surface tension and fluidity of LMs make them difficult to pattern and unstable over time. Additionally, their interfacial compatibility with solid substrates is often poor, affecting both mechanical strength and electrical performance. Finally, creating scalable, uniform nanostructures requires a new level of precision in printing and deposition methods.

4.2.2. Liquid Metal Nanogenerators

In recent years, with the rapid advancement of flexible electronics and sustainable energy technologies, liquid metals have emerged as one of the ideal functional materials for constructing high-performance energy harvesting devices, owing to their unique fluidity, high electrical conductivity, low toxicity, and good biocompatibility. Among various energy conversion mechanisms, liquid metal-based nanogenerators, particularly triboelectric nanogenerators (TENGs) and electric double layer (EDL) generators, have demonstrated remarkable application potential and unique electromechanical behaviors, showing broad prospects in fields such as wearable electronics, soft robotics, and bio-integrated devices [118,119].

The working principle of LM-TENGs primarily relies on the coupling of contact electrification and electrostatic induction effects. When the liquid metal periodically contacts and separates from another dielectric material, charge transfer occurs at the interface. Due to the strong electropositivity of Ga atoms, the liquid metal surface typically carries a positive charge, while the dielectric material surface acquires a negative charge. This charge separation creates a potential difference in the external circuit, driving directional electron flow to achieve mechanical-to-electrical energy conversion [120,121]. Currently, construction strategies for LM-TENGs can be broadly categorized into three types: patterning [122], encapsulation [123,124], and blending [125,126]. These methods not only enable large-scale preparation of liquid metals but also allow precise control over their microstructures (e.g., liquid films, microspheres, or nanospheres), offering rich possibilities for developing high-performance, multifunctional triboelectric materials. Nayak et al. [127] reported a porous composite foam fabricated by a NaCl-templating method using Galinstan liquid metal (Ga₆₂In₂₂Sn₁₆) and Ecoflex elastomer, which functions as a TENG for efficient mechanical energy harvesting. The material demonstrates excellent malleability, high triboelectric output, and capacitive force-sensing capability. At an optimal composition, its electrical performance exceeds that of conventional polymer or composite foam-based TENGs. Yang et al. [121] developed a structurally designable LM-TENG employing eutectic galinstan as a stretchable electrode and silicone rubber as both the triboelectric and encapsulation layer. Benefiting from the fluidity and ultralow Young’s modulus of the liquid metal, the device withstands in-plane strain up to 300% while maintaining stable electrical output under stretching, folding, and twisting. A spontaneous Ga₂O₃ layer prevents further oxidation and leakage, improving reliability. Operating in single-electrode mode at 3 Hz, the TENG delivers an open-circuit voltage of 354.5 V, a short-circuit current of 15.6 μA, and an average power density of 8.43 mW/m², enabling efficient human motion energy harvesting. As shown in Figure 7a, the device functions on the arm, clothing, and foot sole; Figure 7b indicates an output current up to 18.6 μA with increasing motion frequency; and Figure 7c confirms stable electrical performance over repeated 300% stretching, supporting its use in high-deformation applications such as joints.

Tang et al. achieved a record instantaneous energy conversion efficiency of 70.6% for LM-TENGs, significantly exceeding the approximately 55% limit of conventional solid-solid contact TENGs [128]. This breakthrough results from the liquid metal’s excellent rheological adaptability, which enables near perfect conformity with the polymer triboelectric layer, increasing the charge density to 430 μC/m², a four- to fivefold improvement over traditional devices. The liquid metal’s ultralow friction coefficient minimizes mechanical energy loss, while its stable properties inhibit interface wear, ensuring long-term electrical stability. As shown in Figure 7d,e, efficient charge transfer occurs via a cyclic immersion-separation-reimmersion process, with dynamic conformability ensuring full interfacial contact. Furthermore, capacitor charging tests in Figure 7f demonstrate that under 10 Hz vibration, the device can charge a 100 μF capacitor to 1 V within 65 s, confirming its excellent energy harvesting performance and stable output for practical applications.

