Synthesis and Characterization of Heterobimetallic (Pd/B) Nindigo Complexes and Comparisons to Their Homobimetallic (Pd₂, B₂) Analogues

Reactions of Nindigo-BF₂ complexes with Pd­(hfac)₂ produced mixed complexes with Nindigo binding to both a BF₂ and a Pd­(hfac) unit. These complexes are the first in which the Nindigo ligand binds two different substrates, and provide a conceptual link between previously reported bis­(BF₂) and bis­(Pd­(hfac)) complexes. The new Pd/B complexes have intense near IR absorption near 820 nm, and they undergo multiple reversible oxidations and reductions as probed by cyclic voltammetry experiments. The spectral, redox, and structural properties of these complexes are compared against those of the corresponding B₂ and Pd₂ complexes with the aid of time-dependent density functional calculations. In all cases the low-energy electronic transitions are ligand-centered π–π* transitions, but the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energiesand hence the absorption wavelength as well as the oxidation and reduction potentialsare significantly modulated by the moieties bound to the Nindigo ligand

, New Ion-exchange Membranes Derived from Polyketone

Anion-exchange membrane fuel cells (AEMFCs) provide significant advantages over their proton-exchange membrane counterparts. In the alkaline environment, the oxygen reduction reaction (ORR) is more facile, there is diminished fuel crossover, and a greater flexibility regarding fuel and catalyst choice. The membrane at the heart of AEMFCs not only facilitates the ion exchange but also separates the fuel feedstocks and acts as a support for the membrane-electrode assembly (MEA). However, to date there are still no membrane materials that satisfy all the needs (long-term stability in alkaline environment, high ionic conductivity, low swelling and good structural integrity) for use in AEMFCs and this remains one of the larger obstacles for further AEMFC development. The amination and subsequent quarternisation of polyketone leads to a new family of ionomers containing N-substituted pyrrole moieties. The degree of amination can be controlled by manipulating reaction conditions, allowing the composition and resulting structural properties of the polymer to be tuned [1,2]. Membrane fabrication results in thermally stable (TD > 250 \ub0C), structurally robust polymer electrolytes that exhibit ionic conductivity (> 10-3 S cm-1). These new solid-state ion-conducting materials have the potential to be used in a variety of applications including AEMFCs. Here we present an in-depth study focusing on the structure-property relationships of this new polypyrrole/polyketone polymer. A variety of analytical techniques are used to probe the thermal and structural properties of the polymers, these include highresolution thermogravimetric analysis, modulated differential scanning calorimetry, dynamic mechanical analysis, vibrational, NMR and UV-Vis spectroscopies. In addition, broadband electrical spectroscopy is used to gauge the interplay between the structural properties and electrical response [3]. Acknowledgements: The authors wish to thank the Strategic Project of the University of Padova \u201cMaterials for Membrane-Electrode Assemblies to Electric Energy Conversion and Storage Devices (MAESTRA)\u201d for funding. [1] A. Sen, Z. Jiang, and J. T. Chen, Macromolecules 22 (1989) 2012-2014. [2] N. Ataollahi, K. Vezz\uf9, G. Nawn, G. Pace, G. Cavinato, F. Girardi, P. Scardi, V. Di Noto, and R. Di Maggio, Electrochim. Acta 226 (2017) 148-157. [3] V. Di Noto, G. A. Guinevere, K. Vezz\uf9, G. Nawn, F. Bertasi, T. H. Tsai, A. Maes, S. Seifert, B. Coughlin, and A. Herring, Phys. Chem. Chem. Phys. 17 (2015) 31125-31139

Graphene-Supported Au-Ni Carbon Nitride Electrocatalysts for the ORR in Alkaline Environment

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 (ICPAES), 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

Interplay between Composition, Structure, and Properties of New H3PO4-Doped PBI4N-HfO2 Nanocomposite Membranes for High-Temperature Proton Exchange Membrane Fuel Cells

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 structure–property 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 °C and a nanofiller level x ≥ 0.04, of 9.0 × 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)

