Liquid Metal as Energy Conversion Sensitizers: Materials and Applications

Abstract

Energy can exist in nature in a wide range of forms. Energy conversion refers to the process in which energy is converted from one form to another, and this process will be greatly enhanced by energy conversion sensitizers. Recently, an emerging class of new materials, namely liquid metals (LMs), shows excellent prospects as highly versatile materials. Notably, in terms of energy delivery and conversion, LMs functional materials are chemical responsive, heat-responsive, photo-responsive, magnetic-responsive, microwave-responsive, and medical imaging responsive. All these intrinsic virtues enabled promising applications in energy conversion, which means LMs can act as energy sensitizers for enhancing energy conversion and transport. Herein, first the unique properties of the light, heat, magnetic and microwave converting capacity of gallium-based LMs materials are summarized. Then platforms and applications of LM-based energy conversion sensitizers are highlighted. Finally, some of the potential applications and opportunities of LMs are prospected as energy conversion sensitizers in the future, as well as unresolved challenges. Collectively, it is believed that this review provides a clear perspective for LMs mediated energy conversion, and this topic will help deepen knowledge of the physical chemistry properties of LMs functional materials.

Keywords: energy conversion; liquid metal; sensitizers.

Figure 1

Platforms and applications of LMs as energy conversion sensitizers.

Figure 2

The fluidic property of LMs. Comparison of a) water and b) GaIn_24.5 droplets impacting their respective liquid pools during the splashing processes at the same moment. Reproduced with permission.^{[ 30 ]} Copyright 2014, Elsevier. c‐i) Contact angle of a Galinstan droplet on a bare glass slide and a Teflon‐coated glass slide in air and after exposure of the droplet to HCl vapor. Reproduced with permission.^{[ 31 ]} Copyright 2013, American Chemical Society. ii) Contact angle of the LMs with the graphite substrate in different electrolyte solutions. Reproduced with permission.^{[ 32 ]} Copyright 2018, American Chemical Society.d). i) The impacting tests LM‐Cu samples reveal liquid‐ to the solid‐like transition of their impacting behaviors as ϕ increases. ii) Schematic demonstration of fluidity decreases and rigidity increases of the LM‐Cu samples as ϕ increases. Reproduced with permission.^{[ 33 ]} Copyright 2017, American Chemical Society.

Figure 3

Electrochemically induced energy conversion. a) LMs‐based catalysts for catalytic synthesis; i) Ga‐based LMs containing additional metallic elements in the form of supersaturated nanoparticles, solutes, and intermetallic compounds; ii) Bi‐based LMs. b) The surface tension regulation to trigger the deformation or motion of LMs; i) LMs‐graphite galvanic cell; ii) Cu–Ga galvanic cell. c) The autonomous movement of LM droplets, via i) hydrogen bubbles generation enhanced by electric field or ii) actuating fuel introduction, and iii) self‐electrophoresis.

Figure 4

Thermal properties of LMs. a) Pure LMs: i) pure LMs with fluidity and metallicity, showing extremely wide liquid range and high thermal conductivity; ii) the ratio of heat transfer coefficient of water and Ga₆₈In₂₀Sn₁₂ versus Re number. Reproduced with permission.^{[ 63 ]} Copyright 2014, Elsevier. b) LMs‐particles compounds: i) the thermal conductivity of LMs‐ particles compounds can be greatly improved by doping other high thermal conductivity materials, such as carbon nanotubes, copper particles, and silver particles; ii) thermal conductivity (k_T) measurement of LM‐Cu composite as a function of the mass ratios of CuGa₂ (ω) and Cu (ϕ), respectively. Reproduced with permission.^{[ 33 ]} Copyright 2017, American Chemical Society.c) LMs‐polymer composites: i) LMs can be mixed into organic polymers (such as silicone oil, silicone rubber, and polydimethylsiloxane (PDMS)) to achieve thermally‐conductive LM‐polymer composites; ii) thermal conductivities of the thermally‐conductive LM‐polymer composites showing good consistency with Maxwell‐Garnett's model prediction. Reproduced with permission.^{[ 68 ]} Copyright 2018, The Royal Society Of Chemistry.

Figure 5

a) The light responsiveness of LMs materials with different types and sizes. 1) colorful luster under the interference of light, 2) light induced surface plasmon resonance (SPR), 3) light induced ROS generation, 4) light induced shape transformation. The optical performance of LMs NPs: b) Extinction, absorption, and scattering spectra of the EGaIn NPs. c) Calculated absorption efficiency Q_abs as a function of wavelength for 50, 100, 150, and 200 nm sized particles. Reproduced with permission.^{[ 81 ]} Copyright 2019, Springer Nature. d) Ultraviolet‐visible–NIR absorbance spectrum of LMs NPs. e) Transmittance spectrum of LMs NPs. Reproduce with permission.^{[ 82 ]} Copyright 2019, Elsevier.