Beyond triboelectric mechanisms, liquid metal-based EDL generators have also made significant progress. The core component of liquid metal-based EDL generators typically comprises a variable capacitance structure, whose energy harvesting performance is closely linked to the dynamic variation in capacitance. Such capacitors regulate capacitance through the reconstruction of the electric double layer at the interface between the liquid metal and the ionogel. When external mechanical forces induce deformation of the liquid metal within a porous medium, the effective contact area of the electric double layer is altered, thereby enabling reversible modulation of the capacitance [129]. Zavabeti et al. [130] elucidated the dynamic regulation mechanism of the EDL at the liquid metal interface, paving the way for the development of microfluidic energy harvesting systems requiring no external power sources. These generators convert energy via reversible changes in the electric double layer at solid-liquid interfaces, making them particularly suitable for low-frequency mechanical energy harvesting. Che et al. [131] constructed an EDL generator by embedding EGaIn liquid metal into a porous cellulose nanofibril-based ionic gel. Mechanical pulsation induces asymmetric deformation of the liquid metal, restructuring the electric double layer and generating alternating current. The device achieves high energy conversion efficiency and outperforms most biomass-based generators. Figure 7g illustrates the charge redistribution process during compression-release. Figure 7h shows that increasing liquid metal content enhances interface area and charge transfer. The generator also exhibits good cycling stability (Figure 7i), demonstrating potential for sustainable energy and self-powered sensing.

As an emerging mechanical energy harvesting technology, liquid metal nanogenerators exhibit outstanding performance potential and wide application prospects. LM-TENGs, leveraging the superior rheological properties, high conductivity, and interfacial adaptability of liquid metals, achieve higher charge density and energy conversion efficiency than conventional solid TENGs, while demonstrating good stability and adaptability in stretchable, wearable integrated systems [132,133,134]. On the other hand, LM-EDLs, by ingeniously combining liquid metals with porous media such as ionic gels and utilizing asymmetric EDL changes at micro-interfaces, enable efficient low-frequency mechanical energy capture, expanding their applications in biocompatible and sustainable energy systems [135,136,137].

Nevertheless, transitioning this technology from the laboratory to practical applications faces several challenges. First, the impact of the formation and evolution of the oxide layer on the liquid metal surface on interface charge transfer and long-term device stability requires further clarification. Second, current encapsulation strategies are largely limited to laboratory settings, necessitating the development of highly reliable encapsulation techniques for real-world scenarios. Additionally, most studies focus on single energy harvesting functions; effective system integration with sensors, energy storage units, and signal transmission modules is crucial for practicality. For instance, flexible system integration strategies could be adopted to combine LM-TENGs with micro-supercapacitors, constructing self-powered sensing systems [138].

Figure 7. Liquid metal nanogenerators. (a) General applications of the liquid-metal-based triboelectric nanogenerator. (b) Electrical output under various motion frequencies ranging from 0.5 to 3 Hz, including open-circuit voltage (V_OC), short-circuit current (I_SC), and transferred charge (Q_SC). (c) Electrical output at different stretchable strains at the motion frequency of 2 Hz. (a–c) reproduced with permission from Ref. [121], copyright 2018, American Chemical Society. (d) Schematic illustrations of the device. (e) Schematic illustrations of the device and the testing setup. (f) The charging curves of a 100 µF capacitor under various vibration frequencies; (d–f) reproduced with permission from Ref. [128], copyright 2015, Wiley. (g) Schematic illustration of LM moving in and out of ionogel pores under external stress. (h) Dependence of output voltage on EGaIn content. (i) Energy harvest from human motions when by installing within shoe sole; (g–i) reproduced with permission from Ref. [131], copyright 2025, Wiley.

