Showing papers by "Nam Hoon Kim published in 2018"
TL;DR: In this article, a facile two-step strategy is developed to design the large-scale synthesis of hierarchical, unique porous architecture of ternary metal hydroxide nanowires grown on porous 3D Ni foam and subsequent effective sulfurization.
Abstract: A facile two-step strategy is developed to design the large-scale synthesis of hierarchical, unique porous architecture of ternary metal hydroxide nanowires grown on porous 3D Ni foam and subsequent effective sulfurization. The hierarchical Zn–Co–S nanowires (NWs) arrays are directly employed as an electrode for supercapacitors application. The as-synthesized Zn–Co–S NWs deliver an ultrahigh areal capacity of 0.9 mA h cm−2 (specific capacity of 366.7 mA h g−1) at a current density of 3 mA cm−2, with an exceptional rate capability (≈227.6 mA h g−1 at a very high current density of 40 mA cm−2) and outstanding cycling stability (≈93.2% of capacity retention after 10 000 cycles). Most significantly, the assembled Zn–Co–S NWs//Fe2O3@reduced graphene oxide asymmetric supercapacitors with a wide operating potential window of ≈1.6 V yield an ultrahigh volumetric capacity of ≈1.98 mA h cm−3 at a current density of 3 mA cm−2, excellent energy density of ≈81.6 W h kg−1 at a power density of ≈559.2 W kg−1, and exceptional cycling performance (≈92.1% of capacity retention after 10 000 cycles). This general strategy provides an alternative to design the other ternary metal sulfides, making it facile, free-standing, binder-free, and cost-effective ternary metal sulfide-based electrodes for large-scale applications in modern electronics.
228 citations
212 citations
207 citations
TL;DR: The rational design of a 3D hierarchical sandwich Co9 S8 /α-MnS@N-C@MoS2 nanowire architecture is achieved during the hydrothermal sulphurization reaction by the conversion of binary mesoporous metal oxide core to corresponding individual metal sulphides core along with the formation of outer metal sulphide shell at the same time.
Abstract: Supercapacitors suffer from lack of energy density and impulse the energy density limit, so a new class of hybrid electrode materials with promising architectures is strongly desirable. Here, the rational design of a 3D hierarchical sandwich Co9 S8 /α-MnS@N-C@MoS2 nanowire architecture is achieved during the hydrothermal sulphurization reaction by the conversion of binary mesoporous metal oxide core to corresponding individual metal sulphides core along with the formation of outer metal sulphide shell at the same time. Benefiting from the 3D hierarchical sandwich architecture, Co9 S8 /α-MnS@N-C@MoS2 electrode exhibits enhanced electrochemical performance with high specific capacity/capacitance of 306 mA h g-1 /1938 F g-1 at 1 A g-1 , and excellent cycling stability with a specific capacity retention of 86.9% after 10 000 cycles at 10 A g-1 . Moreover, the fabricated asymmetric supercapacitor device using Co9 S8 /α-MnS@N-C@MoS2 as the positive electrode and nitrogen doped graphene as the negative electrode demonstrates high energy density of 64.2 Wh kg-1 at 729.2 W kg-1 , and a promising energy density of 23.5 Wh kg-1 is still attained at a high power density of 11 300 W kg-1 . The hybrid electrode with 3D hierarchical sandwich architecture promotes enhanced energy density with excellent cyclic stability for energy storage.
144 citations
TL;DR: Enhanced electron transfer kinetics from nitrogen-doped carbon shell to core Co nanoparticles, the existence of M-N-C active sites, and protective NC shells are responsible for high ORR activity and durability of the Co@NC-MOF electrocatalyst.
