Showing papers by "Jeonghun Kim published in 2016"

Nanoarchitectures for Metal–Organic Framework-Derived Nanoporous Carbons toward Supercapacitor Applications

Abstract: ConspectusThe future advances of supercapacitors depend on the development of novel carbon materials with optimized porous structures, high surface area, high conductivity, and high electrochemical stability. Traditionally, nanoporous carbons (NPCs) have been prepared by a variety of methods, such as templated synthesis, carbonization of polymer precursors, physical and chemical activation, etc. Inorganic solid materials such as mesoporous silica and zeolites have been successfully utilized as templates to prepare NPCs. However, the hard-templating methods typically involve several synthetic steps, such as preparation of the original templates, formation of carbon frameworks, and removal of the original templates. Therefore, these methods are not favorable for large-scale production.Metal–organic frameworks (MOFs) with high surface areas and large pore volumes have been studied over the years, and recently, enormous efforts have been made to utilize MOFs for electrochemical applications. However, their lo...

Conductive polymers for next-generation energy storage systems: recent progress and new functions

Abstract: Conductive polymers are attractive organic materials for future high-throughput energy storage applications due to their controllable resistance over a wide range, cost-effectiveness, high conductivity (>103 S cm−1), light weight, flexibility, and excellent electrochemical properties. In particular, conductive polymers can be directly incorporated into energy storage active materials, which are essential for building advanced energy storage systems (ESSs) (i.e. supercapacitors and rechargeable batteries). This review summarizes the synthesis of conductive polymers with different chemical structures in various ways and also addresses their widespread applications for a broader range of ESSs. Moreover, we introduce recent progress in ESS development, including new electroactive polymers, new approaches (i.e. flexible, stretchable, binder-free, hybrid, etc.), and new functions (e.g. color changeable electrochromic materials for displays).

All-in-one energy harvesting and storage devices

Abstract: Currently, integration of energy harvesting and storage devices is considered to be one of the most important energy-related technologies due to the possibility of replacing batteries or at least extending the lifetime of a battery. This review aims to describe current progress in the various types of energy harvesters, hybrid energy harvesters, including multi-type energy harvesters with coupling of multiple energy sources, and hybridization of energy harvesters and energy storage devices for self-powered electronics. We summarize research on recent energy harvesters based on the piezoelectric, triboelectric, pyroelectric, thermoelectric, and photovoltaic effects. We also cover hybrid cell technologies to simultaneously generate electricity using multiple types of environmental energy, such as mechanical, thermal, and solar energy. Energy harvesters based on the coupling of multiple energy sources exhibit enhancement of power generation performance with synergetic effects. Finally, integration of energy harvesters and energy storage devices is introduced. In particular, self-charging power cells provide an innovative approach to the direct conversion of mechanical energy into electrochemical energy to decrease energy conversion loss.

Ultrahigh performance supercapacitors utilizing core–shell nanoarchitectures from a metal–organic framework-derived nanoporous carbon and a conducting polymer

Abstract: Hitherto, many reports on composite materials for electrochemical applications are based on one-dimensional carbon nanotubes or two-dimensional graphene materials. However, these composite materials usually suffer from a stacking problem during electrochemical cycling. A smart nanoarchitectural design is needed for composite materials in order to overcome this problem. Recent research on electrochemical energy storage (EES) applications has focused on the development of three-dimensional (3-D) core–shell structures. The basis for high performance electrochemical energy storage is to control the efficient intercalation of ions in such a 3-D structure. Here, we demonstrate controlled synergy between the physicochemical properties of nanoporous carbon and conducting polyaniline polymer (carbon–PANI), which leads to some new interesting electrochemical properties. The time-dependent controlled optimization of the core–shell nanocomposites consisting of nanoporous carbon with a thin layer of PANI nanorod arrays gives useful control over supercapacitor performance. Furthermore, these carbon–PANI nanocomposites can electrochemically access ions with remarkable efficiency to achieve a capacitance value in the range of 300–1100 F g−1. When assembled in a two electrode cell configuration, the symmetric supercapacitor (SSC) based on carbon–PANI//carbon–PANI shows the highest specific energy of 21 W h kg−1 and the highest specific power of 12 kW kg−1. More interestingly, the SSC shows capacitance retention of 86% after 20 000 cycles, which is highly superior compared to previous research reports.

