FABRICATION AND CHARACTERIZATION OF MANGANESE OXIDE SURFACES FROM POLYMER-BASED FIBER PRECURSORS

Supercapacitors are an energy storage technologycombining properties of both capacitors and batteries to deliver high power and energydensities. Supercapacitors store charge through electrostatic and faradaic interactions between the electrode and ionic electrolyte. By improving the physical structure of electrodes, the interfacial area where energy storage occurs can be increased and electrochemical performance improved. New, fibrous, manganese oxide web-based structures tested for use as a supercapacitor electrode were fabricated by electrospinning and direct calcinationof metal salt-containing polymer fibers, and the effects of fabrication parameters on electrochemical performance were investigated. Data show that high polymer concentrations and low oxide precursor concentrations during electrospinning form porous fibers with increased surface area, resulting in capacitance values up to 76 % greater than electrodes prepared with low polymer and high precursor concentrations. Post-electrospinning vapor melting treatments improved mechanical stability of the fiber mats to prevent delamination during calcination, increasing active mass of the prepared electrodes and improving performance by over 50 %. Calcining the structures for at least 4 h improves structural and electrical properties, increasing capacitance by up to 140 % compared to 2 h calcination, but extended calcination times past 4 h have no further beneficial effects.Electrochemical impedance spectroscopy and linear sweep voltammetry on electrospun web electrodes areused to extract system parameters including double layer capacitance and charge transfer resistance. The measured parameters are combined with mathematical models to develop a theoretical description of discharge behavior in electrospun electrodes with varying fiber sizes, porosities, and materials. Modeled discharge curves are used to calculate power and energy densities over current densities ranging from 5 to 5000 A/g and predict that the electrospun electrodes should exhibit remarkably stable power density over a large range of energy densities. The geometry of a fabricated electrode is used to predict relationships between fiber diameter, ivporosity, and surface area. The predictions are used to examine the effect of fiber diameter on the performance of an electrospun system. At low porosity, electrode energy density is maximized by minimizing void space in the electrode. Parametric manipulation of the model shows thatimprovements to electrode conductivity and the material’s specific capacitance are promising, high-impact areas for optimization, while electrolyte conductivity and exchange current density have minimal effects. The model is also expanded to MnO2, Fe2O3, Co3O4, V2O5, and WO3in order to predict suitability for use in electrospun web electrodes. The unexpectedly good performance of low-capacitance materials with high conductivities reveals the complex relationship between material parameters and electrospun electrode performance. The model is useful for predicting the effects of changing electrospun electrode parameters while decreasing the amount of necessary experimentation.The work presented in this dissertation has demonstrated the suitability of electrospun structures for use assupercapacitor electrodesand provides insight into the fabrication conditions that improve capacitance. The model produced is a powerful tool for predicting materials and fiber sizes that are well-suited to the application, providing the potential for electrospun electrode fabrication methods to be expanded into higher-performing materials for improved low cost energy storage

Advances in Supercapacitor Technology and Applications

Energy storage is a key topic for research, industry, and business, which is gaining increasing interest. Any available energy-storage technology (batteries, fuel cells, flywheels, and so on) can cover a limited part of the power-energy plane and is characterized by some inherent drawback. Supercapacitors (also known as ultracapacitors, electrochemical capacitors, pseudocapacitors, or double-layer capacitors) feature exceptional capacitance values, creating new scenarios and opportunities in both research and industrial applications, partly because the related market is relatively recent. In practice, supercapacitors can offer a trade-off between the high specific energy of batteries and the high specific power of traditional capacitors. Developments in supercapacitor technology and supporting electronics, combined with reductions in costs, may revolutionize everything from large power systems to consumer electronics. The potential benefits of supercapacitors move from the progresses in the technological processes but can be effective by the availability of the proper tools for testing, modeling, diagnosis, sizing, management and technical-economic analyses. This book collects some of the latest developments in the field of supercapacitors, ranging from new materials to practical applications, such as energy storage, uninterruptible power supplies, smart grids, electrical vehicles, advanced transportation and renewable sources

