Jae Chan Kim

Characterization of Fe–Co alloyed nanoparticles synthesized by chemical vapor condensation

Abstract Iron–cobalt alloyed (Fe 1− x Co x , x ≤50 wt.%) nanoparticles with core–shell structure was prepared by chemical vapor condensation (CVC) process and characterized via X-ray diffraction (XRD), transmission electron microscopy (TEM), and vibrating sample magnetometer. The particles having the mean size of 5–25 nm consisted of metallic cores and oxide shells. The nanoparticle size increased with increasing gas flow rate. The saturation magnetization and coercivity increased with increasing Co content, and the saturation magnetization reached its maximum rate at 40 wt.% Co.

Tailoring uniform γ-MnO2 nanosheets on highly conductive three-dimensional current collectors for high-performance supercapacitor electrodes

Recent efforts have focused on the fabrication and application of three-dimensional (3-D) nanoarchitecture electrodes, which can exhibit excellent electrochemical performance. Herein, a novel strategy towards the design and synthesis of size- and thickness-tunable two-dimensional (2-D) MnO2 nanosheets on highly conductive one-dimensional (1-D) backbone arrays has been developed via a facile, one-step enhanced chemical bath deposition (ECBD) method at a low temperature (∼50 °C). Inclusion of an oxidizing agent, BrO3−, in the solution was crucial in controlling the heterogeneous nucleation and growth of the nanosheets, and in inducing the formation of the tailored and uniformly arranged nanosheet arrays. We fabricated supercapacitor devices based on 3-D MnO2 nanosheets with conductive Sb-doped SnO2 nanobelts as the backbone. They achieved a specific capacitance of 162 F·g−1 at an extremely high current density of 20 A·g−1, and good cycling stability that shows a capacitance retention of ≈92% of its initial value, along with a coulombic efficiency of almost 100% after 5,000 cycles in an aqueous solution of 1 M Na2SO4. The results were attributed to the unique hierarchical structures, which provided a short diffusion path of electrolyte ions by means of the 2-D sheets and direct electrical connections to the current collector by 1-D arrays as well as the prevention of aggregation by virtue of the well-aligned 3-D structure.

High-power and long-life supercapacitive performance of hierarchical, 3-D urchin-like W18O49 nanostructure electrodes

We report the facile, one-pot synthesis of 3-D urchin-like W18O49 nanostructures (U-WO) via a simple solvothermal approach. An excellent supercapacitive performance was achieved by the U-WO because of its large Brunauer–Emmett–Teller (BET) specific surface area (ca. 123 m2·g–1) and unique morphological and structural features. The U-WO electrodes not only exhibit a high rate-capability with a specific capacitance (Csp) of ~235 F·g–1 at a current density of 20 A·g–1, but also superior long-life performance for 1,000 cycles, and even up to 7,000 cycles, showing ~176 F·g–1 at a high current density of 40 A·g–1.

An approach to flexible Na-ion batteries with exceptional rate capability and long lifespan using Na2FeP2O7 nanoparticles on porous carbon cloth

As post-Li-ion batteries (LIBs), rechargeable Na-ion batteries (NIBs) are considered as one of the potential candidates for large-scale energy storage systems because of the abundance and low cost of sodium resources, and similar electrochemical behavior of Na ions to Li ions for intercalation in cathodes. While there exist many challenges in the fabrication of cathodes, a polyanionic compound, Na2FeP2O7, has been in the spotlight as a potential cathode material for NIBs because of its rate capability, cyclability, and thermal stability. In this study, Na2FeP2O7 nanoparticles (NFP-NPs) embedded in carbon were prepared via a citric acid-assisted sol–gel method, followed by a post-heat treatment process. For the first time, NFP-NPs exhibited a reversible capacity close to the theoretical value (95 mA h g−1) over the voltage range of 2.0–4.0 V (vs. Na/Na+). Moreover, they displayed a superior rate capability of 77, 70, 66 and 65 mA h g−1 even at high rates of 10, 20, 30 and 60C, respectively. Equally notable is their exceptional long-term cyclability at high rates. At the rate of 10 and 60C, the capacity retention after 10 000 cycles is 83 and 84%, respectively. In addition, NFP-NPs uniformly loaded on the surface of flexible porous carbon cloth (NFP-NPs@PCC) electrodes without any conductive agents and polymeric binders also exhibit excellent rate capability and long-term cyclability at a high rate of 10C (56 mA h g−1 after 2000 cycles). We show high-performance free-standing NFP-NPs@PCC electrodes for possible application in flexible NIBs.

Germanium microflower-on-nanostem as a high-performance lithium ion battery electrode

We demonstrate a new design of Ge-based electrodes comprising three-dimensional (3-D) spherical microflowers containing crystalline nanorod networks on sturdy 1-D nanostems directly grown on a metallic current collector by facile thermal evaporation. The Ge nanorod networks were observed to self-replicate their tetrahedron structures and form a diamond cubic lattice-like inner network. After etching and subsequent carbon coating, the treated Ge nanostructures provide good electrical conductivity and are resistant to gradual deterioration, resulting in superior electrochemical performance as anode materials for LIBs, with a charge capacity retention of 96% after 100 cycles and a high specific capacity of 1360 mA h g−1 at 1 C and a high-rate capability with reversible capacities of 1080 and 850 mA h g−1 at the rates of 5 and 10 C, respectively. The improved electrochemical performance can be attributed to the fast electron transport and good strain accommodation of the carbon-filled Ge microflower-on-nanostem hybrid electrode.

