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.

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A facile strategy is reported for the synthesis of Fe/Co mixed metal oxide nanoparticles supported on, and embedded inside, high purity oxidized multiwalled carbon nanotubes (MWCNTs) of narrow diameter distribution as effective bifunctional catalysts able to reversibly drive the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR) in alkaline solutions. Variation of the Fe/Co ratio resulted in a pronounced trend in the bifunctional ORR/OER activity. Controlled synthesis and in-depth characterization enabled the identification of an optimal Fe/Co composition, which afforded a low OER/OER reversible overvoltage of only 0.831 V, taking the OER at 10 mA cm and the ORR at -1 mA cm . Importantly, the optimal catalyst with a Fe/Co ratio of 2:3 exhibited very promising long-term stability with no evident change in the potential for both the ORR and the OER after 400 charge/discharge (OER/ORR) cycles at 15 mA cm in 6 m KOH. Moreover, detailed investigation of the structure, size, and phase composition of the mixed Fe/Co oxide nanoparticles, as well as their localization (inside of or on the surface of the MWCNTs) revealed insight of the possible contribution of the individual catalyst components and their synergistic interaction in the catalysis.

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Isomerization of glucose, galactose and arabinose to corresponding keto-sugars was studied in the present work over a range of heterogeneous catalysts. Magnesium aluminates with different ratios between oxides resulting in materials with a Mg/Al ratio from 0.2 to 0.9 were prepared, characterized and evaluated in terms of their catalytic behavior. The catalyst with a Mg/Al ratio close to hydrotalcites was the most efficient considering activity, selectivity and stability. The sugar structure was shown to have a minor influence on catalytic activity and selectivity.