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Srivastava, M.,Elias Uddin, Md.,Singh, J.,Kim, N.H.,Lee, J.H. Elsevier Sequoia 2014 JOURNAL OF ALLOYS AND COMPOUNDS Vol.590 No.-
NiCo<SUB>2</SUB>O<SUB>4</SUB> nanoparticles dispersed on reduced graphene oxide (RGO) are prepared by simultaneously reducing graphene oxide (GO), nickel and cobalt nitrate via a hydrothermal method assisted by post annealing at low temperature. The method involves formation of hydroxides on GO using ammonia under hydrothermal conditions. Subsequent thermal treatment at 300<SUP>o</SUP>C led to the conversion of hydroxides into single-phase NiCo<SUB>2</SUB>O<SUB>4</SUB> atop the RGO. The synthesized products are characterized through several techniques including X-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy (RS), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The FE-SEM investigations reveal the growth of a layer by layer assembly of NiCo<SUB>2</SUB>O<SUB>4</SUB>-RGO (2:1) nanocomposite, where the NiCo<SUB>2</SUB>O<SUB>4</SUB> nanoparticles are tightly packed between the layers of RGO. Further, the catalytic properties of the NiCo<SUB>2</SUB>O<SUB>4</SUB>-RGO nanocomposite are investigated for the oxygen evolution reaction (OER) through cyclic voltammetry (CV) measurements. It is observed that the special structural features of the NiCo<SUB>2</SUB>O<SUB>4</SUB>-RGO (2:1) nanocomposite, including layer by layer assembly, integrity and excellent dispersion of the NiCo<SUB>2</SUB>O<SUB>4</SUB> nanoparticles atop the RGO, produced a synergistic effect and therefore significantly improved the electrochemical performance. The oxidation potential (0.135V) of NiCo<SUB>2</SUB>O<SUB>4</SUB>-RGO (2:1) nanocomposite was observed to be lower than that of bare NiCo<SUB>2</SUB>O<SUB>4</SUB> nanoparticles (0.33V), whereas the corresponding current densities were measured to be 4.1mA/cm<SUP>2</SUP> and 3.11mA/cm<SUP>2</SUP>, respectively.
Kuila, Tapas,Mishra, Ananta Kumar,Khanra, Partha,Kim, Nam Hoon,Uddin, Md. Elias,Lee, Joong Hee American Chemical Society 2012 Langmuir Vol.28 No.25
<P>A simple and effective method for the preparation of water dispersible graphene using sulfonated poly(ether–ether–ketone) (SPEEK) has been described. The SPEEK macromolecules are noncovalently adsorbed on the surface of graphene through π–π interactions. The SPEEK-modified graphene (SPG) forms an aqueous dispersion that is stable for more than six months. An analysis of the ultraviolet–visible spectra shows that the aqueous dispersion of SPG obeys Beer’s law and the molar extinction coefficient has been found to be 149.03 mL mg<SUP>–1</SUP> cm<SUP>–1</SUP>. Fourier transform infrared, Raman, and X-ray photoelectron spectroscopy analyses confirm successful reduction and surface modification of graphene. An atomic force microscopy (AFM) analysis reveals the formation of a single layer of functionalized graphene. Transmission electron microscopy results are also in good agreement with the AFM analysis and support the formation of single-layer graphene. SPG shows good electrochemical cyclic stability during cyclic voltammetry and charge/discharge process when used as a supercapacitor electrode. A specific capacitance of 476 F g<SUP>–1</SUP> at a current density of 6.6 A g<SUP>–1</SUP> is observed for SPG materials.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/langd5/2012/langd5.2012.28.issue-25/la301469u/production/images/medium/la-2012-01469u_0009.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/la301469u'>ACS Electronic Supporting Info</A></P>