Synthesis Of Carbon-based Hierarchical Nanocomposites And Their Electrochemical Applications

Nanomaterials have been extensively applied to electrochemical sensors, supercapacitors, catalysts and so on. However, a fatal weakness of these nanomaterials is that they can form close-packed structures after they are assembled on an electrode surface, which will reduce their specific surface area and restrain their electrochemical performance. To alleviate the problem, different supporting materials(e.g. graphene, porous carbon or carbon nanotube) are developed to load the nanomaterials. Graphene has the unique properties, e.g. remarkable surface area, high carrier mobility, excellent conductivity, good electrocatalytic activity and wide electrochemical window. Biomass-derived porous carbon materials have drawn much attention due to their extensive sources, low cost, environmentally friendly behaviors, large specific surface area, short diffusion pathway, good electrical conductivity and high porosity. In this paper, a series of nanomaterials designed by electrodeposition, chemical oxidation reduction and chemical vapor deposition method to load bimetal, metal, enzyme and polymer on graphene and biomass-derived porous carbon, and successfully used for glucose sensor, oxygen reduction reaction, hydrogen peroxide sensor, supercapacitors and other fields. The main works included the following five parts:1. Nickel-cobalt nanostructures(Ni-Co NSs) electrodeposited on reduced graphene oxide(r GO)-modified glassy carbon electrode(GCE) was prepared and used for highly sensitive glucose detection. The electrochemical and electrocatalytic behaviors of the Ni-Co NSs/r GO/GCE towards glucose oxidation were evaluated by cyclic voltammograms, chronoamperometry and amperometric method. The effects of some factors related to the fabrication of Ni-Co NSs/r GO/GCE, such as potential scan number and the molar ratio of Ni2+/Co2+ in a solution, on the catalytic performance of the Ni-Co NSs/r GO/GCE were also explored. The results showed that the Ni-Co NSs/r GO/GCE exhibited the best catalytic activity at the potential scan cycles of 20 and the Ni2+/Co2+ molar ratio of 1:1. The glucose concentration in the range of 0.01 to 2.65 m M linearly depended on the catalytic current. The sensitivity was 1773.61 μA cm-2 m M-1, and the detection limit was 3.79 μM(S/N=3).2. A novel nonenzymatic glucose sensor was prepared based on Cu coralloid granules/polyaniline(PANI)/reduced graphene oxide(r GO) nanocomposite modified glassy carbon electrode(GCE). The PANI nanowire arrays/r GO nanocomposite was synthesized by using in situ chemical oxidative polymerization method, then was dropped on GCE surface. Cu coralloid granules were constructed on PANI/r GO/GCE by constant potential deposition. The electrochemical and electrocatalytic behaviors of the Cu/PANI/r GO/GCE towards glucose oxidation were evaluated by cyclic voltammograms, electrochemical impedance spectroscopy, chronoamperometry and amperometric method. The amperometric response of Cu/PANI/r GO/GCE showed high catalytic activity towards the oxidation of glucose with a wide linear range of 0.01 to 9.66 m M, high sensitivity of 603.59 μA cm-2 m M-1 and low detection limit of 4.02 μM(S/N=3).3. This work reports a one-step synthesis of reduced graphene oxide(r GO) supported platinum-nickel oxide nanoplate arrays(denoted as Pt-Ni O/r GO) for nonenzymatic glucose sensing. It found that the existence of a small quantity of Pt could significantly enhance the catalytic activity of Ni O and play an important role in controlling the morphology of Pt-Ni O nanoplate arrays. The Pt-Ni O nanoplate arrays were vertically formed on the surface of r GO, which reduced the aggregation of Pt-Ni O nanoplates and enlarged the exposed surface area. Similarly, the vertical array structure of Pt-Ni O/r GO nanocomposite avoided forming close-packed structure on electrode surface and accordingly increased the effective loading of Pt-Ni O/r GO catalyst. Therefore, the Pt-Ni O/r GO/GCE was successfully used for highly sensitive and selective nonenzymatic glucose detection. The linear range was from 0.008 to 14.5 m M. The sensitivity was 832.95 μA cm-2 m M-1, and the detection limit was 2.67 μM(S/N=3).4. A three-dimensional(3D) kenaf stem-derived porous carbon/nitrogen-doped carbon nanotubes(denoted as KSC/NCNTs) composite was constructed based on the 3D KSC loaded on NCNTs through CVD method. The network NCNTs were densely distributed on the channel walls of the KSC, which could greatly increase the effective surface area and active sites. Hence, the composite showed good catalytic properties for ORR. Moreover, the KSC/NCNTs composite was used as a supporter to immobilize PB NPs for H2O2 sensor and GOD for glucose biosensor, respectively. The KSC/NCNTs/PB NPs exhibited good catalytic performance for H2O2 sensing due to its large surface area, honeycomb porous structure and fast mass transfer. The as-prepared glucose biosensor showed effective direct electron transfer and wide linear range, because it overcome some disadvantages of traditional enzymes electrodes, such as difficult direct electron transfer of enzymes, mechanical instability and stacking of supporters, and negative influence of dispersants. The results indicated that the 3D KSC/NCNTs composite can be a potential material for a variety of fields, e.g. fuel cells, sensing platforms, supercapacitors.5. The KSC/NCNTs/PANI composites were obtained by in situ chemical oxidative polymerization method with adding a certain proportion of ammonium persulfate and aniline monomers under an acid condition. The composites shared the advantages of PANI and KSC, showed high specific capacitance and long-term cycling stability. At the current density of 0.1 A g-1, the specific capacitance was 1090.36 F g-1. After 1000 cycles of charge/discharge at the current density of 0.1 A g-1, its specific capacitance still remained 96.9 %.