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A family of hybrid inorganic-organic ion-exchange membranes (IEMs) is prepared, indicated as [Nafion/(WO3)x]. The IEMs consist of Nafion® dispersing different loadings (x) of tungsten oxide nanofiller. Morphology studies carried out by scanning electron microscopy (SEM) and micro-Raman investigations reveal that one side of each hybrid IEM exhibits a high concentration of the WO3 nanofiller. In the remaining part of each IEM the concentration of the filler is much lower and constant. The correlation between the asymmetrical nature and the performance of the hybrid IEMs is studied in a single-cell vanadium redox flow battery (VRFB). In comparison with the Nafion 212 reference, at the same current density of 50 mA∙cm−2, [Nafion/(WO3)0.587] demonstrates: (i) a higher Coulombic efficiency (93% vs. 88%), a higher energy efficiency (75% vs. 65%) and a higher capacity retention (62% vs. 42%).

The electrical relaxation and polarization phenomena of electrospun PVDF (P)/Nafion (N) blended fiber mats ([P/N0.9]M and β–[P]M) and membranes ([P/N0.9]MM) are compared with those of the solvent-c...

Platinum nanoparticles have been deposited onto hybrid carriers composed of iron hexacyanoferrate (Prussian Blue) pretreated or functionalized reduced graphene oxide (rGO), and the resulting system’s electrocatalytic activity has been investigated during oxygen reduction reaction in acid solution. Physicochemical properties of the Pt nanoparticle-containing materials have been obtained using transmission electron microscopy, X-ray diffraction and various electrochemical diagnostic techniques including cyclic voltammetry and rotating ring-disk electrode (RRDE) voltammetry. Although functionalization of rGO carriers with Prussian Blue, followed by the system’s thermal treatment at 300°C, does not change activity of Pt catalytic centers in terms of the electroreduction potential of oxygen in 0.5 mol dm−3 H2SO4 (under rotating disk voltammetric conditions), the presence of cyanide-bridged iron ionic sites tends to decrease formation of the undesirable hydrogen peroxide intermediate, as demonstrated by monitoring ring currents during RRDE measurements. The results imply usefulness of PB-modified rGO supports for dispersed Pt nanoparticles at the low loading of 10 μg cm−2 in the oxygen reduction electrocatalysis. In addition to the possible metal-support activating interactions, the mechanism, in which oxygen reduction is initiated at Pt centers and the hydrogen peroxide intermediate is reductively decomposed at reactive PB-modified rGO supports, is feasible.

Mixed-metal olivine cathode materials are one of the most promising systems in the field of lithium batteries. Their main drawback is their low electronic conductivity, which limits the current rate at which they can be cycled. Herein, the effect on electrochemical properties of vicariant high-valence transition metals (HVTMs) inserted in the olivine crystal structure has been studied. The strategy adopted herein consists of doping a LiFe1/3Ni1/15Co3/5PO4 cathode by substituting part of the cobalt(II) ions with vanadium(IV), niobium(V), or tantalum(V) HVTMs. The WAXD studies reveal that small HVTMs in molar quantities (HVTM/P = 0.04) are vicariant into the olivine crystal lattice. Single-cell tests show that the Nb-doped cathode has a high-voltage (ca. 4.5 V) and a specific capacity of 149 mA h g−1 (656 mW h g−1). Thus, the insertion of HVTMs in the cathode structure exceptionally improved the electric conductivity of the material and yielded an improved cyclability and rate capability owing to its electro-compensation effect.

Hybrid systems composed of the reduced graphene oxide-supported platinum and multiwalled carbon nanotube-supported iridium (both noble metals utilized at low loadings on the level of 15 and &le, 2 &micro, g cm&minus, 2, respectively) were considered as catalytic materials for the reduction of oxygen in acid media (0.5-mol dm&minus, 3 H2SO4). The electrocatalytic activity toward reduction of oxygen and formation of hydrogen peroxide intermediate are tested using rotating ring&ndash, disk electrode (RRDE) voltammetric experiments. The efficiency of the proposed catalytic systems was also addressed by performing galvanodynamic measurements with gas diffusion electrode (GDE) half-cell at 80 &deg, C. The role of carbon nanotubes is to improve charge distribution at the electrocatalytic interface and facilitate the transport of oxygen and electrolyte in the catalytic systems by lowering the extent of reduced graphene oxide restacking during solvent evaporation. The diagnostic electrochemical experiments revealed that&mdash, in iridium-containing systems&mdash, not only higher disk currents, but also somehow smaller ring currents are produced (when compared to the Ir-free reduced graphene oxide-supported platinum), clearly implying formation of lower amounts of the undesirable hydrogen peroxide intermediate. The enhancement effect originating from the addition of traces of iridium (supported onto carbon nanotubes) to platinum, utilized at low loading, may originate from high ability of iridium to induce decomposition of the undesirable hydrogen peroxide intermediate.