Abstract: Herein, a new type of cobalt encapsulated nitrogen-doped carbon (Co@NC) nanostructure employing Znx Co1-x (C3 H4 N2 ) metal-organic framework (MOF) as precursor is developed, by a simple, ecofriendly, solvent-free approach that utilizes a mechanochemical coordination self-assembly strategy. Possible evolution of Znx Co1-x (C3 H4 N2 ) MOF structures and their conversion to Co@NC nanostructures is established from an X-ray diffraction technique and transmission electron microscopy analysis, which reveal that MOF-derived Co@NC core-shell nanostructures are well ordered and highly crystalline in nature. Co@NC-MOF core-shell nanostructures show excellent catalytic activity for the oxygen reduction reaction (ORR), with onset potential of 0.97 V and half-wave potential of 0.88 V versus relative hydrogen electrode in alkaline electrolyte, and excellent durability with zero degradation after 5000 potential cycles; whereas under similar experimental conditions, the commonly utilized Pt/C electrocatalyst degrades. The Co@NC-MOF electrocatalyst also shows excellent tolerance to methanol, unlike the Pt/C electrocatalyst. X-ray photoelectron spectroscopy (XPS) analysis shows the presence of ORR active pyridinic-N and graphitic-N species, along with CoNx Cy and CoNx ORR active (M-N-C) sites. Enhanced electron transfer kinetics from nitrogen-doped carbon shell to core Co nanoparticles, the existence of M-N-C active sites, and protective NC shells are responsible for high ORR activity and durability of the Co@NC-MOF electrocatalyst.
133 citations
TL;DR: In this article, the important progress to date in the development of 2D-TMDs/Gr hybrids has been systematically assessed, and the synthesis methods for fabricating diverse types of nanostructured architectures are highlighted.
120 citations
TL;DR: In this article, the authors developed a new type of zinc nickel phosphide nanosheet (Zn-Ni-P NS) arrays via a simple, scalable, and cost-effective hydrothermal and subsequent effective phosphorization technique to enhance the electrochemical performance of SCs.
Abstract: High-performance all-solid-state supercapacitors (SCs) have potential applications in modern electronics, such as portable and flexible electronics; however, their low specific capacity and operating voltage window limit their industrial applications. Herein, we developed a new type of zinc nickel phosphide nanosheet (Zn–Ni–P NS) arrays via a simple, scalable, and cost-effective hydrothermal and subsequent effective phosphorization technique to enhance the electrochemical performance of SCs. The hierarchical Zn–Ni–P NS array electrode exhibits an ultra-high specific capacity of ∼384 mA h g−1 at a current density of 2 mA cm−2 with excellent rate capability (79.43% of capacity retention at 50 mA cm−2), and outstanding cycling stability (∼96.45% of capacity retention after 10 000 cycles). Furthermore, the Zn–Ni–P NS//Fe2O3@NG all-solid-state asymmetric SC (ASC) delivers an ultra-high volumetric capacity of ∼1.99 mA h cm−3, excellent energy density of ∼90.12 W h kg−1 at a power density of 611 W kg−1, and extraordinary cycling stability (93.05% of initial capacity after 20 000 cycles at a high current density of 15 mA cm−2). Such enhanced electrochemical performances are ascribed to the 3D hierarchical nanostructures, porous nanonetworks, improved conductivity, and synergistic interaction between the active components of Zn–Ni–P NS arrays.
115 citations
TL;DR: In this article, a hierarchical CoMoO4-MnO2 core-shell and Fe2O3 nanosheet arrays on 3D graphene foam (GF) were used as a binder-free electrode in supercapacitor applications.
