ELECTROCHEMICAL DISPERSION OF GRAPHITE IN 58% NITRIC ACID TO PRODUCE MULTILAYER GRAPHENE OXIDE

Electrochemical oxidation of graphite powder in 58% HNO3 was studied. Samples of oxidized graphite were obtained with a imparting of the amount of electricity 500, 700, 1500 mAh g-1. The character of the galvanostatic dependencies allows to select a region of the formation of intercalated compounds of graphite prior to the accumulation of quantity of electricity of 500 mA h g-1. It was found that when the quantity of electricity of over 700 mA h g-1 the process of electrochemical peroxidation of intercalated graphite begins with the formation of multilayer graphene oxide, as confirmed by comprehensive studies using X-ray diffraction, scanning electron microscopy, FTIR spectroscopy, laser diffraction. The synthesized multilayer graphene oxide is characterized by the presence of a spectrum of oxygen-containing functional groups, mainly hydroxyl, as well as carboxyl, epoxy and alkoxyl. X-ray images show a peak at 2θ = 11.45° which intensity increases for re-oxidized graphite compounds and also indicate the formation of a multilayer graphene oxide with an interlayer distance of 7.8 Å. The synthesized material in aqueous suspensions under the action of ultrasound is dispersed with a 7-11-fold reduction in particle size. Graphene layers remains layered structure but the degree of their deformation increases, and the thickness of the layers decreases with an increase in the imparted amount of electricity.

A Comparison of “Bottom-Up” and “Top-Down” Approaches to the Synthesis of Pt/C Electrocatalysts

Three 40 wt % Pt/C electrocatalysts prepared using two different approaches—the polyol process and electrochemical dispersion of platinum under pulse alternating current—and a commercial Pt/C catalyst (Johnson Matthey prod.) were examined via X-ray diffraction (XRD) and transmission electron microscopy (TEM). The stability characteristics of the Pt/C catalysts were studied via long-term cycling, revealing that, for all cycling modes, the best stability was achieved for the Pt/C catalyst with the largest platinum nanoparticle sizes, which was synthesized via electrochemical dispersion of platinum under pulse alternating current. Our results show that the mass and specific electrocatalytic activities of Pt/C catalysts toward ethanol electrooxidation are determined by the value of the electrochemically active Pt surface area in the catalysts.

INVESTIGATION OF STRUCTURAL, MICROSTRUCTURAL AND ELECTROCHEMICAL CHARACTERISTICS OF Pt/SnOx-C ELECTROCATALYSTS PREPARED VIA ELECTROCHEMICAL DISPERSION OF TIN AND PLATINUM

Tin oxides powders (SnOx) with different structure and composition and Pt/SnOx-C electrocatalysts for the direct ethanol fuel cells have been prepared via the electrochemical dispersion of tin and platinum electrodes under a pulse alternating current using various types of anion electrolytes (Cl- and F- anions). As-prepared tin oxides powders, SnOx-C composite supports and Pt/SnOx-C catalysts have been examined by different methods: X-ray diffraction, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy. SnO2 nanoparticles with average sizes of 5 – 8 nm was prepared in a Cl- – containing solution. In turn, the F- – containing solution was found to contain SnO nanoparticles with pronounced shape anisotropy and diverse size of particles. These tin oxides were used as precursors in the synthesis of Pt/SnOx-C catalysts (20% Pt loading, D111=10.5 – 13.5 nm) by the same pulse alternating current technique. Electrochemical active surface area of the Pt/SnOx-C electrocatalysts determined via CO-stripping method was 13-15 m2g-1. Electrocatalytic activity of the electrocatalysts was study for the ethanol electrochemcail oxidation reaction by cyclic voltammetry, rotating disc electrode technique. It was found that the presence of tin oxides is found to exert the same promoting effect on the CO-stripping and ethanol electrochemical oxidation reaction independently on structural features of their particles.