Showing papers by "Nam Hoon Kim published in 2021"

Alkaline Water Splitting Enhancement by MOF-Derived Fe-Co-Oxide/Co@NC-mNS Heterostructure: Boosting OER and HER through Defect Engineering and In Situ Oxidation.

Abstract: Introducing defects and in situ topotactic transformation of the electrocatalysts generating heterostructures of mixed-metal oxides(hydroxides) that are highly active for oxygen evolution reaction (OER) in tandem with metals of low hydrogen adsorption barrier for efficient hydrogen evolution reaction (HER) is urgently demanded for boosting the sluggish OER and HER kinetics in alkaline media. Ascertaining that, metal-organic-framework-derived freestanding, defect-rich, and in situ oxidized Fe-Co-O/Co metal@N-doped carbon (Co@NC) mesoporous nanosheet (mNS) heterostructure on Ni foam (Fe-Co-O/Co@NC-mNS/NF) is developed from the in situ oxidation of micropillar-like heterostructured Fe-Co-O/Co@NC/NF precatalyst. The in situ oxidized Fe-Co-O/Co@NC-mNS/NF exhibits excellent bifunctional properties by demanding only low overpotentials of 257 and 112 mV, respectively, for OER and HER at the current density of 10 mA cm-2 , with long-term durability, attributed to the existence of oxygen vacancies, higher specific surface area, increased electrochemical active surface area, and in situ generated new metal (oxyhydr)oxide phases. Further, Fe-Co-O/Co@NC-mNS/NF (+/-) electrolyzer requires only a low cell potential of 1.58 V to derive a current density of 10 mA cm-2 . Thus, the present work opens a new window for boosting the overall alkaline water splitting.

Fe and P Doped 1T-Phase Enriched WS23D-Dendritic Nanostructures for Efficient Overall Water Splitting

Abstract: 1T-WS2 is known for its higher hydrogen evolution reaction (HER) performance than 2H-WS2. However, the lack of thermodynamic stability and absence of large-scale synthesis procedures kept 1T-WS2 significantly ignored to date. In this report, for the first time, we have fabricated 1T-WS2 in 3D-dendritic nanostructures over flexible carbon cloth (CC) following doping and intercalation of Fe and P (1T-Fe/P-WS2@CC). The HER and OER activities of 1T-Fe/P-WS2@CC outperform state-of-the-art electrocatalysts, demonstrating a low overpotential (ηHER =116 mV, ηOER =267 mV @ 10 mA cm−2), small Tafel slope (HER =65 mV dec-1, OER =70.1 mV dec-1), and significant durability. The 1T-Fe/P-WS2@CC (+,−) alkaline elctrolyzer also shows exceptional high performance, required only 1.53 V cell voltage at the current density of 10 mA cm−2. Overall, this work opens up a new dimension for simple and scalable fabrication of highly efficient and low-cost electrocatalyst based on WS2.

3D nickel molybdenum oxyselenide (Ni1-xMoxOSe) nanoarchitectures as advanced multifunctional catalyst for Zn-air batteries and water splitting

Abstract: Rational design of 3D nickel molybdenum oxyselenide (Ni1-xMoxOSe) nanoarchitectures with numerous oxygen vacancies is developed through facile and low-cost hydrothermal and followed by selenium ion modulation approach. The experimental and theoretical studies reveal that the optimal Ni0.5Mo0.5OSe possesses ultrafast charge-transfer kinetics, which would boost the catalytic activities, enhance the accessibility of electroactive sites, and increase the diffusion networks for oxygen species. Most impressively, the optimal Ni0.5Mo0.5OSe affords superior trifunctional activities, outperforming benchmark Pt/C and IrO2 catalysts. When employed as an air-cathode in flexible Zn-air batteries, it achieves a peak power density of 166.7 mW cm−2 and outstanding durability for 300 h in ambient air. Furthermore, the water electrolyzer realizes a current density of 10 mA cm−2 at a cell voltage of 1.51 V, outperforming benchmark Pt/C||IrO2 couple and reported state-of-the-art catalysts. This consequence provides a general strategy to explore highly efficient multifunctional catalysts with enhanced durability.

Metal organic framework-derived cobalt telluride-carbon porous structured composites for high-performance supercapacitor

Abstract: Abstract: Porous nanostructured composites are emerging electrode materials for energy storage devices. This work reports the fabrication of metal-organic framework (MOF)-derived cobalt telluride-carbon porous structured composite on nickel foam (CoTe@C–NiF) as electrodes for supercapacitor. The CoTe@C–NiF electrode can store charge in different potential regions of 0 to 0.5 V as positive and −0.8 to 0 V as negative electrodes. Benefitting from its bifunctional charge storage property, the CoTe@C–NiF, when employed as electrodes in a symmetric supercapacitor, produces an optimum output voltage of 1.45 V in aqueous alkaline electrolyte, resulting in an energy density of 43.84 Wh Kg−1 at a power density of 738.88 W kg−1, and retains 21.95 Wh Kg−1 even at the high power density of 6173.44 W kg−1. Moreover, the CoTe@C–NiF is reproducible via a large-scalable and straightforward synthesis protocol, comprising two-steps, followed by an annealing process at 400 °C in argon. The results suggest that the CoTe@C–NiF is a promising electrode material for high-performance symmetric supercapacitor.

