Facile Fabrication of Bimetallic Ag-Bi High Dense Nanospheres on Carbon Nanotubes for High Performance Supercapacitor Electrodes

<b>Abstract body</b><br/>Efficient energy conversion and storage is essential to develop various platforms such as mobility platforms and portable electronics. Supercapacitor is a promising candidate to perform fast charging and discharging within high-capacity energy and being developed as a type of next-generation energy conversion and storage device. Hybrid nanostructures involving high specific surface area and outstanding stability are required for more advanced supercapacitor electrodes since the theoretical performance of constituent materials used in current supercapacitors has reached the limit. A hybrid structure of metal/metal oxides and carbon-based materials have attracted a lot of attention as a rational design to satisfy such requirements in terms of the pseudocapacitive characteristics, extended surface areas and superior physicochemical stability. However, the fabrication of the hybridized meta/metal oxides/carbon-based materials inevitably require complex multi-step processes that incur high-cost and long-processing time.<br/>In this work, we report a novel synthesis route toward one-step fabrication of bimetallic Ag-Bi nanospheres on carbon nanotubes (CNTs) using a combustion process and their applications for high-performance supercapacitor electrodes. After preparing the dispersed solution of silver oxides, bismuth powders, and CNTs in distilled water through sonication, a vacuum filtration method was used to deposit them on a nitrocellulose membrane. Then, the collodion was dropped on it to provide a chemical fuel for a combustion process and dried for 12 hours. The precursors comprising of silver oxides, bismuth powders, and CNTs with the nitrocellulose was heated to 500 °C for 30 seconds in a furnace to induce spontaneous ignition, thereby implementing a completed combustion process which applied instant thermochemical energy conversion. In this process, the amount of bismuth powders was adjusted to lower the melting point of the alloy to induce a very short cooling time (~0.21 s) for fabricating hybrids of physicochemically stable Ag-Bi high-dense nanospheres (~20 nm). The resulting nanospheres were directly obtained on CNTs. Morphology and micro-nanostructures of the bimetallic Ag-Bi-CNTs were precisely analyzed using Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM). The high-temperature processing provided by a combustion process could implement dual-function of synthesizing Ag-Bi high dense nanospheres and concomitantly adhering them on CNTs. Based on optimizing the fabrication process in terms of the precursors and combustion, the hybrid nanostructure was developed as supercapacitor electrodes and their electrochemical performances exhibited high specific capacitance (1093 F/g at 5 mVs^-1) and outstanding capacitance retention (&gt; 80% after 10000 charge-discharge cycles). Because the combustion synthesis route does not require a long processing time, bulky setup, or any special environment, it can apply to various field for multimetallic nanostructures. The fabrication strategy in this work could contribute to an efficient method for developing versatile electrochemical electrodes enabling excellent capacity and durability.