A new type of polymer blend, prepared by electrospinning nanofibers containing the immiscible polymers polyvinylidene fluoride (PVDF, 10 wt%) and Nafion® perfluorosulfonic acid (90 wt%), has been characterized experimentally. The internal nanofiber morphology is unique and unlike a normal blend, with individual phase-separated and randomly distributed fibrils of Nafion and PVDF (∼2-7 nm in diameter) that are bundled together and aligned in the fiber axis direction (where the fiber diameter is ∼500 nm). This morphology is retained when fiber mats are hot-pressed into dense films. The physicochemical properties of the electrospun blended fibers are also highly unusual and unanticipated. As shown in this study, each polymer component influences the thermal and structural behavior of the other, especially in the dry state. Thus, dry composite polymer mats and membranes exhibit properties and attributes that are not observed for either pure PVDF or pure Nafion. Experimental results indicate that: (i) PVDF imparts conformational constraints on the polytetrafluoroethylene (PTFE) backbone chains of Nafion, resulting in an increased 21 helical conformation that effects Nafion's water uptake and thermal properties; and (ii) dipole-dipole interactions between PVDF polymer chains and Nafion make the β-phase polymorph of PVDF much more stable at elevated temperatures. Such "reciprocal templating" in electrospun fibers may not be unique to Nafion and PVDF, thus the procedure represents a new method of creating nanostructured multi-component polymer materials with innovative features.

The development of innovative proton-conducting membranes exhibiting an improved [H+/VO2+] ion selectivity in comparison with baseline perfluorinated ionomers (e.g., Nafion) is critical to prompt the large-scale implementation of vanadium redox flow batteries (VRFBs) characterized by a performance and cyclability compatible with the applications. This paper pursues this objective by reporting the preparation and characterization of a new family of hybrid inorganic-organic membranes, that are labeled “[SPEEK/(WO3)x]”, consisting of a sulfonated poly (ether ether ketone) (SPEEK) matrix hosting between 0 and 23.6 wt% of WO3 nanoparticles (NPs). The physicochemical characterization of the [SPEEK/(WO3)x] membranes elucidates the impact of the introduction of WO3 NPs on the thermal, structural and transport properties of the SPEEK host. It is found that the [SPEEK/(WO3)0.20] membrane presents the highest [H+/VO2+] ion selectivity (2.1 × 104 S min cm−3), that is more than three times higher than that of recast Nafion (6.5 × 103 S min cm−3). [SPEEK/(WO3)0.20] is then mounted in a single cell VRFB, that is tested extensively under realistic operating conditions and demonstrates a coulombic efficiency and cyclabilty that are improved with respect to the corresponding figures of a VRFB incorporating a Nafion 212 membrane to provide the basis for a comparison. This outcome is in compliance with the result of the “ex-situ” investigations, and allows for the proposal of a structural model correlating the physicochemical properties of the [SPEEK/(WO3)x] membranes with the transport properties and the proton conductivity.

A polyketone-b-poly[N-(4 methyl-methylpyridium)-ethylenepyrrole+][X−], with X− = I− or OH−, is investigated as an example of anion-exchange membrane with potential applications in fuel cells. The polyketone starting material PK and the functionalized polyketones Pyr-FPKmI and Pyr-FPKmOH are investigated via Broadband Electrical Spectroscopy (BES) to understand the conductivity mechanism. BES signals are collected in the frequency range of 10−2 – 107 Hz and from −100° to 120 °C. BES measurements reveal the presence of up to three interdomain polarizations phenomena, one electrode polarization event and two β dielectric relaxation modes for both wet Pyr-FPKmI and Pyr-FPKmOH. Ion conductivity for Pyr-FPKmI and Pyr-FPKmOH is found to be 0.0086 and 0.0105 S cm−1 at 80 °C, respectively. The overall conductivity mechanism is attributed to the superposition of two conduction pathways, via delocalization bodies and via interdomain percolation pathways, which are associated with two different physical phenomena.