Figure 7. Liquid metal nanogenerators. (a) General applications of the liquid-metal-based triboelectric nanogenerator. (b) Electrical output under various motion frequencies ranging from 0.5 to 3 Hz, including open-circuit voltage (V_OC), short-circuit current (I_SC), and transferred charge (Q_SC). (c) Electrical output at different stretchable strains at the motion frequency of 2 Hz. (a–c) reproduced with permission from Ref. [121], copyright 2018, American Chemical Society. (d) Schematic illustrations of the device. (e) Schematic illustrations of the device and the testing setup. (f) The charging curves of a 100 µF capacitor under various vibration frequencies; (d–f) reproduced with permission from Ref. [128], copyright 2015, Wiley. (g) Schematic illustration of LM moving in and out of ionogel pores under external stress. (h) Dependence of output voltage on EGaIn content. (i) Energy harvest from human motions when by installing within shoe sole; (g–i) reproduced with permission from Ref. [131], copyright 2025, Wiley.

4.3. Nano-Liquid Metals for Catalysis and Energy Conversion

The application of liquid metals in catalysis primarily benefits from their excellent intrinsic catalytic activity, recyclability, and flexible surface functionalization capabilities [14,139]. Compared to traditional solid catalysts, liquid metals exhibit remarkable self-healing properties during reactions, effectively preventing catalyst deactivation caused by surface area reduction or structural sintering [140]. Furthermore, their surface oxide layers not only confer good mechanical stability to the system but also provide a unique solid-liquid interface environment for various chemical reactions, significantly enhancing performance in electrocatalysis, photocatalysis, and thermoelectric conversion processes [141].

In the field of photoelectrochemistry, composite photoanodes incorporating nano-LMs and semiconductors demonstrate significant advantages. Studies confirm that tuning the work function of liquid metals allows precise optimization of the electronic structure at the three-dimensional metal/semiconductor interface, thereby enhancing the separation and collection efficiency of photogenerated charge carriers [142]. In thermal catalysis, liquid metals are particularly suitable for high-temperature processes such as ammonia synthesis, methane conversion, and higher hydrocarbon synthesis. Their dynamic interfaces and surface effects help lower reaction activation energies, improving atom utilization and reaction efficiency [143]. For instance, Cao et al. [144] successfully synthesized high-entropy alloy nanoparticles under moderate conditions using a liquid metal as the reaction medium. The negative mixing enthalpy between Ga and key catalytic elements (Fe, Co, Ni, Cu) indicates strong binding affinity, effectively suppressing element segregation; whereas Sn and In, with positive ΔH_mix, tend to agglomerate. This synthesis strategy leverages the negative mixing enthalpy between Ga and most metals to reduce the system’s Gibbs free energy, overcoming thermodynamic immiscibility limitations. Coupled with a dynamic fusion-fission mechanism, it enables uniform multi-element mixing, ultimately yielding structurally stable high-entropy alloy nanoparticles without requiring extreme temperatures or quenching.

In electrocatalysis, liquid metal-based catalysts demonstrate exceptional performance in the oxygen reduction reaction (ORR) [145], hydrogen evolution reaction (HER) [146], and carbon dioxide reduction reaction (CO2RR) [147]. Their high conductivity and tunable electronic structure provide an ideal platform for multi-electron reactions. The 3D nanoporous structure, shown in Figure 8a,b, originates from the synergy between component segregation, selective oxidation, and dealloying processes in the liquid phase, providing a foundation for exposing high-density active sites. Electrochemical double-layer capacitance (C_dl) tests (Figure 8c) indicated a threefold increase in the electrochemical active surface area for nh-CuIn, the nanoporous Cu-In bimetallic material. Its abundant interface structures not only enhance CO₂ adsorption capacity but also optimize the adsorption behavior of key intermediates through electronic interactions between Cu and In, thereby improving catalytic activity and product selectivity [148].

