DANILO DINI

CORSO DI ELETTROCHIMICA

Definizioni e concetti di base: Ioni, elettroliti e carica elettrica quantizzata. Transizione da conduzione elettronica a conduzione ionica in una cella. Celle elettrolitiche e celle galvaniche. Leggi di Faraday. Sistema di unità di misura.

Conduzione elettrica e interazioni fra ioni: I fondamenti; Leggi empiriche della conduttività negli elettroliti; Mobilità ionica e trasporto secondo Hittorf. Teorie sulla conduttività: equazione di Debye-Hueckel-Onsager. Il concetto di attività dal punto di vista elettrochimico. Le proprietà degli elettroliti deboli.

Potenziali elettrodici e struttura del doppio strato elettrochimico: Potenziali di elettrodo e loro dipendenza da T, P e a. Elettrodi di riferimento e serie elettrochimica. Il doppio strato e gli effetti di elettrocapillarità). Modelli di doppio strato secondo Helmholtz, Gouy-Chapman e Stern. Metodi di determinazione del punto di zero carica.

Cinetica elettrochimica e corrente elettrica: relazione fra potenziali d’elettrodo e flusso di corrente; sovratensioni. Il transfer elettronico e il modello del complesso
attivato. Equazione di Butler-Volmer e i limiti a basso e alto campo. Sovratensione da concentrazione e problemi associati alla diffusione ionica. Diffusione stazionaria, non-stazionaria planare e sferica, microelettrodi. Altri problemi di cinetica elettrochimica. Adsorbimento su elettrodi, isoterme di adsorbimento. Elettrocristallizzazione con e senza diffusione sulla superficie.

Corrosione: Termodinamica della corrosione. Diagrammi di Pourbaix per vari metalli. Cinetica della corrosione. Diagramma di Evans. Esempi di pattern di corrosione.

A completamento del corso lo studente avra' appreso:

a) i  meccanismi della conduzione di corrente nei diversi tipi di materiali (conduttori ionici, elettronici e misti) e di tutti i fattori che la controllano;

b) i fenomeni alla base della formazione dell’interfaccia elettrochimica

c) la termodinamica alla base del funzionamento dei dispositivi elettrochimici

d) i fattori cinetici che controllano il passaggio della corrente in un dispositivo elettrochimico

CORSO DI CHIMICA FISICA DELLO STATO SOLIDO E MATERIALI NANOSTRUTTURATI

Definizione di polimeri conduttori di natura organica ed inorganica. Concetto di drogaggio dei polimeri semiconduttori. Metodi di sintesi di polimeri conduttori. Analisi della struttura, delle proprietà di trasporto elettrico, proprietà elettrochimiche e caratteristiche ottiche dei sistemi polisolfonitrile e poliftalocianine. Nanotubi di carbonio.

Alla fine del corso lo studente dovra' aver appreso:

a) il significato di polimero conduttore/semiconduttore ed il concetto di drogaggio di un polimero semiconduttore;

b) come si preparano e si caratterizzano i polimeri conduttori;

c) la scienza dei materiali alla base della scelta dei polimeri conduttori come materiali attivi in dispositivi elettrochimici, ottici ed elettronici

Ricevimento: martedi' e giovedi' dalle 14.30 alle 15.30 previo appuntamento

http://www.chem.uniroma1.it/dipartimento/persone/danilo-dini

Danilo Dini si e’ laureato in Chimica all’Università di Roma “La Sapienza” (voto 110/110 e lode) con una tesi sull’elettrocromismo di ossidi metallici. Per questa ha ottenuto nel 1994 il Premio “Luigi Grifone” della Societa’ Chimica Italiana per la miglior tesi italiana in elettrochimica dell’anno. Ha conseguito nel 1998 il dottorato in Scienza dei Materiali nella stessa università con una tesi sulla deposizione e la modulazione elettrochimica delle proprietà spettrali, elettroniche e fotoelettrochimiche di politiofeni. E’ stato nel gruppo di Allen J. Bard (Dipartimento di Chimica dell’Università del Texas ad Austin, USA), per l’utilizzo del microscopio a scansione elettrochimica nello studio dell’attività elettrocatalitica di polimeri coniugati. Ha svolto un postdottorato all’ Istituto di Chimica Fisica del Fritz-Haber-Institut der Max-Planck-Gesellschaft (Berlino, Germania) con Gerhard Ertl (Premio Nobel per la Chimica nel 2008) sulla formazione di patterns e sull’ elettrochemiluminescenza di polimeri. Successivamente ha svolto un post-dottorato presso l’ Istituto di Chimica Organica dell’Università di Tubinga (Germania) con Michael Hanack sulla sintesi e caratterizzazione di ftalocianine per ottica non lineare utilizzando sorgenti luminose di tipo laser ad impulsi. Svolge attualmente attività di ricerca sulla fattibilità di semiconduttori inorganici e sensibilizzatori per celle fotovoltaiche a colorante di tipo Grätzel. Ha pubblicato più di 90 lavori su riviste scientifiche internazionali [indice di Hirsch: 24 (a Giugno 2015)], ed ha partecipato a più di 30 congressi internazionali.