Directed evolution of ancestral and modern enzymes

Tesis Doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Biología Molecular. Fecha de lectura: 18-10-2019Esta tesis tiene embargado el acceso al texto completo hasta el 18-04-2021Ancestral sequence reconstruction (ASR) and resurrection (i.e. functional expression in a heterologous host) allows enzymes with different properties to be disclosed while its combination with directed evolution may lead to the development of a new generation of biocatalysts. In this Doctoral Thesis we have explored the combination of such powerful methods using as blueprints two different enzyme systems, Rubisco and laccase. In the first chapter of this Thesis we reconstructed and resurrected (in Escherichia coli) Precambrian Rubisco nodes which were evolved in parallel with the extant Rubisco counterpart. An in vitro dual high-throughput screening (HTS) method was set out to identify thermostable and functional variants after- applying a palette of directed evolution strategies. The stronger tolerance to mutational loads, the improved expression and the different kinetic behavior were some of the traits that highlighted in the Precambrian enzyme. Particularly, the evolved ancestral Clone B2 stood out as a case study of this elusive protein due to its alternative performance in the classical equilibrium of Rubisco kinetic constants. In the second chapter we focused ASR and directed evolution on basidiomycete laccases. Firstly, ancestral nodes from the Paleozoic were reconstructed and resurrected in Saccharomyces cerevisiae. The resurrected enzymes showed a higher heterologous expression and a broader pH stability profile than the modern -laboratory evolved- counterpart. The most promising ancestral node was subjected to structure-guided evolution for the oxidation of β–diketones, an unusual type of redox mediators capable to initiate the polymerization of vinyl monomers. The final chapter of the Thesis deals with consensus design, a long-standing protein engineering method to increase stability without compromising activity. We applied an in-house consensus method to stabilize a laboratory evolved high-redox potential laccase. Multiple sequence alignments were carried out and computationally refined by applying relative entropy and mutual information thresholds. Through this approach, an ensemble of 20 consensus mutations were identified, 18 of which were consensus ancestral mutations. After analyzing potential epistasis by site directed recombination in vivo, the best mutant was characterized displaying dramatically improved thermostability, kinetic values and secretion levels.La reconstrucción y resurrección (i.e. expresión funcional en un hospedador heterólogo) de secuencias ancestrales permite obtener enzimas con diferentes propiedades que al ser combinadas con la evolución dirigida pueden dar lugar al desarrollo de una nueva generación de biocatalizadores. En la presente Tesis Doctoral hemos explorado la combinación de estos potentes métodos usando como modelos dos sistemas enzimáticos diferentes, Rubisco y lacasa. En el primer capítulo se reconstruyeron y resucitaron (en Escherichia coli) nodos de rubiscos Precámbricas con el fin de evolucionarlos en paralelo con una versión moderna de Rubisco. Se desarrolló un método de cribado dual in vitro para poder identificar variantes termoestables y funcionales tras aplicar varias estrategias de evolución dirigida. Las enzimas Precámbricas destacaron por una alta tolerancia a tasas mutagénicas, expresión funcional mejorada y valores cinéticos diferentes a los de las enzimas modernas. En particular, la rubisco ancestral evolucionada, clon B2, despuntó como caso de estudio de esta complicada enzima debido al comportamiento alternativo que muestra con respecto al equilibrio clásico de las constantes cinéticas de la Rubisco. En el segundo capítulo se llevo a cabo la resurrección y evolución dirigida de lacasas de basidiomicetos. En primer lugar se reconstruyeron y resucitaron en Saccharomyces cerevisiae nodos ancestrales del Paleozoico. Las enzimas ancestrales mostraron mayor nivel de expresión heteróloga así como un perfil de estabilidad a diferentes pHs más amplio que el de la versión –evolucionada en el laboratorio- moderna. El nodo ancestral más prometedor fue sometido a evolución estructuralmente guiada para la oxidación de β-dicetonas, un tipo de mediador redox poco usual capaz de iniciar la polimerización de monómeros de vinilo. El capítulo final de la Tesis trata sobre el diseño consenso, un método clásico de ingeniería de proteínas para aumentar la estabilidad sin afectar a la actividad. Se aplicó un método consenso propio para la estabilización de una lacasa de alto potencial redox evolucionada en el laboratorio. Se llevó a cabo un alineamiento de múltiples secuencias que fue refinado computacionalmente mediante el uso de los marcadores de entropía relativa e información mutua. Mediante este procedimiento se identificaron 20 mutaciones consenso, 18 de las cuales corresponden a mutaciones ancestrales-consenso. Se analizó la posible epistasia de estas mutaciones mediante recombinación dirigida in vivo y se caracterizó el mejor mutante que presentó mayores niveles de estabilidad, valores cinéticos y secreciónLa presente Tesis Doctoral se ha llevado a cabo gracias a la financiación recibida a través de una beca para la formación de personal investigador (FPI) del Ministerio de Economía y Competitividad (BES-2014-068887) dentro de los proyectos nacionales DEWRY (BIO2013-43407-R) y LIGNOLUTION (BIO2016-79106-R)

