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

Advanced Materials for High-Performance Secondary Li and Mg Batteries

In order to obtain advanced energy storage systems with high energy density, the research activity here described, is focused on the study of electrolyte and cathodic materials for application in Lithium and Magnesium batteries. The materials are synthesized through inert atmosphere procedures and characterized with several techniques such as: Thermogravimetric Analyses (TGA), Differential Scanning Calorimetry (DSC), Vibrational spectroscopies (MIR, FIR, Raman), Solid state MAS-NMR, several electrochemical techniques (CV, CA, EIS) and Broadband Electrical Spectroscopy (BES). The results are used to study the interplay between the structure and the conduction mechanism of these materials. The most promising materials are then tested in prototype cells in order to evaluate their performance in operating devices. As a general procedure, the electrolytes are synthesized with different concentrations of Li+ or Mg2+ charge carriers in order to evaluate the effect of the cation concentration on the thermal properties and conductivity of the materials. In addition, the complexation of the cations and its effect on the long-range charge transfer migration is carefully studied by Infrared and Raman spectroscopy. In the case of the cathodic materials the and their composition are modulated in order to study their effect on the lithium intercalation/deintercalation processes, efficiencies and on battery prototype performance. The investigated materials comprise: a) an inorganic Solid-state Li-ion conductors, based on lithium-functionalized fluorinated titanium oxide NPs; b) a new class of single-ion conducting nanocomposite polymer electrolytes for Li batteries; and c) two electrolytes for Mg secondary batteries based on ILs and an innovative Mg salt. Moreover two studies about dielectric relaxation phenomena in 4a) Magnesium-polymer electrolytes and 4b) clay-based solid polymer electrolytes (SPEs) are presented which elucidate the interplay existent between molecular relazations in host polymer matrices and long range charge transfer processes. Concerning cathodic materials a family of high voltage multi-metal phosphate cathodic materials for secondary lithium batteries is proposed, studied and tested in button battery prototypes. Firstly, a general introduction about the state of art of electrolytes and cathodes, with a particular attention on drawbacks and possible solution, which characterize these materials, is presented. Secondly, details about the synthesis and the characterizations of each class of materials is described in great details. Thirdly a concluding remark is provided.Al fine di ottenere sistemi di accumulo di energia elettrica sempre più performanti, l'attività di ricerca qui descritta, è focalizzata sullo studio di elettroliti e materiali catodici per applicazioni in batterie al litio e magnesio. I materiali vengono sintetizzati attraverso sintesi in atmosfera inerte e caratterizzati con diverse tecniche quali: analisi termogravimetrica (TGA), calorimetria a scansione differenziale (DSC), spettroscopie vibrazionali (FT-MIR, FT-FIR, Raman), NMR di stato solido, diverse tecniche elettrochimiche (voltammetria ciclica, cronoamperometria, impedenza elettrochimica) e spettroscopia elettrica a banda larga. I risultati sono utilizzati per studiare l'interazione tra la struttura e il meccanismo di conduzione di questi materiali. I materiali più promettenti sono testati in batterie a bottone prototipo tipo CR2032 per valutare la loro ciclabilità e stabilità su lungo periodo. Come procedura generale, gli elettroliti vengono sintetizzati con differenti concentrazioni di portatori di carica tipo Mg2+ o Li+ per valutare l'effetto della concentrazione di cationi sulle proprietà termiche e sulla conducibilità dei materiali. Inoltre, la complessazione dei cationi e il suo effetto sul trasferimento di carica a lungo raggio sono studiati accuratamente tramite spettroscopia infrarossa e Raman. Nel caso dei materiali catodici la struttura e la composizione chimica di questi sistemi è modulata al fine di studiare il loro effetto sul processo di intercalazione/deinteracalazione dello ione litio, sull’efficienza e le prestastazioni dei prototipi di batteria a bottone tipo CR2032. I materiali studiati comprendono: a) un conduttore inorganico di stato solido a singolo catione di litio basato su di un ossido di titanio fluorurato; b) una nuova classe di elettroliti nanocompositi polimerici per batterie al litio; e c) due elettroliti per batterie al magnesio basati su liquidi ionici e un sale innovativo di Mg. Inoltre, al fine di evidenziare le correlazioni esistenti tra le dinamiche dei rilassamenti molecolari degli elettroliti e i processi di trasferimento di carica a lungo raggio, sono stati effettuati due studi sui meccanismi di rilassamento dielettrico di: a) elettroliti polimerici al Mg; e b) elettroliti polimerici solidi a base di alluminio silicati (SPE). Infine viene proposta una nuova promettente famiglia di materiali catodici di cui si studiano le correlazioni tra struttura, morfologia e prestazioni in batterie secondare prototipo a bottone. La tesi inizia con un’ introduzione generale sullo stato dell'arte degli elettroliti e dei catodi. Particolare attenzione è rivolta sugli svantaggi e sulle possibili future soluzioni. In secondo luogo, vengono descritti I n dettaglio la sintesi e caratterizzazione di ciascuna classe di materiali qui proposti. Quindi, si conclude evidenziando I risultati più salient ottenuti sui vari sistemi proposti