Activated CuNi@Ni Core@shell structures via oxygen and nitrogen dual coordination assembled on 3D CNTs-graphene hybrid for high-performance water splitting

Abstract: Herein, a unique nanohybrid, in which CuNi@Ni core@shell nanoparticles were dual-coordinated with oxygen and nitrogen heteroatoms (CuNi@Ni(ON) NPs) and uniformly assembled on 3D porous carbon nanotubes-graphene (CNTs-Gr), was well-designed via an effective synthesis process. The CuNi@Ni(ON)/CNTs-Gr material with tunable electronic properties and conductivity displayed favorite adsorption energies towards reactants, thus manifesting its remarkable bifunctional activities for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) operating in 1.0 M KOH. To achieve current responses of 10 and 100 mA cm−2, small overpotential values of 42.1 and 410 mV were needed for HER and OER, respectively. An electrolyzer employing CuNi@Ni(ON)/CNTs-Gr electrodes delivered an exciting cell voltage of 1.51 V at 10 mA cm−2 and good stability over 25 h operation, surpassing performance of a commercial Pt/C//RuO2-based system. These achievements suggested the CuNi@Ni(ON)/CNTs-Gr is one of the most effective nonprecious catalysts for high-performance production of green hydrogen gas via water splitting.

Novel cobalt-doped molybdenum oxynitride quantum dot@N-doped carbon nanosheets with abundant oxygen vacancies for long-life rechargeable zinc–air batteries

Abstract: Rechargeable zinc–air batteries (ZABs) have emerged as promising alternatives for conventional Li-ion batteries due to their high energy density and low manufacturing cost. However, Pt/C and RuO2-based conventional rechargeable ZABs are mainly constrained by the sluggish kinetics of oxygen reduction/oxygen evolution reactions (ORR/OER), limiting commercialization possibilities. Herein, a new type of oxygen vacancies enriched cobalt-doped molybdenum oxynitride quantum dot-anchored N-doped carbon nanosheets (VO-CMON@NCNs) was demonstrated as an advanced air-cathode for long-life rechargeable ZABs. Such VO-CMON@NCN catalyst has an exceptional ORR performance with a high half-wave potential of 0.857 V and tremendous OER performance with an ultrasmall overpotential of 240 mV at a current density of 10 mA cm−2, outperforming conventional Pt/C and RuO2 catalysts. As proof of concept, rechargeable ZABs with an optimal VO-CMON@NCN-800 air-cathode showed an ultrahigh specific capacity of 721.2 mA h gZn−1 at a current density of 5 mA cm−2, a tremendous peak power density of 143.7 mW cm−2, and ultralong cycling life of 500 h. These consequences suggest that the oxygen vacancies enriched VO-CMON@NCN can serve as promising bifunctional catalysts for next-generation metal–air batteries and other energy-related applications.

Highly Effective Freshwater and Seawater Electrolysis Enabled by Atomic Rh-Modulated Co-CoO Lateral Heterostructures.

Abstract: Atomic metal-modulated heterostructures have been evidenced as an exciting solution to develop high-performance multifunctional electrocatalyst toward water splitting. In this research, a catalyst of continuous cobalt-cobalt oxide (Co-CoO) lateral heterostructures implanted with well-dispersed rhodium (Rh) atoms and shelled over conductive porous 1D copper (Cu) nano-supports for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in both freshwater and seawater under alkaline condition is proposed. It is found that synergistic effects coming from uniform Rh atoms at doping level and Co-CoO heterostructures afford rich multi-integrated active sites and excellent charge transfer, thereby effectively promoting both HER and OER activities. The material requires overpotentials of 107.3 and 137.7 mV for HER and 277.7 and 260 mV for OER to reach an output of 10 mA cm-1 in freshwater and mimic seawater, respectively, surpassing earlier reported catalysts. Compared to a benchmark a Pt/C//RuO2 -based two-electrode electrolyzer, a device derived from the 1D-Cu@Co-CoO/Rh on copper foam delivers comparable cell voltages of 1.62, 1.60, and 1.70 V at 10 mA cm-2 in freshwater, mimic seawater, and natural seawater, respectively, together with robust stability. These results evidence that 1D-Cu@Co-CoO/Rh is a promising catalyst for green hydrogen generation via freshwater and seawater electrolysis applications.