3D Printing Technologies

The family of technologies collectively known as additive manufacturing (AM) technologies, and often called 3D-printing technologies, is rapidly revolutionizing industrial production. AM’s potential to produce intricate and customized parts starting from a digital 3D model makes it one of the main pillars for the forthcoming Industry 4.0. Thanks to its advantages over traditional manufacturing methodologies, AM finds potential applicability in virtually all production fields. As a natural consequence of this, research in this field is primarily focused on the development of novel materials and techniques for 3D printing. This Special Issue of Technologies, titled “3D Printing Technologies”, aims at promoting the latest knowledge in materials, processes, and applications for AM. It is composed of six contributions, authored by influential scientists in the field of advanced 3D printing. The intended audience includes professors, graduate students, researchers, engineers and specialists working in the field of AM

Synthesis of electrolytic manganese dioxide (EMD) and biomass waste-derived carbon for hybrid capacitors

Renewable energy (RE) is expected to be the primary energy supplier in the future energy mix. This has created the necessity for low-cost, safe, and reliable energy storage to guarantee a continuous energy supply by the intermittent RE sources. Due to the inbuilt rich chemistry of manganese dioxide (MnO2) and the advantageous characteristics; of low cost, environmentally friendliness, and nontoxic, it can be adapted for a wide range of applications such as biosensors, humidity sensors, catalysts, and so on. Among the different forms of MnO2, electrolytic manganese dioxide (EMD) is well-demanded energy storage material. However, the limitations such as lower capacitance, irreversibility, and cyclability of EMD in comparison with other metal oxides such as cobalt and nickel oxides, have hindered its application in capacitor energy storage, which was one of the focuses of this thesis. Therefore, this Ph.D. research project aimed at synthesizing modified EMD materials as the positive electrode for hybrid capacitor applications. The modified EMD was coupled with the biomass-derived activated carbon (AC) which is synthesized as the negative electrode to fabricate hybrid capacitors. This Ph.D. research work has contributed to the existing knowledge through the following: 1) synthesizing pristine EMD using galvanostatic electrodeposition and studying its suitability for capacitor applications via experimental and theoretical analysis, 2) biopolymer alginate assisted EMD synthesis and optimization via experimental and computational modeling, 3) studying the effect of varying surfactants to improve the electrochemical characteristics of EMD, 4) synthesis of biomass waste-derived activated carbon and modeling their parameters for capacitance prediction. The results indicated the challenge and importance of the delicate tailoring of the EMD characteristics for capacitor application. Pristine EMD was synthesized under different electrodeposition experiment conditions by varying applied current density (100, 200, 300 A m-2) and deposition duration (4, 5, 6 h). The electrodeposition was carried out in a low acidic medium electrolytic bath where a lead (Pb) anode and stainless steel (SS) cathode were used. The EMD was deposited on the Pb anode via Mn2+ oxidation to form Mn4+ and its oxide MnO2. The physicochemical and electrochemical characterization of the obtained EMD powder concluded that the material deposited at 200 A m-2 for 5 hours, showing the spindle-like morphology was suitable over others for supercapacitor (SC) application. The pristine EMD at these experimental conditions delivered 98 F g-1 capacitance at 1 mA cm-2 applied current density tested in 2 M NaOH aqueous electrolyte and proved its potential development by modifying its characteristics. Therefore, the pristine EMD was modified by introducing the biopolymer alginic acid crosslinking to improve its electrochemical performance. The alginic acid was added to the electrolytic bath at varying concentrations; 0, 0.1, 0.25, 0.5, and 1 g l-1, to optimize the added bio-polymer amount to maximize the capacitance. At 0.5 g l-1, the pristine EMD morphology was rearranged to a cactus-shaped with flutes. The calculated specific capacitance of the modified EMD was ~5 times higher (487 F g-1) than the pristine EMD. The molecular dynamics simulation results determined the polymer-ion interactions in the electrolytic bath and provided evidence, showing that the alginic acid could act as a template for binding the Mn2+ ions in a relatively ordered manner for the growth of the EMD deposit. 