In this study, N/S co-doped carbon felt (N/S-CF) was prepared and characterized as an electrode m... more In this study, N/S co-doped carbon felt (N/S-CF) was prepared and characterized as an electrode material for electric double-layer capacitors (EDLCs). A commercial carbon felt (CF) was immersed in an aqueous solution of thiourea and then thermally treated at 800 o C under an inert atmosphere. The prepared N/S-CF showed a large specific surface area with hierarchical pore structures. The electrochemical performance of the N/S-CF-based electrode was evaluated using both 3electrode and 2-electrode systems. In the 3-electrode system, the N/S-CF-based electrode showed a good specific capacitance of 177 F/g at 1 A/g and a good rate capability of 41% at 20 A/g. In the 2-electrode system (symmetric capacitor), the freestanding N/S-CF-based electrode showed a specific capacitance of 275 mF/cm 2 at 2 mA/cm 2 , a rate capability of 62.5 % at 100 mA/cm 2 , a specific power density of ~25,000 mW/cm 2 at an energy density of 23.9 mWh/cm 2 , and a cycling stability of ~100 % at 100 mA/cm 2 after 20,000 cycles. These results indicate the N/S co-doped carbon felts can be a promising candidate as a new electrode material in a symmetric capacitor.
CrN and Cr-Al-SiN coatings were deposited on SUS304 and Si-wafers by a hybrid coating system. The... more CrN and Cr-Al-SiN coatings were deposited on SUS304 and Si-wafers by a hybrid coating system. The Cr and Al-Si target were connected to the cathode arc ion plating (AIP) and high power impulse magnetron sputtering (HiPIMS), respectively. Various Al and Si contents in the coatings were obtained by changing the power of Al-Si target from 0 to 1 kW. The results demonstrated a face-centered cubic structure in all of the coatings. With increasing Al-Si target power, both the density and mean diameter of the macroparticles on the coating surface declined. As Al and Si contents increased, the microstructure of the Cr-Al-SiN coatings evolved from a dense column structure, to a finer grain column structure, and then to a compact granular-like structure. The hardness of the coatings increased from 21.5 GPa for the pure CrN coating, to a maximum value of~27 GPa for the Cr-Al-SiN coating deposited at 0.4 kW, which was mainly attributed to the solid solution strengthening and increased residual stress. The addition of Al and Si contents led to enhanced wear resistance against alumina balls at both room and elevated temperatures. Meanwhile, the Cr-Al-SiN coatings also exhibited an excellent resistance to high-temperature oxidation at 800 and 1000 • C, and improved corrosion resistance, as compared with CrN coatings.
Hierarchically porous carbon materials synthesized from sustainable tannic acid with sodium citrate via ice-templating and carbonization for high-performance supercapacitors
Preparation and electrochemical characterization of porous carbon pearls from carboxymethyl cellulose for electrical double-layer capacitors
Korean Journal of Chemical Engineering, Jan 28, 2022
Porous carbon pearls (PCPs) were successfully prepared from syringe droplets of highly concentrat... more Porous carbon pearls (PCPs) were successfully prepared from syringe droplets of highly concentrated carboxymethyl cellulose solution via ice-templating followed by carbonization. The PCPs, which look like a solid bead with a pearly luster, were found to have well-developed bi-modal pore structures with a large specific surface area of 1,338.6 m2/g and a total pore volume of 0.81 cm3/g (a mesopore volume of 0.28 cm3/g and a micropore pore volume of 0.53 cm3/g). In a three-electrode system, the PCPs-based electrode exhibited high supercapacitive performance, such as a high specific capacitance of 217 F/g at 1 A/g in 6 M aqueous KOH electrolyte, outstanding cycling stability of 100% after 10,000 cycles at 30 A/g, and excellent rate capability of 63.7%. To investigate actual supercapacitive performance, a symmetric capacitor device was assembled using a coin cell. The PCPs-based device showed a specific capacitance of 37 F/g at a current density of 1 A/g and a power density of 5.0 kW/kg at an energy density of 2.88 Wh/kg. Furthermore, the PCPs-based device also exhibited superior cycling stability with capacitance retention of 98.5% after 10,000 cycles at a current density of 10 A/g.
Interfacial engineering is of particular signifi cance for self-assembling materials, such as liq... more Interfacial engineering is of particular signifi cance for self-assembling materials, such as liquid crystals, [ 1 ] amphiphiles, [ 2 ] and block copolymers. [ 3 , 4 ] The molecular ordering and the nanodomain alignment of self-assembling materials are delicately infl uenced by the surface energy and functionality. To date, various interfacial engineering methods, ranging from the simple deposition of a surface modifi er to a self-assembled monolayer (SAM) [ 5 ] or layer-by-layer assembly, [ 6 ] have been exploited. Nevertheless, currently available methods are substrate-specifi c and unable to modify low surface energy or chemically inert surfaces. Recently, polydopamine treatment, inspired by the adhesive proteins secreted by marine mussels, has been suggested as a facile and universal strategy for surface modifi cation. The versatile catechol unit provides a unique opportunity to modify virtually all types of material surfaces, regardless of their chemical functionality or surface energy. Moreover, the robust polydopamine treated surface can accommodate the surface reaction site for the formation of secondary ad-layer. [ 7-11 ] Here, we present that polydopamineassisted interfacial engineering can be synergistically integrated with block copolymer lithography for surface nanopatterning of low-surface-energy substrate materials, including Tefl on, graphene, and gold. Block copolymer lithography is a self-assembly based nanopatterning technology that holds great www.advmat.dewww.MaterialsViews.com
ABSTRACT Graphene offers great promise to complement the inherent limitations of silicon electron... more ABSTRACT Graphene offers great promise to complement the inherent limitations of silicon electronics. To date, considerable research efforts have been devoted to complementary p- and n-type doping of graphene as a fundamental requirement for graphene based electronics. Unfortunately, previous efforts suffer from undesired defect formation, poor controllability of doping level, and subtle environmental sensitivity. Here we present that graphene can be complementary p- and n-doped by simple polymer coating with different dipolar characteristics. Significantly, spontaneous vertical ordering of dipolar pyridine side groups of poly(4-vinylpyridine) at graphene surface can stabilize n-type doping at room temperature ambient condition. The dipole field also enhances and balances the charge mobility by screening the impurity charge effect from bottom substrate. We successfully demonstrate ambient stable inverters by integrating p- and n-type graphene transistors, which demonstrated clear voltage inversion with a gain of 0.17 at a 3.3 V input voltage. This straightforward polymer doping offers diverse opportunities for graphene based electronics, including logic circuits, particularly in mechanically flexible form.
