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sintesi di materiali catodi per batterie Na aria

Scouting di nuove coppie redox alternative al vanadio per applicazione stazionaria

Test di caratterizzazione su materiali catodici

9 figures, 3 tables; © 2020. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/, In the present work, an iron-cobaltite spinel supported on N-containing carbon nanofibers (CNFs) shows a remarkable activity for the oxygen evolution reaction (OER) in alkaline solution, with an overpotential (η10mAcm-2) of 130 mV, one of the lowest values in literature so far. This material is also an excellent catalyst for the oxygen reduction reaction (ORR), what leads to an extraordinary reversible behavior (ΔE = EOER – EORR=480 mV), being an economic and easy scalable candidate for the air electrode of metal-air batteries or for electrochemical devices where the oxygen evolution or the oxygen reduction is involved. In the present research, Fe partially replaces Co atoms in the Co3O4 spinel structure to obtain a more economically feasible material, leading to a FeCo2O4/CNF, by using an electrospinning preparation procedure previously adopted for the Co3O4/CNF synthesis. The substitution of iron in the Co3O4/CNF spinel entails an outstanding onset potential toward the OER of 1.36 V vs. reversible hydrogen electrode, which is 120 mV lower compared with the pure spinel (Co3O4/CNF). An optimal distribution of the FeCo2O4 particles on the CNF surface, with 3-nm-size particles, allows exposing abundant active sites, mainly Co3+ and Fe3+, responsible for the enhanced activity toward the OER, and Fe-Nx moieties and N-sites (N-graphitic/pyridinic), more active for the ORR. Besides, FeCo2O4/CNF shows a well-developed porous structure, favoring the mass transfer, a parameter particularly important for the ORR. To assess the stability of the catalysts for rechargeable alkaline metal-air batteries, cycling operation and chronopotentiometric experiments are carried out, showing a stable potential for 24 h., The research leading to these results has received funding from the ‘Accordo di Programma CNR-MiSE, RdS PTR 2019–2021 - Progetto 1.2 Sistemi di accumulo, compresi elettrochimico e power to gas, e relative interfacce con le reti’. C.A. thanks the Ministry of Economy, Industry and Competitiveness for her research contract Juan de la Cierva (IJCI-2017-32354).

Rechargeable alkaline metal-air batteries are envisaged as commercially viable energy storage devices due to their high theoretical energy densities respect to lithium-ion batteries. However, they do not still offer adequate practical energy density and life cycle due to critical problems arising from the positive electrode, such as slow kinetics of the oxygen reduction (ORR) and oxygen evolution (OER) reactions. In the last few years, research was focused on the development of highly efficient oxygen reduction/evolution catalysts based on transition metals, such as Co, Fe, Mn, La, etc, in the form of mixed oxides (perovskites, spinels, etc.), or advanced carbon materials. Co-based catalysts have been thoroughly investigated for the ORR/OER, and, usually, Co3O4 is the most employed formulation. However, the electrical conductivity of bare Co3O4 is not appropriate for the application in most of these devices. Other transition metals (Ni, Fe, Mn, etc.) can partially replace Co atoms in the Co3O4 spinel structure, improving its electronic conductivity while promoting oxygen evolution. Another approach is to combine these oxides with carbon nanostructures, in particular graphitic ones, in order to maintain suitable stability under cycling operation. These approaches are evaluated and presented in this work.

Le batterie ricaricabili alcaline a base di ferro, come i sistemi ferro-aria, sono molto promettenti grazie al basso costo, la relativa abbondanza, la riciclabilità e l'eco-compatibilità dei loro componenti. Nell'ambito del precedente programma (PAR2016-17) i prototipi di cella realizzati hanno permesso di raggiungere densità di energia maggiori di 350 Whkg-1Fe e capacità superiori a 500 mAh/gFe. Tuttavia, la cella ha presentato fenomeni di degradazione nei primi cicli, dovuta alla passivazione delle particelle di ferro e alla loro dissoluzione dall'elettrodo, a causa della formazione di bolle di H2. Inoltre, anche la stabilità nel tempo dell'elettrodo ad aria deve essere migliorata. A tal fine, il programma di attività del primo anno è rivolto sia all'ottimizzazione del prototipo di cella sviluppato nei programmi precedenti, cercando di minimizzare le resistenze elettriche e favorire il trasporto dei reagenti, che alla messa a punto di catalizzatori a basso costo per l'elettrodo positivo e strutture elettrodiche in grado di incrementare l'utilizzo della materia attiva all'elettrodo negativo.