Rechargeable lithium–air batteries: a perspective on the development of oxygen electrodes

Abstract: Lithium–air battery (LAB) technology is currently being considered as a future technology for resolving energy and environmental issues. During the last decade, much effort has been devoted to realizing state-of-the-art LABs, and remarkable scientific advances have been made in this research field. Although LABs possess great potential for efficient energy storage applications, there are still various technical limitations to be overcome before the full transition. It has been well recognized that the battery performance of LABs is mainly governed by the electrochemical reactions that occur on the surface of the cathode. Thus, the rational design of highly reliable cathodes is essential for building high-performance LABs. In this respect, we introduce recent advances in the development of LABs, particularly focusing on the cathodes based on a fundamental understanding of Li–O2 electrochemistry. Furthermore, we review the remaining technical challenges in order to formulate a strategy for future research and consolidate Li–O2 electrochemistry for successful implementation of LABs in the near future.

Superior Electrocatalytic Activity of a Robust Carbon-Felt Electrode with Oxygen-Rich Phosphate Groups for All-Vanadium Redox Flow Batteries.

Abstract: A newly prepared type of carbon felt with oxygen-rich phosphate groups is proposed as a promising electrode with good stability for all-vanadium redox flow batteries (VRFBs). Through direct surface modification with ammonium hexafluorophosphate (NH4 PF6 ), phosphorus can be successfully incorporated onto the surface of the carbon felt by forming phosphate functional groups with -OH chemical moieties that exhibit good hydrophilicity. The electrochemical reactivity of the carbon felt toward the redox reactions of VO(2+) /VO2 (+) (in the catholyte) and V(3+) /V(2+) (in the anolyte) can be effectively improved owing to the superior catalytic effects of the oxygen-rich phosphate groups. Furthermore, undesirable hydrogen evolution can be suppressed by minimizing the overpotential for the V(3+) /V(2+) redox reaction in the anolyte of the VRFB. Cell-cycling tests with the catalyzed electrodes show improved energy efficiencies of 88.2 and 87.2 % in the 1(st) and 20(th) cycles compared with 83.0 and 81.1 %, respectively, for the pristine electrodes at a constant current density of 32 mA cm(-2) . These improvements are mainly attributed to the faster charge transfer allowed by the integration of the oxygen-rich phosphate groups on the carbon-felt electrode.

Si/SiOx‐Conductive Polymer Core‐Shell Nanospheres with an Improved Conducting Path Preservation for Lithium‐Ion Battery

Abstract: Non-stoichiometric SiOx based materials have gained much attention as high capacity lithium storage materials. However, their anode performance of these materials should be further improved for their commercial success. A conductive polymer, poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS), is employed as a flexible electrical interconnector to improve the electrochemical performance of Si/SiOx nanosphere anode materials for lithium ion batteries (LIBs). The resulting Si/SiOx-PEDOT:PSS core–shell structured material with the small amount (1 wt %) of PEDOT:PSS shows the improved initial reversible capacity of 968.2 mA h g−1 with excellent long-term cycle performance over 200 cycles. These promising properties can be attributed to the use of the electroconductive and flexible PEDOT:PSS shell layer, which protects the electrical conduction pathways in the electrode from the large volume changes of silicon during cycling.

Synthesis of Cobalt Sulfide/Sulfur Doped Carbon Nanocomposites with Efficient Catalytic Activity in the Oxygen Evolution Reaction

Abstract: Cobalt sulfide/sulfur doped carbon composites (Co9S8/S-C) were synthesized by calcining a rationally designed sulfur-containing cobalt coordination complex in an inert atmosphere From the detailed transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) analyses, the electrocatalytically active Co9S8 nanoparticles were clearly obtained and combined with the thin sulfur doped carbon layers Electrochemical data showed that Co9S8/S-C had a good activity and long-term stability in catalyzing oxygen evolution reaction in alkaline electrolyte, even better than the traditional RuO2 electrocatalyst The excellent electrocatalytic activity of Co9S8/S-C was mainly attributed to the synergistic effect between the Co9S8 catalyst which contributed to the oxygen evolution reaction and the sulfur doped carbon layer which facilitated the adsorption of reactants, prevented the Co9S8 particles from aggregating and served as the electrically conductive binder between each component

The smallest quaternary ammonium salts with ether groups for high-performance electrochemical double layer capacitors