Magnesium Electrolyte Based on EMImBF4 and -[MgCl2]n for Secondary Magnesium Batteries

this report, a new magnesium ion electrolyte is proposed, based on \u3b4-[MgCl2]n and ethylmethylimidazolium tetrafluoroborate (EMImBF4) ionic liquid. Anhydrous \u3b4-[MgCl2]n was obtained by reacting metallic magnesium with n-chlorobutane in a strictly anhydrous atmosphere as described elsewhere. \u3b4-[MgCl2]n consists of inorganic polymer chains where Mg atoms are bonded together by chloride bridges. The \u3b4-[MgCl2]n chains show a high crystallographic disorder and reactivity toward Lewis bases. Twelve magnesiumconducting electrolytes with formula EMImBF4/(\u3b4-[MgCl2]n)f with f ranging between 0 and 0.117 were prepared by dissolving directly \u3b4-[MgCl2]n into EMImBF4; f is the molar ratio between \u3b4-[MgCl2]n and EMImBF4. The metal concentration of the electrolytes was determined by ICP-AES. The correlation between structure, thermal properties and conduction mechanism of EMImBF4/(\u3b4-[MgCl2]n)f was investigated by several techniques: (a) Medium- and Far-infrared spectroscopy, to reveal the structural features and interactions between the various components of each electrolyte; (b) Differential Scanning Calorimetry (DSC), to detect the thermal transitions; (c) Broadband Electric Spectroscopy (BES), to investigate the relaxation phenomena taking place in the materials and the conduction mechanism. In addition, a detailed study of the mechanism of ion conduction in these electrolytes was carried out by BES in the 10E-2 Hz to 10 MHz and -150\ub0C to 150\ub0C frequency and temperature ranges, respectively. These studies were performed by analyzing the imaginary and real components of conductivity and permittivity spectra by suitable models