A composite material based on nickel manganite and carbon nanofibers (NiMn2O4/CNF) is synthesized by electrospinning method and investigated as a symmetric electrode for vanadium redox flow battery (VRFB). The X-ray diffraction pattern shows the formation of NiMn2O4/CNF, characterized by a cubic spinel-type structure and a high graphitization degree of the carbon nanofiber. XPS analysis reveals the presence of mixed oxidation state of nickel and manganese as Ni2+/Ni3+ and Mn2+/Mn3+, respectively. As evident by scanning electron microscope analysis (SEM), a complete covering of carbon nanofibers surface by NiMn2O4 nanoparticles occurs. Charge-discharge curves are carried out from 80 mA/cm(2) up to 500 mA/cm(2). The best result shows an energy efficiency (EE) of about 68% with corresponding deep of discharge (DoD) of about 55% at 500 mA/cm(2). The high electrical conductivity as well as the high hydrophilicity, useful for improving the active surface area utilization, could be responsible for the remarkable results of the electrospun electrodes. In fact, thanks to the structural defects of the NiMn2O4/CNF and the presence of hydroxyl (OH), carboxyl (COOH) and nitrogen functional groups, the electrocatalytic activity increases at the electrode/electrolyte interface. Therefore, a remarkable power density at very high current density was achieved, 550 mW/cm(2) at 500 mA/cm(2). (c) 2020 Elsevier Ltd. All rights reserved.

Sintesi di materiali catodici mediante tecnica di electrospinning

Attività di caratterizzazione chimico-fisica ed elettrochimica su materiali 2D structure simili al grafene del tipo MoO2, MoS2, WO2, WS2 ed MnO2, tutti depositati su nanaofibre di carbonio mediante tecniche di electrospinning .

Rechargeable alkaline metal-air batteries can be considered one of the most promising next energy storage systems owing to their extremely high energy densities. However, this kind of batteries requires very efficient and durable bifunctional electrocatalysts to accelerate the kinetics of oxygen reduction reaction (ORR), taking place during the discharge, and oxygen evolution reaction (OER), occurring during charging of the battery. In the last few years, research was focused on the development of highly efficient oxygen reduction/evolution catalysts based on transition metals, such as Co, Fe, Mn, La, etc, in the form of mixed oxides (perovskites, spinels, etc.), or advanced carbon materials. Co-based catalysts have been thoroughly investigated for the ORR/OER, and, usually, Co3O4 is the most employed formulation. However, the electrical conductivity of bare Co3O4 is not appropriate for the application in most of these devices. Ni and other transition metals can partially replace Co atoms in the Co3O4 spinel structure, improving its electronic conductivity while promoting oxygen evolution. Another approach is to combine these oxides with carbon nanostructures, in particular graphitic ones, in order to maintain suitable stability under cycling operation. Recently, carbon nanofibers (CNF) synthesized by electrospinning, modified with a combination of cobalt oxide and metallic cobalt (CoO-Co/CNF)1 or loaded with nickel and cobalt (both in the metallic and oxide forms)2, were investigated in our laboratories as bifunctional air electrodes showing good reversibility and stability. In the present work, the latter catalyst (NiCo-loaded CNFs 2), after the electrospinning preparation, has been oxidized with the aim of synthesizing the pure spinel structure (NiCo2O4) supported on CNFs. The electrochemical behavior of the spinel has been compared with the previously developed catalyst to elucidate the catalytic activity of the two systems for ORR and OER in relation with their physico-chemical properties. References 1. Alegre, C.; Busacca, C.; Di Blasi, O.; Antonucci, V.; Arico, A. S.; Di Blasi, A.; Baglio, V. Journal of Power Sources 2017, 364, 101-109. 2. Alegre, C.; Modica, E.; Di Blasi, A.; Di Blasi, O.; Busacca, C.; Ferraro, M.; Antonucci, V.; Arico, A. S.; Baglio, V. Renewable Energy 2018, 125, 250-259.

