Layer-by-Layer Self-Assembled Multilayer Films Composed of Graphene/Polyaniline Bilayers: High-Energy Electrode Materials for Supercapacitors

Sarker, Ashis K.,Hong, Jong-Dal American Chemical Society 2012 Langmuir Vol.28 No.34

<P>Multilayer assemblies of uniform ultrathin film electrodes with good electrical conductivity and very large surface areas were prepared for use as electrochemical capacitors. A layer-by-layer self-assembly approach was employed in an effort to improve the processability of highly conducting polyaniline (PANi) and chemically modified graphene. The electrochemical properties of the multilayer film (MF-) electrodes, including the sheet resistance, volumetric capacitance, and charge/discharge ratio, were determined by the morphological modification and the method used to reduce the graphene oxide (GO) to reduced graphene oxide (RGO) in the multilayer films. The PANi and GO concentrations could be modulated to control the morphology of the GO monolayer film in the multilayer assemblies. Optical ellipsometry was used to determine the thickness of the GO film in a single layer (1.32 nm), which agreed well with the literature value (∼1.3 nm). Hydroiodic acid (HI), hydrazine, or pyrolysis were tested for the reduction of GO to RGO. HI was found to be the most efficient technique for reducing the GO to RGO in the multilayer assemblies while minimizing damage to the virgin state of the acid-doped PANi. Ultimately, the MF-electrode, which could be optimized by fine-tuning the nanostructure and selecting a suitable reduction method, exhibited an excellent volumetric capacitance, good cycling stability, and a rapid charge/discharge rate, which are required for supercapacitors. A MF-electrode composed of 15 PANi/RGO bilayers yielded a volumetric capacitance of 584 F/cm<SUP>3</SUP> at a current density of 3.0 A/cm<SUP>3</SUP>. Although this value decreased exponentially as the current density increased, approaching a value of 170 F/cm<SUP>3</SUP> at 100 A/cm<SUP>3</SUP>, this volumetric capacitance is one of the best yet reported for the other carbon-based materials. The intriguing features of the MF-electrodes composed of PANi/RGO multilayer films offer a new microdimensional design for high energy storage devices for use in small portable electronic devices.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/langd5/2012/langd5.2012.28.issue-34/la3021589/production/images/medium/la-2012-021589_0009.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/la3021589'>ACS Electronic Supporting Info</A></P>

Flexible and Transparent Plastic Electrodes Composed of Reduced Graphene Oxide/Polyaniline Films for Supercapacitor Application

Ashis K. Sarker,홍종달 대한화학회 2014 Bulletin of the Korean Chemical Society Vol.35 No.6

In this article, we described about the preparation and electrochemical properties of a flexible energy storage system based on a plastic polyethylene terephthalate (PET) substrate. The PET treated with UV/ozone was fabricated with multilayer films composed of 30 polyaniline (PANi)/graphene oxide (GO) bilayers using layerby- layer assembly of positively charged PANi and negatively charged GO. The conversion of GO to the reduced graphene oxide (RGO) in the multilayer film was achieved using hydroiodic acid vapor at 100 °C, whereby PANi structure remained nearly unchanged except a little reduction of doping state. Cyclic voltammetry and charge/discharge curves of 30 PANi/RGO bilayers on PET substrate (shorten to PANi- RGO30/PET) exhibited an excellent volumetric capacitance, good cycling stability, and rapid charge/discharge rates despite no use of any metal current collectors. The specific capacitance from charge/discharge curve of the PANi-RGO30/PET electrode was found to be 529 F/cm3 at a current density of 3 A/cm3, which is one of the best values yet achieved among carbon-based materials including conducting polymers. Furthermore, the intrinsic electrical resistance of the PANi-RGO30/PET electrodes varied within 20% range during 200 bending cycles at a fixed bend radius of 2.2 mm, indicating the increase in their flexibility by a factor of 225 compared with the ITO/PET electrode.

Flexible and Transparent Plastic Electrodes Composed of Reduced Graphene Oxide/Polyaniline Films for Supercapacitor Application

Sarker, Ashis K.,Hong, Jong-Dal Korean Chemical Society 2014 Bulletin of the Korean Chemical Society Vol.35 No.6

In this article, we described about the preparation and electrochemical properties of a flexible energy storage system based on a plastic polyethylene terephthalate (PET) substrate. The PET treated with UV/ozone was fabricated with multilayer films composed of 30 polyaniline (PANi)/graphene oxide (GO) bilayers using layer-by-layer assembly of positively charged PANi and negatively charged GO. The conversion of GO to the reduced graphene oxide (RGO) in the multilayer film was achieved using hydroiodic acid vapor at $100^{\circ}C$, whereby PANi structure remained nearly unchanged except a little reduction of doping state. Cyclic voltammetry and charge/discharge curves of 30 PANi/RGO bilayers on PET substrate (shorten to PANi-$RGO_{30}$/PET) exhibited an excellent volumetric capacitance, good cycling stability, and rapid charge/discharge rates despite no use of any metal current collectors. The specific capacitance from charge/discharge curve of the PANi-$RGO_{30}$/PET electrode was found to be $529F/cm^3$ at a current density of $3A/cm^3$, which is one of the best values yet achieved among carbon-based materials including conducting polymers. Furthermore, the intrinsic electrical resistance of the PANi-$RGO_{30}$/PET electrodes varied within 20% range during 200 bending cycles at a fixed bend radius of 2.2 mm, indicating the increase in their flexibility by a factor of 225 compared with the ITO/PET electrode.

