DESIGN AND SYNTHESIS OF POLYMER, CARBON AND COMPOSITE ELECTRODES FOR HIGH ENERGY AND HIGH POWER SUPERCAPACITORS

Supercapacitors (SCs) are promising energy storage devices because they deliver energy faster than Li-ion batteries and store larger amounts of charge compared to dielectric capacitors. SCs are classified in electrical double layer capacitors (EDLCs) and pseudocapacitors, based on their charge storage mechanism. EDLCs store charge electrostatically, i.e. by physical charge separation. This mechanism limits the storable amount of energy to the available surface area of the electrode, typically made of carbon materials, but grants good cycling stability of the SC device. Pseudocapacitor electrodes, commonly made of conducting polymers or metal oxides, store charge faradaically, i.e. through redox reactions throughout the bulk material, which allows them to store significantly larger amounts of energy than EDLCs, but their stability is compromised due to the partial irreversibility of the faradaic processes. To accomplish the commercialization of SCs, devices must show a combination of high charge storage capacities and long-term stability, besides being cost-effective. To tackle the current issues of SCs, this field of study has taken mainly two directions: 1) the development of new architectures and nanostructures of the active materials, which has shown to increase the surface area, enhance stability, and facilitate ion diffusion; and 2) fabrication of composites between non-faradaic (carbon), faradaic materials, and/or redox-active components to achieve a balance between the amount of energy stored and the stability. Following the first approach, a continuous process to grow vertically aligned carbon nanotubes (VACNTs) on cost-effective aluminum foil was developed. The resulting electrodes were analyzed as SC electrodes and in symmetric cells, and the influence of the arrangement of the nanotubes and the synthesis conditions was studied. The performance of the VACNTs produced continuously showed similar performance to the VACNTs produced stationarily and the ordered structure of the VACNTs showed superior performance compared to randomly oriented CNTs. To increase the energy density, the second approach was taken, by combining pre-synthesized conducting polymers (CPs) and carbon nanotubes (CNTs) using a facile scalable dispersion filtration method to produce free-standing electrodes. Composites with the three main CPs were prepared, analyzed in various electrolytes, and their performance was comparable with polymer/ CNT films prepared with more complex techniques such as in-situ polymerization and pellet pressing. Then, based on the idea that the quinone molecules present in lignin store charge by undergoing a 2 proton, 2 electron redox reaction, a composite between polypyrrole, a stable conducting polymer, and the prototypical molecule p-benzoquinone was fabricated by electropolymerization of pyrrole in the presence of the redox molecule. A significant increase in capacitance and capacity was obtained with respect to polypyrrole films. Furthermore, an important obstacle in the application of CPs in SCs is the lack of easily reduced (n-dopable) polymers. Poly(aminoanthraquinone) (PAQ) is a conjugated polymer that shows electroactivity in the negative potential range of 0 to -2 V, due to the redox moieties of the polymer. PAQ was electropolymerized on free-standing CNT films and its performance as anode for SCs was studied. The materials and processing techniques described in this dissertation are useful to further develop high power/high energy electrodes for SCs

Defect-engineered graphene for bulk supercapacitors with high energy and power densities

The development of high-energy and high-power density supercapacitors (SCs) is critical for enabling next-generation energy storage applications. Nanocarbons are excellent SC electrode materials due to their economic viability, high-surface area, and high stability. Although nanocarbons have high theoretical surface area and hence high double layer capacitance, the net amount of energy stored in nanocarbon-SCs is much below theoretical limits due to two inherent bottlenecks: i) their low quantum capacitance and ii) limited ion-accessible surface area. Here, we demonstrate that defects in graphene could be effectively used to mitigate these bottlenecks by drastically increasing the quantum capacitance and opening new channels to facilitate ion diffusion in otherwise closed interlayer spaces. Our results support the emergence of a new energy paradigm in SCs with 250% enhancement in double layer capacitance beyond the theoretical limit. Furthermore, we demonstrate prototype defect engineered bulk SC devices with energy densities 500% higher than state-of-the-art commercial SCs without compromising the power density.Comment: 15 pages, 5 figures, and 8 supplemental figure

Diagnóstico técnico del acueducto comunitario de San Fernando del municipio de Dosquebradas

CD-T 628.14 V543; 108 pEn el 2012 Colombia fue el tercer país más vulnerable del mundo en lo que respecta al cambio climático, siendo semestralmente embestida por sequías, lluvias, inundaciones y otros fenómenos de riesgo ambiental. Esta situación invita a reflexionar en la forma cómo las comunidades se encuentran gestionando los recursos naturales, especialmente del agua por medio de acueductos comunitarios. El presente proyecto se acerca a este propósito desde la Ingeniería Civil. A través de un amplio diagnóstico técnico, se aborda la infraestructura de la captación, tratamiento y distribución del sistema del acueducto ¿San Fernando¿, en el municipio de Dosquebradas. Un sector ampliamente poblado del segundo municipio en importancia de Risaralda, y que cuenta con un número aproximado de 600 usuarios.Universidad Libre Seccional Pereir

Redox electrode materials for supercapatteries

Redox electrode materials, including transition metal oxides and electronically conducting polymers, are capable of faradaic charge transfer reactions, and play important roles in most electrochemical energy storage devices, such as supercapacitor, battery and supercapattery. Batteries are often based on redox materials with low power capability and safety concerns in some cases. Supercapacitors, particularly those based on redox inactive materials, e.g. activated carbon, can offer high power output, but have relatively low energy capacity. Combining the merits of supercapacitor and battery into a hybrid, the supercapattery can possess energy as much as the battery and output a power almost as high as the supercapacitor. Redox electrode materials are essential in the supercapattery design. However, it is hard to utilise these materials easily because of their intrinsic characteristics, such as the low conductivity of metal oxides and the poor mechanical strength of conducting polymers. This article offers a brief introduction of redox electrode materials, the basics of supercapattery and its relationship with pseudocapacitors, and reviews selectively some recent progresses in the relevant research and development

Can Faradaic Processes in Residual Iron Catalyst Help Overcome Intrinsic EDLC Limits of Carbon Nanotubes?

The promise of multiwalled carbon nanotubes (MWNTs) for supercapacitor electrodes remains unfulfilled due to their poor energy density, which is limited by their redox inactivity. Here, we show a simple, alternative path to achieve Faradaic charge storage by harnessing intrinsic heterogeneity (e.g., Fe catalyst) of as-synthesized MWNTs, obviating the challenges of combining disparate materials in hybrid composite electrodes. In acidic solutions, MWNTs are ruptured by voltammetric cycling beyond the electrolysis limit, thereby exposing residual catalyst nanoparticles. The addition of Faradaic charge storage associated with the Fe²⁺/Fe³⁺ transition, results in a 4-fold increase in peak capacitance of MWNT electrodes (290 F/g) compared to purified MWNT electrodes (70 F/g), along with a 60% increase in charge capacity