A new way to produce and store electrical energy is necessary to address future energy demands and reduce polluting emissions. Rechargeable alkaline metal-air batteries are envisaged as commercially viable energy storage devices due to their high theoretical energy densities respect to lithium-ion batteries. However, they do not still offer adequate practical energy density and life cycle due to critical problems arising from the positive electrode, such as slow kinetics of the oxygen reduction (ORR) and oxygen evolution (OER) reactions. In the last few years, research was focused on the development of highly efficient oxygen reduction/evolution catalysts based on transition metals, such as Co, Fe, Mn, La, etc, in the form of mixed oxides (perovskites, spinels, etc.), or advanced carbon materials. Co-based catalysts have been thoroughly investigated for the ORR/OER, and, usually, Co3O4 is the most employed formulation. However, the electrical conductivity of bare Co3O4 is not appropriate for the application in most of these devices. Other transition metals (Ni, Fe, Mn, etc.) can partially replace Co atoms in the Co3O4 spinel structure, improving its electronic conductivity while promoting oxygen evolution. Another approach is to combine these oxides with carbon nanostructures, in particular graphitic ones, in order to maintain suitable stability under cycling operation. Recently, carbon nanofibers (CNF) synthesized by electrospinning, modified with a spinel Co3O4 [1] or a combination of cobalt oxide and metallic cobalt (CoO-Co/CNF) [2] or loaded with Nickel-cobaltite [3], were investigated in our laboratories as bifunctional air electrodes showing good reversibility and stability. In this work, Fe partially replaces Co atoms in the Co3O4 spinel structure, leading to a FeCo2O4/CNF, by using the same electrospinning preparation procedure previously reported. The FeCo2O4/CNF catalyst is physico-chemically studied in terms of structure, morphology and surface properties; these features are correlated to the electrochemical behavior for the oxygen reduction (ORR) and oxygen evolution (OER) reactions in comparison with previously developed Co3O4/CNF [1] and state-of-the-art materials. An outstanding onset potential towards the OER of 1.40 V vs. RHE is observed, which is 140 and 250 mV lower compared to the pure spinel (Co3O4/CNF) and Pt/Vulcan, respectively. A remarkable reversibility (?E = EOER - EORR) value of 495 mV is obtained, due to a good activity also for the ORR. To assess the stability of the catalysts for rechargeable alkaline metal-air batteries, cycling operation and chronopotentiometric experiments are carried out, showing promising results. References [1] C. Alegre, C. Busacca, A. Di Blasi, O. Di Blasi, A.S. Aricò, V. Antonucci, E. Modica, V. Baglio, Journal of Energy Storage 23 (2019) 269-277. [2] C. Alegre, C. Busacca, O. Di Blasi, V. Antonucci, A.S. Arico, A. Di Blasi, V. Baglio, Journal of Power Sources 364 (2017) 101-109. [3] C. Alegre, C. Busacca, A. Di Blasi, et al., ChemElectroChem 7 (2020) 124-130.

Il programma di attività del primo anno è stato rivolto alla messa a punto di catalizzatori a basso costo per l'elettrodo positivo e strutture elettrodiche in grado di incrementare l'utilizzo della materia attiva all'elettrodo negativo. In particolare, per quanto concerne l'elettrodo positivo, l'obiettivo era quello di ottimizzare/sviluppare ossidi metallici con struttura spinello (NiMn2O4/CNF, MnCo2O4/CNF, etc.) tramite elettrospinning e/o perovskite. Ulteriore obiettivo è stato lo studio di catalizzatori metal-free a base di carboni nanostrutturati dopati con N, o con piccole percentuali di metallo (Fe-N-C). Per quanto riguarda l'elettrodo negativo, lo studio della struttura dell'elettrodo è stata prevista, cercando di ottimizzare il rapporto Fe:C, introducendo "pore former" nella materia attiva, per favorire l'accessibilità dell'elettrolita, ed additivi (solfuri, tioli) sia nell'elettrolita che nell'elettrodo, per ridurre l'evoluzione di idrogeno.

The electrocatalysis of oxygen in alkaline media is a challenging issue, influencing the performance of many electrochemical devices: fuel cells, unitized regenerative fuel cells, electrolyzers and metal-air batteries. This new manuscript proposes the synthesis of graphitic carbon nanofibers obtained by electrospinning with a cobalt-based spinel oxide, Co3O4/CNF. By means of a simple, reproducible and scalable method, a bifunctional catalyst with a promising performance is obtained, being able of carrying out the electrocatalysis of oxygen (oxidation of water, evolution and reduction of oxygen) in a basic solution. The combination of the active species on cobalt oxide (Co2+, Co3+ and Co-Nx), along with active species in the carbon nanofiber (graphitic and pyridinic N), gives rise to a catalyst with a remarkable reversibility (difference between E10 mA/cm2 (evolution) and Ehalf-wave-potential (reduction)): ΔE =795 mV), a low over-potential for the evolution of oxygen (η =416 mV) and 919 mV of oxygen reduction onset potential, very similar to that of a benchmark catalyst, Pt/C., Funding for this work was obtained from the “Accordo di Programma CNR-MiSE, Gruppo tematico Sistema Elettrico Nazionale – Progetto: Sistemi elettrochimici per l’accumulo di energia”.