A Zinc Porphyrin Sensitizer Modified with Donor and Acceptor Groups for Dye-Sensitized Solar Cells

Seewoo Lee,Ashis K. Sarker,홍종달 대한화학회 2014 Bulletin of the Korean Chemical Society Vol.35 No.10

In this article, we have designed and synthesized a novel donor-π-acceptor (D-π-A) type porphyrin-based sensitizer (denoted UI-5), in which a carboxyl anchoring group and a 9,9-dimethyl fluorene were introduced at the meso-positions of porphyrin ring via phenylethynyl and ethynyl bridging units, respectively. Long alkoxy chains in ortho-positions of the phenyls were supposed to reduce the degree of dye aggregation, which tends to affect electron injection yield in a photovoltaic cell. The cyclic voltammetry was employed to determine the band gap of UI-5 to be 1.41 eV based on the HOMO and LUMO energy levels, which were estimated by the onset oxidation and reduction potentials. The incident monochromatic photon-to-current conversion efficiency of the UI-5 DSSC assembled with double-layer (20 nm-sized TiO2/400 nm-sized TiO2) film electrodes appeared lower upon overall ranges of the excitation wavelengths, but exhibited a higher value over the NIR ranges (λ = 650-700 nm) compared to the common reference sensitizer N719. The UI-5-sensitized cell yielded a relatively poor device performance with an overall conversion efficiency of 0.74% with a short circuit photocurrent density of 3.05 mA/cm2, an open circuit voltage of 0.54 mV and a fill factor of 0.44 under the standard global air mass (AM 1.5) solar conditions. However, our report about the synthesis and the photovoltaic characteristics of a porphyrin-based sensitizer in a D-π-A structure demonstrated a significant complex relationship between the sensitizer structure and the cell performance.

A Zinc Porphyrin Sensitizer Modified with Donor and Acceptor Groups for Dye-Sensitized Solar Cells

Lee, Seewoo,Sarker, Ashis K.,Hong, Jong-Dal Korean Chemical Society 2014 Bulletin of the Korean Chemical Society Vol.35 No.10

In this article, we have designed and synthesized a novel donor-${\pi}$-acceptor (D-${\pi}$-A) type porphyrin-based sensitizer (denoted UI-5), in which a carboxyl anchoring group and a 9,9-dimethyl fluorene were introduced at the meso-positions of porphyrin ring via phenylethynyl and ethynyl bridging units, respectively. Long alkoxy chains in ortho-positions of the phenyls were supposed to reduce the degree of dye aggregation, which tends to affect electron injection yield in a photovoltaic cell. The cyclic voltammetry was employed to determine the band gap of UI-5 to be 1.41 eV based on the HOMO and LUMO energy levels, which were estimated by the onset oxidation and reduction potentials. The incident monochromatic photon-to-current conversion efficiency of the UI-5 DSSC assembled with double-layer (20 nm-sized $TiO_2$/400 nm-sized $TiO_2$) film electrodes appeared lower upon overall ranges of the excitation wavelengths, but exhibited a higher value over the NIR ranges (${\lambda}$ = 650-700 nm) compared to the common reference sensitizer N719. The UI-5-sensitized cell yielded a relatively poor device performance with an overall conversion efficiency of 0.74% with a short circuit photocurrent density of $3.05mA/cm^2$, an open circuit voltage of 0.54 mV and a fill factor of 0.44 under the standard global air mass (AM 1.5) solar conditions. However, our report about the synthesis and the photovoltaic characteristics of a porphyrin-based sensitizer in a D-${\pi}$-A structure demonstrated a significant complex relationship between the sensitizer structure and the cell performance.

Efficient and convenient synthesis of 1H-pyrazolo[1,2-b]phthalazine-5,10-dione derivatives mediated by L-proline

Roy, Harendra Nath,Rana, Masud,Munsur, Abu Zafar Al,Lee, Kee-In,Sarker, Ashis K. Informa UK (TaylorFrancis) 2016 Synthetic communications Vol.46 No.16

<P>An efficient, four-component, one-pot condensation reaction of phthalimide or phthalic anhydride, aromatic aldehydes, and ethyl cyanoacetate for the synthesis of 1H-pyrazolo[1,2-b]phthalazine-5,10-dione derivatives mediated by L-proline in excellent yields is reported. [GRAPHICS] .</P>

ChemInform Abstract: Efficient and Convenient Synthesis of 1H‐Pyrazolo[1,2‐b]phthalazine‐5,10‐dione Derivatives Mediated by L‐Proline.

Roy, Harendra Nath,Rana, Masud,Munsur, Abu Zafar Al,Lee, Kee‐,In,Sarker, Ashis K. WILEY‐VCH Verlag 2016 Chem Inform Vol.47 No.52

<P><B>Abstract</B></P><P>An environmentally friendly, four‐component, one‐pot condensation reaction of phthalimide or phthalic anhydride, various aromatic aldehydes, ethylcyanoacetate, and hydrazine hydrate is presented.</P>