This work reports two quasi-solid composite electrolytes based on LiFT (Lithiated Fluorinated Titania) nanopowder and either 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF(4)) or 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMImTFSI) ionic liquid (IL). In details, LiFT nanopowder is doped with ca. 30 wt% of IL, giving rise to materials with formula LiFT/(EMImBF(4))(0.)(183) and LiFT/(EMImTESI)(0.)(087). The resulting composite electrolytes appear as powder-like solids as the IL is completely absorbed by LiFT. The correlation between structure, thermal properties and long-range charge migration processes of the here proposed electrolytes is investigated by several characterization techniques, as follows: i) differential scanning calorimetry (DSC) and high-resolution thermog-ravimetry (HR-TGA); ii) Fourier-transform infrared spectroscopy in both the medium and the far infrared (FT-MIR and FT-FIR); and iii) broadband electrical spectroscopy (BES). The conductivity of the here proposed composite electrolytes is promising. Indeed, at 30 and 100 degrees C it corresponds respectively to 1.75 x 10(-3) S cm(-1) and 1.05 x 10(-2) S cm(-1) for LiFT/(EMImBF(4))(0.183), and 1.36 x 10(-2) S cm(-1) and 4.42 x 10(-2) S cm(-1) for LiFT/(EMIMITSI)(0.087). Finally, LiFT/(EMImTESI)(0.087) is used to fabricate a coin cell prototype, that is tested by galvanostatic cycling for performance and durability. (C) 2019 Elsevier Ltd. All rights reserved.

We report on the development of two new Pt-free electrocatalysts (ECs) for the oxygen reduction reaction (ORR) process based on graphene nanoplatelets (GNPs). We designed the ECs with a core-shell morphology, where a GNP core support is covered by a carbon nitride (CN) shell. The proposed ECs present ORR active sites that are not associated with nanoparticles of metal/alloy/oxide but are instead based on Fe and Sn subnanometric clusters bound in coordination nests formed by carbon and nitrogen ligands of the CN shell. The performance and reaction mechanism of the ECs in the ORR are evaluated in an alkaline medium by cyclic voltammetry with the thin-film rotating ring-disk approach and confirmed by measurements on gas-diffusion electrodes. The proposed GNP-supported ECs present an ORR overpotential of only ca. 70 mV higher with respect to a conventional Pt/C reference EC including a XC-72R carbon black support. These results make the reported ECs very promising for application in anion-exchange membrane fuel cells. Moreover, our methodology provides an example of a general synthesis protocol for the development of new Pt-free ECs for the ORR having ample room for further performance improvement beyond the state of the art.

This study reports the preparation and characterization of a new family of electrocatalysts (ECs) for the oxygen reduction reaction (ORR) exhibiting a “core-shell” morphology. The “core” consists of graphene sheets, which are covered by a carbon nitride (CN) “shell” embedding Au and Ni active sites. The investigated ECs are labeled AuNi10-CNl 600/Gr and AuNi10-CNl 900/Gr. The chemical composition and thermal stability are studied by inductively-coupled plasma atomic emission spectroscopy (ICP-AES), elemental analysis and by high-resolution thermogravimetric analysis (HR-TGA). The morphology of the ECs is probed by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM) and powder X-ray diffraction (XRD). The ORR performance of the ECs is studied both in acid (0.1 M HClO4) and in alkaline medium (0.1 M KOH) by Cyclic Voltammetry with the Thin-Film Rotating Ring-Disk Electrode (CV-TF-RRDE) method. Both ECs exhibit a promising performance in the ORR in the alkaline medium.

Graphene is, in principle, a promising material for consideration as component (support, active site) of electrocatalytic materials, particularly with respect to the reduction of oxygen, an electrode reaction of importance to low-temperature fuel cell technology. Different concepts of utilization, including nanostructuring, doping, admixing, preconditioning, modification or functionalization of various graphene-based systems for catalytic electroreduction of oxygen are elucidated, as well as important strategies to enhance the systems’ overall activity and stability are discussed.

