Discovering precious metal-free electrocatalysts exhibiting high activity and stability toward both the oxygen reduction (ORR) and the oxygen evolution (OER) reactions remains one of the main challenges for the development of reversible oxygen electrodes in rechargeable metal-air batteries and reversible electrolyzer/fuel cell systems. Herein, a highly active OER catalyst, Fe 0.3 Ni 0.7 O X supported on oxygen-functionalized multi-walled carbon nanotubes, is substantially activated into a bifunctional ORR/OER catalyst by means of additional incorporation of MnO X . The carbon nanotube-supported trimetallic (Mn-Ni-Fe) oxide catalyst achieves remarkably low ORR and OER overpotentials with a low reversible ORR/ OER overvoltage of only 0.73 V, as well as selective reduction of O 2 predominantly to OH − . It is shown by means of rotating disk electrode and rotating ring disk electrode voltammetry that the combination of earthabundant transition metal oxides leads to strong synergistic interactions modulating catalytic activity. The applicability of the prepared catalyst for reversible ORR/OER electrocatalysis is evaluated by means of a fourelectrode configuration cell assembly comprising an integrated two-layer bifunctional ORR/OER electrode system with the individual layers dedicated for the ORR and the OER to prevent deactivation of the ORR activity as commonly observed in single-layer bifunctional ORR/OER electrodes after OER polarization.

Electrocatalytic oxidation of glycerol (GOR) as the anode reaction in water electrolysis facilitates the production of hydrogen at the cathode at a substantially lower cell voltage compared with the oxygen evolution reaction. It simultaneously provides the basis for the production of value-added compounds at the anode. We investigate earth-abundant transition-metal oxide nanoparticles (Fe, Ni, Mn, Co) embedded in multiwalled carbon nanotubes as GOR catalysts. Out of the four investigated composites, the Ni-based catalyst exhibits the highest catalytic activity toward the GOR according to rotating disk electrode voltammetry, reaching a current density of 10 mA cm −2 already at 1.31 V vs RHE, a potential below the formation of Ni 3+ . Chronoamperometry conducted in a flow-through cell followed by HPLC analysis is used to identify and quantify the GOR products over time, revealing that the applied potential, electrolyte concentration, and duration of the experiment impact strongly the composition of the products' mixture. Upon optimization, the GOR is directed toward oxalate production. Moreover, oxalate is not further converted and hence accumulates as a major organic product under the chosen conditions in a concentration ratio of 60:1 with acetate as a minor product after 48 h electrolysis in 7 M KOH, which represents a promising route for the synthesis of this highly valued product.

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Phone: þ7 383 326 9510, Fax: þ7 383 330 8056Curved graphene fragments can be considered as building blocks of carbon nanotubes. Thus, the size of graphene fragments may be considered as one of the most important characteristics of their structural disorder. In this paper, we have performed a comparative Raman study of CVD multi-walled carbon nanotubes (MWCNTs) and graphene flakes deposited on MWCNTs. Raman data have been considered in combination with HRTEM characterization of nanotubes. The basic attention has been paid to the behavior of D (disorder-induced), G (tangential mode), and 2D (two-phonon scattering) bands in Raman spectra in order to use them for MWCNT characterization. A ratio of intensities of 2D and D bands (I 2D /I D ) demonstrates almost a linear dependence on the mean diameter of MWCNTs produced with two different types of catalysts (see abstract figure). It should be mentioned that each type of catalyst provides the linear dependence with its own specific slope. The graphene fragments have been proposed to form a mosaic structure of nanotube walls. I 2D /I D ratio depends on the amount of graphene flakes deposited on nanotube surface via ethylene decomposition.A dependence of intensity ratio I 2D /I D on the diameter of nanotubes produced with different types of catalysts.A Raman spectroscopy has obvious advantages because it provides an express and nondestructive control of structural and electronic characteristics of carbon materials. Graphite, diamond, graphene, nanotubes, fullerenes in form of monocrystals, polycrystalline films, and powders show their own features in Raman spectra and, thus, can be identified with this technique [4][5][6][7][8][9][10][11][12]. The graphene fragments can be considered as building blocks of sp 2 -carbon materials. The size of graphene fragments may be considered