Abstract: Electrochemical double layer capacitors (EDLCs) are energy storage devices that have been used for a wide range of electronic applications. In particular, the electrolyte is one of the important components, directly related to the capacitance and stability. Herein, we first report a series of the smallest quaternary ammonium salts (QASs), with ether groups on tails and tetrafluoroborate (BF4) as an anion, for use in EDLCs. To find the optimal structure, various QASs with different sized head groups and ether-containing tail groups were systematically compared. Comparing two nearly identical structures with and without ether groups, QASs with oxygen atoms showed improved capacitance, proving that ions with oxygen atoms move more easily than their counterparts at lower electric fields. Moreover, the ether containing QASs showed low activation energy values of conductivities, leading to smaller IR drops during the charge and discharge processes, resulting in an overall higher capacitance.

A facile approach for constructing conductive polymer patterns for application in electrochromic devices and flexible microelectrodes

Abstract: We developed a novel strategy for fabricating poly(3,4-ethylenedioxythiophene) (PEDOT) patterns on various substrates, including hydrogels, via sequential solution procedure without multistep chemical etching or lift-off processes. First, PEDOT nanothin films were prepared on a glass substrate by solution phase monomer casting and oxidative polymerization. As a second step, after UV-induced poly(ethylene glycol) (PEG) photolithography at the PEDOT/PEG interface through a photomask, the hydrogel was peeled away from the PEDOT-coated glass substrate to detach the UV-exposed PEDOT region, which left the UV nonexposed PEDOT region intact on the glass substrate, resulting in PEDOT patterns. In a final step, the PEDOT patterns were cleanly transferred from the glass to a flexible hydrogel substrate by a direct-transfer process based on a second round of gelation process. Using this strategy, PEDOT patterns on ITO glass or ITO film were used to successfully fabricate an electrochromic (EC) device that exhibited ...

Strategic synthesis of mesoporous Pt-on-Pd bimetallic spheres templated from a polymeric micelle assembly

Abstract: Core–shell–corona type triblock copolymer poly(styrene-b-2-vinylpyridine-b-ethylene oxide) (PS-b-P2VP-b-PEO) micelles have been selected here to direct the synthesis of mesoporous Pt-on-Pd spheres, consisting of a Pd concentrated core and a Pt shell, as established by elemental mapping It is important to note that the size of the PS core determines the resultant size of the mesopores A self-evaporation method has been developed to prepare swollen micelles, so as to further enlarge the pore size (∼40 nm) Compared with commercially available catalysts (eg, Pt black or Pt, 20 wt% on carbon black), good oxygen reduction reaction performance on the mesoporous Pt-on-Pd spheres is observed, due to the exposure of the most active Pt (111) planes and the synergistic effects from Pt and Pd in the pseudo core–shell structure

Photothermal ablation of cancer cells using self-doped polyaniline nanoparticles

Abstract: Water-stable confined self-doping polyaniline nanocomplexes are successfully fabricated by nano-assembly using lauric acid both as a stabilizer and as a localized dopant. In particular, the colloidal stability of the polyaniline nanocomplexes in neutral pH and the photothermal potential by near-infrared light irradiation are characterized. We demonstrate that confined self-doping polyaniline nanocomplexes as a photothermal nanoagent are preserved in the doped state even at a neutral pH. Finally, confined self-doping polyaniline nanocomplexes aided by lauric acid are successfully applied for the photothermal ablation of cancer cells.

Rechargeable Lithium‐Air Batteries: A Perspective on the Development of Oxygen Electrodes

Abstract: Lithium–air battery (LAB) technology is currently being considered as a future technology for resolving energy and environmental issues. During the last decade, much effort has been devoted to realizing state-of-the-art LABs, and remarkable scientific advances have been made in this research field. Although LABs possess great potential for efficient energy storage applications, there are still various technical limitations to be overcome before the full transition. It has been well recognized that the battery performance of LABs is mainly governed by the electrochemical reactions that occur on the surface of the cathode. Thus, the rational design of highly reliable cathodes is essential for building high-performance LABs. In this respect, we introduce recent advances in the development of LABs, particularly focusing on the cathodes based on a fundamental understanding of Li–O2 electrochemistry. Furthermore, we review the remaining technical challenges in order to formulate a strategy for future research and consolidate Li–O2 electrochemistry for successful implementation of LABs in the near future.