All papers published in this conference proceedings have been peer reviewed through a peer review... more All papers published in this conference proceedings have been peer reviewed through a peer review process administered by the proceedings Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a conference proceedings.
A harmonized three-component composite system which preserves the characteristics of individual c... more A harmonized three-component composite system which preserves the characteristics of individual components is of interest in the field of energy storage. Here, we present a graphene-encapsulated MXene Ti CT x @polyaniline composite (GMP) material realized in a systematically stable configuration with different ternary nanomaterials for supercapacitor electrodes. Due to the different zeta potentials in a high-pH solution, chemically converted graphene (negatively charged) is thoroughly unfolded to allow full encapsulation, but the MXene Ti 2 CT x @polyaniline composite with a low positive zeta potential is easily attracted toward a counter-charged substance. The obtained GMP electrode exhibits improved cycle stability and better electrochemical performance owing to the use of mechanically robust and chemically inert graphene and the densely intercalated conductive polyaniline between the multi-layer MXenes. The GMP electrode has a high gravimetric capacitance of 635 F g −1 (volumetric capacitance of 1143 F cm-3) at a current density of 1 A g −1 with excellent cycling stability of 97.54% after 10,000 cycles. Furthermore, the asymmetric pouch-type supercapacitor assembled using the GMP as a positive electrode and graphene as a negative electrode yields a high energy density of 42.3 Wh kg −1 at a power density of 950 W kg −1 and remarkable cycle stability (94.25% after 10,000 cycles at 10 A g −1).
Biocompatible photoresists as nonchemically amplified resist systems and their biomolecular patterning applications = 비화학증폭형 레지스트계열로서 바이오적합성 포토레지스트 연구 및 바이오분자 패턴에의 응용
KCl-assisted synthesis of hierarchically porous carbon materials from water-soluble 2-hydroxyethyl cellulose for high-performance green supercapacitors
Mesoporous nickel and cobalt hydroxide composites are directly grown onto 3D macroporous Ni foam ... more Mesoporous nickel and cobalt hydroxide composites are directly grown onto 3D macroporous Ni foam as a binder-free electrode for supercapacitors by using the successive ionic layer adsorption and reaction (SILAR) method. This method is the cheapest and simplest among several deposition processes for supercapacitor applications. An as-obtained porous NiCo(OH) 2 electrode exhibits a remarkable specific capacity (1113.6 mAh g-1 at a current density of 3 A g-1) and excellent cycling stability (85.62 % capacity retention after 5,000 cycles). Furthermore, an asymmetric supercapacitor assembled with NiCo(OH) 2 as a positive electrode and graphene as a negative electrode shows a high energy density of 20.07 W h kg-1 at a power density of 2302.73 W kg-1 and excellent cycling stability (76.46 % retention after 5,000 cycles). As a result, it shows that the NiCo(OH) 2 fabricated by the SILAR method can be a promising electrode towards energy-storage devices with high energy and power densities.
3D yolk–shell NiGa2S4 microspheres confined with nanosheets for high performance supercapacitors
Journal of Materials Chemistry A, 2017
Recent advances in the development of two-dimensional transition-metal chalcogenides (2D TMCs) ha... more Recent advances in the development of two-dimensional transition-metal chalcogenides (2D TMCs) have opened up new avenues for supercapacitor applications.
The NbN x>1 coatings were deposited on Si wafer and SUS 304 stainless steel substrates by a high ... more The NbN x>1 coatings were deposited on Si wafer and SUS 304 stainless steel substrates by a high power impulse magnetron sputtering (HiPIMS) system at various bias voltages and the ratios of nitrogen and argon (N 2 /Ar). By virtue of electron probe microanalysis (EPMA), X-ray diffraction pattern (XRD), scanning electron microscope (SEM), atomic force microscope (AFM) and nano indentation test, the relationships between deposition parameters and coatings properties were examined in detail. These coatings show a strong preferred orientation of (200) plane at free bias voltage. With increasing bias voltage, the intensity of (200) plane peak became weaker and the full width at half maximum of peaks ((200) and (111) peaks) became broader, implying the crystalline grain size were decreased. The (200) plane almost is disappeared at −150 V bias voltage and the phase transition maintains the same change tendency with the increase of N 2 /Ar gas ratio. The coating microstructure gradually evolved from coarse columnar to dense columnar, and then to compact featureless structure with increase of the bias voltage, corresponding to the decreased surface roughness. The columnar structure of coatings is unrelated to N 2 /Ar gas ratio and the thickness is minimum at high N 2 /Ar ratio, which is attributed to the poor sputtering capability of nitrogen compared with argon instead of target poisonous effect. The higher hardness (H) and elastic recovery value are obtained for NbN x>1 (H = 31.3 GPa and W e = 69.2%) at −150 V bias voltage, suggesting considerable influence of bias voltage on hardness than that of the N 2 /Ar gas ratio.
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Papers by Je Moon Yun