In photocatalysis, liquid metals show great promise in applications such as water splitting, pollutant degradation, and artificial photosynthesis due to their excellent photothermal conversion efficiency and tunable surface plasmon resonance behavior [149]. Parker et al. [150]. developed star-shaped liquid metal nanodroplets (Figure 8d) with a well-defined core-shell structure: an outer metal oxide shell for interface stabilization and reaction path modulation, a middle liquid metal mantle layer serving as the main body for light harvesting and energy conversion, and a core of highly active solid metal phase. This structure was constructed via high-temperature ultrasonication in molten sodium acetate, effectively avoiding dealloying issues common in room-temperature preparations and yielding size-uniform, structurally stable liquid metal nano-building blocks. Research indicates that their photocatalytic performance and selectivity can be further optimized by controlling size, surface chemistry, and doping strategies. The Cu-Ga planetary nano-droplets in alkaline electrolyte exhibit a peak current density of 0.0015 A/cm² for electrocatalytic ethanol oxidation, which is significantly higher than that of pure Ga nano-droplets (0.0005 A/cm²) and the bare carbon cloth substrate (close to 0 A/cm²). The outer shell not only provides stability but also directly participates in the adsorption and activation of reactants [151].

Particularly noteworthy is the Rebinder effect, whereby liquid metals can permeate and disrupt the oxide layer on aluminum surfaces, significantly catalyzing the aluminum-water reaction and promoting hydrogen generation [152]. Based on this mechanism, Zhang et al. [153] developed a self-driven liquid metal soft machine that synergistically combines autonomous motion and energy conversion (Figure 8e). In an alkaline environment, the liquid metal and aluminum constitute a galvanic cell system, inducing bipolar electrochemical reactions that create surface charge and wettability gradients. These gradients, in turn, drive continuous system motion via the Marangoni effect, accompanied by the helical generation and release of hydrogen, showcasing potential applications in autonomous energy systems and soft robotics.

Figure 8. Nano-LM for catalysis and energy conversion. (a) Nanoscale structure schematic diagram and photographs of the nh-CuIn. (b) SEM patterns of the nh-CuIn. (c) Charging current density differences for the Cu foam, EGaIn/Cu, CuGa₂ & In, and nh-CuIn; (a–c) reproduced with permission from Ref. [148], copyright 2022, Springer Nature. (d) Schematic of the hot sonication setup depicting heating and sonication of the system and thus the nanodroplet formation. Reproduced with permission from Ref. [150], copyright 2024, Wiley. (e) Self-fueled liquid metal motor running in a circular Petri dish and in a circular channel. Reproduced with permission from Ref. [153], copyright 2015, Wiley.

Figure 8. Nano-LM for catalysis and energy conversion. (a) Nanoscale structure schematic diagram and photographs of the nh-CuIn. (b) SEM patterns of the nh-CuIn. (c) Charging current density differences for the Cu foam, EGaIn/Cu, CuGa₂ & In, and nh-CuIn; (a–c) reproduced with permission from Ref. [148], copyright 2022, Springer Nature. (d) Schematic of the hot sonication setup depicting heating and sonication of the system and thus the nanodroplet formation. Reproduced with permission from Ref. [150], copyright 2024, Wiley. (e) Self-fueled liquid metal motor running in a circular Petri dish and in a circular channel. Reproduced with permission from Ref. [153], copyright 2015, Wiley.

Liquid metals exhibit unique advantages in catalysis and energy conversion, including dynamic interfaces, multivariate synergistic catalysis, and cross-scale structural control. However, transitioning from fundamental research to practical applications faces substantial challenges. Firstly, the mechanistic understanding of liquid metal catalytic systems requires deepening. The dynamic structural evolution of the liquid interface during reactions, the true state of active sites, and mass transfer/adsorption processes at the solid-liquid interface remain unclear and necessitate precise elucidation through in situ characterization techniques and theoretical calculations. Secondly, the long-term cycling stability and practicality of liquid metal catalysts need rigorous assessment. Component volatilization, oxidation, and structural creep of the liquid carrier under high-temperature reaction conditions may lead to gradual activity decay. Furthermore, current synthesis methods are largely confined to laboratory scales. Achieving the scalable production of liquid metal nanocatalysts with high uniformity and loading remains a significant challenge warranting further investigation.

