Design, synthesis, characterization and development of novel organic conducting polymers with technological applications

In this thesis, a series of novel organic conducting polymers have been synthesized using alternative methods based on electrochemical techniques, which have allowed to broaden the knowledge in the field of the characterization by means of topological, spectroscopic, electrochemical and structural techniques. Among the variety of synthesis techniques of conducting polymers, layer-by-layer (LbL) has been one of the most important to build multilayered systems. Thus, in this thesis the LbL has shown to be an excellent procedure to explore new applications in the field of energy storage using conducting polymers. On the other hand, recently, the influence of new sustituents on functionalized conducting polymers has been proved to modify the structural, optical and physical properties of conducting polymers. Within this context, synthesis of novel functionalized conducting polymers bearing strong electron-withdrawing sustituents such as cyano group or halide atoms have been widely studied and characterized throughout this thesis. The presence of these substituents have emerged as promising candidates in the field of chemical sensors and electrochromic devices. Although the functionality of polymers or the development of new techniques are excellent procedures to synthesize and to develop new properties on the field of conducting polymers, it is worth mentioning that the substrate plays a crucial role on the electrochemical field. Accordingly, the substrates can also modify and change the properties of conducting polymers during the electropolymerization process. In this way, different substrates were employed in this work with the aim of achieving new applications in the field of corrosion inhibitors and as supercapacitors. Supercapacitors as energy storage device has been an outstanding application during this thesis. Thus, the field of nanotechnology has taken an important part in this thesis through development and design of promising hybrid nanocomposites based on conducting polymers and clay with technological applications and interesting optoelectronic properties. The contribution of theoretical techniques based on quantum mechanical calculations have allowed to predict some electronic and structural properties of conjugated polymers, which could be corroborated experimentally. The quantum mechanics is a useful tool to check experimental results and to understand mechanisms not fully understood at experimental level. Therefore, theoretical calculations have provided promising information to obtain new insights in the field of conducting polymers.La presente tesis se encuentra focalizada en el estudio de nuevos polímeros conductores orgánicos obtenidos a partir de métodos alternativos basados en principios electroquímicos. Entre los principales métodos de polimerización la técnica conocida como capa-a-capa ha emergido con gran fuerza en los últimos años dada sus numerosas ventajas y propiedades. En este contexto, la síntesis de polímeros conductores mediante este procedimiento permitió comprender y analizar el efecto sinérgico entre capas, consiguientemente la caracterización de estos nuevos materiales a partir de técnicas estructurales, espectroscópicas, morfológicas, electroquímicas y ópticas permitió indagar y desarrollar aplicaciones en diferentes campos tecnológicos tales como la electrónica o la corrosión. Otro de los factores que influyen en las propiedades de los polímeros conductores es el proceso de funcionalización. En esta tesis, la incorporación de grupos funcionales con elevado carácter aceptor de electrones centró una parte importante del trabajo, de este modo, los polímeros conductores funcionalizados con átomos halogenados o mediante el grupo ciano evidenciaron una gran influencia en las propiedades físicas, estructurales, ópticas y morfológicas de las estructuras químicas en tiofeno y pirrol. La modificación de determinadas propiedades en estos polímeros permitió desarrollar componentes basados en sensores químicos o dispositivos electrocrómicos. Acorde a esta temática, la modificación de la superficie juega también un papel importante y crucial en las propiedades de los polímeros conductores durante el proceso de síntesis electroquímica. Análogamente al caso de la funcionalización el estudio de la modificación de la superficie denotó una gran expectativa en el desarrollo de nuevos supercondensadores orgánicos, así como una gran alternativa para aplicación como inhibidores de corrosión. Finalmente, en el ámbito experimental de esta tesis, se han orientado estudios en el campo de la nanotecnología en la síntesis y caracterización de nuevos materiales híbridos nanocompuestos con interesantes propiedades optoelectrónicas y electroquímicas. A nivel teórico, la contribución de cálculos teóricos basados en mecánica quántica permitieron predecir determinadas propiedades electrónicas y estructurales de polímeros conductores, cuyos valores fueron corroborados experimentalmente. Así, la química teórica proporcionó un amplio conocimiento en la exploración y comprensión de los mecanismos estructurales de los polímeros conductores

Solvent effects on the properties of hyperbranched polythiophenes

The structural and electronic properties of all-thiophene dendrimers and dendrons in solution have been evaluated using very different theoretical approaches based on quantum mechanical (QM) and hybrid QM/molecular mechanics (MM) methodologies: (i) calculations on minimum energy conformations using an implicit solvation model in combination with density functional theory (DFT) or time-dependent DFT (TD-DFT) methods; (ii) hybrid QM/MM calculations, in which the solute and solvent molecules are represented at the DFT level as point charges, respectively, on snapshots extracted from classical molecular dynamics (MD) simulations using explicit solvent molecules, and (iii) QM/MM-MD trajectories in which the solute is described at the DFT or TD-DFT level and the explicit solvent molecules are represented using classical force-fields. Calculations have been performed in dichloromethane, tetrahydrofuran and dimethylformamide. A comparison of the results obtained using the different approaches with the available experimental data indicates that the incorporation of effects associated with both the conformational dynamics of the dendrimer and the explicit solvent molecules is strictly necessary to satisfactorily reproduce the properties of the investigated systems. Accordingly, QM/MM-MD simulations are able to capture such effects providing a reliable description of electronic properties–conformational flexibility relationships in all-Th dendrimers.Peer ReviewedPostprint (author's final draft