Abstract: Recently, graphene-based three-dimensional (3D) architectures have attracted a lot of attention because of their multifunctional properties. In this paper, we report on hierarchical nanohoneycomb-like CoMoO4–MnO2 core–shell and Fe2O3 nanosheet arrays on 3D graphene foam (GF) and explore their use as a binder-free electrode in supercapacitor applications. The GF was prepared by solution casting on a Ni foam scaffold. The nanohoneycomb-like CoMoO4–MnO2 core–shell nanosheet arrays were prepared by a hydrothermal method under optimized conditions. The unique core–shell network provides efficient space and a short diffusion length for faradaic reactions. The as-synthesized CoMoO4–MnO2@GF hybrid electrode exhibits excellent areal and specific capacitances of 8.01 F cm−2 and 2666.7 F g−1, respectively, at a current density of 3 mA cm−2. In addition, Fe2O3@GF was also prepared using a hydrothermal process followed by hydrogen treatment. Under optimized conditions Fe2O3@GF exhibits a high areal capacitance of 1.26 (572.7 F g−1) F cm−2. The asymmetric supercapacitor (ASC) assembled from CoMoO4–MnO2@GF as the positive electrode and Fe2O3@GF as the negative electrode delivers an excellent specific capacitance of 237 F g−1 and a high rate capability of 61%. Moreover, the as-fabricated ASC also exhibits an ultra-high energy density of 84.4 W h kg−1 and an outstanding power density of 16 122 W kg−1 as well as an exceptional capacitance retention of 92.1% after 10 000 cycles.
106 citations
TL;DR: In this article, a nitrogen-doped carbon (N-C) layer sandwiched between MnCo2O4 and MnO2 was used as a core/sandwich/shell type heterostructure on Ni foam.
Abstract: The design and development of innovative heterostructures with multifunctional properties are technically very important for efficient practical energy storage and conversion applications. Herein, we report the synthesis of a nitrogen-doped carbon (N–C) layer sandwiched between MnCo2O4 and MnO2 (MnCo2O4@N–C@MnO2) as a core@sandwich@shell type heterostructure on Ni foam. The thin layer of sandwiched N–C acts as a “superhighway” for good electron/ion transport and protects the MnCo2O4 and MnO2 from destructive morphological changes during repeated charge–discharge processes. The MnCo2O4@N–C@MnO2 material is well characterized by standard techniques, and its energy storage performance is studied in a three-electrode system and solid-state asymmetric capacitor device. The resultant electrochemical performance is compared with those of MnCo2O4 and MnCo2O4@N–C. The MnCo2O4@N–C@MnO2 electrode exhibits an excellent areal/gravimetric capacity of 0.75 mA h cm−2/312 mA h g−1 at 3 mA cm−2 with ca. 89.6% capacitance retention after 10 000 cycles. A solid-state asymmetric supercapacitor device assembled with MnCo2O4@N–C@MnO2 as a cathode and nitrogen-doped graphene hydrogel as an anode exhibits a high energy density of 68.2 W h kg−1 at 749.2 W kg−1 power density without compromising long cycle life (ca. 91.1% retention after 10 000 cycles). The highly efficient energy storage performance of this new class of heterostructures synthesized with earth-abundant materials enables commercial applications.
98 citations
TL;DR: The developed three types of electrolyzers to produce H2, are very efficient, cost-effective, and offer no complications in synthesis of materials and fabrication of electrolyzing activities in alkaline medium, which can greatly enable the realization of clean renewable energy infrastructure.
Abstract: Large-scale H2 production from water by electrochemical water-splitting is mainly limited by the sluggish kinetics of the nonprecious-based anode catalysts for oxygen evolution reaction (OER). Here, we report layer-by-layer in situ growth of low-level Fe-doped Ni-layered double hydroxide (Ni1–xFex-LDH) and Co-layered double hydroxide (Co1–xFex-LDH), respectively, with three-dimensional microflower and one-dimensional nanopaddy-like morphologies on Ni foam, by a one-step eco-friendly hydrothermal route. In this work, an interesting finding is that both Ni1–xFex-LDH and Co1–xFex-LDH materials are very active and efficient for OER as well as hydrogen evolution reaction (HER) catalytic activities in alkaline medium. The electrochemical studies demonstrate that Co1–xFex-LDH material exhibits very low OER and HER overpotentials of 249 and 273 mV, respectively, at a high current density of 50 mA cm–2, whereas Ni1–xFex-LDH exhibits 297 and 319 mV. To study the overall water-splitting performance using these elect...
