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7 Figures, 2 Tables.-- This article also appears in: Giornate dell’Elettrochimica Italiana (GEI 2019)., Transition‐metal‐based materials are among the most active and durable catalysts for the effective electrocatalysis of oxygen‐related reactions. Herein, we present a study on bifunctional catalysts as air electrodes aimed at metal‐air batteries based on nickel and cobalt spinel (NiCo2O4) supported on electrospun carbon nanofibers. The physicochemical features of these transition‐metal‐based catalysts are essential for the understanding of their electrochemical activity. Results show that the major presence of oxidized Ni and Co species (Ni3+ and Co3+) produces higher activity for the oxygen evolution reaction (OER), whereas lower oxidation states of the metals (Ni2+, Co2+, Ni0 and Co0) together with the presence of N‐doped carbon lead to enhanced oxygen reduction reaction (ORR) performance. This study highlights the importance of designing catalysts in terms of crystallographic structure and proper oxidation states of the elements for maximizing their performance., The research leading to these results has received funding from the “Accordo di Programma CNR‐MiSE, Gruppo tematico Sistema Elettrico Nazionale e Progetto: Sistemi elettrochimici per l′accumulo di energia”.

Electrodes based on electrospun nickel carbon nanofibers (Ni/CNF) are investigated as highly active both for anodic and cathodic reaction. Scanning electron microscopy (SEM) aswell as transmission electron microscopy (TEM) analyses showmetal nanoparticles embedded in graphitic carbon nanofibers. A high surface area due to large mesoporous structure formation is calculated for the Ni/CNF by BET analysis. Cyclic voltammetry (CV) results indicate the higher electrocatalytic activity toward the [VO](2+)/[VO2](+) as well as V2+/V3+ redox reactions for Ni/CNF with respect to the bare CNF. Charge-discharge tests show energy efficiency (EE) value of 68%, voltage efficiency (VE) of 72% and a coulomb efficiency (CE) of 94% for Ni/CNF at 160 mA center dot cm(-2). The electrochemical performance recorded at high current density could be ascribed to the high electrical conductivity as well as the polarity on the carbon surface due to the nickel nanoparticles. In particular, an increment in terms of wettability improves the accessibility to the aliphatic and carboxyl groups on the composite surface sample enhancing the reversibility at the electrode/electrolyte interface. (c) 2018 The Electrochemical Society.

Composite Nafion-based membranes, containing 5 wt % of high-purity mesoporous titania with an average pore size of about 3.5 nm heated to 350, 450, and 600 degrees C as a filler were successfully recasted. Field emission scanning electron microscopy observations showed a high degree of dispersion of mesoporous titania particles in Nafion. Direct methanol fuel cell investigation of such membranes at temperatures higher than 100 degrees C revealed a considerable influence of the presence of the ceramic oxide and of its specific surface area on the electrochemical behavior. The composite membranes allowed operation up to 145 degrees C, showing a significant performance improvement with respect to pure Nafion. At 145 degrees C with oxygen feed, a power density of about 335 mW/cm(2) was recorded for the composite Nafion-based membranes, containing 5 wt % of mesoporous titania calcined at 450 degrees C. (c) 2005 The Electrochemical Society. All rights reserved.

An electrochemical investigation has been carried out by using ethanol as alternative liquid fuel to methanol in a Direct Alcohol Fuel Cell (DAFC). Although methanol shows better performance with respect to ethanol, this latter represents a suitable fuel for DAFC; it is not toxic, it can be obtained from biomasses and it has a theoretical mass energy density larger than methanol. 85%Pt-Ru/C and 60%Pt/C in-house catalysts have been prepared for ethanol electro-oxidation and oxygen electro-reduction reactions, respectively, by the sulfite complex route. A composite membrane composed by Nafion ionomer and silica was fabricated in order to maintain the advantageous water retention properties of these materials at high temperatures (90-145{degree sign}C). The electrochemical behaviour of the composite membranes was also investigated in DEFCs at low temperatures (60-80{degree sign}C).

Composite Nafion membranes containing various amounts of TiO2 (3%, 5% and 10%) were prepared by using a recast procedure for application in high temperature Direct Methanol Fuel Cells (DMFCs). The electrochemical behaviour was compared to that of a membrane-electrode assembly (MEA) based on a bare recast Nafion membrane. All the MEAs containing the Nafion-titania membranes were able to operate up to 145°C, whereas the assembly equipped with the bare recast Nafion membrane showed the maximum performance at 120°C. A maximum power density of 340 mW cm-2 was achieved at 145°C with the composite membrane in the presence of oxygen feed, whereas the maximum power density with air feed was about 210 mW cm-2.