The centre piece at the heart of numerous energy storage and conversion devices, such as fuel cells and redox flow batteries, is the ion-exchange membrane (IEM). This typically polymeric material is responsible for the migration of ionic species, separation of fuel stocks and for providing additional support to the electrode assemblies. As a result, IEMs are required to possess excellent stability (both thermal and chemical), long lifetimes, electrical insulation, and high ionic conductivity and specificity. Current state-of-the-art polymer electrolytes possessing the more desirable properties tend to come with a price tag that can render their use in energy storage/conversion technologies somewhat cost prohibitive [1]. This has created a strong driving force aimed towards new, cheaper but still high performing materials, for use in energy storage/exchange systems. The copolymerization of carbon monoxide and ethylene (two readily available and cheap feedstocks) leads to the formation of polyketone, a high performance thermoplastic that has found many applications resulting in its global production of thousands of tonnes per annum. The alternating 1,4-dicarbonyl functionality of aliphatic polyketone enables access, via classic Paal-Knorr chemistry, to a variety of new functionalized polymers [2]. Here we present a new ion conducting polymeric material derived from polyketone, that possess N-functionalized pyrrole units in the backbone (FPK) [3]. Ion-conductivities on the order of 10.6 and 8.6 mScm-1 for the hydroxide and iodide forms of methylated FPKs have been achieved at 80 oC, with the hydroxide FPK demonstrating high resistance towards alkaline conditions for over 20 hours at 80 oC. The flexibility in the choice of the N-substituent renders these new materials higher tailorable and potentially useful in a range of energy storage/conversion technologies as either proton or anion exchange membranes. Acknowledgements The authors wish to thank the Strategic Project of the University of Padova “Materials for Membrane-Electrode Assemblies to Electric Energy Conversion and Storage Devices (MAESTRA)” for funding. V.D.N. thanks the University Carlo III of Madrid for granting him the “Catedra de Excelentia” (Chair of Excellence). References [1] S. Eckroad in Handbook of Energy Storage for Transmission or Distribution Applictions, Electric Power Research Institute Report 1007189, California, USA (2002) [2] A. Sen et al., Macromolecules, 22, (1989), 2012, A.A. Broekhuis et al., J. Apply. Polm. Sci., (2016), 42924, A.A. Broekhuis et al., J. Appl. Polym. Sci., 107, (2008), 107, 262, A.A. Broekhuis, Dyes and Pigments, 98, (2013), 51 [3] N. Ataollahi, K. Vezzù, G. Nawn, G. Pace, G. Cavinato, F. Girardi, P. Scardi, V. Di Noto, R. Di Maggio, Electrochimica Acta., 226 (2017) 148-157.

The potential for metallic lithium batteries that exhibit high specific capacities has stimulated a large interest within the energy research field. For safety reasons, the use of metallic lithium anodes requires electrochemically stable electrolytes. However, to date there has been limited success in this area. This work introduces a solid, lithium single-ion conductor thus providing new perspectives in the field of solid-state lithium-batteries. This new-concept material (LiFT), obtained by a direct reaction of nanometric fluorinated titanium oxide (FT) with molten metallic lithium, consists of nanoparticles (NPs) with anionic surface groups that are neutralized with lithium cations. The material displays fast lithium ion transport via an efficient migration mechanism occurring at the interfaces between different nanoparticles. The electrolyte comprises 1.34 mol kg−1 of Li and a conductivity of 2.8·10−4 S cm-1 at 25 °C is demonstrated. This level of performance, in conjunction with a native electrochemical stability towards lithium, extremely low cost starting materials (TiO2) and a facile one-pot synthesis, renders this electrolyte very attractive for applications in future full solid-state lithium batteries.

Nafion‑tungsten oxide hybrid membranes, [Nafion/(WO3)x], with varying loading levels of WO3 nanofiller (x = 0, 0.024, 0.329) are prepared and investigated as candidates for application as solid electrolytes in vanadium redox flow batteries (VRFBs). The thermal properties of [Nafion/(WO3)x] hybrid membranes are probed both by high-resolution thermogravimetric analysis (HR-TGA) and by modulated differential scanning calorimetry (MDSC). Vibrational spectroscopy studies are carried out by: (i) Attenuated Total Reflectance - Fourier Transform Infrared spectroscopy (ATR-FTIR); and (ii) Raman spectroscopy, to elucidate the secondary structure of [Nafion/(WO3)x] and study the interactions taking place between the nanofiller and the Nafion matrix. The electrical response of [Nafion/(WO3)x] is determined by Broadband Electrical Spectroscopy (BES) and the permeability towards VO2+ is measured by UV-VIS spectrometry. It is demonstrated that the [Nafion/(WO3)x] hybrid membranes exhibit a high ion selectivity (up to 10.6∙103 S∙min∙cm−3 for [Nafion/(WO3)0.329]) that is much improved in comparison with that characterizing recast Nafion (6.5∙103 S∙min∙cm−3). A structural model and a conductivity mechanism for the [Nafion/(WO3)x] hybrid membranes are proposed, in order to rationalize the experimental results and correlate the electrical response with the transport properties.