5. Discussion and Conclusions

Liquid metal nano-enabled energy systems, an emerging frontier at the intersection of materials science, nanotechnology, and energy engineering, have demonstrated transformative potential. This review systematically summarizes recent advances in liquid metals and their nanomaterials, covering fundamental physicochemical properties, controlled synthesis strategies, and applications in energy storage, harvesting, conversion, and catalysis (Figure 9). The unique liquid-solid duality, excellent electrical and thermal conductivity, remarkable deformability, and spontaneous surface oxidation of liquid metals form the basis for their functional applications. Nanoscaling not only preserves these intrinsic properties but also introduces nanoscale features such as high specific surface area, quantum confinement effects, and tunable plasmonic resonance, significantly enhancing performance in electrochemical interfacial reactions, mechanical energy harvesting, and heterogeneous catalysis.

In energy storage, nano-LMs suppress dendrite growth and electrode volume expansion through dynamic self-healing mechanisms, substantially improving battery cycling stability and safety. For energy harvesting, liquid metal-based triboelectric nanogenerators and photothermal devices enable efficient capture of mechanical and solar energy, while their excellent stretchability and adaptive interfacial contact offer new pathways for flexible wearable electronics. In catalysis and energy conversion, the dynamic interfaces, negative mixing enthalpy, and surface reconfigurability of liquid metals provide novel paradigms for constructing high-performance electrocatalytic and photocatalytic systems, as well as synthesizing high-entropy alloy catalysts.

Nevertheless, challenges remain. The long-term stability of nano-LMs requires resolution, as the evolution of surface oxide layers, leakage of liquid cores, and aggregation may compromise device longevity and performance consistency. Current synthesis methods struggle to balance scalable production with precise control, and large-scale, uniform, low-cost fabrication techniques are still underdeveloped. Understanding of structure-property relationships and underlying mechanisms is incomplete, particularly regarding in situ characterization of interfacial ion/electron transport and plasmon relaxation under operational conditions.

Future research should focus on multidimensional material design and performance modulation-developing core-shell structures, heterointerfaces, and multicomponent nano-LM systems, while improving environmental stability and functionality through surface modification and composite encapsulation. Overcoming bottlenecks in cross-scale fabrication and integration is essential, necessitating scalable yet precise techniques such as template-assisted self-assembly, continuous-flow synthesis, and additive manufacturing. Mechanistic studies and bio-inspired innovation should be strengthened, employing in situ electron microscopy and synchrotron radiation to probe structural evolution and carrier dynamics in real time, and designing self-healing, adaptive bionic energy systems. Furthermore, environmental compatibility and system-level applications should be expanded-exploring potential in implantable medical devices, soft robotics, and deep-space exploration-while considering lifecycle environmental impact and sustainable recycling strategies.

Meanwhile, the environmental impact and safety of liquid metal nanomaterials warrant further investigation. Current research continues to prioritize performance enhancement, while studies on their environmental behavior remain limited. A better understanding of their biotoxicity, environmental transport, and ecological accumulation is essential for sustainable energy applications. This should include clarifying the release dynamics and toxicology of metal ions such as gallium and indium in various environments. In addition, effective recycling strategies for these nanomaterials are still lacking. Future efforts should focus on designing recyclable systems and developing practical methods such as low-temperature phase separation, electrochemical deposition, and magnetic capture. These approaches will improve the life-cycle environmental compatibility of liquid metal nanomaterials.

As a vibrant research field, liquid metal nano-enabled energy systems continue to drive innovation in energy technology. Through interdisciplinary collaboration and the integration of fundamental research with engineering applications, breakthroughs can be expected, providing critical materials and technological support for building efficient, intelligent, and sustainable next-generation energy systems.