94 citations
TL;DR: A novel strategy for locating and securing a single target analyte in a SERS hot spot at a plasmonic nanojunction is described and it is revealed that one can reproducibly treat the SERS substrate such that 96% of the hot spots contain a single analyte molecule.
Abstract: Single-molecule surface-enhanced Raman spectroscopy (SERS) offers new opportunities for exploring the complex chemical and biological processes that cannot be easily probed using ensemble techniques. However, the ability to place the single molecule of interest reliably within a hot spot, to enable its analysis at the single-molecule level, remains challenging. Here we describe a novel strategy for locating and securing a single target analyte in a SERS hot spot at a plasmonic nanojunction. The “smart” hot spot was generated by employing a thiol-functionalized cucurbit[6]uril (CB[6]) as a molecular spacer linking a silver nanoparticle to a metal substrate. This approach also permits one to study molecules chemically reluctant to enter the hot spot, by conjugating them to a moiety, such as spermine, that has a high affinity for CB[6]. The hot spot can accommodate at most a few, and often only a single, analyte molecule. Bianalyte experiments revealed that one can reproducibly treat the SERS substrate such ...
TL;DR: In this paper, a cobalt iron carbide nanoparticles encapsulated by nitrogen doped graphene nanosheets is successfully synthesized through a simple refluxing strategy followed by a post annealing process.
TL;DR: In this paper, the transition metal-based catalysts encapsulated in 2D-carbon supporting material hybrids are discussed in detail to understand the relationships between unique morphology/structure and physicochemical properties for enhanced catalytic performance.
TL;DR: In this article, a novel 3D graphene-CNTs/MoO3 hybrid film as a binder free electrode material with unique morphology and outstanding electrochemical performance was reported.
TL;DR: In this article, a facile and green approach using Benedict's solution and glucose solution at room temperature without the need of any toxic reagent, surfactant or any special treatment was proposed.
Abstract: Ternary nanocomposites (NCs) comprising Ag-Cu2O supported on glucose-reduced graphene oxide (rGO) with enhanced stability and visible light photocatalytic activity were synthesized via a facile and green approach using Benedict's solution and glucose solution at room temperature without the need of any toxic reagent, surfactant or any special treatment. Besides mild reducing capability to GO, glucose also induces the functionalization of rGO sheets, preventing the aggregation of reduced sheets and providing in situ stabilization to Cu2O. The resulting Ag-Cu2O/rGO NCs showed excellent photocatalytic efficiency for the photodegradation of methyl orange (MO), and the degradation rate was found to be higher than the pristine Cu2O and Cu2O/rGO NCs. Further, for the first time Ag-Cu2O/rGO NCs showed markedly enhanced photocatalytic efficiency for the photodegradation of phenol solution which is mainly attributed to its high electron injection rate and effective separation of electron–hole pairs. Thus, present strategy explores the facile synthesis way of varieties of Cu2O-based NCs materials using harmless reagents and their feasible applications.
TL;DR: Novel nitrogen-doped graphene-encapsulated nickel cobalt nitride (Ni xCo3- xN/NG) core-shell nanostructures with a controllable molar ratio of Ni/Co are successfully fabricated and employed as highly sensitive and selective electrodes for glucose and H2O2 sensing applications.
Abstract: To explore a natural nonenzymatic electrode catalyst for highly sensitive and selective molecular detection for targeting biomolecules is a very challenging task. Metal nitrides have attracted huge interest as promising electrodes for glucose and hydrogen peroxide (H2O2) sensing applications due to their exceptional redox properties, superior electrical conductivity, and superb mechanical strength. However, the deprived electrochemical stability extremely limits the commercialization opportunities. Herein, novel nitrogen-doped graphene-encapsulated nickel cobalt nitride (NixCo3–xN/NG) core–shell nanostructures with a controllable molar ratio of Ni/Co are successfully fabricated and employed as highly sensitive and selective electrodes for glucose and H2O2 sensing applications. The highly sensitive and selective properties of the optimized core–shell NiCo2N/NG electrode are because of the high synergistic effect of the NiCo2N core and the NG shell, as evidenced by a superior glucose sensing performance wit...