This work reports the synthesis, the physicochemical characterization and the electrochemical studies of new electrocatalysts (ECs) for the oxygen reduction reaction (ORR) that: (i) exhibit a hierarchical architecture; and (ii) do not comprise platinum. The active sites of the ECs consist of Fe and Sn species stabilized in “coordination nests” of a carbon nitride (CN) matrix. The latter exhibits a rough, microporous morphology and acts as a “shell” covering a graphene “core”. This paper: (i) discusses the role played by Fe as the “active metal” in this family of ECs; and (ii) examines in detail how the physicochemical properties and, correspondingly, the electrochemical performance are affected by a suitable activation procedure A meant to boost the ORR kinetics. The results lead to an improved fundamental understanding on the features of the active sites, including the impact of both A and the pH of the environment in their performance and ORR mechanism. These insights clarify the most desirable features to be included in high-performing ECs belonging to this family, paving the way to the synthesis of next-generation, efficient ECs for the ORR that do not comprise platinum.

Chemically-reduced graphene-oxide-supported gold nanoparticles with a diameter, of 40–60 nm are considered here as catalytic materials for the reduction of oxygen in alkaline medium in comparison to analogous systems based on conventional Vulcan carbon carriers. Gold nanoparticles are prepared by the chemical reduction method, in which the NaBH 4 -prereduced Keggin-type phosphomolybdate heteropolyblue acts as the reducing agent for the precursor (HAuCl 4 ). Polyoxometallate (PMo 12 O 40 3− ) capping ligands stabilize gold nanoparticle deposits, facilitate their dispersion and attachment to carbon supports. Indeed, it is apparent from the independent diagnostic voltammetric experiments (in 0.5 mol dm −3 H 2 SO 4 ) that heteropolymolybdates form readily stable adsorbates on nanostructures of both gold and carbon (reduced graphene oxide and Vulcan). It is reasonable to expect that the polyoxometallate-assisted nucleation of gold has occurred in the proximity of oxygenated defects existing on carbon substrates. Under conditions of electrochemical diagnostic experiments (performed in 0.1 mol dm −3 KOH): ( i ) the phosphomolybdate adsorbates are removed from the interface as they undergo dissolution in alkaline medium; and ( ii ) the Au nanoparticles (Au loading, 30 μg cm −2 ) remain well-dispersed on the carbon as evident from transmission electron microscopy. High electrocatalytic activity of the reduced-graphene oxide-supported Au nanoparticles toward reduction of oxygen in alkaline medium is demonstrated using cyclic and rotating ring-disk voltammetric experiments. The latter system could also act as the active support for Pt nanoparticles during the reduction of oxygen. Among important issues are possible activating interactions between gold and the support, as well as presence of structural defects existing on poorly organized graphitic structure of reduced graphene oxide (as evident from Raman spectroscopy).

In the recent research years is observed huge interest in design of new functional nanomaterials for developing new electrocatalysts for oxygen reduction reaction (ORR) in acid and alkaline media. The research has been focused on developing carbon nanostructures especially graphene/graphene oxide materials with the different transition metals (e.g. Co, Ni, Ag, Au, Cu, Mn) analogue of polynuclear Prussian Blue, namely with ultra-thin Co, and Ni hexacyanoferrate layers and trace amount of platinum for fuel cell applications. Electrocatalysts based on graphene and graphene-oxide (GO) are more homogeneous and possess properties such as excellent conductivity, good chemical stability and can be functionalized in a controlled manner. Following the heat-treatment step at higher temperatures, some thermal decomposition of the cyanometallate network occurs and, consequently, metallic sites are generated. Their formation and distribution are facilitated by the voltammetric potential cycling in acid and alkaline electrolytes. The most promising electrocatalytic results with respect to the reduction of oxygen (the highest currents and the most positive electroreduction potentials) have been obtained when graphene nanostructures are combined with analogue of polynuclear Prussian Blue and trace amount of Pt nanoparticles. What is even more important that, due to the presence of the polynuclear cyanoferrate modifier or linker, the amounts of the undesirable hydrogen peroxide intermediate are significantly decreased. An electrocatalytic system, that utilizes metal hexacyanometallates nanoparticles with trace amount of Pt modified graphene and graphene related materials, is developed and characterized here using transmission electron microscopy and such electrochemical diagnostic techniques as cyclic volammetry and rotating ring-disk voltammetry in a 0.5 M H2SO4 electrolyte and in a 0.1 M KOH electrolyte and upon introduction (as cathode) to the low-temperature hydrogen-oxygen fuel cell. Comparative measurements have been performed against the model noble metal (Vulcan-supported platinum nanoparticles) catalyst.