Messa a punto di materiali a base di Fe ed additivi (solfuri) in modo da aumentare la ciclabilità dell'elettrodo negativo in soluzione alcalina e ottimizzazioni di catalizzatori bifunzionali per l'elettrodo ad aria in termini di prestazioni per le reazioni di riduzione ed evoluzione di Ossigeno e di stabilità ai cicli in ambiente alcalino.

Sviluppo di materiali ed il design di un prototipo di batteria Ferro-aria di nuova generazione operante a bassa temperatura in presenza di elettrolita alcalino

Spinel oxide electrocatalysts supported on carbon nanofibers (CNFs), denoted as and NiMn2O4/CNF and NiCo2O4/CNF, are investigated for the oxygen evolution reaction (OER) in alkaline electrolyte. NiCo2O4/CNF and NiMn2O4/CNF are prepared according to an optimized electrospinning method using polyacrylonitrile (PAN) as carbon nanofibers precursor. After the thermal treatment at 900 °C for 1 h in the presence of helium and the subsequent one at 350 °C for 1 h in air, nanosized metal oxides with a spinel structure supported on carbon nanofibers are obtained. The physico-chemical investigation shows relevant difference in the crystallite size (9 nm for the NiCo2O4/CNF and 20 nm for the NiMn2O4/CNF) and a more homogeneous distribution for NiMn2O4 supported on carbon nanofibers. These characteristics derive from the different catalytic effects of Co and Mn during the thermal treatment as demonstrated by thermal analysis. The OER activity of NiCo2O4/CNF and NiMn2O4/CNF is studied in a single cell based on a zero gap anion-exchange membrane-electrode assembly (MEA). The NiMn2O4/CNF shows a better mass activity than NiCo2O4/CNF at 50 °C (116 A g−1 @ 1.5 V and 362 A g−1 @ 1.8 V vs. 39 A g−1 @ 1.5 V and 253 A g−1 @ 1.8 V) but lower current density at specific potentials. This is the consequence of a lower concentration of the active phase on the support resulting from the need to mitigate the particle growth in NiMn2O4/CNF.

L'attività di ricerca è stata focalizzata sulla caratterizzazione elettrochimica in cella singola dei materiali elettrodici a base di metalli misti, già sintetizzati e testati in semicella all'interno del precedente PAR 2015. L'attività ha altresì visto la selezione del materiale più performante finalizzata allo scale-up per test su sistema prototipale di batteria V-redox flow a densità di corrente >=100 mA/cm2.

L'attività è stata indirizzata verso lo sviluppo di una nuova configurazione di stack per batterie al vanadio con componentistica a basso costo. Gli obiettivi previsti da progetto sono stati raggiunti operando ad elevati valori di densità di corrente in fase di carica e di scarica, superiore al target di progetto. Il rendimento totale del sistema prototipale VRFB è stato pari al 66% @ 120 mA/cm2 (36 A).

Spinel electrocatalysts supported on carbon nanofibers (CNFs) denoted as NiCo2O4/CNF and NiMn2O4/CNF were investigated for oxygen evolution reaction (OER) in alkaline electrolyte. NiCo2O4/CNF and NiMn2O4/CNF were prepared according to an optimized electrospinning method using polyacrylonitrile (PAN) as carbon nanofibers precursor. After the thermal treatment at 900°C for 1 h in the presence of helium and the subsequent one at 350°C for 1h in air, nanosized metal oxides with a spinel structure supported on carbon nanofibers were obtained. The physico-chemical investigation showed relevant difference in crystallite sizes (9 nm for the NiCo2O4/CNF and 20 nm for the NiMn2O4/CNF) and more homogeneous distribution for NiMn2O4 supported on carbon nanofibers. These characteristics derived from the different catalytic effects of Co and Mn during the thermal treatment as demonstrated by the TG-DSC analysis. The OER activity of NiCo2O4/CNF and NiMn2O4/CNF was studied in a single cell based on a zero gap anion-excange membrane-electrode assembly (MEA). The NiMn2O4/CNF showed a better mass activity than NiCo2O4/CNF at 50 °C (116 A g-1 @ 1.5 V and 383 A g-1 @ 1.8 V vs. 39 A g-1 @ 1.5 V and 272 A g-1 @ 1.8 V) but lower current density at specific potentials. This was the consequence of a lower concentration of the active phase on the support resulting from the need to mitigate the particle growth in NiMn2O4/CNF.

