Towards 'Pt-free' Anion-Exchange Membrane Fuel Cells: Fe-Sn Carbon Nitride-Graphene 'Core-Shell' Electrocatalysts for the Oxygen Reduction Reaction

We report on the development of two new Pt-free electrocatalysts (ECs) for the oxygen reduction reaction (ORR) 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 to nanoparticles of metal/alloy/oxide, but are instead based on Fe and Sn sub-nanometric 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

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

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

(POSTER

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)

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)

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)

Nanocomposite Membranes Based on PBI and ZrO2 for HT-PEMFCs

Fuel cells (FCs) are able to convert the chemical energy stored in hydrogen into electrical energy with a very high efficiency, up to two-three times higher in comparison with traditional internal combustion engines, and do not produce greenhouse gas emissions. Despite these attractive features, FCs do not experience a widespread market penetration yet owing to a variety of drawbacks including expensive functional materials, complex and/or bulky power plants and an insufficient durability. Among the FC families, high-temperature proton exchange membrane fuel cells (HT-PEMFCs) show great promise to provide a viable solution to the shortcomings mentioned above. HT-PEMFCs operate at a high temperature, 120 < T < 250\ub0C; in these conditions, the electrocatalysts are not poisoned easily by the most common contaminants found in the reactant streams (e.g., CO in the H2 fuel). Furthermore, HTPEMFCs do not require external humidification. In summary, HT-PEMFCs can be very compact, resulting particularly suitable for application in the automotive sector. The state of the art of electrolyte membranes for application in HT-PEMFCs consists in a polymer characterized by a high thermal and chemical stability such as polybenzimidaziole (PBI), which is doped with H3PO4. In this work, a new family of hybrid inorganic-organic PEM is developed, based on PBI and nanometric ZrO2 with formula PBI/(ZrO2)x with x ranging from 0.7 to 16 wt%. ZrO2 are chosen as the filler for their high chemical stability in an acid environment and for the ZrO2 \u2013 PBI interactions in membranes. This feature is expected to give rise to strong interactions between the different components constituting the final hybrid inorganic-organic membranes (i.e., PBI, H3PO4 and ZrO2), thus improving their conductivity, thermal and mechanical properties. The membranes are obtained by solvent-casting processes, and undergo an extensive characterization. ICP-AES and microanalysis are used to determine the chemical composition of the membranes; HR-TG is adopted to study their thermal stability, while the thermal transitions are investigated by DSC. The structure of the proposed membrane is studied by FT-MIR ATR vibrational spectroscopy; the electric behavior is characterized by broadband electrical spectroscopy in the 5 \u2013 190\ub0C and 1 \u2013 106 Hz temperature and frequency ranges, respectively. It is observed that, with respect to pristine PBI, in the hybrid membranes the condensation of H3PO4 to H4P2O7 is brought to higher temperatures. Furthermore, the conductivity at 190\ub0C of the membrane including 10 wt% of ZrO2 is higher in comparison with pristine PBI (4.65\ub710-2 S/cm and 4.46\ub710-2 S/cm, respectively). The integration of the results allows to shed light on the complex interplay between the structural features, the thermal properties and the electrical response of this family of hybrid inorganic-organic proton conducting membranes. Acknowledgements. The authors thank 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 activity

Conductivity and Relaxation Phenomena in Proton and Anionic Exchange Membranes by Broadband Electric Spectroscopy

Ionically conducting materials (ICM) are of great importance for the fabrication of portable batteries for electronic devices such as computers, tools, video and still cameras, and for the development of fuel cell and battery-powered electric vehicles, dye-sensitized solar cells, supercapacitors and sensors [1]. It has been suggested that conductivity in ICMs occurs via a number of different processes. The predominant conductivity processes are attributed to: a) the charge migration of ions between coordination sites in the host materials; [2-5] and b) the increase of conductivity due to relaxation phenomena involving the dynamics of the host materials [2-5]. Ions \u201chopping\u201d to new chemical environments can lead to successful charge migration only if ion-occupying domains relax via reorganizational processes [2-5], which generally are coupled with relaxation events associated with the host matrix. Here, it will be described in a concise fashion, the instruments used to comprehensively study the electric response of ionic conductors. To provide the reader with the basic tools necessary for understanding broadband electric spectroscopy [6-8], the first part will review the general phenomena and basic theory behind each type of electric response that materials may exhibit when they are subjected to static or dynamic electric fields. This will be achieved by focusing on the practical use of equations, while referring to specialized texts for detailed explanations of the equations. Then, an overviews of the application of BES in the study of the charge transfer mechanisms pristine and hybrid inorganic-organic proton-conducting and anion-conducting membranes and the models adopted for the interpretation of conductivity mechanisms are described and a unified conductivity mechanism is proposed. References [1] Polymer Electrolytes: Fundamentals and Applications; Sequeira, C.; Santos, D., Eds.; Woodhead Publishing Limited: Oxford, 2010. [2] Di Noto, V. J. Phys. Chem. B, 104 (2000) 10116. [3] Di Noto, V.; Vittadello, M.; Lavina, S.; Fauri, M.; Biscazzo, S. J. Phys. Chem. B, 105 (2001) 4584. [4] Di Noto, V. J. Phys. Chem. B, 106 (2002) 11139. [5] Di Noto, V.; Vittadello, M.; Greenbaum, S. G.; Suarez, S.; Kano, K.; Furukawa, T. J. Phys. Chem. B, 108 (2004) 18832. [6] Di Noto, V.; Giffin, G. A.; Vezz\uf9, K.; Piga, M.; Lavina S. Broadband Dielectric Spectroscopy: A Powerful Tool for the Determination of Charge Transfer Mechanisms in Ion Conductors, in Solid State Proton Conductors: Properties and Applications in Fuel Cells, P. Knauth, M. L. Di Vona, Eds., John Wiley & Sons Weinheim, Germany, 2012. [7] Runt, J. P.; Fitzgerald, J. J. Dielectric Spectroscopy of Polymeric Materials: Fundamentals and Applications; American Chemical Society: Washington, D.C., 1997. [8] Schoenhals, A.; Kremer, F. Broadband Dielectric Spectroscopy; Springer-Verlag: Berlin, 2003. Acknowledgements The authors thank 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 activity

A Rechargeable magnesium battery based on chloroaluminate ionic liquids

(ABSTRACT