Relaxation and polarization phenomena of phosphoric acid-doped [PBI4N(HfO 2 ) x ](H 3 PO 4 ) y nanocomposite membranes for high-temperature proton-exchange membrane fuel cells are studied using Dynamic Mechanical Analysis (DMA) and Broadband Electrical Spectroscopy (BES). The membranes are obtained by casting combinations of a polybenzimidazole polymer (PBI4N) with increasing amounts of hafnium oxide nanofiller, resulting in [PBI4N(HfO 2 ) x ] hybrid systems with 0 ≤ x ≤ 0.32. Phosphoric acid at varying content levels (0 ÷ 18 wt%) is used as a doping agent, giving rise to [PBI4N(HfO 2 ) x ](H 3 PO 4 ) y membranes. DMA and BES studies lead us to determine that the electric response of the membranes is modulated by polarization phenomena and by α and β dielectric relaxation events of the polymer matrix. Additionally, the experimental results suggest that in [PBI4N(HfO 2 ) x ](H 3 PO 4 ) y membranes the conductivity occurs owing to three conductivity pathways: two mechanisms involving inter-domain proton migration phenomena by “hopping” events; and one mechanism in which proton exchange occurs between delocalization bodies. These results highlight the significant effect of the hafnium oxide nanofiller content on the conductivity of [PBI4N(HfO 2 ) x ](H 3 PO 4 ) y where, at x ≥ 0.04, demonstrates conductivity higher (9.0 × 10 −2 S/cm) than that of pristine H 3 PO 4 -doped PBI4N (4.8 × 10 −2 S/cm) at T ≥ 155 °C.

This report describes the preparation, characterization, and coin cell prototype testing of new Li[Fe 1/3 Ni 1/3 Co 1/3 ]PO 4 high voltage olivine cathodes for lithium secondary batteries (LFNCPs) obtained by treating the precursors with Cu and Cu+C sources. The morphology, structure, interactions, and electrochemical properties of the obtained materials are extensively studied in order to elucidate the interplay in LFNCPs between graphite (C) and copper(II) carbonate (Cu) addition to the precursors and structural flexibility, relaxations, and electrochemical performance of obtained materials. In particular, the investigated LFNCPs cathodes are obtained by treating the reaction precursors with graphite nanoparticles and/or copper(II) carbonate. It is found that copper does not behave like a vicariant metal ion within the olivine structure of the cathodes, instead it forms segregated CuO nanoparticles which improve the charge-transfer kinetics during the charge/discharge processes of the cathode material. The graphite additive in precursors is found to decompose during the synthesis, resulting in an improved elasticity of the 3D structure of the olivine backbone. This increased structural flexibility facilitates the percolation of lithium ions along the 1D channels of the materials during the charge/discharge processes. Coin cell prototypes assembled with the proposed cathode materials show good specific capacities (>100 mAh g −1 ), good specific energies (455 mWh g −1 ), and a high working potential (>4.0 V).

