Search

Abstract: In this report, three hybrid inorganic-organic proton-conducting membranes based on a novel fluorinated titania labeled TiO2F dispersed in Nafion were prepared. The mass fraction of TiO2F nanofiller ranged between 0.05 and 0.15. The water uptake and the proton exchange capacity of the membranes were determined; the membranes were further characterized by TG, DMA and FT-IR ATR investigations. Finally, the hybrid membranes were used in the fabrication of membrane-electrode assemblies (MEAs), which were tested in operating conditions as a function of the back pressure and of the hydration degree of the reagents streams. It was demonstrated that, with respect to pristine recast Nafion, at 25%RH the MEA fabricated with the membrane including a mass fraction of TiO2F equal to 0.10 yielded a higher maximum power density (0.206 W cm−2 vs. 0.121 W cm−2). Finally, it was proposed a coherent structural model of this family of hybrid membranes accounting for both the properties determined from “ex-situ” characterizations and for the performance obtained from measurements in a single fuel cell in operating conditions. [Copyright &y& Elsevier]

Abstract: This report describes a new family of bimetal carbon nitride (CN) electrocatalysts for the oxygen reduction reaction (ORR) for application in polymer electrolyte membrane fuel cells (PEMFCs). The materials, which bear active sites based on Pt and Rh, are prepared with a three-step protocol consisting of: (1) the synthesis of a homogeneous zeolitic inorganic–organic polymer electrolyte (Z-IOPE) precursor; (2) the pyrolysis of the precursor at a temperature T f =400, 500, 600, 700 or 900°C; (3) the activation, yielding the final product. It is found that T f has a major effect on the structure and the electrochemical properties of these electrocatalysts, as determined from a wide array of independent characterization techniques including: high-resolution thermogravimetry (HR-TGA); Fourier-transform medium infrared (FT-MIR), Fourier-transform far infrared (FT-FIR) and confocal micro-Raman spectroscopies; powder X-ray diffraction (powder XRD); X-ray photoelectron spectroscopy (XPS); and electrochemical investigations carried out with the cyclic voltammetry thin-film rotating disk electrode (CV-TF-RDE) method. All the information is integrated to propose a comprehensive model correlating the effect of T f on the structure of the materials with the corresponding electrochemical performance. The best results in the ORR are obtained with materials prepared at 600≤ T f ≤700°C. These systems present the optimal compromise between the size of the metal-rich nanoparticles, the degree of graphitization of the carbon nitride support and the concentration of ligands blocking the active sites. The best Pt-Rh electrocatalysts exhibit an ORR activity very similar to the Pt/C reference. In addition, the peculiar structure of the proposed materials, which are characterized by active sites supported on the carbon nitride bulky materials, results in a better tolerance toward typical contaminants in the ORR process such as chloride anions with respect to the Pt/C reference. [Copyright &y& Elsevier]

Abstract: In this report are presented the preparation and the characterization of six nanocomposite membranes of formula with in the range 0–2.988. These materials are based on Nafion and [(TiO2)·(WO3)0.148] nanofiller. The effect of [(TiO2)·(WO3)0.148] nanopowders on the structural, thermal, mechanical and electrical properties of membranes was studied. The water uptake (WU) value of materials was lower than that of pristine Nafion and was correlated with . The thermal transitions were investigated by modulated differential scanning calorimetry (MDSC). The mechanical parameters and relaxation processes on temperature were studied by dynamical mechanical analyses (DMA). The FT-IR ATR and μ-Raman vibrational investigations allowed to determine the structure of the hydrophobic polytetrafluoroethylene (PTFE) domains of Nafion and the interactions Nafion–[(TiO2)·(WO3)0.148] and Nafion–[H2O] in bulk materials. The analysis of complex conductivity plots were evaluated in the 10−2 Hz–10MHz and 5–155°C regions. Results indicated that the conductivity of nanocomposite membrane, with , at 135°C, is 5.0×10−2 Scm−1, while its stability range of conductivity (SRC) extends up to 135°C. [Copyright &y& Elsevier]

This paper describes the effect of nanopowders acting as fillers on the structure and properties of [Nafion/(MxOy)n] membranes with n = 5 wt.%. The films were prepared by a solvent casting procedure using MxOy oxoclusters (M = Ti, Zr, Hf, Ta and W) and Nafion. Five new homogeneous membranes were prepared with thicknesses ranging from 170 to 350 μm. The membranes were characterized by means of thermal analyses carried out by thermogravimetry (TG), morphological measurements by scanning electron microscopy (ESEM) and vibrational spectroscopy by FT-IR ATR, FT-Raman measurements. Vibrational investigations allowed us to obtain information on: (a) the network structure and the conformation of fluorocarbon hydrophobic domains of the Nafion host polymer, (b) the MxOy⋯HSO3R interactions occurring in ionic polar cages of membranes and (c) the various water domains present in the hydrophilic polar cages of membranes. TG allowed us to determine that the membranes are thermally stable up to about 170 °C.In conclusion, it was disclosed that: (a) the hydrophobic Nafion polymer host domains consist of a blend of PTFE chains with helical conformations 103 and 157 and (b) the fraction of each fluorocarbon helical conformation is modulated by the type of nano-fillers and the dynamic cross-links RSO3H⋯MxOy⋯HSO3R which occur in hydrophilic polar cages of membranes. In hydrophobic domains of Nafion, the highest percentage of fluorocarbon chains with helical conformation 103 is observed for [Nafion/(HfO2)n] composite membrane, ρ (%) = 16. [Copyright &y& Elsevier]