Oleic-acid-assisted carbon coating on Sn nanoparticles for Li ion battery electrodes with long-term cycling stability

We report the one-pot synthesis of high-performance Sn@C nanocomposite anode materials obtained by uniform carbon coating onto Sn nanoparticles induced by electrical Sn-wire explosion in oleic acid liquid media at room temperature. This Sn@C nanocomposite exhibits highly reversible Li-storage performance with a specific capacity of ∼730 mA h g−1, even after 200 cycles.

Biomineralized Multifunctional Magnetite/Carbon Microspheres for Applications in Li-Ion Batteries and Water Treatment

Advanced functional materials incorporating well-defined multiscale architectures are a key focus for multiple nanotechnological applications. However, strategies for developing such materials, including nanostructuring, nano-/microcombination, hybridization, and so on, are still being developed. Here, we report a facile, scalable biomineralization process in which Micrococcus lylae bacteria are used as soft templates to synthesize 3D hierarchically structured magnetite (Fe3O4) microspheres for use as Li-ion battery anode materials and in water treatment applications. Self-assembled Fe3O4 microspheres with flower-like morphologies are systematically fabricated from biomineralized 2D FeO(OH) nanoflakes at room temperature and are subsequently subjected to post-annealing at 400 °C. In particular, because of their mesoporous properties with a hollow interior and the improved electrical conductivity resulting from the carbonized bacterial templates, the Fe3 O4 microspheres obtained by calcining the FeO(OH) in Ar exhibit enhanced cycle stability and rate capability as Li-ion battery anodes, as well as superior adsorption of organic pollutants and toxic heavy metals.

Electrospun Cu/Sn/C nanocomposite fiber anodes with superior usable lifetime for lithium- And sodium-ion batteries

Cu/Sn/C composite nanofibers were synthesized by using dual-nozzle electrospinning and subsequent carbonization. The composite nanofibers are a homogeneous amorphous matrix comprised of Cu, Sn, and C with a trace of crystalline Sn. The Li- and Na-ion storage performance of the Cu/Sn/C fiber electrodes were investigated by using cyclic voltammetry, galvanostatic cycling, and electrochemical impedance spectroscopy. Excellent, stable cycling performance indicates capacities of 490 and 220 mA h g(-1) for Li-ion (600 cycles) and Na-ion (200 cycles) batteries, respectively. This is a significant improvement over other reported Sn/C nanocomposite devices. These superior electrochemical properties could be attributed to the advantages of incorporating one-dimensional nanostructures into the electrodes, such as short electron diffusion lengths, large specific surface areas, ideal homogeneous structures for buffering volume changes, and better electronic conductivity that results from the amorphous copper and carbon matrix.

Waste Windshield-Derived Silicon/Carbon Nanocomposites as High-Performance Lithium-Ion Battery Anodes

Silicon has emerged as the most promising high-capacity material for lithium-ion batteries. Waste glass can be a potential low cost and environmentally benign silica resource enabling production of nanosized silicon at the industry level. Windshields are generally made of laminated glass comprising two separate glass bonded together with a layer of polyvinyl butyral sandwiched between them. Herein, silicon/carbon nanocomposites are fabricated from windshields for the first time via magnesiothermic reduction and facile carbonization process using both waste glass and polyvinyl butyral as silica and carbon sources, respectively. High purity reduced silicon has unique 3-dimensional nanostructure with large surface area. Furthermore, the incorporation of carbon in silicon enable to retain the composite anodes highly conductive and mechanically robust, thus providing enhanced cycle stability.

3D Architectures of CoxP Using Silk Fibroin Scaffolds: An Active and Stable Electrocatalyst for Hydrogen Generation in Acidic and Alkaline Media

Developing nonprecious, highly active, and stable catalysts is essential for efficient electrocatalytic hydrogen evolution reaction in water splitting. In this study, the facile synthesis of a 3D flower-like Cox P/carbon architecture is proposed composed of an assembly of nanosheets interconnected by silk fibroin that acts as 3D scaffolds and a carbon source. This unique 3D architecture coupled with a carbon matrix enhances catalytic activity by exposing more active sites and increasing charge transport. The flower-like Cox P/carbon can facilitate a lower overpotential, Tafel slope, charge transfer resistance, and a higher electrochemically active surface than carbon-free and silk-free Cox P. The nanostructured architecture exhibits excellent catalytic performance with low overpotentials of 109 and 121 mV at 10 mA cm-2 and Tafel slopes of 55 and 62 mV dec-1 in acidic and alkaline media, respectively. Furthermore, it minimally degrades the overpotential and current density after long-term stability tests 10 000 cyclic voltammetry cycles and a chronoamperometric test over 40 h, respectively, in acidic media, which confirms the high durability and stability of the flower-like Cox P/carbon.