The development of advanced energy conversion systems characterized by a high efficiency and a low environmental impact is one of the most relevant targets of modern research [1]. As of today, important research efforts are devoted to low-temperature fuel cells (FCs) mounting an acid electrolyte, typically a proton-conducting membrane (e.g., Nafion®). To achieve a performance level compatible with current applications, these systems must adopt electrocatalysts (ECs) with a significant loading of platinum-group metals (PGMs). In conventional low-temperature FCs, most of the PGM loading is typically concentrated at the FC cathode to promote the poor kinetics of the oxygen reduction reaction (ORR), one of the major bottlenecks in FC operation. Very recently, viable OH--conducting membranes were developed [2], opening the possibility to devise efficient anion-exchange membrane fuel cells (AEMFCs). In these systems the ORR takes place in an alkaline environment; accordingly, AEMFCs can adopt “Pt-free” ORR ECs and still achieve a high performance level. In this work, new “Pt-free” ORR ECs are reported; the materials comprise a graphene support “core”, which is covered by a carbon nitride “shell” coordinating the ORR active sites [3]. The proposed materials reap the benefits offered by graphene, including: (i) a high electrical conductivity, minimizing the ohmic losses; and (ii) a low microporosity, to facilitate the mass transport of reactants and products. The carbon nitride “shell” coordinates the bimetallic active sites, which include: (i) a 3d-“active metal” (i.e., Fe, Co, Ni), which bestows most of the ORR performance; and (ii) an oxophilic “co-catalyst” (Sn), which stabilizes the “active metal”and improves the ORR kinetics with a bifunctional mechanism. The chemical composition of the ECs is determined by inductively-coupled plasma atomic emission spectroscopy (ICP-AES) and microanalysis; the thermal stability is studied by high-resolution thermogravimetry (HR-TG); the surface chemical composition is explicated by X-ray photoelectron spectroscopy (XPS); the morphology is elucidated in detail by high-resolution scanning electron microscopy (HR-SEM) and high-resolution transmission electron microscopy (HR-TEM); the porosity is inspected by nitrogen physisorption techniques; the structure is investigated by wide-angle X-ray diffraction (WAXD), electron diffraction and micro-Raman; finally, the ORR performance and mechanism are clarified by means of cyclic voltammetry with the thin-film rotating ring-disk electrode (CV-TF-RRDE) method. The results proved very promising, clearly showing the potential of this family of “Pt-free”, “core-shell” graphene-supported ECs for application at the cathode of AEMFCs. In particular, CV-TF-RRDE measurements in an alkaline environment demonstrated that the best material exhibits an ORR overpotential ca.70 mV higher with respect to a 10 wt.% Pt/C reference (see Figure). References [1] F. Bonaccorso, L. Colombo, G. Yu, M. Stoller, V. Tozzini, A. C. Ferrari, R. S. Ruoff, V. Pellegrini, Science 347, 1246501 (2015). [2] G. A. Giffin, S. Lavina, G. Pace, V. Di Noto, J. Phys. Chem. C 116, 23965 (2012). [3] V. Di Noto, E. Negro, K. Vezzù, F. Bertasi, G. Nawn, The Electrochemical Society Interface, Summer 2015, 63 (2015). Figure 1

Dielectric properties of polyurethanes containing poly(propylene oxide) (PO) and poly(ethylene oxide) (EO) units are discussed, along with the results of direct current (DC) measurements and broadband electrical spectroscopy (BES) studies. The dielectric properties of polyether-containing polyurethanes (PUs) are compared to those of PUs containing 1000 ppm of ionic liquids (ILs) as antistatic agents. The effects of the chemical environment of these ILs, including anion-fixed polymers (PU-AF), cation-fixed polymers (PU-CF), and a simple mixture of IL with the PUs (PU-IL), are compared and discussed on the basis of ion mobility. DC measurements suggest that the charge current is attributed not only to the electrode polarization but also to continuous dielectric relaxation. BES studies elucidate that both fast and slow relaxations are taking place in EO-rich domains in pristine PU and PU-AF. The activation energies of the slow relaxation and of the ionic conductivity are similar, suggesting that the ionic conductivity of these materials is attributed to the ion exchange reaction in EO/ion complexes. In contrast, only fast relaxations are observed in the domains mostly comprised of ion-depleted EO in the PUs containing "free" anions, i.e., PU-CF and PU-IL. This suggests that [Tf2N](-) ligands are weakly interacting with the EO chains and contribute effectively to the ion conduction. Thus, enhanced ionic conductivity is observed in PU-CF and PU-IL, yielding sufficient antistatic effects. Taking into account its long shelf life, arising from the lack of IL bleed-out, PU-CF is concluded to be the most promising candidate.

The in situ identification of fuel-cell material parameters is crucial both for guiding the research for advanced functionalized materials and for fitting multiphysics models, which can be used in fuel cell performance evaluation and optimization. However, this identification still remains challenging when dealing with direct measurements. This paper presents a method for achieving this aim by stochastic optimization. Such techniques have been applied to the analysis of fuel cells for ten years, but typically to specific problems and by means of semi-empirical models, with an increased number of articles published in the last years. We present an original formulation that makes use of an accurate zero-dimensional multi-physical model of a polymer electrolyte membrane fuel cell and of two cooperating stochastic algorithms, particle swarm optimization and differential evolution, to extract multiple material parameters (exchange current density, mass transfer coefficient, diffusivity, conductivity, activation barriers …) from the experimental data of polarization curves (i.e. in situ measurements) under some controlled temperature, gas back pressure and humidification. The method is suitable for application in other fields where fitting of multiphysics nonlinear models is involved.

