• Energy Research

In this work, carbon nanofibers (CNF) synthesized by electrospinning are loaded with a combination of nickel and cobalt, both in the metallic and oxide forms (NiCo-loaded CNF), and studied as bifunctional air electrodes for metal-air batteries. The performance of the NiCo-loaded CNF sample is compared with a similarly prepared CoOCo/CNF catalyst both for oxygen reduction and evolution reactions. The combination of nickel and cobalt, both in metallic and oxide form, leads to a bifunctional catalyst with a halfwave potential for the ORR of 874mV vs. RHE and a reversibility (DEOER-ORR) of 764 mV. The stability of the catalyst is assessed by means of a 24 h chronopotentiometric test at 80 mA cm2 and chargedischarge cycles (30 min each) at ±20 mAcm2. NiCo-loaded CNF shows a remarkable stability, maintaining a constant potential during both tests.

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9 páginas.- 1 tabla.- 18 figuras. Several graphite-based electrodes are investigated for vanadium flow battery applications. These materials are characterized both as-received and after chemical or electrochemical treatments in order to vary the content of oxygen functional groups on the electrode surface. The surface properties of the samples are investigated by X-ray photoelectron spectroscopy. Electrochemical performance is evaluated by cyclic voltammetry and electrochemical impedance spectroscopy measurements in a three electrode half-cell. The chemical treatment with HNO3 causes a cleaning of the electrode surface from adsorbed oxygen species or labile bonded functional groups in highly graphitic samples. Whereas, carbonaceous materials characterized by smaller graphitic domains or a higher degree of amorphous carbon show an increase of oxygen functional groups upon chemical and electrochemical pre-treatments. In both cases, an increase of oxygen species content on the surface above 5% causes a decrease of electrochemical performance for the redox battery determined by an increase of ohmic and charge transfer resistance Authors from CNR-ITAE acknowledge the financial support from “Ministero dello Sviluppo Economico – Accordo di Programma MSE-CNR per la Ricerca del Sistema elettrico Nazionale”. Peer reviewed

The heterogeneous catalytic etherification of glycerol with tert-butyl alcohol was investigated in presence of lab-made silica supported acid catalysts. As reference, two commercial acid ion-exchange resins were also used. Experiments were carried out in batch mode at TR ranging from 303 to 363 K. An increase in reaction temperature favors the formation of di-substituted ethers. The etherification reaction proceeds according to a consecutive path and the surface reaction between adsorbed glycerol and protonated tert-butanol (tertiary carbocation) can be considered as the rate determining step. Steric hindrance phenomena and water hinder the formation of tri-substituted ether (TBGE). As expected, water removal was necessary to allow the higher ethers formation. The specific activity (turnover frequency, TOF) of A-15 catalyst is significantly higher than that of the other studied acid systems, due to the wide pore diameter that allows an easier accessibility of the reagent molecules.

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Flexible carbon nanofiber (CNF)-based electrodes and CNF with a 20% of manganese oxide incorporated (Mn3O4/CNF) are prepared by using the electrospinning method for vanadium redox flow battery (VRFB) application. A blend consisting of manganese acetate (Mn(OAc)2) and polyacrilonitrile (PAN) is electrospun and successively subjected to different thermal treatments in which the growth of Mn3O4 particles and CNFs occurred together guaranteeing an appropriate electron conductivity for electrodes thus synthesized. Cyclic voltammetry (CV) measurements show an interesting electrocatalytic activity toward the [VO]2+/[VO2] + as well as the V2+/V3+ redox reactions for the Mn3O4/CNF electrospun sample. Charge-discharge tests, carried out at 80 mA cm2 , show a state of charge (SOC) and a depth of discharge (DoD) of 81% and 73%, respectively, for the cells assembled with Mn3O4/CNF electrodes. These data are indicative of a high vanadium active species utilization thanks to the better electrocatalytic activity at high current densities. Furthermore, the cell with Mn3O4/CNF shows EE values of about 81% (88% of VE and 92% of CE) vs. 70% (75% of VE and 93% of CE) with respect to a commercial carbon felt (CF) electrode used for comparison. These results are attributable to the higher oxygen species content as well as the improved electron conductivity due to the synergetic effect of the more graphitic carbon and to the structural defects within the Mn3O4 spinel structure.