1,721,139 research outputs found
Smart Electrochromic Windows: New architectural elements for the realization of dynamic buildings
No full textNanostructured materials for p-type dye-sensitised solar cells (p-DSCs) and tandem devices
No full textThe present review article reports on the recent developments on the determination and analysis of the electrochemical and
photoelectrochemical properties of p‐type semiconducting materials, namely nickel oxide (NiO), prepared with different
modalities of deposition and thermal treatment. All these electrodic materials possess a mesoporous morphology as required
by the specific application of the dye‐sensitized solar cell (DSC), or Grätzel’s cell. In particular, NiO thin film electrodes
prepared with the methods of screen‐printing, spray deposition and sintering under various thermal conditions have been
reviewed for the elevated reproducibility of their photoelectrochemical behavior, and the possibility offered by these methods
of being scalable. The performance of these electrodes as photoactive cathodes of p‐DSCs has been compared with the
performance of the NiO samples obtained via other methods of sysnthesis/deposition. The choice of the dye sensitizers for p‐
DSCs has been confined to those colorants that have been purposely designed for p‐type semiconductors, i.e. erythrosine b as
benchmark, P1 and perylenemonoimides as highly performing hole photoinjectors, fast green and squaraines. The latter class of
dyes is particularly useful for the envisage of tandem DSCs due to their red shifted main absorption with respect to traditional
organometallic dye‐sensitizers (characteristic of optical complementarity). The recent review of Daeneke et al. (ref. 53 in the
following) analyzed systematically all the factors influencing negatively the poor performances of p‐DSCs. They reached the
important conclusion that the energy conversion losses of p‐DSCs were mainly associated to the low fill factors expressed by the
JV curves of these photoelectrochemical cells. The content of this review differs from that of the work of Daeneke et al. since it
will be here shown that the photoelectrochemical performances of nanostructured NiO films are heavily determined by the
capacitive behavior of NiO. This correlation has been evidenced by the fact that NiO acts as charge storing system in both
forward and reverse bias with the retention of ionic charge either on the surface or within the open structure. Adsorption
and/or intercalation phenomena in NiO will depend on the nature and size of the ions compensating the electronic charge
injected in NiO either electrochemically or photoelectrochemically
Instabilities in electrochemistry
No full textThe occurrence of instabilities in the temporal evolution of electrochemical processes generally manifests itself by producing potential or current time-oscillations with more or less regular features, or by displaying spatiotemporal patterns at the electrode surface and in the electrolyte. It is remarkable that almost every electrochemical reaction can undergo a transition towards a situation of kinetic instability if appropriate conditions are met. Such phenomena are a consequence of the irreversible departure of the system here defined as the combination of the electrodes with the electrolyte traversed by an electrical current, from an initial state which is intrinsically unstable, after being disturbed by a perturbation which alters a parameter characterizing the state of the system. From this it descends that the analysis of the stability of an electrochemical system against perturbations should start firstly with the definition of all variables controlling the stability of the system
Postdottorato presso Fritz Haber Institut (FHI) del Max Planck Gesellschaft (MPG) di Berlino
No full textStudio della convezione elettrodinamica con sistemi coniugati elettrochemiluminescenti ed analisi delle caratteristiche di elettrochemicluminescenza di polimeri conduttor
Preparazione elettrochimica e caratterizzazione di polialchiltertiofeni con regiochimica regolare di sostituzione
No full textThe research activity reported in the PhD thesis 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 research is motivated by the remarkable feature 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 motivated the compared analysis of 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 substituents 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), PBD 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 (mediator). 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 would have fit with the potential range of electroactivity for the polymer substrate. Moreover it was determining the blocking of possible electrochemistry between the mediator redox couple and the underlying metal through the proper thickening of the electrodeposited polymer in order to analyse the electrochemical processes involving the sole polymer
Electrochemiluminescence from organic emitters
No full textElectrically induced light emission from conjugated organic molecules in a condensed phase has constituted one of the most investigated phenomena in the recent past for a variety of reasons. The considerable development achieved in this field has been mainly based on the search of new configurations for luminescent devices such as flexible large area light-emitting diodes, and in the synthesis of improved light-emitting organic materials. In the present review a particular aspect of electrically induced light-emission phenomena from organic materials is considered, namely, organic electrochemiluminescence, which is the phenomenon of light emission from excited organic molecules generated upon occurrence of electrochemically driven redox reactions. Such processes can produce luminescence in the visible range if the resulting oxidized/reduced forms of the conjugated organic molecules form excited species capable of emitting photons within the energy range 1.5-3.5 eV. Electrochemi luminescence from organic emitters in a condensed phase has led to the creation of devices such as light-emitting electrochemical cells, whose realization was decisive in the development of effective light-emitting devices. In the present review the description of the phenomena at the basis of organic electrochemiluminescence is given together with the description of materials and devices configurations for light-emitting electrochemical cells
Formation of electroluminescent patterns with 9.10-diphenylanthracene: examples of electrohydrodynamic structures
No full textIn this work the formation of electrohydrodynamic (EHD) convective patterns has been studied by means of the electrochemiluminescence produced through the electrolysis of 9.10-diphenylanthracene in water- and oxygen-free solvents. The observation of EHD convection could be verified in electrolytes with low conductivity ( 10e4 V m-1) was applied. The electrolysis was run in thin layer electrochemical cells with interelectrode distance lower than 200 micron. Typical convective patterns are here reported and the analysis of the EHD phenomena will be attempted
Conjugated molecules for the smart filtering of intense radiations
No full textThe practical realization of smart optical filters, i.e. devices which change their optical transmission in a suitable way to keep a working state for a general light sensitive element , can involve the use of conjugated molecules whose light absorption properties are light- intensity dependent (nonlinear optical effect). The verification of optical limiting displayed by some particular conjugated molecules, e.g. phthalocyanines, is quite noteworthy and can be successfully exploited for the realization of such smart optical devices. In the present contribution the analysis of the relevant molecular feature of a phthalocyanine are analyzed with the aim of determining useful correlations between optical limiting performance and phthalocyanine chemical structure. In particular , the electronic nature of the substituent is considered as a key factor for the explanation of some observed optical limiting trends
Non-invasive in-situ techniques fof the characterization of processes at thin film electrodes
No full textIn this contribution we report on the application of the Bending Beam Method (BBM) and the Probe Deflection Beam (PDB) as non destructive tools for the in-situ characterization of electrode materials and electrochemical processes. The systems under investigation usually possess a thin film configuration with thickness values ranging between 0.1 and 100 um. the detection of the probing laser beam displacement can be then exploited for the evaluation of the mechanical stress in thin film electrodes with BBM, or for the identification of the actual species flowing to/from the electrode with PBD technique. The PBD and BBM characterization of some electrochemical processes will be here presented
Phthalocyanines as materials for advanced technologies: some examples
No full textMetallophthalocyanine complexes and related compounds play an important role in many advanced applications and modem technologies mostly by virtue of their characteristic optical absorption and high chemical stability. As a class of materials made well-known by their vivid and fast colors, it is expected that metallophthalocyanines and analogues, e.g. naphthalocyanines, are going to keep their role with the increasing use of natural and artificial light in the technologies of the future. In the present review some relevant properties of phthalocyanines and related macrocycles for technological applications are analyzed. In particular the electrical conductivity and photoconductivity as well as some nonlinear optical properties (mostly optical limiting), of phthalocyanines and related compounds are discussed. Copyright (c) 2004 Society of Porphyrins & Phthalocyanines
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