EMImCl/(TiCl4)1.4/(\u3b4-MgCl2)x Ionic Liquid Electrolyte for Mg-ion Batteries

The rapid advance in the fields of portable electronics, load leveling and peak shaving for the power grid and zero-emission automotive applications require the development of new and improved electrical energy storage systems (1). Since the 90\u2019s major improvements have been achieved in magnesium battery technology (2-4). In comparison to Li, Mg offers the following advantages: (i) a higher volumetric capacity (3832 vs. 2062 mAh\u2022cm-3); (ii) far greater abundance in the Earth\u2019s crust, lowering the costs; (iii) a safer operation and a better compatibility with the environment; and (iv) an acceptable standard reduction potential (-2.36 vs. -3.04 V) (5-7). The main roadblock for these devices is the development of an efficient and stable electrolyte that is able to reversibly deposit and strip magnesium. Although Grignard and other organo-magnesium compounds exhibit good electrochemical performances (7), they do not exhibit an optimal stability due to their high vapor pressure and flammability. Ionic liquids dissolving a Mg salt with a high crystalline disorder were proposed as promising alternative electrolytes to organo-Mg systems owing to their good electrochemical performance and lack of flammability and thermal stability issues (8,9). In the present work a new family of electrolytes is proposed, based on 1-ethyl-3-methylimidazolium chloride (EMImCl), titanium(IV) chloride (TiCl4) and increasing amounts of \u3b4-MgCl2. Specifically, four EMImCl/(TiCl4)1.4/(\u3b4-MgCl2)x electrolytes, with 0.00 64 x 64 0.23 are prepared and extensively characterized. The chemical composition was determined by Inductively-Coupled Plasma Atomic Emission Spectroscopy (ICP-AES). The thermal stability was gauged using High-Resolution Thermo Gravimetric Analysis (HR-TGA) and the phase transitions are highlighted with Modulated Differential Scanning Calorimetry (MDSC). Chemical interactions were studied through Fourier-Transform spectroscopy in the medium and far infrared (FT-MIR and FT-FIR) regions and confocal micro-Raman spectroscopy. The electrochemical performance was studied with: (i) Cyclic Voltammetry (CV), to probe Mg deposition and stripping; (ii) Linear Sweep Voltammetry (LSV), to evaluate the electrochemical stability window; (iii) Chronopotentiometry (CP) experiments coupled with ICP-AES, to confirm and quantify the Mg deposition; and (iv) Broadband Electrical Spectroscopy (BES), to elucidate the long-range charge migration mechanisms of the electrolytes. High level density functional theory (DFT) based electronic structure calculations were undertaken to elucidate structures and vibrational frequency assignments. References: 1. M. Armand, J. M. Tarascon Nature 451 (2008) 652. 2. V. Di Noto, S. Bresadola Macromolecular Chemistry and Physics 197 (1996) 3827. 3. V. Di Noto, M. Fauri, Magnesium-based Primary (Non Rechargeable) and Secondary (Rechargeable) Batteries, PCT/EP00/07221 (2000). 4. V. Di Noto et al. Electrochim. Acta 43 (1998) 1225. 5. D. Aurbach et al. Adv. Mater. 19 (2007) 4260. 6. T. D. Gregory, R. J. Hoffman, R. C. Winterton J. Electrochem. Soc. 137 (1990) 775. 7. J. Muldoon et al. Energy and Environmental Science 5 (2012) 5941. 8. F. Bertasi, G. Pagot, V. Di Noto et al. ChemSusChem 8 (2015) 3069. 9. F. Bertasi, F. Sepehr, G. Pagot, S. J. Paddison, V. Di Noto Advanced Functional Materials 26 (2016) 4860

Effects of Ni/Co Doping on the Properties of LiFeaNibCocPO4 High-Performance Olivine Cathodes for Lithium Batteries