L'attività condotta sulle batteria redox a flusso di vanadio (VRFB) è stata indirizzata verso l'ottimizzazione di materiali elettrodici a basso costo, innovati ed altamente efficienti in grado di migliorare i parametri elettrochimici di cella di una batteria.

L'obiettivo dell'attività è lo studio e la verifica di soluzioni innovative sulle geometrie di cella e la scelta dei materiali più appropriati per migliorare le prestazioni e la stabilità del dispositivo nel tempo. Sono stati realizzati e testati tre nuovi prototipi di cella accoppiando diversi materiali e gasket. Il risultato finale è stata la selezione dei migliori materiali per la realizzazione di celle di larga area per le successive attività di stack e sistema.

Proton exchange membrane (PEM) water electrolysis represents a valid technology for hydrogen production by using renewable energy [1]. Higher current density, low cost for hydrogen purification process and low overpotential voltage are some of the main advantages of this method if compared to alkalyne electrolysis. However, high costs related to the outstanding platinum catalyst activity and stability lead to a slow technology introduction into the market. In this respect, electrospinning method was utilized to reduce the platinum loading on carbon based material supports increasing the utilization of noble metal thanks to an appropriate distribution of the noble metal nanoparticles throughout the electrospun samples [2-3] as well as to the introduction of alternative and low cost metals. Therefore, home-made electrocatalysts based on pristine Platinum and Platinum-Cobalt embedded on carbon nanofiber (Pt/CNF and Pt-Co/CNF) are synthesized starting from platinum acetylacetonate and cobalt acetate as precursors. Polyacrylonitrile (PAN) was utilized as polymer precursor for CNF formation. The mixed solution was subjected to electrospinning technique. The obtained electrospun samples were treated to thermal treatments consisting in two different steps, at 270°C in air and at 900°C in inert gas. The physico-chemical properties of Pt/CNF and Pt-Co/CNF samples are investigated by termogravimetry-differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM). Electrochemical characterization are carried out in 5 cm2 single cell configuration by using an home-made Ir-RuO2 as negative electrode [4] and a Aquivion membrane as electrolyte.

SVILUPPO DI BATTERIE FERRO-ARIA DI NUOVA GENERAZIONE OPERANTI A BASSA TEMPERATURA IN PRESENZA DI ELETTROLITA ALCALINO

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 half-wave potential for the ORR of 874 mV vs. RHE and a reversibility (ΔEOER-ORR) of 764 mV. The stability of the catalyst is assessed by means of a 24 h chronopotentiometric test at −80 mA cm−2 and charge-discharge cycles (30 min each) at ±20 mA cm−2. NiCo-loaded CNF shows a remarkable stability, maintaining a constant potential during both tests.

Electrode materials, having a different graphitic character, are investigated by using a zero-gap flow field cell configuration for vanadium redox flow battery applications (VRFBs). Carbon felt (CF) and carbon paper (CP) are used as electrodes for the membrane–electrode assemblies (MEAs) realization. The samples are electrochemically characterized both as-received and after chemical treatment by using a 5 cm2 single cell. A Nafion 117 membrane is used as polymer electrolyte separators. A MEAs scale-up from 5 to 25 cm2 is carried out in order to assembly a 3-cells short stack in series connected. Charge–discharge cycles are carried out both in a small area single cell and in a 3-cells short stack for all samples. CF treated and untreated samples show SOC values of 45% vs. 22% at 60 mA cm−2, respectively. After the chemical treatment, the worst performance of the CF sample is attributed to the mass transport issues due to the beginning of corrosion phenomena. On the contrary, CP treated electrode shows a better energy efficiency values than raw sample (72% vs. 67% at 60 mA cm−2) without any morphology change on the electrode surface. A proper stack assembly and flow field scale-up record similar performance to the small single cell configuration.

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”.