Desarrollo de sistemas altamente electroactivos a partir de polímeros conductores convencionales

Premi al millor Projecte de Fi de Carrera presentat durant el curs 2008-2009 en l'àmbit de Química que atorga BASF Española, S.L.En el presente proyecto se pretende estudiar las propiedades físicas y químicas de dos de los polímeros conductores más importantes en la actualidad, ya que representan un gran número de aplicaciones dentro del campo tecnológico y biológico, concretamente el PEDOT(3,4 etilenodioxitiofeno) y el poli(N-metilpirrol). El estudio en cuestión pretende evaluar sus propiedades en dos escalas de estructura, por un lado la micrométrica y por otro lado la nanométrica. Actualmente se han realizado estudios sobre dichos polímeros en forma de homopolímero puro y copolímero, sin embargo en el presente proyecto se ha querido evaluar la variación de sus propiedades en forma de sistema multi-capa para las dos escalas con su respectiva comparación con los homopolímeros puros. La primera parte del proyecto consiste en el estudio de la generación de los polímeros conductores citados anteriormente mediante procesos electroquímicos, por lo que se lleva a cabo una evaluación de principios teóricos de electropolimerización, así como la evaluación de las principales técnicas empleadas (ciclovoltamperometría, cronoamperometría,…) para el desarrollo de los sistemas multi-capa en ambas escalas. Una vez se ha realizado el estudio y análisis de las condiciones de los procesos de electropolimerización de los respectivos sistemas se procede al estudio de la microestructura de los polímeros conductores citados anteriormente. Para ello se han empleado dos técnicas de microscopía, por un lado la microscopía de barrido (SEM) y por otro lado la microscopía de fuerzas atómicas (AFM). A partir de aquí se ha podido evaluar características tales como la morfología, topografía y rugosidad que ha permitido esclarecer, evaluar y justificar las diferencias observadas de las respectivas propiedades físicas y químicas en ambas escalas. Finalmente se ha llevado a cabo el estudio de las propiedades físicas (electroactividad, estabilidad temporal, conductividad…) y químicas (enlace, reactividad….) para las dos escalas estudiadas, lo que ha permitido justificar y poner de manifiesto las enormes diferencias que se establecen en las propiedades físicas y químicas de un mismo material cuando se evalúan en escalas estructurales tan diferentes como son la escala micrométrica y nanométrica. Este hecho abre una puerta de aplicaciones a campos tecnológicos tan importantes como la electrónica o la microelectrónica donde el empleo y la utilización de microcomponentes resulta de vital importancia.Award-winnin

One-step synthesis of highly reduced graphene hydrogels for high power supercapacitor applications

Graphene hydrogels with high electrical conductivity were prepared by a one-step process using hydrazine hydrate as gel assembly agent (GH-HD). Conventional two-step process of gel formation and further reduction to prepare highly conducting gels was replaced by a single step involving equivalent amount of hydrazine. Optimized graphene oxide concentration was established to facilitate such monolith formation. Extensive characterization and control studies enabled understanding of the material properties and gel formation mechanism. The synthesized gel shows a high electrical conductivity of 1141 S/m. The supercapacitor based on GH-HD delivers a high specific capacitance of 190 F/g at a current density of 0.5 A/g and 123 F/g at very high current density of 100 A/g. Furthermore, excellent power capability and cyclic stability were also observed. 3D macroporous morphology of GH-HD makes it ideal for high rate supercapacitor applications

High performance of symmetric micro supercapacitors based on silicon nanowires using N-methyl-N-propylpyrrolidinium bis(trifluoromethylsulfonyl)imide as electrolyte

This work describes the development and performance of a symmetric microsupercapacitor made of nanostructured electrodes based on silicon nanowires (SiNWs) deposited using chemical vapor deposition (CVD) on silicon substrates. The performance of the SiNWs micro-supercapacitor employing an aprotic ionic liquid (N-methyl-N-propylpyrrolidinium bis(trifluoromethylsulfonyl)imide) (PYR13TFSI) as an electrolyte was able to deliver a maximal power density of 182 mW cm-2 and a specific energy of 190 µJ cm-2 operating at a wide cell voltage of 4V with a quasi-ideal capacitive behaviour. The lifetime of the device exhibited a remarkable electrochemical stability retaining 75 % of the initial capacitance after several million galvanostatic charge-discharge cycles at a high current density of 1 mA cm-2. Furthermore, a coulombic efficiency of approximately 99 % was obtained after galvanostatic cycling test without structural degradation on the morphology of SiNWs

