Ji Soo Sohn

High-performance supercapacitor electrode based on a polyaniline nanofibers/3D graphene framework as an efficient charge transporter

The current paper describes chemically grown polyaniline (PANI) nanofibers on porous three dimensional graphene (PANI/3D graphene) as a supercapacitor electrode material with enhanced electrochemical performance. The chemical and structural properties of the electrode are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy with confirmation of a semi-crystalline nature. The homogeneous growth of PANI on the 3D graphene network is visualized by field emission scanning electron microscopy (FESEM) and shows a nanofibers-based morphology. The maximum specific capacitance of the PANI/3D graphene electrode is found to be ∼1024 F g−1 in 1 M H2SO4 within the potential window of −150 to 800 mV vs. Ag/AgCl at 10 mV s−1 scan rate (∼1002 F g−1 at 1 mA cm−2 discharge current density). The high surface area offered by the conducting, porous 3D graphene framework stimulates effective utilization of the deposited PANI and improves electrochemical charge transport and storage. This signifies that the 3D graphene framework is a proficient contender for high-performance capacitor electrodes in energy storage applications.

Enhanced Supercapacitive Performance of Chemically Grown Cobalt–Nickel Hydroxides on Three-Dimensional Graphene Foam Electrodes

Chemical growth of mixed cobalt-nickel hydroxides (CoxNi1-x(OH)2), decorated on graphene foam (GF) with desirable three-dimensional (3D) interconnected porous structure as electrode and its potential energy storage application is discussed. The nanostructured CoxNi1-x(OH)2 films with different Ni:Co (x) compositions on GF are prepared by using the chemical bath deposition (CBD) method. The structural studies (X-ray diffraction and X-ray photoelectron spectroscopy) of electrodes confirm crystalline nature of CoxNi1-x(OH)2/GF and crystal structure consists of Ni(OH)2 and Co(OH)2. The morphological properties reveal that nanorods of Co(OH)2 reduce in size with increases in nickel content and are converted into Ni(OH)2 nanoparticles. The electrochemical performance reveals that the Co0.66Ni0.33(OH)2/GF electrode has maximum specific capacitance of ∼1847 F g(-1) in 1 M KOH within a potential window 0 to 0.5 V vs Ag/AgCl at a discharge current density of 5 A g(-1). The superior pseudoelectrochemical properties of cobalt and nickel are combined and synergistically reinforced with high surface area offered by a conducting, porous 3D graphene framework, which stimulates effective utilization of redox characteristics and communally improves electrochemical performance with charge transport and storage.

Controlled electrochemical growth of Co(OH)2 flakes on 3D multilayered graphene foam for high performance supercapacitors

The present research describes successful enchase of Co(OH)2 microflakes by the potentiodynamic mode of electro-deposition (PED) on porous, light weight, conducting 3D multilayered graphene foam (MGF) and their synergistic effect on improving the supercapacitive performance. Structural and morphological analyses reveal uniform growth of Co(OH)2 microflakes with an average flake width of ∼30 nm on the MGF surface. Moreover, electrochemical capacitive measurements of the Co(OH)2/MGF electrode exhibit a high specific capacitance of ∼1030 F g−1 with ∼37 W h kg−1 energy and ∼18 kW kg−1 power density at 9.09 A g−1 current density. The superior pseudoelectrochemical properties of cobalt hydroxide are synergistically decorated with high surface area offered by a conducting, porous 3D graphene framework, which stimulates the effective utilization of redox characteristics and mutually improves electrochemical capacitive performance with charge transport and storage. This work evokes scalable electrochemical synthesis with the enhanced supercapacitive performance of the Co(OH)2/MGF electrode in energy storage devices.

Surface plasmon enhancement of photoluminescence in photo-chemically synthesized graphene quantum dot and Au nanosphere

Graphene quantum dots (GQDs) are promising candidates for potential applications such as novel optoelectronic devices and bio-imaging. However, insufficient light absorption to exhibit their intriguing characteristics. The strong confinement of light caused by the Au nanoparticles as an antenna can considerably boost the light absorption. With the assistance of ultraviolet irradiation, we prepared bluish-green luminescent nanospheres by the hybridization of GQD and Au nanoparticles (GQD/Au). These nanospheres showed a photoluminescence quantum yield of up to 26.9%. The GQD/Au nanospheres were synthesized using a solution of GQDs and HAuCl4 by a photochemical method with the reduction of GQDs and the formation of metallic Au. The GQDs and Au nanoparticles self-assembled and aggregated into nanospheres via aurophilicity and hydrogen bonding interactions. The average size of the GQD/Au nanospheres was found to be in the range of 150–170 nm, which is much larger than that of the pristine GQDs (4–7 nm). The GQD/Au nanospheres exhibited an absorption band at 541 nm, which indicates the presence of Au in the nanospheres. The typical absorbance features of GQDs were observed near 236 and 303 nm. The photoluminescence characteristics were investigated using the excitation and emission spectra. The GQD/Au nanospheres exhibited two emission peaks at 468 and 529 nm in the visible range. The green fluorescent peak located at 529 nm was newly generated by the hybridization. The GQD/Au nanospheres showed an emission efficiency which was two times more than that of the intrinsic GQDs. The reason for this increase was the surface plasmon resonance from the Au particles, which improved the fluorescence property of the resulting nanospheres. These nanospheres can be perceived as outstanding candidates for applications such as displays, optoelectronic devices, and imaging of the biological samples with high emission intensity.