CURRICULUM VITAE (in inglese)
The research activities of Danilo Dini (D.D.) have involved mainly the preparation, evaluation and design of materials and prototypes for the development of advanced devices such as electrochromic windows, sensors, displays, high-power sources, light emitting devices and nonlinear optical devices.
In the field of electrochromism the contribution of D.D. was the discovery of the effect of the chemical nature of the electrolyte upon the electrochromic efficiency of tungsten trioxide (WO3).  expresses the ratio of the absorption variation in the material to the amount of electrical charge responsible for that variation. Consequently it has been optimized the electrolyte for improving  in WO3 thin films prepared by evaporation. Traditional values of electrochromic efficiency in the visible range ranged between 30 and 40 cm2 C-1 with electrolytes based upon lithium and sodium salts. The use of an acidic electrolyte brought about an increase of  up to 70 cm2 C-1. In addition to that, the kinetics and the reversibility of the coloration process were improved with the use of these new electrolytes. Once the operating conditions were optimized it was started a study of the coloration mechanism with a special technique (laser beam deflection method, LBDM) which was developed in the laboratory of Photochemistry and Photolectrochemistry (Dept. of Chemistry, University of Rome "La Sapienza"). The LBDM detects the in-situ deformation of a thin film undergoing a mechanical stress. In the case of electrochromic materials the coloration process is associated with an intercalation reaction which brings about the swelling and the shrinking of the electrochromic material. Consequently, the electrochromic material undergoes a mechanical stress in the working conditions. The LBDM study of WO3 coloration led to the discovery of a double mechanism of charge compensation during the chromatic changes of WO3 which was later confirmed by other research groups with different independent techniques. Moreover the LBDM could detect the actual limit of reversibility for the electrochromic materials.
The research activity reported in the PhD thesis of D.d. has involved the electrochemical synthesis and the characterization of conjugated polymers which can be employed in the realization of technologically advanced applications such as smart windows, displays, supercapacitors, sensors, artificial muscles and photovoltaic cells. This is because D.D. was interested in the remarkable property of conjugated polymers to vary their electronic conductivity within a large range (10-18 - 102 S cm-1) by means of "doping" processes. In this framework "doping" processes are redox reactions between an electrically neutral polymer and an oxidizing/reducing agent. Despite of the many works on the synthesis and characterization of conjugated polymers, a study on the effect of spacers position upon the electric properties of the substituted conjugated polymer was still missing. This lack motivatewd D.D. to analyse and compare the electric properties of substituted polymers differing in the position of the substituting groups along the chain. For this purpose it has been accomplished the investigation of the properties of the systems derived from the polymerization of the starting monomers 3',4' didodecyl 2,2':5',2" terthiophene (and 3,3" didodecyl 2,2':5',2" terthiophene. The polymerization of these monomers has been realized through electrochemical oxidative coupling. The electrochemical polymerization has been preferred to the chemical route. The choice of the dodecylic chain as substituting group has been motivated by the great solubility of dodecyl-derivatized polymers in the most common organic solvents. The electrochemical polymerization of oligomeric species as 3',4' and 3,3" DDTT could be achieved in relatively milder conditions with respect of the polymerization of a single thiophene ring. The electrochemical polymerization of 3',4' DDTT and 3,3" DDTT has been accomplished in the potentiodynamic mode because the deposition yield of polythiophenes resulted higher when the oxidation process is followed by a cathodic wave. This has been confirmed by means of the electrochemical quartz crystal microbalance (EQCM) which measured the increases of the electrode mass in correspondence of the whole range of the applied potential. The polyterthiophenes electrodeposition was also analysed with the probe beam deflection (PBD) technique which detects the changes of refractive index of an electrolyte in correspondence of the diffusion layer in front of the electrode as determined by fluxes of dissolved species. The PBD analysis is made necessary by the fact that thick polymeric deposits can give artifacts in the response of EQCM if the electrodeposited polymers don't possess a rigid layer behavior.