Poly(vinyl alcohol)-based Electrolyte for Lithium Batteries

Polymer electrolytes (PEs) were first proposed in the early 1970s [1]. Since then, this class of materials has attracted the attention of many scientists, becoming one of the most prolific research field in solid-state electrochemistry [2, 3]. PEs, when used in Li-ion secondary batteries, are able to overcome many of the disadvantages of classic liquid organic electrolytes, which typically show: a) a high flammability and a high vapor pressure; b) a low thermal, chemical, and electrochemical stability; and c) dendrites formation. Nevertheless, classical PEs show low values of ionic conductivity (\u3c3 < 10-6 S cm-1) with respect to the typically requested conductivity values for practical applications. It has been shown that systems based on poly(vinyl alcohol) (PVA) are able to dissolve lithium salts, giving rise to ion conducting materials that present higher conductivity values with respect to any other solid and solvent-free polymer electrolyte [4]. Nonetheless, in classic PEs, the ionic conductivity is mainly attributed to the migration of anionic species. Indeed, in these materials the Li+ transference number is usally very low (< 0.3) [5]. Here, we present a new ion conducting polymer electrolyte based on a Li+ poly(vinyl alkoxide) macromolecular salt. In this material, Li+ ions are provided by PVA alkoxide groups (-RO-Li+) which are obtained by a direct lithiation of hydroxyl groups of pristine polymer. Thus, a PE is obtained with Li+ cations coordinated by the O- ligand functionalities directly bonded to the PVA backbone chains. The lithium assay is determined by Inductively-Coupled Plasma Atomic Emission Spectroscopy. The thermal stability is gauged using High-Resolution Thermo Gravimetric Analysis and the thermal transitions are investigated by means of Modulated Differential Scanning Calorimetry measurements. The structure and the interactions in proposed electrolytes are studied by vibrational spectroscopies both in the mid- and far-infrared and Raman spectroscopy. The interplay between structure and conductivity is investigated by Broadband Electrical Spectroscopy. Insights on the long range charge migration phenomena in these materials are presented. Acknowledgements: The authors thank the strategic project MAESTRA of the University of Padova for funding these research activities and the \u201cCentro studi di economia e tecnica dell\u2019energia Giorgio Levi Cases\u201d for PhD grant to G.P. References [1] D.E. Fenton, J.M. Parker, P.V. Wright, Polymer, 14 (1973) 589-. [2] V. Di Noto, S. Lavina, G.A. Giffin, E. Negro, B. Scrosati, Electrochim. Acta, 57 (2011) 4-13. [3] J. Muldoon, C.B. Bucur, N. Boaretto, T. Gregory, V. Di Noto, Polymer Reviews, 55 (2015) 208-246. [4] M. Forsyth, H.A. Every, F. Zhou, D.R. MacFarlane, Ionic Conductivity in Glassy PVOH-Lithium Salt Systems, ACS Symp. Ser., 1998, pp. 367-382. [5] F. Bertasi, K. Vezz\uf9, E. Negro, S. Greenbaum, V. Di Noto, Int. J. Hydrogen Energy, 39 (2014) 2872-2883

"Core-Shell" ORR Nano-Electrocatalysts Based on a PtNi Carbon Nitride "Shell" and Cu NP "Core"

One of the most severe bottlenecks in the operation of proton exchange membrane fuel cells (PEMFCs) is the sluggish kinetics of the Oxygen Reduction Reaction (ORR). Thus, suitable ORR Electrocatalysts are required in order to obtain PEMFCs able to yield a sufficiently high performance. State-of-the-art ORR electrocatalysts for application in PEMFCs are obtained by supporting Pt nanocrystals on active carbon supports characterized by a very large surface area. However, despite extensive investigations the performance of these electrocatalysts does not meet yet the strict requirements necessary for a large-scale application of PEMFC technology. A new preparation protocol has been proposed recently to obtain nano-electrocatalysts with a well-controlled chemical composition, based on the pyrolysis and activation of hybrid inorganic-organic precursors. The resulting carbon nitride nano- electrocatalysts thus prepared show an outstanding ORR performance both in \u201cex-situ\u201d studies and in a single-cell configuration. In this work, a new family of multimetal carbon nitride nano-electrocatalysts is described. The materials are synthesized by pyrolysis of a hybrid inorganic-organic precursor including Pt and Ni atoms impregnating Cu nanoparticles acting as the support. The final ORR electrocatalysts are obtained after an extensive electrochemical dealloying activation process. The products are fully characterized before and after the activation processes. The chemical composition of the Electrocatalysts is determined by Inductively-Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) and microanalysis. The morphology is investigated by High-Resolution Scanning Electron Microscopy (HR-SEM) and High-Resolution Transmission Electron Microscopy (HR-TEM). The structure is probed by powder X-Ray Diffraction (XRD). The electrochemical performance of the electrocatalysts in the ORR is determined both by \u201cex-situ\u201d measurements carried out by cyclic voltammetry with the rotating ring disk electrode (CV-TF-RRDE method) and by \u201cin-situ\u201d fuel cell studies in a PEM single-cell configuration. Preliminary results indicate clearly that the proposed electrocatalysts show a remarkable ORR performance, which is significantly enhanced in comparison with the Pt/C reference both in terms of overpotential and selectivity in the 4-electron mechanism of the ORR