Abstract: In this paper is described the preparation of new platinum-free Pd-Co carbon-nitride electrocatalysts (Pd-Co-CNs) for application in low-temperature fuel cells. Two groups of materials with formula K n [Pd x Co y C z N l H m ] were synthesized, which are grouped in two ensembles: the first is characterized by a molar ratio y/x >1 (I), and the second by y/x <1 (II). K n [Pd x Co y C z N l H m ] materials were prepared through a two-step synthesis protocol. The effect of the Pd/Co molar ratio and of the temperature of the thermal treatments on the structure and properties of the products were studied extensively by thermogravimetry, scanning electron microscopy, and vibrational (FT-IR and micro-Raman) and XPS spectroscopy. Vibrational studies revealed that I and II systems consist of two polymorphs of α- and graphitic-like carbon-nitride nanomaterials. The electrochemical activity towards the oxygen reduction reaction (ORR) and the hydrogen oxidation reaction (HOR) was measured by cyclic voltammetry measurements with thin-film rotating disk electrode (CV-TF-RDE). The electrochemical performance of Pd-Co-CNs of group I obtained at t f ≥700°C resulted higher than that measured for a platinum-based commercial electrocatalyst in terms of both the activity towards the ORR and the HOR and of the resistance towards the poisoning effect of methanol towards the ORR. [Copyright &y& Elsevier]

The synthesis of Li2PdCl4 and Li3Fe(CN)6 precursors, and the preparation of the first lithium Z-IOPE material obtained by reacting these precursors with poly(ethylene glycol)600 (PEG600) is reported. This new material has been obtained through a sol⇒gel and gel⇒plastic transition. FIR and MIR spectroscopy studies, Raman laser and UV–vis investigations and detailed compositional data allowed us to propose a structural hypothesis and to detect the interactions between ions and the coordinating segments of the host network. It has been concluded that: (1) this compound is a mixed inorganic–organic network in which clusters formed by palladium and iron complexes are bonded together by PEG bridges; (2) the conformation of polyether chains in the bulk material is of the TGT (T=trans, G=gauche) type. The conductivity of the proposed [FexPdy(CN)zClv(C2nH4n+2On+1)Lil] is &ap;5.3×10−5 S cm−1 at 35.1 °C. [Copyright &y& Elsevier]

This paper describes the synthesis and characterization of three-dimensional hybrid inorganic–organic networks prepared by a polycondensation reaction between Zr(O(CH2)3CH3)4 and polyethylene glycol 400 (PEG400). Eleven hybrid networks doped with varying concentrations of LiClO4 salt were prepared. On the basis of analytical data and FT-Raman studies it was concluded that these polymer electrolytes consist of inorganic–organic networks with zirconium atoms bonded together by PEG400 bridges. These polymers are transparent with a solid rubber consistency and are very stable under inert atmosphere. Scanning electron microscopy revealed a smooth glassy surface. X-ray fluorescence microanalysis with energy dispersive spectroscopy demonstrated that all the constituent elements are homogeneously distributed in the materials. Thermogravimetric measurements revealed that these materials are thermally stable up to 262 °C. Differential Scanning Calorimetry measurements indicated that the glass transition temperature Tg of these inorganic–organic hybrids varies from −43 to −15 °C with increasing LiClO4 concentration. FT-Raman investigations revealed the TGT (T=trans, G=gauche) conformation of polyether chains and allowed characterization of the types of ion-ion and ion–polymer host interactions in the bulk materials. The conductivity of the materials at different temperatures was determined by impedance spectroscopy over the 20 Hz–1 MHz frequency range. Results indicated that the materials conduct ionically and that their ionic conductivity is strongly influenced by the segmental motion of the polymer network and the type of ionic species distributed in the bulk material. Finally, it is to be highlighted that the hybrid network with a nLi/nO molar ratio of 0.0223 shows a conductivity of ca. 1×10−5 S cm−1 at 40 °C. [Copyright &y& Elsevier]

Nafion‑tungsten oxide hybrid membranes, [Nafion/(WO 3 ) x ], with varying loading levels of WO 3 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/(WO 3 ) 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/(WO 3 ) x ] and study the interactions taking place between the nanofiller and the Nafion matrix. The electrical response of [Nafion/(WO 3 ) x ] is determined by Broadband Electrical Spectroscopy (BES) and the permeability towards VO 2+ is measured by UV-VIS spectrometry. It is demonstrated that the [Nafion/(WO 3 ) x ] hybrid membranes exhibit a high ion selectivity (up to 10.6∙10 3  S∙min∙cm −3 for [Nafion/(WO 3 ) 0.329 ]) that is much improved in comparison with that characterizing recast Nafion (6.5∙10 3  S∙min∙cm −3 ). A structural model and a conductivity mechanism for the [Nafion/(WO 3 ) x ] hybrid membranes are proposed, in order to rationalize the experimental results and correlate the electrical response with the transport properties. [ABSTRACT FROM AUTHOR]