(ORAL) Nowadays, the rapid development in portable electronics, load leveling/peak shaving for the power grid and electric automotive, requires significant progress in high voltage and high capacity storage systems [1,2]. Lithium batteries are, to date, the most promising systems that can sustain this demand [3]; they have high specific energy, high efficiency and a long lifespan [4]. Lithium cobalt oxide (LiCoO2) based cathode materials currently dominate the market [5], but, due to a low working potential (3.0 \u2013 4.0 V vs. Li) and to a high cost and toxicity, there is a broad scope for the development of new cathodic materials [6]. Lithium-transition metal-phosphates (LiMPO4, M=Co, Fe, Mn or Ni) show very good performance: their olivine structure with a 2D framework of crossed tunnels allows the insertion and de-insertion of lithium ions during the discharge/charge of the battery [7]. The highest specific capacity is reached by lithium iron phosphate (LiFePO4), but at low potential, while the highest working potential can be obtained using lithium cobalt phosphate (LiCoPO4) or lithium nickel phosphate (LiNiPO4), however, the lifespan and the specific capacity become very low [8-10]. In this work we describe the synthesis and the characterization of a new family of high voltage cathodic materials based on lithium-transition metal mixture-phosphates of iron, nickel and cobalt, in order to best take advantage of all the positive characteristics of each element presents in the structure (high voltage and high capacity) [11]. Five materials have been produced, varying the Ni/Co molar ratio; the effect of different degrees of Co and Ni doping on structure, morphology and electrochemical properties have been thoroughly studied. The stoichiometry is evaluated using Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES), the thermal stability is investigated by High Resolution \u2013 Thermo Gravimetric Analyses (HR-TGA), morphology and size distribution are characterized by Field Emission - Scanning Electron Microscopy (FE-SEM) and High-Resolution Transmission Electron Microscopy (HR-TEM); the structure is examined by powder X-Ray Diffraction (XRD) as well as variety of IR spectroscopy techniques. Electrochemical characterization is achieved by Cyclic Voltammetry (CV) and charge/discharge tests. Indeed, the proposed materials are good cathodic candidates for the development of high voltage lithium batteries: the best of our materials LFNCP0.61 showed a specific capacity and a specific energy of 125 mAh 19g-1 and 560 mWh 19g-1, respectively. Acknowledgements The authors thank, a) the strategic project \u201cFrom Materials for membrane electrode Assemblies to electric Energy conversion and SToRAge devices\u201d (MAESTRA) of the University of Padova for funding this study; b) the \u201cCentro studi di economia e tecnica dell\u2019energia Giorgio Levi Cases\u201d for grants to G.P. and E.N. References 1 M. Armand and J. M. Tarascon Nature 451, 652-657, (2008). 2 B. Dunn, H. Kamath and J. M. Tarascon Science 334, 928-935, (2011). 3 V. Di Noto, T. A. Zawodzinski, A. M. Herring, G. A. Giffin, E. Negro and S. Lavina Int. J. Hydrogen Energy 37, 6120-6131, (2012). 4 B. Scrosati and J. Garche J. Power Sources 195, 2419-2430, (2010). 5 K. Zaghib, A. Mauger, H. Groult, J. B. Goodenough and C. M. Julien Mater. 6, 1028-1049, (2013). 6 K. Zaghib, J. Dub\ue9, A. Dallaire, K. Galoustov, A. Guerfi, M. Ramanathan, A. Benmayza, J. Prakash, A. Mauger and C. M. Julien J. Power Sources 219, 36-44, (2012). 7 V. A. Streltsov, E. L. Belokoneva, V. G. Tsirelson and N. K. Hansen Acta Crystallogr., Sect. B: Struct. Sci. B49, 147-153, (1993). 8 N. N. Bramnik, K. G. Bramnik, T. Buhrmester, C. Baehtz, H. Ehrenberg and H. Fuess J. Solid State Electrochem. 8, 558-564, (2004). 9 A. K. Padhi, K. S. Nanjundaswamy and J. B. Goodenough J. Electrochem. Soc. 144, 1188-1194, (1997). 10 J. Wolfenstine and J. Allen J. Power Sources 142, 389-390, (2005). 11 G. Pagot, F. Bertasi, G. Nawn, E. Negro, G. Carraro, D. Barreca, C. Maccato, S. Polizzi and V. Di Noto Adv. Funct. Mater. 25, 4032-4037, (2015)

Hydrothermal Synthesis of Vanadium Sulfate supported on Graphene Oxide as Novel Cathode for Magnesium Ion Batteries

(POSTER

Novel graphene-supported bimetallic Pt-Ni, Au-Ni and Fe-Sn CN-electrocatalysts for the oxygen reduction reaction

(POSTER) One of the main drawbacks for the commercialization of the proton exchange membrane fuel cells (PEMFCs) and anion exchange membrane fuel cells (AEMFCs) is the sluggish kinetics of the oxygen reduction reaction (ORR). Up to now, carbon-supported Pt/C is the most efficient electrocatalyst (EC) for the ORR. Nonetheless, the low abundance of platinum and the insufficient durability of these ECs, which results from the degradation of the carbon support, constitute some of the major challenges for large-scale commercialization of PEMFC and AEMFC technology [1, 2].Thus, the development of very efficient cathodic electrocatalysts is primordial to substitute the current commercialized Pt/C. In this work, a new type of electrocatalysts for the ORR is synthesized, following an innovative preparation protocol [3]. The electrocatalysts consist of a carbon nitride (CN) matrix coordinating bimetallic Pt-Ni, Au-Ni and Fe-Sn nanoparticles; the carbon nitride matrix further coats graphene particles, which act as the support. In this way, a \u201ccore-shell\u201d morphology is successfully prepared with a CN "shell" and a "core" made of graphene supported bimetallic nanoparticles [4]. The chemical composition of the electrocatalysts is investigated by inductively-coupled plasma atomic emission spectroscopy (ICP-AES) and microanalysis; the morphology is characterized by high-resolution scanning electron microscopy (HR-SEM) and high-resolution transmission electron microscopy (HR-TEM). The structure of the electrocatalysts is studied by powder X-ray diffraction (XRD). Finally, the performance of the electrocatalysts for the ORR and the reaction mechanism are determined by cyclic voltammetry with the thin-film rotating ring-disk electrode (CV-TF-RRDE) technique (Figure 1). REFERENCES [1] R. Othman, A. L. Dicks, Z. Zhu, Int. J. Hydrogen Energy 37, 357 (2012). [2] S. Zhang, X.-Z. Yuan, J. N. C. Hin, H. Wang, K.A. Friedrich, M. Schultze, J. Power Sources 194, 588 (2009). [3] V. Di Noto, E. Negro, F. Bertasi et al., Patent application 102015000055603. [4] V. Di Noto, E. Negro, S. Polizzi et al., ChemSusChem. 5, 2451 (2012)