TL;DR: A well-defined nanostructured catalyst of highly dispersed CuAg@ Ag core-shell nanoparticle (NP)-encapsulated nitrogen-doped graphene nanosheets (CuAg@Ag/N-GNS) exhibiting a superior catalytic activity toward ORR in alkaline medium is reported.
Abstract: Development of a robust, cost-effective, and efficient catalyst is extremely necessary for oxygen reduction reaction (ORR) in fuel cell applications. Herein, we reported a well-defined nanostructured catalyst of highly dispersed CuAg@Ag core–shell nanoparticle (NP)-encapsulated nitrogen-doped graphene nanosheets (CuAg@Ag/N-GNS) exhibiting a superior catalytic activity toward ORR in alkaline medium. The synergistic effects produced from the unique properties of CuAg@Ag core–shell NPs and N-GNS made such a novel nanohybrid display a catalytic behavior comparable to that of the commercial Pt/C product. In particular, it demonstrated a much better stability and methanol tolerance than Pt/C under the same conditions. Because of its outstanding electrochemical performance and ease of synthesis, CuAg@Ag/N-GNS material was expected to be a promising low-cost catalyst for ORR in alkaline fuel cell applications.
TL;DR: In this article, the authors reported the synthesis of single crystalline CuCo2O4 octahedrons and their application in a supercapacitor using the ethylenediaminetetraacetic acid assisted hydrothermal approach.
Abstract: Shape tailoring of active materials could alter the performance of supercapacitors. Herein, we report the ethylenediaminetetraacetic acid (EDTA) assisted hydrothermal approach for the synthesis of single crystalline CuCo2O4 octahedrons and their application in a supercapacitor. Morphology and BET surface area analysis demonstrates the formation of CuCo2O4 octahedrons with a surface area of 61.97 m2 g−1. As an active material, the CuCo2O4 octahedrons exhibited a high specific capacity of 989 C g-1 at 5 mV s−1. In addition, a long-term cyclic stability with 87% of its initial specific capacity retention was achieved after 5000 cycles at 10 A g−1. This outstanding performance could be ascribed to its unique octahedron morphology. The electrochemical results demonstrate that CuCo2O4 with such a unique octahedron architecture could be a potential active material for the development of a high performance supercapacitor.
TL;DR: In this paper, a hierarchical nanostructure of carbon nanotubes supported electrospun carbon nanofiber networks (CNTs@CNFs) was successfully fabricated by using two facile techniques: electrospinning and chemical vapor deposition (CVD).
TL;DR: In this article, a series of proton-functionalized graphitic carbon nitride (fgC3N4) modified reduced graphene oxide (rGO)/nickel-aluminium layered double hydroxide (LDH) composites were prepared by a novel scalable strategy using different amounts of fgC 3N4-rGO as a conductive matrix.
TL;DR: In this article, a novel strategy for the synthesis of nickel vanadium oxide (Ni3V2O8) and iron vanadium dioxide (Fe2VO4) nanoparticles (NPs) anchored nitrogen doped graphene (NG) for high energy solid-state asymmetric supercapacitors through a simple and cost-effective hydrothermal technique was demonstrated.
Abstract: Solid-state supercapacitors (SCs) are well-known as one of the most competitive power sources for modern electronics. However, most of the reported solid-state SCs suffer from low specific capacitance and energy density. Herein, a novel strategy for the synthesis of nickel vanadium oxide (Ni3V2O8) and iron vanadium oxide (Fe2VO4) nanoparticles (NPs) anchored nitrogen doped graphene (NG) for high energy solid-state asymmetric SC (ACS) through a simple and cost-effective hydrothermal technique was demonstrated. SEM and TEM analysis reveals that active Ni3V2O8 and Fe2VO4 NPs with uniform size are anchored on NG sheets. Electrochemical performance of Ni3V2O8/NG and Fe2VO4/NG electrodes showed that both have ultra-high specific capacitances (∼1898 F g−1 and 590 F g−1 at current density of 1 A g−1, respectively), tremendous rate capabilities, and superior cycling stabilities. Most significantly, solid-state ASC consisting of Ni3V2O8/NG as a cathode and Fe2VO4/NG as an anode which achieves a high energy density of ∼77.2 W h kg−1 at a power density of 863 W kg−1 and an ultra-long cycle life (capacitance retention of ∼83.3% after 20,000 cycles). This study emphasizes the development of a wide variety of energy storage systems for modern electronics.
