In this paper, we show the carbonization of binary composites consisting of graphene nanoplatelets and melamine (GNP/MM), multi-walled carbon nanotubes and melamine (CNT/MM) and trinary composites containing GNP, CNT, and MM. Additionally, the manuscript presents results on the influence of structural factors for the electrochemical performance of carbon composites on their catalytic activity. This study contributes to the wide search and design of novel hybrid carbon composites for electrochemical applications. We demonstrate that intensive nitrogen atom insertion is not the governing factor since hybrid system modifications and porous structure sometimes play a more crucial role in the tailoring of electrochemical properties of the carbon hybrids seen as a noble metal-free alternative to traditional electrode materials. Additionally, HRTEM and Raman spectra study allowed for the evaluation of the quality of the obtained hybrid materials.
Boron-doped multi-walled carbon nanotubes (B-MWCNTs) were deposited on oxidized silicon substrate via decomposition of ethanol and boric acid in the presence of the catalyst ferrocene by means of chemical vapor deposition in a thickness of typically 900 nm. The B-MWCNTs were characterized using Raman spectroscopy and scanning electron microscopy and transmission electron microscopy in combination with energy dispersive X-ray spectroscopy. The deposited BMWCNTs were electrochemically characterized using the ferrocyanide/ferricyanide redox system by means of cyclic voltammetry and electrochemical impedance spectroscopy. The response of B-MWCNTs towards oxidation of dopamine (DA), uric acid (UA), and ascorbic acid (AA) was studied. DA, UA and AA can be determined at working potentials of typically 0.267, 0.412, and 0.127 V (vs. Ag/AgCl) with detection limits of 0.11, 0.65, and 1.21 μM, respectively.
The electron-transport properties of adatom-graphene system are investigated for different spatial configurations of adsorbed atoms: when they are randomly-, correlatively-, or orderly-distributed over different types of high symmetry sites with various adsorption heights. Potassium adatoms in monolayer graphene are modeled by the scattering potential adapted from the independent selfconsistent ab initio calculations. The results are obtained numerically using the quantum-mechanical Kubo-Greenwood formalism. A band gap may be opened only if ordered adatoms act as substitutional atoms, while there is no band gap opening for adatoms acting as interstitial atoms. The type of adsorption sites strongly affect the conductivity for random and correlated adatoms, but practically does not change the conductivity when they form ordered superstructures with equal periods. Depending on electron density and type of adsorption sites, the conductivity for correlated and ordered adatoms is found to be enhanced in dozens of times as compared to the cases of their random positions. These the correlation and ordering effects manifest weaker or stronger depending on whether adatoms act as substitutional or interstitial atoms. The conductivity approximately linearly scales with adsorption height of random or correlated adatoms, but remains practically unchanged with adequate varying of elevation of ordered adatoms. Correlations between electron transport properties and heterogeneous electron transfer kinetics through potassium-doped graphene and electrolyte interface are investigated as well. The ferri-/ferrocyanide redox couple is used as an electrochemical benchmark system. Potassium adsorption of graphene electrode results to only slight suppress of the heterogeneous standard rate constant. Band gap, opening for ordered and strongly short-range scatterers, has a strong impact on the dependence of the electrode reaction rate as a function of electrode potential.
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