Hierarchical "Core-Shell" Pt-Ni ORR Electrocatalysts Based on Graphene "Cores" and Carbon Nitride "Shells"

One of the main bottlenecks in the operation of proton-exchange membrane fuel cells (PEMFCs) is the sluggish kinetics of the oxygen reduction reaction (ORR). The latter gives rise to large overpotentials, which degrade significantly the energy conversion efficiency of the device [1]. Our work addresses this issue by the development of innovative ORR electrocatalysts (ECs) characterized by an improved turnover frequency in comparison with state-of-the-art materials [2]. The proposed ECs comprise a hierarchical support \u201ccore\u201d based on graphene flakes, which is covered by a carbon nitride (CN) \u201cshell\u201d embedding the ORR active sites. The hierarchical support \u201ccore\u201d, which typically comprises both graphene flakes and a carbon black spacer, is devised to facilitate the charge and mass transport phenomena by: (i) reaping the benefits of graphene (e.g., a very high electron mobility, up to 200000 cm2\ub7V-1\ub7sec-1, and specific surface area, up to ca. 2630 m2\ub7g-1); and (ii) fine-tuning the morphology of the final ECs [3-6]. The proposed ECs are obtained by the optimization of the preparation protocol devised in our research group [7]. In particular, the physicochemical properties and the morphology of the final materials are modulated by a post-synthesis activation step carried out by electrochemical de-alloying. The final ECs bear bimetallic ORR active sites comprising Pt as the \u201cactive metal\u201d and Ni as the \u201cco-catalyst\u201d [8]. Preliminary results clearly evidence that this approach is capable to yield hierarchical ECs exhibiting a very promising performance in the ORR despite a very low loading of Pt. In detail, the best EC exhibits an ORR onset potential ca. 30 mV higher with respect to that of the Pt/C reference. The chemical composition of the ECs is determined by inductively-coupled plasma atomic emission spectroscopy (ICP-AES) and microanalysis. The structure is elucidated by wide-angle X-ray diffraction (WAXD) and vibrational spectroscopies (e.g., confocal micro-Raman); the morphology is probed by, both conventional and high-resolution, scanning electron microscopy (SEM) and transmission electron microscopy (TEM); the \u201cex-situ\u201d electrochemical performance and ORR reaction mechanism are gauged by cyclic voltammetry with the rotating ring-disk electrode method (CV-TF-RRDE). Finally, the ECs are implemented at the cathode of single fuel cell prototypes which are tested in operating conditions. REFERENCES [1] I. Katsounaros, S. Cherevko, A. R. Zeradjanin, K. J. J. Mayrhofer, Angew. Chem. Int. Ed., 53, 102 (2014). [2] J. Zhang, Front. Energy, 5, 137 (2011). [3] S. Sharma, B. G. Pollet, J. Power Sources, 208, 96 (2012). [4] M. Liu, R. Zhang, W. Chen, Chem. Rev., 114, 5117 (2014). [5] A. C. Ferrari, F. Bonaccorso, V. Fal\u2019ko et al., Nanoscale, 7, 4587 (2015). [6] J. H. Chen, C. Jang, S. Xiao, M. Ishigami, M. S. Fuhrer, Nature Nanotech., 3, 206 (2008). [7] V. Di Noto, E. Negro, K. Vezz\uf9, F. Bertasi, G. Nawn, L. Toncelli, S. Zeggio, F. Bassetto, Patent application 102015000055603 filed on 28 September 2015. Applicants: Universit\ue0 degli Studi di Padova and Breton S.p.A. (2015). [8] V. Di Noto, E. Negro, K. Vezz\uf9, F. Bertasi, G. Nawn, The Electrochemical Society Interface, Summer 2015, 59 (2015)