Polybenzimidazole (PBI) has become a popular polymer of choice for the preparation of membranes for potential use in high-temperature proton exchange membrane polymer fuel cells. Phosphoric acid-doped composite membranes of poly[2,2'-(m-phenylene)-5,5'-bibenzimidazole] (PBI4N) impregnated with hafnium oxide nanofiller with varying content levels (0-18 wt %) have been prepared. The structureproperty relationships of both the undoped and acid-doped composite membranes are studied using thermogravimetric analysis, modulated differential scanning calorimetry, dynamic mechanical analysis, wide-angle X-ray scattering, infrared spectroscopy, and broadband electrical spectroscopy. Results indicate that the presence of nanofiller improves the thermal and mechanical properties of the undoped membranes and facilitates a greater level of acid uptake. The degree of acid dissociation within the acid-doped membranes is found to increase with increasing nanofiller content. This results in a conductivity, at 215 degrees C and a nanofiller level x = 0.04, of 9.0 x 10(-2) S cm(-1) for [PBI4N(HfO2)(x)](H3PO4)(y). This renders nanocomposite membranes of this type as good candidates for use in high temperature proton exchange membrane fuel cells (HT-PEMFCs).

Recent advances in technological fields such as portable electronic devices, automotive, load levelling and peak shaving for the power grid applications, as well as other specific low and high temperature applications, have resulted in an urgent need to develop new and improved energy conversion and storage systems.1 Magnesium secondary batteries, first proposed in the late 1990s,2,3 demonstrate intrinsic fundamental advantages over other competing technologies i.e., Li secondary batteries, and are therefore promising candidates for energy conversion and storage. Early Mg secondary batteries comprised of a metallic magnesium anode, a composite cathode and a polymer electrolyte based on polyethylene glycol incorporating an innovative δ-MgCl2 salt.4,5 Subsequent electrolytes based on Grignard and other organo-Mg compounds have also been explored,6 and were shown to exhibit good Mg deposition/stripping. Nevertheless, these electrolytes suffer from several drawbacks associated with their chemical stability in ethereal-based solvents, which are characterized by high vapour pressure and flammability. In order to overcome these drawbacks, the use of ionic liquids (ILs) as a solvent for stable Mg-ion source precursors is appealing in order to obtain electrolytes with a high chemical inertia, a wide electrochemical stability window, a low volatility and negligible flammability.7 Here we present a new room temperature ionic liquid synthesized by reacting 1-ethyl-3 methylimidazolium iodide with aluminium iodide. δ-MgI2 8 is used as the magnesium source to obtain a family of Mg2+ conducting electrolytes with the general formula [EMImI/(AlI3)m]/(δ-MgI2)n. δ-MgI2 which is a highly disordered form of MgI2 and synthesized by reacting metallic Mg with n-iodobutane. Similar to the previously described δ-MgCl2,9 δ-MgI2 forms concatenated polymer chain complexes with aluminium through iodine bridging atoms. The chemical composition of the samples was determined by ICP-AES and microanalysis. Their thermal stability and transitions were studied by differential scanning calorimetry (DSC). The applicability of the [EMImI/(AlI3)m]/(δ-MgI2)n electrolytes in prototype cells was evaluated by studying the conductivity of the materials as well as the electrochemical performance in terms of Mg deposition/stripping, coulombic efficiency, and exchange current density. Results of the deposition/stripping performance for a selected concentration are shown in Figure 1. References (1) Armand, M.; Tarascon, J.-M. Nature 2008, 451, 652. (2) Di Noto, V.; Fauri, M. Batterie primarie (non ricaricabili) e secondarie (ricaricabili) a base di elettroliti polimerici basati su ioni magnesio. PD99A000179, 1999. (3) Di Noto, V.; Fauri, M. Magnesium-based Primary (Non Rechargeable) and Secondary (Rechargeable) Batteries. PCT/EP00/07221, 2000. (4) Di Noto, V.; Lavina, S.; Longo, D.; Vidali, M. Electrochim. Acta 1998, 43, 1225. (5) Di Noto, V.; Marigo, A.; Viviani, M.; Marega, C.; Bresadola, S.; Zannetti, R. Makromol. Chem. 1992, 193, 123. (6) Liebenow, C.; Yang, Z.; Lobitz, P. Electrochem. Commun. 2000, 2, 641. (7) Armand, M.; Endres, F.; MacFarlane, D. R.; Ohno, H.; Scrosati, B. Nat. Mater. 2009, 8, 621. (8) Vittadello, M.; Waxman, D. I.; Sideris, P. J.; Gan, Z.; Vezzù K.; Negro, E.; Safari, A.; Greenbaum, S. G.; Di Noto, V. Electrochim. Acta 2011, 57, 112. (9) Vittadello, M.; Stallworth, P. E.; Alamgir, F. M.; Suarez, S.; Abbrent, S.; Drain, C. M.; Di Noto, V.; Greenbaum, S. G. Inorg. Chim. Acta 2006, 359, 2513. Figure 1