TL;DR: A hierarchical three-dimensional architecture of ultrasmall hematite nanoparticles homogeneously encapsulated in MoS2/nitrogen-doped graphene nanosheets is synthesized, as a novel non-Pt cathodic catalyst for oxygen reduction reaction in fuel cell applications.
Abstract: In this study, a facile approach has been successfully applied to synthesize a hierarchical three-dimensional architecture of ultrasmall hematite nanoparticles homogeneously encapsulated in MoS2/nitrogen-doped graphene nanosheets, as a novel non-Pt cathodic catalyst for oxygen reduction reaction in fuel cell applications. The intrinsic topological characteristics along with unique physicochemical properties allowed this catalyst to facilitate oxygen adsorption and sped up the reduction kinetics through fast heterogeneous decomposition of oxygen to final products. As a result, the catalyst exhibited outstanding catalytic performance with a high electron-transfer number of 3.91–3.96, which was comparable to that of the Pt/C product. Furthermore, its working stability with a retention of 96.1% after 30 000 s and excellent alcohol tolerance were found to be significantly better than those for the Pt/C product. This hybrid can be considered as a highly potential non-Pt catalyst for practical oxygen reduction r...
TL;DR: A new type of face-centered tetragonal PdFe-alloy nanoparticle-encapsulated Pd anchored onto nitrogen-doped graphene (NG) hybrid that exhibits an excellent catalytic activity for ORR, which is significantly higher than that of marketable Pt/C catalyst.
Abstract: Development of highly active and durable catalysts for oxygen reduction reaction (ORR) alternative to Pt-based catalyst is an essential topic of interest in the research community but a challenging task. Here, we have developed a new type of face-centered tetragonal (fct) PdFe-alloy nanoparticle-encapsulated Pd (fct-PdFe@Pd) anchored onto nitrogen-doped graphene (NG). This core–shell fct-PdFe@Pd@NG hybrid is fabricated by a facile and cost-effective technique. The effect of temperature on the transformation of face-centered cubic (fcc) to fct structure and their effect on ORR activity are systematically investigated. The core–shell fct-PdFe@Pd@NG hybrid exerts high synergistic interaction between fct-PdFe@Pd NPs and NG shell, beneficial to enhance the catalytic ORR activity and excellent durability. Impressively, core–shell fct-PdFe@Pd@NG hybrid exhibits an excellent catalytic activity for ORR with an onset potential of ∼0.97 V and a half-wave potential of ∼0.83 V versus relative hydrogen electrode, ultra...
TL;DR: The Zn1- x Fex -oxyselenide/Ni-foam shows superior bifunctional catalytic activities and excellent durability at a very high current density of 50 mA cm-2 .
