Browsing by Author "Cupolillo, Anna"

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Development of advanced systems for energy conversion based on innovative two- dimensional materials
(Università della Calabria, 2021-09-27) Zappia, Isabella; Critelli, Salvatore; Chiarello, Gennaro; Cupolillo, Anna
The even growing energy demand due to the demographic growth and the consequent economic expansion has led to the search for innovative technologies available for energy production and conversion from green and renewable sources such as solar energy. In this context, twodimensional (2D) materials, including either single- and few-layer flake forms, are constantly attracting more and more interest as potential advanced photo(electro)catalysts for redox reactions leading to green fuel production. Recently, layered semiconductors of group-III and group-IV, which can be exfoliated in their 2D form due to low cleavage energy (typically < 0.5 J m-2), have been theoretically predicted as water splitting photocatalysts for hydrogen production. For example, their large surface-to-volume ratio intrinsically guarantees that the charge carriers are directly photogenerated at the interface with the electrolyte, where redox reactions take place before they recombine. Moreover, their electronic structure can be tuned by controlling the number of layers, fulfilling the fundamental requirements for water splitting photocatalysts, i.e.: 1) conduction band minimum (CBM) energy (ECBM) > reduction potential of H+/H2 (E(H+/H2)); 2) valence band maximum (VBM) energy (EVBM) < reduction potential of O2/H2O (E(O2/H2O)). A requirement for large-scale applications is the development of low-cost, reliable industrial production processes. In this scenario, liquid-phase exfoliation (LPE) methods provide scalable production of 2D materials in form of liquid dispersions, enabling their processing in thin-film through low‐cost and industrially relevant deposition techniques. This thesis investigates, for the first time, the photoelectrochemical (PEC) activity of single-/fewlayer flakes of GaS, GaSe, and GeSe produced through ultrasound-assisted LPE in environmentally friendly solvents (e.g., 2-propanol) in aqueous media. Our results are consequently used to design proof-of-concept PEC water splitting photoelectrodes, as well as PEC-type photodetectors. Moreover, structural and electronic properties of PtTe2 have been investigated, being this material a potential catalyst for the hydrogen evolution reaction (HER) and other fuel-producing electrochemical reactions.
Proprietà elettroniche collettive del grafene supportato: influenza del substrato
(2014-11-12) Ligato, Nadia; Pantano, Pietro; Caputi, Lorenzo; Cupolillo, Anna
Synthesis and cherization of low-dimensional materials
(Università della Calabria, 2020-04-16) Alessandro, Francesca; Critelli, Salvatore; Caputi, Lorenzo; Cupolillo, Anna
The main aim of this thesis is to synthesize and study low-dimensional materials, with special focus on: silicene, PtTe2, carbon nano-onions and activated carbon. The first section of this work describes the study of the collective modes in silicene and PtTe2. Silicene, the silicon equivalent of graphene, is attracting increasing scientific and technological interest in view of the exploitation of its exotic electronic properties. This material has been theoretically predicted to exist as a free-standing layer in a low-buckled, stable form, and can be synthesized by the deposition of Si on appropriate crystalline substrates. Using a combined experimental (High-Resolution Electron-Energy-Loss Spectroscopy, HR-EELS) and theoretical (Time Dependent Density Functional Theory, TDDFT) approach the electronic excitations of two phases of silicene growth on silver were studied showing that silicene grown in a mixed phase on Ag(111), preserves part of the semimetallic character of its freestanding form, exhibiting an interband π-like plasmon. Recently, the PtTe2 has emerged as one of the most promising among layered materials ―beyond graphene‖. In this work, the electronic excitations of the bulk PtTe2 were investigated by means of EELS and DFT detecting a sequence of modes at 3.9, 7.5 and 19.0 eV. The comparison of the excitation spectrum with the calculated density of states (DOS) allowed to ascribe spectral features to transitions between specific electronic states. Moreover, it has been observed that, in contrast to graphene, the high-energy plasmon in PtTe2 gets red-shifted by 2.5 eV with increasing thickness. The second section of this thesis reports the synthesis of polyhedral carbon nano-onions by arc discharge in water and the electrochemical performance of activated carbon in aqueous electrolytes. CNOs, in their spherical or polyhedral forms, represent an important class of nanomaterials, due to their peculiar physical and chemical properties. In this work, polyhedral carbon nano-onions (CNOs) were obtained by underwater arc discharge of graphite electrodes using an innovative experimental arrangement. Dispersed nanomaterials and a black hard cathodic deposit were generated during the discharges and studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy and thermogravimetric analysis (TGA). A model for the formation of the deposit was proposed, in which the crystallization is driven by an intense temperature gradient in the space very close to the cathode surface. Electric double layer capacitors (EDLC) are gaining increasing popularity in high power energy storage applications. Novel carbon materials with high surface area, high electrical conductivity, as well as a range of shapes, sizes and pore size distributions are being constantly developed and tested as potential supercapacitor electrodes. In this thesis, the electrochemical behavior of a highly microporous activated carbon was studied as electrode for symmetric and asymmetric capacitors in acid and neutral media. The highest capacity and energy density values were obtained in the case of the activated carbon in acid solution.