Preparation and Electrochemical Properties of NiCo2 O4 Nanospinels Supported on Graphene Derivatives as Earth-Abundant Oxygen Bifunctional Catalysts.

This work reports on the facile synthesis and characterisation of a non-precious-metal bifunctional catalyst for oxygen reduction and evolution reactions (ORR and OER). A few-layer reduced graphene oxide-supported NiCo2 O4 catalyst is prepared using a rapid and easy two-step method of synthesis. It consists of the solvothermal poyl(vinylpyrrolidone)-assisted assembly of metal complexes onto few-layer graphene followed by a calcination step aiming at converting metal complexes into the spinel phase. Using this synthesis approach, the most active material demonstrates an outstanding activity towards the OER and ORR, making it one of the best bifunctional catalysts of these reactions ever reported. This composite catalyst exhibits improved bifunctional behaviour with a low reversibility criterion of 746 mV. The ORR process follows a four-electron pathway and the hydroxyl selectivity is higher than those with pure reduced graphene oxide or NiCo2 O4 materials, showing the synergistic effect between the two phases. Moreover, the high activity of this composite catalyst is confirmed by comparing its performance with those obtained on other cobaltite catalysts prepared using a different synthesis method, or those obtained using a different graphene-based support.

Impact of Nonthermal Atmospheric Plasma on the Structure of Cellulose: Access to Soluble Branched Glucans.

We have investigated the effect of non-thermal atmospheric plasma (NTAP) on the structure of microcrystalline cellulose. In particular, by means of different characterization methods, we demonstrate that NTAP promotes the partial cleavage of the ß-1,4 glycosidic bond of cellulose leading to the release of short-chain cellodextrins that are reassembled in situ, preferentially at the C6 position, to form branched glucans with either a glucosyl or anhydroglucosyl terminal residue. The ramification of cellulosic chain induced by NTAP yields branched glucans that are soluble in DMSO or in water, thus opening a straightforward access to processable glucans from cellulose. Importantly, the absence of solvent and catalyst considerably facilitates downstream processing as compared to (bio)catalytic processes which typically occur in diluted conditions.

The effect on the electrocatalytic activity of the chemical interaction of selenium with palladium centers: oxygen reduction and methanol oxidation reactions in alkaline medium.

The chemical reactivity of two different selenium precursors (SeO2and Se) with nanoparticulated palladium was studied in a simple aqueous phase synthesis to generate palladium selenides (PdxSey). As confirmed by XRD, XPS, TEM and energy dispersive spectroscopy analyses, the products generated showed different degrees of selenization according to the nature of the chemical precursor. Such degree of selenization was more important with elemental selenium, in contrast to SeO2. Surface electrochemistry and CO stripping in alkaline medium, clearly revealed the different interactions and stability of PdxSeyachieved with the Pd/C precursor depending on the selenium source. The electrocatalysis of the oxygen reduction reaction was also influenced by the Se source, first in the different degree of reactivity, and second in the selectivity of the reduction product between H2O and H2O2, as well as the tolerance to the methanol oxidation reaction.