Thermal Shock Synthesis of Metal Nanoclusters within On-the-Fly Graphene Particles

Abstract

Metal nanoclusters (1–10 nm) have drawn great attention because of their potential applications including energy storage, catalysis, nanomedicine, and electronic devices. However, manufacturing ultrasmall metal nanoparticles at high concentrations in an unaggregated state is not a solved problem. Here, we report an aerosol-based thermal shock technique for in situ synthesis of well-dispersed metal nanoclusters in on-the-fly graphene aerosols. A rapid thermal shock to the graphene aerosol has been used to nucleate and grow the metal nanoclusters with subsequent quenching to freeze the newly formed nanoclusters in the graphene aerosol matrix. A characteristic time analysis comparison with the experiment shows that the nanocluster formation is governed by nucleation and subsequent surface growth and that the graphene retards coagulation, enabling unaggregated metal nanoclusters. The method is generic, and we show the formation of sub-10 nm Ni, Co, and Sn nanoclusters. This continuous aerosol-based thermal shock technique offers considerable potential for the scalable synthesis of well-dispersed and uniform metal nanoclusters stabilized within a host matrix. As an example of potential application, we demonstrate very favorable catalytic properties.

Rapid Laser Pulse Synthesis of Supported Metal Nanoclusters with Kinetically Tunable Size and Surface Density for Electrocatalytic Hydrogen Evolution

“…This saturation ratio change is mainly affected by four primary processes: (a) generation of Pt atoms from thermal decomposition of H 2 PtCl 6 , (b) consumption of Pt atoms due to nucleus formation, (c) evaporation of Pt atoms from the surface of the stable nuclei, and (d) consumption of vapor phase Pt atoms due to Pt condensation onto the surface of the existing nuclei. These processes can be well described by the moment model as follows: 17,18…”

“…This saturation ratio change is mainly affected by four primary processes: (a) generation of Pt atoms from thermal decomposition of H 2 PtCl 6 , (b) consumption of Pt atoms due to nucleus formation, (c) evaporation of Pt atoms from the surface of the stable nuclei, and (d) consumption of vapor phase Pt atoms due to Pt condensation onto the surface of the existing nuclei. These processes can be well described by the moment model as follows: , Here, R H is the reaction rate of metal salt precursor decomposition to zerovalent metal atoms, and A is the total surface area of all the nuclei in the reaction volume; both R H and A are time-dependent variables. k * is the number of monomers in a single particle with a critical radius r c , and n s is the monomer concentration at saturation condition.…”

Theoretical Framework Based on Molecular Dynamics and Data Mining Analyses for the Study of Potential Energy Surfaces of Finite-Size Particles

“…15 (iv) Pyrolysis-based procedures can be used to produce welldefined metallic nanoclusters in a carbon media/substrate, with activation temperatures ranging from 600 to 900 °C. 16,17 Therefore, we can expect the coexistence of two fundamental mechanisms, both in synthesis and application, namely, (i) the temperature will change the nanocluster morphology and (ii) the morphological change will affect the observed properties of the system. However, we do not yet know how these morphological changes modulate the properties observed experimentally in these materials.…”

Rapid Carbothermal Shock Enhances the Double-Layer Response of Graphene Oxide–Carbon Nanotube Electrodes

“…33−35 To perform CTS via Joule heating, the carbon substrate requires sufficient electrical conductivity to generate high temperatures at ultrafast heating rates. Studies have shown CTS being applied to commercial and synthetic carbon substrates, such as a CO 2 -activated carbon nanofiber, 33,36 aligned electrospun carbon nanofiber, 37 carbon fiber cloth, 30 graphene, 38,39 and rGO. 40,41 These freestanding carbon films are binderless to minimize resistive heating loss across the carbon electrode during CTS; an example of such a film that has yet to be studied with CTS treatment includes GO as a result of its poor electrical conductivity.…”

“…Recently, researchers have demonstrated numerous benefits of CTS, including the ability to deposit nanoparticles onto carbon substrates with precise control of the nanoparticle density, size, and composition (e.g., nanoparticles comprising up to eight elemental constituents). − To perform CTS via Joule heating, the carbon substrate requires sufficient electrical conductivity to generate high temperatures at ultrafast heating rates. Studies have shown CTS being applied to commercial and synthetic carbon substrates, such as a CO 2 -activated carbon nanofiber, , aligned electrospun carbon nanofiber, carbon fiber cloth, graphene, , and rGO. , These free-standing carbon films are binderless to minimize resistive heating loss across the carbon electrode during CTS; an example of such a film that has yet to be studied with CTS treatment includes GO as a result of its poor electrical conductivity. Of note, a pre-annealing step is typically performed at a high temperature under an inert atmosphere to slightly improve the conductivity of GO, which is then subsequently subjected to Joule heating to produce rGO. , In this manner, where Joule heating is carried out on a longer time scale, rGO has shown to exhibit promising electrochemical performance. , The low electrical conductivity of GO (∼10 –5 S cm –1 ) limits itself to any rapid Joule heating-induced reduction; thus, preparing a composite with an electrically conductive additive, like CNTs (up to 10 6 –10 7 S cm –1 ), is necessary and unique to this work.…”