Two-dimensional materials modified layered double hydroxides: A series of fillers for improving gas barrier and permselectivity of poly(vinyl alcohol)

Abstract: A series of modified 2D nanosheets (graphene oxide-layered double hydroxide, GO-LDH; boron nitride-LDH, BN-LDH; and molybdenum disulfide-LDH, MoS2-LDH) are prepared via a cost-effective, environmentally-friendly, and effortless method based on the concept of electrostatic interaction. The modified 2D nanosheet/Poly(vinyl alcohol) (PVA) nanocomposite films show a comprehensive improvement of physicochemical properties. Among the synthesized films, the O2 barrier performance of the 1% GO-LDH/PVA nanocomposite film (1.44 × 10−13 cm3 cm/cm2·s·cmHg) is 25-fold higher than that of the pure PVA film (3.68 × 10−12 cm3 cm/cm2·s·cmHg). The 1% GO-LDH/PVA shows tremendous improvement in tensile strength (84.7 MPa) and modulus (3032 MPa) values than the PVA film (46.7 and 371 MPa). Furthermore, the 2% BN-LDH/PVA nanocomposite shows the H2/CO2 permselectivity value of 102.5, which is superior to the Robeson upper bound and most reported separation films. In addition to the improved gas barrier and permselectivity performances, an exceptional combination of the thermal stability, tensile strength/modulus, flexibility, and transparency of the nanocomposite film could lead to applications in food packaging, H2 purification, and CO2 capture.

Bifunctional Catalyst Derived from Sulfur-Doped VMoOx Nanolayer Shelled Co Nanosheets for Efficient Water Splitting.

Abstract: A novel sulfur-doped vanadium-molybdenum oxide nanolayer shelling over two-dimensional cobalt nanosheets (2D Co@S-VMoOx NSs) was synthesized via a facile approach. The formation of such a unique 2D core@shell structure together with unusual sulfur doping effect increased the electrochemically active surface area and provided excellent electric conductivity, thereby boosting the activities for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). As a result, only low overpotentials of 73 and 274 mV were required to achieve a current response of 10 mA cm-2 toward HER and OER, respectively. Using the 2D Co@S-VMoOx NSs on nickel foam as both cathode and anode electrode, the fabricated electrolyzer showed superior performance with a small cell voltage of 1.55 V at 10 mA cm-2 and excellent stability. These results suggested that the 2D Co@S-VMoOx NSs material might be a potential bifunctional catalyst for green hydrogen production via electrochemical water splitting.

Covalently bonded boron nitride quantum dot and reduced graphene oxide composite electrode for highly efficient supercapacitors

Abstract: This study investigates the synthesis and application of boron nitride quantum dot (BNQD) covalently bonded reduced graphene oxide (rGO) hybrid materials as a novel electrode material for supercapacitors. Because of the p-doping as well as the enhanced hydrophilicity and interfacial bonding force enabled by the hybridization of amine-functionalized boron nitride quantum dot (A-BNQD) with rGO via the chemical coupling reaction, the A-BNQD/rGO shows improved charge carrier density, wettability of electrolyte, and durability. As a result of the synergistic effects, the A-BNQD/rGO as a supercapacitor electrode shows much higher specific capacitance compared to those of rGO and raw BNQD/rGO at a current density of 1 A g−1. Further, the A-BNQD/rGO shows high cycling stability, maintaining almost 94.38%, even after 10,000 cycles due to the enhanced interfacial bonding force between the A-BNQD and rGO. Besides, the fabricated symmetric supercapacitor exhibits high specific capacitance (90 F g−1@1 A g−1), an energy density (12.5 Wh kg−1@0.5 kW kg−1), and good cycling stability. This result suggested that the fabricated A-BNQD/rGO has great potential as electrode materials for high-performance supercapacitors.

Hierarchically 3D Nanoporous Structured Co9S8@Nix:Moy–Se Core–shell Nanowire Arrays Electrode for the High-performance Asymmetric Supercapacitors

Abstract: The rational design of free-standing hierarchic core–shell nanoporous architectures is a good strategy for fabricating next-generation electrode materials for application to electrochemical energy conversion/storage systems. Herein, hierarchical core–shell 3D Co9S8@Nix:Moy–Se nanowire arrays (NWAs) are constructed by a low-cost, straightforward two-step hydrothermal method and an effective electrodeposition process. The optimal 3D Co9S8@Ni0.5Mo0.5–Se NWAs electrode displays the excellent specific capacity of 460.81 mAh g-1 with a corresponding areal capacity of 0.93 mA h cm-2 at 1.5 mA cm-2. It also demonstrates superb rate capability (~68.4 % capacity retention at 20 mA cm-2) and remarkable cyclic stability (~ 94.3 % capacity retention after 10,000 charge and discharge cycles). Additionally, an asymmetric supercapacitor (ASC) is assembled using the hierarchical 3D Co9S8@Ni0.5Mo0.5–Se NWAs as the positive electrode, and the as-obtained Fe2O3@PANNFs/N-rGO aerogel as the negative electrode. The assembled Co9S8@Ni0.5Mo0.5–Se//Fe2O3@PANNFs/N-rGO ASC shows a larger operating voltage range of 1.7 V, a high electrochemical energy storage capability (96.90 W h kg−1 at 1,158 W kg−1), and excellent cyclic stability (capacity remained ~ 94.47 % of the original capacity before 10,000 cycles). The all-solid-state ASC device that is also fabricated exhibits a high export working potential window of ~1.8 V, and an outstanding energy density of ~ 102.94 W h kg−1 at ~1,534 W kg−1, demonstrating that the hierarchical 3D Co9S8@Ni0.5Mo0.5–Se NWAs electrode materials are potential candidates for the high-performance energy storage device.