Metal-air batteries are envisaged as next-generation batteries, with extraordinary high energy densities (depending on the metal used, Li, Na, Zn, Al, Mg, Fe...). These devices represent a promising future for a clean and sustainable storage of energy. Bifunctional electrodes able to carry out both the reduction of oxygen (oxygen reduction reaction, ORR) and the oxidation of water (also known as oxygen evolution reaction, OER) are of vital importance for the progress of this technology. In the last few years, research has focused on the development of highly efficient oxygen reduction/ evolution catalysts based on transition metals, such as Co, Fe, Mn, La, etc , in the form of mixed oxides (perovskites, spinels, etc), or advanced carbon materials, such as N or S-doped carbon materials, like graphene, or macrocycles incorporating transition metals . The novelty of the present work regards on the use of carbon nanofibers supported CoO/Co as bifunctional catalyst for rechargeable metal-air batteries. Besides, the material has been obtained by a simple and easy-scalable process, electrospinning of polyacrilonitrile and Co-precursors, giving rise to a Co-based material in combination with a highly resistant carbon, electrospun carbon nanofibers.

Home-made electrospun catalyst based on urchin-like vanadium (III) oxide-carbon nanofiber (V2O3-CNF) composite is synthesized from a solution containing vanadium (V) oxytriisopropoxide VO-(OiPr)3 as metal oxide precursor and polyvinylpyrrolidone (PVP) as carbon source for vanadium redox flow battery (VRFB) application. X-ray diffraction (XRD) as well as scanning electron microscopy (SEM) analysis show a typical V2O3 rhombohedral structure and an urchin-like V2O3-CNF morphology, respectively. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements show a high electrocatalytic activity for the composite electrospun samples both in terms of peak to peak separation (ΔE = 0,02 V) and lower charge transfer resistance (Rct = 0.12 ohm cm2) with respect to a pristine CNF. The better reversibility is ascribed to the oxygen functional groups presence that act as catalytic sites reducing kinetic overpotentials. Moreover, thanks to the rhombohedral structure of V2O3, as well as to the more graphitic structure of the carbon, a suitable electrical conductivity is guaranteed for reducing ohmic overpotentials.

Composite membranes based on sulfonated polysulfone and acidic silica filler were prepared and investigated for direct methanol fuel cells. A significant influence of nanosized acidic silica on composite membrane properties was observed. A better distribution of acidic silica than bare silica was found in the membranes as well as a higher ionic conductivity of acidic silica membrane. The composite membranes based on sulfonated polysulfone modified silica (SPSf–SiO2–S) and bare silica (SPSf–SiO2) showed also an increase of DMFC performance compared to bare SPSf. The best electrochemical performance was obtained with the composite SPSf–SiO2–S membrane that showed satisfactory proton conductivity, low methanol crossover and low swelling in comparison to bare SPSf membrane. Methanol crossover currents of 20, 25 and 31 mA cm− 2 were measured for SPSf–SiO2–S, SPSf–SiO2 and SPSf membranes, respectively. The highest DMFC performance of 60 mW cm− 2 was obtained with the composite acidic silica-SPSf membrane (SPSf–SiO2–S) at 60 °C.

Sviluppo di componenti innovativi e nuove configurazioni di cella per batterie metallo-aria Sviluppo di batterie Fe-aria operanti a bassa temperatura

La finalità dell'attività sperimentale è l'ottimizzazione dei parametri elettrochimici, quali la densità di potenza (>100 mWcm-2 @ densità di corrente > 40-50 mA/cm2) e l'efficienza energetica (EE>70%). Attraverso i test di caratterizzazione elettrochimica condotti in semicella a tre elettrodi è stato individuato il materiale elettrodico più performante in termini di attività elettrocatalitica. Cicli di carica-scarica a diverse densità di corrente (> 40-50 mA/cm2) hanno consentito la determinazione e la validazione dei parametri elettrochimici in cella singola, registrando valori di EE=80% e VE=87% nonché elevati valori di SOC e DoD, pari a circa 81% e 73% @ 80mA cm-2 e densità di potenza di circa 106 mW cm-2 @ 80mA cm-2.