Figure 6

a) Magnetic behaviors of LMs‐based magnetic fluid under permanent magnetic field (PMF): i) magnetic curing behavior: high‐speed videos for the dynamic impact of striking LMs droplets (GaIn_24.5) and magnetic LMs droplets (Ni nanoparticles loaded GaIn_24.5) on a magnet plate. Reproduced with permission.^{[ 90 ]} Copyright 2013, Elsevier. ii) magnetic manipulation behavior: magnetic actuation for steering LMs droplet locomotion^{[ 91 ]}; iii) magnetic stretching behavior: the sequential snapshots of the magnetic LMs droplets under the magnetic manipulation in the horizontal level. Reproduced with permission.^{[ 86 ]} Copyright 2019, American Chemical Society.b) Magnetic behaviors of LMs fluid under alternating magnetic field (AMF): i) dynamic transformation: morphological changes of LMs and Terfenol‐D under AMF induction Reproduced with permission.^{[ 16 ]} Copyright 2018, The Authors.ii) controllable manipulation behavior: time‐lapsed electromagnetic levitation images of an LMs droplet in water. Reproduced with permission.^{[ 16 ]} 2018, The Authors. c) The magnetocaloric phenomenon under AMF: thermal IR images of oxidized LMs and LMs with different field intensities under the AMF. Reproduced with permission. ^{[ 17 ]} Copyright 2020, John Wiley and Sons.

Figure 7

LMs NPs with microwave response. a) IL‐LM‐ZrO₂ supernanoparticles (IL‐LM‐ZrO₂ SNPs) were constructed by loading LMs (generation source of ROS) and ionic liquid (microwave heating enhancer) into mesoporous ZrO₂ nanoparticles. b) The ROS generation mechanism of LMs NPs. c) Fluorescence intensity of ·OH generated in PBS and LMs NPs under different treatments. d) Maximum fluorescence intensity of ·OH generated in PBS under different treatments. Electron paramagnetic resonance (EPR) detection of LMs NPs under MW irradiation to produce e) ·OH and f) ·O₂. Reproduced with permission.^{[ 18 ]} Copyright 2019, American Chemical Society.

Figure 8

LMs enhanced energy conversion platforms and applications. a) LMs materials as heat sensitizers for enhanced heat transfer. 1) Liquid metal compact heat spreader. Reproduced with permission.^{[ 102 ]} Copyright 2018, Springer Nature. 2) Experimental device diagram of the actual cooling effect of methyl silicone oil, thermally conductive paste, and LM‐TIMs. Reproduced with permission.^{[ 68 ]} Copyright 2018, The Royal of Society Chemistry. 3) The temperature distribution of the whole tumor is more concentrated and uniform with LMs paste. Reproduced with permission.^{[ 104 ]} Copyright 2020, American Chemistyr Society. b) Applications of LMs materials as laser sensitizers used in photothermal conversion. 1) Photothermal responses of EGaIn nanodroplets with different shapes upon NIR laser irradiation. 2) Schematic illustration of Mg‐GaIn mediated heat concentration in vivo cancer PTT. Reproduced with permission.^{[ 13 ]} Copyright 2018, John Wiley and Sons. 3) Cryopreservation of HBMSCs using LMs NPs under NIR. Reproduced with permission.^{[ 82 ]} Copyright 2020, Elsevier. c) LMs materials as magnetocaloric conversion sensitizers in drug release and hyperthermia therapy. 1) Schematic illustration of gel‐sol transition of LMs‐agarose gel composite upon AMF induction. Reproduced with permission.^{[ 16 ]} Copyright 2018, The Authors. 2) AMF‐driven transformable LMs hybrid for cancer thermochemotherapy. Reproduced with permission.^{[ 114 ]} Copyright 2019, John Wiley and Sons. 3) Schematic illustration of conformable oxidized GaIn bioelectrodes on in vivo tumors under an AMF. Reproduced with permission.^{[ 105 ]} Copyright 2019, John Wiley and Sons. d) LMs as microwave sensitizers for dynamic therapy. Reproduced with permission.^{[ 18 ]} Copyright 2019, American Chemical Society. e) LMs as medical imaging sensitizers for enhanced imaging. 1) X‐ray angiogram of the heart filled with LMs Ga (left) and iohexol (right). Reproduced with permission.^{[ 117 ]} Copyright 2014, IEEE. 2) 3D renderings of in vivo CT scans before and after LMs injection. Reproduced with permission.^{[ 114 ]} Copyright 2019, John Wiley and Sons. 3) CT image and the MRI T2 image of mice after LMs injection. Reproduced with permission.^{[ 118 ]} Copyright 2020, John Wiley and Sons. 4) Ultrasound (US, gray) and photoacoustic (PA, red) images were taken through the tumor by 750 nm laser excitation. Reproduced with permission.^{[ 9 ]} Copyright 2017, Springer Nature.