Ion Sieving Effects in Chemically Tuned Pillared Graphene Materials for Electrochemical Capacitors

Supercapacitors offer high power densities but require further improvements in energy densities for widespread commercial applications. In addition to the conventional strategy of using large surface area materials to enhance energy storage, recently, matching electrolyte ion sizes to material pore sizes has been shown to be particularly effective. However, synthesis and characterization of materials with precise pore sizes remain challenging. Herein, we propose to evaluate the layered structures in graphene derivatives as being analogous to pores and study the possibility of ion sieving. A class of pillared graphene based materials with suitable interlayer separation were synthesized, readily characterized by X-ray diffraction, and tested in various electrolytes. Electrochemical results show that the interlayer galleries could indeed sieve electrolyte ions based on size constrictions: ions with naked sizes that are smaller than the interlayer separation access the galleries, whereas the larger ions are restricted. These first observations of ion sieving in pillared graphene-based materials enable efficient charge storage through optimization of the d-spacing/ion size couple

Ultracapacitors made with Hybrid conducting polymer–clay exfoliated nanocomposites

Ultracapacitors form exfoliated nanocomposites of poly(3,4-ethylenedioxythiophene) (PEDOT), and montmorillonite (MMT), have been fabricated, and have been characterized by electrochemical and macroscopic methods, found to present very good electrical properties (e.g. the specific capacitance), evidencing the favorable effect of the clay, and the thinness of the film.Peer Reviewe

SiNWs-based electrochemical double layer micro-supercapacitors with wide voltage window (4V) and long cycling stability using a protic ionic liquid electrolyte

The present work reports the use and application of a novel protic ionic liquid (triethylammonium bis(tri fluoromethylsulfonyl)imide; NEtH TFSI) as an electrolyte for symmetric planar micro-supercapacitors based on silicon nanowire electrodes. The excellent performance of the device has been successfully demonstrated using cyclic voltammetry, galvanostatic charge-discharge cycles and electrochemical impedance spectroscopy. The electrochemical characterization of this system exhibits a wide operative voltage of 4 V as well as an outstanding long cycling stability after millions of galvanostatic cycles at a high current density of 2 mA cm. In addition, the electrochemical double layer micro-supercapacitor was able to deliver a high power density of 4 mWcm in a very short time pulses (a few ms). Our results could be of interest to develop prospective on-chip micro-supercapacitors using protic ionic liquids as electrolytes with high performance in terms of power and energy densities

Morphology and growing of nanometric multilayered films formed by alternated layers of poly(3,3-ethylenedioxythiophene) and poly(N-methylpyrrole)

Multilayered nanometric films formed by alternated layers of conducting poly(3,4- ethylenedioxythiophene) and poly(N-methylpyrrole) doped with perchlorate anions (ml- PEDOT/PNMPy) have been prepared using a layer-by-layer electrodeposition technique combined with a very small polymerization time. The mechanisms of formation and growth of the resulting multilayered systems have been investigated using Atomic Force Microscopy (AFM), and compared with those obtained for the corresponding homopolymers, which were prepared using identical experimental conditions. Furthermore, the local conductivity, electroactivity and electrostability have been also examined. Analyses of the morphology, topography and roughness of the surfaces indicate that the formation and growth of the multilayered films strongly depends on the number of layers as well as on the chemical nature of the conducting polymer. Interestingly, AFM reflects that the formation and growth of the ml-PEDOT/PNMPy films are significantly different from those of PEDOT and PNMPy homopolymers. The electrical and electrochemical properties of the systems under study are fully consistent with the proposed mechanisms. Results evidenced that multilayered systems formed by two conducting polymers are more advantageous from a technological point of view than the corresponding copolymers

Morphology and growing of nanometric multilayered films formed by alternated layers of poly(3,3-ethylenedioxythiophene) and poly(N-methylpyrrole)

Multilayered nanometric films formed by alternated layers of conducting poly(3,4- ethylenedioxythiophene) and poly(N-methylpyrrole) doped with perchlorate anions (ml- PEDOT/PNMPy) have been prepared using a layer-by-layer electrodeposition technique combined with a very small polymerization time. The mechanisms of formation and growth of the resulting multilayered systems have been investigated using Atomic Force Microscopy (AFM), and compared with those obtained for the corresponding homopolymers, which were prepared using identical experimental conditions. Furthermore, the local conductivity, electroactivity and electrostability have been also examined. Analyses of the morphology, topography and roughness of the surfaces indicate that the formation and growth of the multilayered films strongly depends on the number of layers as well as on the chemical nature of the conducting polymer. Interestingly, AFM reflects that the formation and growth of the ml-PEDOT/PNMPy films are significantly different from those of PEDOT and PNMPy homopolymers. The electrical and electrochemical properties of the systems under study are fully consistent with the proposed mechanisms. Results evidenced that multilayered systems formed by two conducting polymers are more advantageous from a technological point of view than the corresponding copolymers