A flexible electrospun carbon nanofiber (CNF)-based electrode decorated with Mn3O4 is prepared starting from a solution containing polyacrilonitrile (PAN) mixed with manganese acetate (Mn(OAc)2). A thermal treatment at 270°C in air and a subsequent at 900°C in inert gas allow to obtain a flexible electrospun carbon nanofibers decorated with spinel manganese oxide (denoted as Mn3O4/CNF) characterized by suitable performance for vanadium redox flow battery (VRFB) application. Pristine electrospun carbon nanofibers CNF were prepared by using a similar method to compare the electrochemical data with respect to the decorated CNF. A homogeneous distribution of the metal oxides on the carbon nanofibers is showed by scanning electron microscopy (SEM) analysis. Cyclic voltammetry (CV) curves show a higher electrocatalytic activity toward the [VO]2+/[VO2]+ as well as the V2+/V3+ redox reactions with respect to the pristine electrospun CNF electrode, both in terms of peak to peak separation, DE[VO]2+/[VO2]+ = 0,15 V vs. 0,28 V, and Ipa/Ipc[VO]2+/[VO2]+ ratio, 1,48 vs 1,58, respectively. The improved performance is attributed to the hydrophilicity enhancement due to the oxygen groups availability that favour the surface mechanism process on the carbon nanofibers decorated with metal oxide nanoparticles.

Thermically treated graphene oxides (TT-GOs) are synthesized at different temperatures, 100 °C, 150 °C, 200 °C and 300 °C in a reducing environment (20% H2/He) and investigated as electrode materials for vanadium redox flow battery (VRFB) applications. The treated graphene oxide-based electrodes are prepared by the wet impregnation method using carbon felt (CF) as support. The main aim is to achieve a suitable distribution of the dispersed graphene oxides on the CF surface in order to investigate the electrocatalytic activity for the VO2+/VO2+ and V2+/V3+ redox reactions in the perspective of a feasible large area electrodes scale-up for battery configuration of practical interest. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) are carried out in a three electrode half-cell to characterize the electrochemical properties of the TT-GO-based electrodes. Physico-chemical characterizations are carried out to corroborate the electrochemical results. The TT-GO sample treated at 100 °C (TT-GO-100) shows the highest electrocatalytic activity in terms of peak to peak separation (ΔE = 0.03 V) and current density intensity (∼0.24 A cm−2 at 30 mV/s) both toward the VO2+/VO2+ and V2+/V3+ redox reactions. This result is correlated to the presence of hydroxyl ( OH) and carboxyl ( COOH) species that act as active sites. A valid candidate is individuated as effective anode and cathode electrode in the perspective of electrodes scale-up for battery configuration of practical interest.

Le attività svolte dal CNR-ITAE per il progetto PON01_01366 "Nuovo processo a basso impatto ambientale ed a ridotto rischio operativo per il recupero ed il riciclo dei materiali costituenti le batterie al piombo" riportate in questo rapporto e facenti parte dell'obiettivo realizzativo OR.1, sono finalizzate a valutare le caratteristiche fisiche, chimico-fisiche ed elettrochimiche dei materiali, a base di ossido di piombo, rigenerati allo scopo di essere riutilizzati per la realizzazione di batterie piombo-acide nuove. I materiali analizzati sono stati forniti dal partner STC s.r.l. che ha curato il processo di rigenerazione del pastello esausto. Sono state analizzati circa 20 campioni di polvere piombifera così come sono stati ottenuti dal processo di rigenerazione di volta in volta testato da STC o miscelati con polvere piombifera commerciale fresca. Le analisi dovevano servire a verificare quanto i materiali rigenerati fossero simili a quelli utilizzati dalle imprese commerciali nel produrre batterie nuove e se eventualmente potevano essere apportate modifiche al processo di rigenerazione alla luce dei risultati ottenuti al CNR per migliorare le proprietà del materiale.

