Thin, Porous, and Conductive Networks of Metal Nanoparticles through Electrochemical Welding on a Liquid Metal Template

Abstract

interfacial forces, [6][7][8] surface modifications, [9,10] as well as well-controlled external fields [11][12][13][14][15] have been adopted, which yield vast types of complex yet delicate particle structures with outstanding functionalities. By virtue of interfacial forces, fluid-interface-assisted self-assembly (or self-organization) has been proven to be a simple yet powerful method. [6,7,11,[16][17][18][19][20][21][22][23] Although self-assembled particle structures are stable at the confining template, losing interfacial confinements causes immediate breakdown because the particles are not physically connected. For limited types of particles, for instance polymeric particles, a sintering process at elevated temperature has been performed for stabilization purpose. [17][18][19][20] Metal particles represent another important group of particle materials that offer numerous editable properties stemming from both the diversity of metals and their hierarchical size effects. High-melting-point metal particles can only be molded at exceedingly high temperatures through methods such as laser or electron-beam-assisted additive manufacturing [24] and liquid phase sintering. [25] Although highenergy methods are able to construct large-scale, high-strength objects, they are not feasible for micro/nanoscale fabrication due to their precision limitation and the requirement for highenergy source. Significant effort has been devoted to exploring methods for low-temperature fabrication of metal nanostructures. [26][27][28][29][30][31] Fluid-interface-assisted fabrication still remains as one of the few, if not the only, available methods to fabricate multi-scale well-designed structures out of metal particles. [32][33][34][35] Unfortunately, interfacial metal particles cannot be sintered under moderate temperature range due to their intrinsic highmelting metallic nature.To address this challenge, here we propose a particle cross-linking strategy that can stabilize interfacial metal particle structures at room temperature. We show that discrete copper nanoparticles (Cu NPs) can be cross-linked to form continuous porous phases at a liquid metal (LM)-electrolyte template, which is electrochemically reducing. In reminiscence of the high-energy metallurgical welding, we call this in-solution particle cross-linking process "electrochemical welding". We conduct surface composition analyses to clarify the underlying mechanisms. We also characterize the mechanical properties and the electrical properties Manipulating particles using a fluid interface has both fundamental implications and technological promises. However, the stabilization of interfacial particle structures remains challenging. This study proposes a room-temperature particle cross-linking strategy achieved by introducing a surface transition process to metal particles confined at a liquid metal-electrolyte template, which is electrochemically reducing. The method enables cross-linking Cu nanoparticles into nanoporous networks of micrometric thickness. It is shown that...

Discoloration Effect and One-Step Synthesis of Hydrogen Tungsten and Molybdenum Bronze (HxMO3) using Liquid Metal at Room Temperature

“…22−27 It was reported that CO 2 was reduced to carbon species and copper oxide was reduced to copper phases on the surface of liquid metal at room temperature. 28,29 Moreover, a series of findings on biomimetic chromatic liquid-metal soft robots was disclosed recently. 30,31 Lightened by the above research studies, the discoloration effect of TMOs via liquid metal reduction was first expounded in the present work.…”

Interfacial Engineering of Room Temperature Liquid Metals

“…Left: Reproduced with permission. [19] Copyright 2018, Wiley-VCH. (h) The schematic diagram of carbon dioxide fixation based on liquid metal.…”

“…Figure 7B described the synthesis of thin and conductive Cu-LM particles, which provided a general strategy for particle-based, interface-assisted fabrication. [19] Liquid metals provide a brand-new avenue for the catalytic synthesis and fixation of carbon materials in ambient circumstances. RTLMs can break the chemical bonds like CO, CN, and CH bonds in organic molecules at room temperature and reconstruct them into CC bonds of graphite-type.…”

“…Reproduced with permission. [19] Copyright 2018, Wiley-VCH. C) 2D graphite nanomaterials by electrochemical synthesis via liquid metal.…”

“…The wetting paradigm of the solid-liquid interface is of great significance for revealing the correspondence between properties of interfacial products and wetting behaviors, which would provide a scientific basis for engineering potential applications, such as welding, [19,104] electronic device packaging, [3,105] chemical reaction in solution, [22,65] and fabrications of composite materials. [106][107][108] The wetting phenomenon of the solid-liquid metal interface could be segmented into physical wetting (inert wetting) and reactive wetting (chemical wetting), according to whether chemical reactions occur and new substances form at the interface.…”