Abstract: The scalable and cost-effective H2 fuel production via electrolysis demands an efficient earth-abundant oxygen and hydrogen evolution reaction (OER, and HER, respectively) catalysts. In this work, for the first time, the synthesis of a sheet-like Zn1- x Fex -oxyselenide and Zn1- x Fex -LDH on Ni-foam is reported. The hydrothermally synthesized Zn1- x Fex -LDH/Ni-foam is successfully converted into Zn1- x Fex -oxyselenide/Ni-foam through an ethylene glycol-assisted solvothermal method. The anionic regulation of electrocatalysts modulates the electronic properties, and thereby augments the electrocatalytic activities. The as-prepared Zn1- x Fex -LDH/Ni-foam shows very low OER and HER overpotentials of 263 mV at a current density of 20 mA cm-2 and 221 mV at 10 mA cm-2 , respectively. Interestingly, this OER overpotential is decreased to 256 mV after selenization and the HER overpotential of Zn1- x Fex -oxyselenide/Ni-foam is decreased from 238 to 202 mV at 10 mA cm-2 after a stability test. Thus, the Zn1- x Fex -oxyselenide/Ni-foam shows superior bifunctional catalytic activities and excellent durability at a very high current density of 50 mA cm-2 . More importantly, when the Zn1- x Fex -oxyselenide/Ni-foam is used as the anode and cathode in an electrolyzer for overall water splitting, Zn1- x Fex -oxyselenide/Ni-foam(+)ǁZn1- x Fex -oxyselenide/Ni-foam(-) shows an appealing potential of 1.62 V at 10 mA cm-2 . The anionic doping/substitution methodology is new and serves as an effective strategy to develop highly efficient bifunctional electrocatalysts.
TL;DR: 3D Fe-WO3 NF/NG hybrid nanoarchitecture reveals an outstanding electrocatalytic performance with a remarkable onset potential value, a half-wave potential versus relative hydrogen electrode, significant methanol tolerance, and extraordinary durability, which is superior to a commercial Pt/C.
Abstract: A unique and novel structural morphology with high specific surface area, highly synergistic, remarkable porous conductive networks with outstanding catalytic performance, and durability of oxygen reduction electrocatalyst are typical promising properties in fuel cell application; however, exploring and interpreting this fundamental topic is still a challenging task in the whole world. Herein, we have demonstrated a simple and inexpensive synthesis strategy to design three-dimensional (3D) iron tungsten oxide nanoflower-anchored nitrogen-doped graphene (3D Fe-WO3 NF/NG) hybrid for a highly efficient synergistic catalyst for oxygen reduction reaction (ORR). The construction of flowerlike Fe-WO3 nanostructures, based on synthesis parameters, and their ORR performances are systematically investigated. Although pristine 3D Fe-WO3 NF or reduced graphene oxides show poor catalytic performance and even their hybrid shows unsatisfactory results, impressively, the excellent ORR activity and its outstanding durabil...
TL;DR: A facile hydrothermal approach is suggested for the synthesis of porous CuCo2O4 composite sheets and their application as an active electrode material for supercapacitor application as mentioned in this paper.
Abstract: The synthesis of metal oxide composites with porous structures for supercapacitor application has drawn much attention owing to their high surface area and easy access of the electrolyte ions to the electrode surface through the pores of the active materials. A facile hydrothermal approach is suggested for the synthesis of porous CuCo2O4 composite sheets and their application as an active electrode material for supercapacitor application. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) measurements show the formation of porous CuCo2O4 composite sheets. BET surface area measurements show that the porous CuCo2O4 composite sheet has 69.44 m2 g−1 surface area, which is 4.7 times higher than quasi-spherical CuCo2O4 nanoparticles. The porous CuCo2O4 composite sheet delivered 1037 C g−1 specific capacity at 5 mV s−1. Additionally, the porous CuCo2O4 composite sheet retained 94% of its initial specific capacity after 5000 charge-discharge cycles at 10 A g−1 indicating an excellent cyclic stability. This excellent supercapacitive performance is attributed to the high surface area and enhanced ion transport through the pores of the CuCo2O4 sheets. This high specific capacity and excellent cyclic stability of the porous CuCo2O4 composite sheets prove to be a promising candidate for supercapacitor application.
TL;DR: In this article, a hydroxylated boron nitride (BN(OH)x) functionalized p-phenylenediamine modified reduced graphene oxide (rGO) filler was synthesized for the first time using a facile and novel strategy.