This report describes the synthesis and the properties of twelve iodide-conducting Plastic Crystal Electrolytes (PCEs) based on N,N-dimethyl-2-(methylsilyloxy) ethanaminium cations (MESEA n+) and I−/I3 − anions for application in dye-sensitized solar cells (DSSCs). The PCEs are obtained in three steps. In the first, the MESEA n+(Cl−) n precursor is prepared by reacting different chlorosilanes (CH3)4−n SiCl n with 1 ≤ n ≤ 4 with N,N-dimethyl ethanolamine (DMEA). In the second step, the MESEA n+(I−) n PCEs are obtained by treating MESEA n+(Cl−) n with CH3I. In the final step, the MESEA n+(I−) n are doped with different aliquots of I2 to obtain blends of MESEA n+(I−) n and MESEA n+(I3 −) n PCEs bearing the active I−/I3 − redox couple. Twelve PCEs based on siloxane cations, with general formula {[MESEA n+(I3 −) n ] ρ%·[MESEA n+(I−) n ]100−ρ%} with 1 ≤ n ≤ 4 and 0 ≤ ρ % ≤ 8.3 are obtained. ρ % is the percentage of I3 − on the total anions included in the PCEs. The properties of the PCEs are investigated by vibrational spectroscopy (MIR FT-IR), high-resolution thermogravimetric analysis (HR-TGA), differential scanning calorimetry (DSC) and broadband electrical spectroscopy (BES) in order to study the correlations between the structural features, the conductivity and the composition of the proposed electrolytes. Results show that the PCEs with n = 3 and ρ % = 3.7 exhibit: (a) a melting temperature below 100 °C, which is typically observed in room-temperature ionic liquids; (b) a thermal stability up to 200 °C and (c) a conductivity of 0.8·10−4 S cm−1 at 50 °C. [ABSTRACT FROM AUTHOR]

Abstract: New hybrid inorganic–organic nanocomposite proton conducting membranes based on Nafion, SiO2 and triethylammonium trifluoromethanesulfonate (TEATF), a protic ionic liquid, were prepared in two steps. First, various [Nafion/(SiO2) ψ ] membranes with a SiO2 weight percentage ranging from 0 to 15wt.% were prepared by a solvent-casting protocol from DMF solutions. Second, the resulting hybrid membranes were neutralized with triethylammine (TEA) and then impregnated with triethylammonium trifluoromethanesulfonate (TEATF). The structure of the bulk hybrid materials and the interactions occurring between their components were investigated by vibrational spectroscopy (FT-IR ATR and FT-Raman). These latter studies allowed to determine that: (a) the fluorocarbon domains of Nafion consist of a mixture of helical chains with 103 and 157 helical conformations; (b) interactions take place between the components of the hydrophilic domains, which give rise to micelle-like nanoparticles where a SiO2 core is covered by a shell of solvating TEATF molecules. The thermal, mechanical and electrical properties of the proposed materials were investigated by thermogravimetry (TG) and differential scanning calorimetry (DSC) measurements, by dynamical mechanical analyses (DMA) and by broadband dielectric spectroscopy (BDS), respectively. The electric measurements indicated that [Nafion/(SiO2) ψ (TEA)]3.67/(TEATF)1.2 exhibits a σ dc of 4.7×10−3 Scm−1 at T =105°C and a SRC of 5< T <135°C. These results classified this membrane as a very promising material for application in fuel cells. [Copyright &y& Elsevier]

Abstract: This report presents detailed studies on the elemental analysis, vibrational spectroscopy, thermal stability and electrical spectroscopy of two new hybrid inorganic–organic polymers which have been synthesised by a sol–gel method using glycerol and zirconium(IV)butoxide as precursors. These materials have been doped by means of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIm-TFSI) ionic liquid (IL), which is insoluble in water. The elemental composition of the obtained polymers [Zr(C6O5H11)] (1) and [Zr(C11O4H31)] (2) has been determined by CHN analysis and by ICP-AES measurements. FT-IR and FT-Raman spectroscopy investigations have been performed to study the molecular structure of the polymers and the interactions of EMIm-TFSI with the host networks. Differential scanning calorimetry measurements show the presence of at least one glass transition temperature (T g) in both 1 and 2 materials. The broadband dielectric spectroscopic measurements have been carried out between 10−2 Hz to 10MHz from −100°C to 100°C with a 5°C step. The conductivities of the polymers 1 and 2 have been found to be in the order of 10−8 to 10−11 Scm−1 at 25°C, so they can be defined as dielectric materials. After doping 2 with EMIm-TFSI, the conductivity at 25°C of the obtained complex [Zr(C11O4H31)]15/(EMIm-TFSI) (2′) increased three orders of magnitude resulting ca. 10−5 Scm−1. The permittivity spectra revealed two relaxation bands which were attributed to the α relaxation modes of the polymer networks. [Copyright &y& Elsevier]