The reversibility of the optical , electrical, magnetic, morphological, mechanical and mass effects associated with the simultaneous exchange of ions and electrons occurring during the doping processes was checked with in-situ visible and IR spectroscopy, conductimetry, in-situ electron spin resonance (ESR), scanning electron microscopy (SEM), LBDM and EQCM. The comparison of the results for the two isomeric polymers showed that the pattern of monomer substitution mainly affects the kinetics of the electrochemical growth. This led to the electrochemical synthesis of isomeric polymers with different physical properties such as the degree of polymerization, film morphology, the optical absorption and the electrical conductivity.
In the case of one polymer, it has been accomplished the study of the electron transfer between poly 3,3" DDTT and a redox couple dissolved in the electrolyte through the scanning electrochemical microscope (SECM). The SECM study was motivated by the fact that in the field of conducting polymers only few works were addressed to the effect of polymer conductivity upon the rate of electron transfer between a conducting polymer and a redox couple. This is because of the complexity of the phenomena which involve simultaneously the polymer doping, the electronic transport through the polymeric film and the heterogeneous electron transfer at the polymer/electrolyte interface. The main critical point for the realization of SECM experiment with poly 3,3" DDTT has been the choice of the mediator redox couple whose potential range of stability should have fit with the potential range of electroactivity for the polymer substrate. Moreover it was relevant the blocking of possible electrochemistry between the mediator redox couple and the underlying metal through the proper thickening of the electrodeposited polymer to analyse the electrochemical processes involving solely the polymer.
Another field of interest of D.D. research activity has been the characterization of the anodic treatment of silicon wafers for wet silicon processing. The most important achievement has been the creation of a model accounting the variation of silicon oxide formation and dissolution rate in the diverse regimes of electrochemical Si processing (electropolishing, porous Si, electrochemical oscillations), from experiments of probe beam deflection (PBD) in acidic media containing fluoride species. The PBD method allows the evaluation of refractive index variations in that part of the liquid layer facing the silicon electrode. In the present case such index variations are provoked by the release or the uptaking of chemical species due to the occurrence of reactions between the silicon surface and the electrolyte. The use of the LBDM has been then exploited to evaluate the compactness and the passivating properties of the silicon oxide layer during the different steps of the anodic treatment.
The postdoctoral activity of DD concerned the study of the electrochemiluminescence (ECL) of conjugated molecules in solution and in the configuration of thin films for the development of sensors and light emitting electrochemical cells. In the characterization of ECL from solution it has been found a relationship between the intensity of the emitted light from the electrolyzed molecules and the pressure exerted on the electrolyte when the configuration of thin film electrochemical cell was adopted. Moreover, the evolution of self-organizing hydrodynamic structures could be also observed by visualizing the development of ECL. The latter work represents one of the first attempts of flow control in fluids having low electrical conductivity through the application of an electrical field in an electrochemical cell with thin layer configuration. In another work on ECL form conducting polymers the kinetics of ECL from thin films of poly 4-methoxy-(2-ethylethoxyl)-2,5-phenylenevinylene (MEH-PPV) has been reported. These results showed for the first time that kinetics of ECL from conjugated polymers is determined by the nature of the ions which compensate the charge inside the electroluminescent polymer.
D.D. has been involved in the preparation and the characterization of nonlinear optical properties of new conjugated macrocycles, namely phthalocyanines, to be employed as active materials in optical limiting devices. The main aim of this research has involved the definition of molecular structures based on the phthalocyanine skeleton which have increased nonlinear optical absorption. It has been found that the presence of substituents in the phthalocyanine ring with strong electronic effects, mainly electron acceptors, brings about a noticeable improvement of the effect of optical limiting generated by these systems under intense laser irradiation.
At Dublin City University (Principal Investigator: Prof. Han Vos), D.D. has studied the electrochemical properties of dye-sensitised semiconductors for the realization of photocatalytic devices based on Graetzel-type photoelectrochemical cells.
Presently, D.D. is involved in research projects that involve the electrochemical and photochemical characterization of electrodes and materials for dye-sensitised solar cells and analogous devices.