Abstract: A hydroxylated boron nitride (BN(OH)x) functionalized p-phenylenediamine modified reduced graphene oxide (rGO) filler (BN(OH)x–PrGO) is synthesized for the first time using a facile and novel strategy. BN(OH)x–PrGO/polyurethane (PU) composite films are prepared using different filler loadings via a solution casting technique. BN(OH)x–rGO/PU and BN(OH)x/PU composite films are also prepared in order to compare the reinforcing effects of different fillers. FESEM and TEM analyses show the excellent dispersion and compatibility of BN(OH)x–PrGO sheets in the PU matrix. The tensile strength and modulus of the composite film show 62% and 95% enhancement, respectively, following the inclusion of 3 wt% BN(OH)x–PrGO compared to those of the pure PU film. The BN(OH)x–PrGO/PU composite films exhibit outstanding oxygen gas barrier properties, ideal dielectric properties, and excellent anti-corrosion performances. In particular, the 3BN(OH)x–PrGO/PU film shows nearly 91% reduction in the O2 transmission rate compared to the PU film. The permeability of O2 through the composite film is correlated with the diffusivity, solubility and Bharadwaj model. The dielectric constant (at 103 Hz) increases from 6.8 for the pure PU film to 13.1 for the 3BN(OH)x–PrGO/PU composite, and the dielectric loss also remains low for the composite. The potentiodynamic polarization curve shows a substantial shift of the corrosion potential of 3BN(OH)x–PrGO/PU-coated steel towards the anodic direction compared to the PU film, and it exhibits an ultralow corrosion rate (6.14 × 10−5 mm per year) and excellent corrosion inhibition efficiency (99.96%) in saline solution.
TL;DR: In this article, CoFe2O4 nanospheres ornamented CdS nanorods were successfully assembled over the reduced graphene oxide nanosheets, achieving a specific capacitance retention of 78% up to 5000 cycles, thus demonstrating its good reversibility and cyclic stability.
Abstract: CoFe2O4 nanospheres ornamented CdS nanorods were successfully assembled over the reduced graphene oxide nanosheets. Such hierarchical morphology established by field emission scanning electron microscopy and transmission electron microscopy studies, with high surface area offered a high specific capacitance of 1487 F g–1 at a current density of 5 A g–1 owing to fast diffusion of ions, facile transportation of electrons, and great synergism between the components, which led to reversible redox reactions. Furthermore, the electrode material has specific capacitance retention of 78% up to 5000 cycles, thus demonstrating its good reversibility and cyclic stability. The resulting CdS-CoFe2O4@reduced graphene oxide nanohybrid can deliver excellent electrochemical performance and can be a potential candidate for supercapacitor application.
TL;DR: In this article, a series of boric acid induced cross-linked poly(vinyl alcohol-co-ethylene) (EVOH)/graphene oxide (GO) nanocomposite films are prepared using different amount of GO and BA with respect to EVOH.
TL;DR: In this paper, the synergistic effects of graphene oxide (GO) on the woven carbon fiber (CF)-reinforced epoxy composites were investigated, and the results showed an improvement in tensile strength, Young's modulus, toughness, flexural strength and flexural modulus by 34, 20, 83, 55 and 31%, respectively, when compared to the CF/epoxy composite.
Abstract: This study investigates the synergistic effects of graphene oxide (GO) on the woven carbon fiber (CF)-reinforced epoxy composites. The GO nanofiller was incorporated into the epoxy resin with variations in the content, and the CF/epoxy composites were manufactured using a vacuum-assisted resin transfer molding process and then cured at 70 and 120 °C. An analysis of the mechanical properties of the GO (0.2 wt.%)/CF/epoxy composites showed an improvement in the tensile strength, Young’s modulus, toughness, flexural strength and flexural modulus by ~ 34, 20, 83, 55 and 31%, respectively, when compared to the CF/epoxy composite. The dynamic mechanical analysis of the composites exhibited an enhancement of ~ 56, 114 and 22% in the storage modulus, loss modulus and damping capacity (tanδ), respectively, at its glass transition temperature. The fiber–matrix interaction was studied using a Cole–Cole plot analysis.