Graphene-Iodine Nanocomposites: Highly Potent Bacterial Inhibitors that are Bio-compatible with Human Cells.

Graphene-composites, capable of inhibiting bacterial growth which is also bio-compatible with human cells have been highly sought after. Here we report for the first time the preparation of new graphene-iodine nano-composites via electrostatic interactions between positively charged graphene derivatives and triiodide anions. The resulting composites were characterized by X-ray photoemission spectroscopy, UV-spectroscopy, Raman spectroscopy and Scanning electron microscopy. The antibacterial potential of these graphene-iodine composites against Klebsiella pneumonia, Pseudomonas aeruginosa, Proteus mirobilis, Staphylococcus aureus, and E. coli was investigated. In addition, the cytotoxicity of the nanocomposite with human cells [human white blood cells (WBC), HeLa, MDA-MB-231, Fibroblast (primary human keratinocyte) and Keratinocyte (immortalized fibroblast)], was assessed. DGO (Double-oxidizes graphene oxide) was prepared by the additional oxidation of GO (graphene oxide). This generates more oxygen containing functional groups that can readily trap more H+, thus generating a positively charged surface area under highly acidic conditions. This step allowed bonding with a greater number of anionic triiodides and generated the most potent antibacterial agent among graphene-iodine and as-made povidone-iodine (PVP-I) composites also exhibited nontoxic to human cells culture. Thus, these nano-composites can be used to inhibit the growth of various bacterial species. Importantly, they are also very low-cytotoxic to human cells culture.

Fabrication of ultra-high energy and power asymmetric supercapacitors based on hybrid 2D MoS2/graphene oxide composite electrodes: a binder-free approach

Two-dimensional (2D) atomically thick materials, graphene oxide (GO) and layered molybdenum disulfide (MoS2) nanosheets have been potentially investigated as novel energy storage materials due to their unique physicochemical properties. The present manuscript describes a facile binder-free approach to fabricate large-scale hybrid 2D MoS2/GO nanosheet-based electrodes using the electrophoretic deposition (EPD) method on a conducting substrate (nickel foam) for supercapacitor device applications. Structural and morphological analysis reveals uniform decoration of the electrophoretically assembled 2D MoS2/GO nanosheets over the entire substrate surface. The electrochemical supercapacitive measurements of the MoS2/GO hybrid electrode show a high specific capacitance of ∼613 F g−1 at a low scan rate. Moreover, the MoS2/GO//GO electrode-based asymmetric supercapacitor device reveals ultra-high energy (23 W h kg−1) and power (17 kW kg−1) density. The superior electrochemical properties of the 2D MoS2 synergist with high surface area offered by conducting GO and mutually MoS2/GO improves the electrochemical capacitive performance with charge transport and storage. The direct hybrid electrode fabrication by the EPD method (a binder approach) eliminates the drawbacks offered by resistive binders in conventional electrodes. The present experimental findings can evoke scalable binder-free synthesis of MoS2/GO hybrid electrodes with enhanced supercapacitive performance in energy storage devices.

Impact of different nanostructures of a PEDOT decorated 3D multilayered graphene foam by chemical methods on supercapacitive performance

The present research article describes chemically grown different nanostructures of poly(3,4-ethylenedioxythiophene) (PEDOT) on porous multilayered graphene foam (PEDOT/3D GF) as a supercapacitor electrode material with enhanced electrochemical performance. Different nanostructures of PEDOT on 3D GF are synthesised by a chemical method using an EDOT monomer as a precursor along with ammonium persulfate (APS) or iron chloride (FeCl3) as an oxidizing agent. The changes in structural, morphological and electrochemical properties are examined as an impact of different oxidizing agents. Structural and morphological analysis reveals uniform growth of PEDOT nanofibers/nanoparticles over 3D GF. The morphological development of nanofibers and nanoparticles over the graphene foam is observed as an influence of the oxidizing agent. The electrochemical capacitive measurements of the PEDOT/3D GF electrode in 1 M H2SO4 exhibits a high specific capacitance of ∼522 F g−1 and ∼88 F g−1 at 2 mA cm−2 current density for nanofibers and nanoparticle like structures, respectively. A wide porous structure, excellent conductivity and high surface area offered by multi-layered graphene framework arouses effective utilization of the deposited PEDOT with improved electrochemical charge transport and also storage capacity.