SUPERCAPACITORE DI ALTA ENERGIA CON ELETTRODI A BASE DI CARBONE IN ELETTROLITA ACQUOSO P. Staiti, F. Lufrano, O. Di Blasi, A. Brigandì CNR-ITAE, Istituto di Tecnologie Avanzate per l'Energia "Nicola Giordano" Via salita S. Lucia sopra Contesse, 5 - 98126 S. Lucia - Messina telefono: 090-624226, fax: 090-624247, e-mail: staiti@itae.cnr.it I supercapacitori sono sistemi di accumulo molto interessanti per le loro proprietà di accumulare e erogare energia elettrica in modo veloce (alta potenza) e di poter essere caricati-scaricati per un numero elevatissimo di cicli (>500.000) senza subire apprezzabili decadimenti di prestazioni. Tuttavia la quantità di energia elettrica che questi dispositivi possono accumulare è al momento molto più bassa di quella delle batterie ed è in atto uno sforzo mondiale per migliorare questo aspetto. L'energia specifica (E) di un supercapacitore è definita dalla formula E=1/2 CV2 , nella quale C e la capacitanza e V il voltaggio massimo di carica. Per aumentare quindi l'energia specifica è necessario migliorare la capacitanza o aumentare quanto più possibile il voltaggio di lavoro. Anche presso il CNR-ITAE è stata svolta un'attività finalizzata ad aumentare l'energia specifica del supercapacitore. L'attività è iniziata con un approfondito studio sulle caratteristiche del carbone cui è seguita un'attenta analisi delle proprietà elettrochimiche degli elettrodi basati su tale materiale. Da questa, utilizzando un carbone commerciale Norit A Supra Eur con area superficiale di circa 1500 m2/g, è stato trovato che gli elettrodi mantenevano la loro stabilità, con elettrolita 1M Na2SO4 in soluzione acquosa, quando l'elettrodo positivo e quello negativo si caricavano e scaricavano entro ben determinati limiti di potenziale. Questi potenziali limite erano +0.9 V per l'elettrodo positivo e -1.0V per quello negativo. Con l'aiuto di questi preliminari risultati abbiamo progettato di realizzare un supercapacitore che durante il suo funzionamento facesse caricare e scaricare gli elettrodi all'interno di questi potenziali limite. E' stato inoltre evidenziato che il polo positivo, sul quale il doppio strato in fase acquosa era formato dagli anioni solfato, era quello che si polarizzava in modo più veloce e quindi un eventuale supercapacitore realizzato con eguale quantità di carbone nei due elettrodi, sarebbe stato limitato da problemi di instabilità di questo elettrodo. La maggiore polarizzabilità dell'elettrodo positivo è da imputare al maggior ingombro sterico dello ione solfato rispetto allo ione sodio (elettrodo negativo). Inoltre è stato rilevato che il potenziale di equilibrio che si generava ai due elettrodi quando il supercapacitore era completamente scarico non risultava essere zero ma assumeva un valore intorno a +0.2 V e così il polo positivo per rimanere stabile poteva spostarsi in un intervallo di potenziale di soli 0.7 V (cioè fra +0.2 e +0.9 V) mentre il polo negativo in uno di 1.2 V (cioè fra +0.2 V e -1.0 V). Per poter ottenere un supercapacitore che potesse lavorare negli intervalli di potenziale di stabilità degli elettrodi e dell'elettrolita era quindi opportuno utilizzare due diverse quantità di carbone negli elettrodi. Così facendo è stato possibile far lavorare il supercapacitore fino a un voltaggio massimo di 1.6 V invece di 1.0 V dei comuni supercapacitori a base acquosa con notevole vantaggio sull'incremento dell'energia specifica. Il supercapacitore, che era realizzato con una quantità più che doppia di carbone sull'elettrodo positivo, è stato testato in prove di carica-scarica dalle quali sono state ricavate le prestazioni in termini di energia specifica e di stabilità. La procedura di preparazione degli elettrodi e del supercapacitore così come i risultati dei test elettrochimici saranno presentati nel corso del convegno.

Several polymers with ion exchanging groups showing acidic strength comparable with that of “concentrated” sulfuric acid were used to prepare silica- heterogenized perfluorosulfonic (PFS) acid catalysts by either incipient wetness impregnation of commercial silicas or sol–gel and precipitation routes. Solid-acid catalysts were probed in the synthesis of acetal at 4 °C and 3 atm in a stirred batch reactor. A systematic analysis of activity data and the acid strength of the various catalysts points out a direct relationship between the acidic capacity and catalytic activity, pointing out a minor influence of the strength distribution on the main reaction path.

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 T R 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.

Several iron-based catalysts supported on different oxide carriers (CeO2, MnO, ZnO) were synthesized by the combustion route and probed in the Fischer-Tropsch synthesis reaction in the range 250-300°C and at 10-20 bar total pressure, using a PF-reactor and various COx reaction mixtures (H2/CO=2 or H2/CO2=3 or (CO+CO2)/H2=2). The prepared catalysts feature a catalytic performance superior to that of commercial FT catalysts and suitable for industrial application as a very high activity (100-60 of COx conversion), selectivity (low methane and high long-chain product selectivity; ASF parameter close to 0.9) and long lifetime (500 h).