0.42 of pyrolusite and 0.58 of ramsdellite fractions present in the modified material were quantitatively determined using the neutron powder diffraction (NPD) data. The slight increments of the lattice spacing observed in high-resolution transmission electron microscopy (HRTEM) images were well aligned with the NPD results of unit cell volume expansions of the EMD-polymer composite showing the polymer intercalation within the EMD structure influencing its characteristics. At 2 mA cm-2, the fabricated hybrid capacitor delivered 52 F g-1 specific capacitance, 14 Wh g-1 specific energy, 500 W g-1 specific power, and 94 % capacitance retention over 5000 cycles. The results highlighted the importance of the functional molecular structure of the biopolymer alginic acid to produce a binary composite of EMD-polymer as a capacitor material. Further, the pristine EMD was modified by electrodepositing the MnO2 using surfactant mediated electrolyte solutions. The electrochemical performance of the synthesized EMD in the presence of three novel cationic surfactants was compared with the pristine EMD and the EMD co-deposited with commonly used cetyltrimethylammonium ammonium bromide (C-AB) surfactant. The three surfactants with different molecular structures are Tetradecyltrimethylammonium bromide (T-AB), Didodecyldimethylammonium bromide (D-AB), Benzyldodecyldimethylammonium bromide (B-AB) used at varying concentrations (15, 30, 60 g l-1) in the electrolytic bath. Among the B-AB surfactant at 30 mg l-1, the EMD (EMD/B-AB30) showed the highest capacitance of 602 F g-1 tested at 1 mA cm-2 current density. The molecular dynamics simulation indicated that when the B-AB surfactant was attached to the Pb electrode via electrostatic, Van der Walls interactions, then the nucleation of MnO2 particles occurred surrounding the surfactant molecule. The unique molecular structure influenced the nucleation formation well-ordered, whereas, for pristine EMD, the nucleation was random. The hybrid capacitor comprises the best performed modified EMD (EMD/B-AB30), and biomass waste-derived AC exhibited 91 F g-1 specific capacitance, an outstanding energy density of 32.4 Wh kg-1 for a corresponding power density of 971 W kg-1. Valorization of the biomass waste, Mango seed husk (MS), and the Grape marc (GM) was carried out by converting the waste into AC for capacitor electrodes. The MS was carbonized, followed by chemical activation using KOH as the activating agent. Activation temperature was varied at 800, 900, 1000, and 1100 °C temperatures, among at 1100 °C highest surface area of 1943 m2 g-1, and the specific capacitance of 135 F g-1 was obtained for the MS-AC. The MS-AC experimental data were incorporated in four machine learning (ML) algorithms; linear regression (LR), decision tree (DT), support vector regression (SVR), and multi-layer perceptron (MLP) for capacitance prediction. Among, the MLP model showed the best correlation (R2 = 0.9868) between the experimental and predicted capacitance values and proved its potential application for computing the complex non-linear relationships between the input and output datasets. Further, the porous carbon materials were derived from GM using four synthesis routes by varying the parameters of activating agent (KOH and ZnCl2), dopant (Nitrogen), and carbonization (450, 600 °C) and activation (450, 800 °C) temperatures. Among the different GM-AC products, the GM carbon, doped with urea and activated by KOH (KACurea), exhibited better morphology, hierarchical pore structure, larger surface area (1356 m2 g-1), and the highest specific capacitance of 139 F g-1 in 2 M NaOH aqueous electrolyte. The miscellaneous collection of datasets based on AC experiments was used for specific capacitance and power prediction using the MLP ML model. Overall, this thesis showed that the EMD could be produced in bulk to be used for hybrid capacitor applications. Particularly, it provided insights about the specie interactions in the electrolyte solution that improved the material performance. This built the platform for further studies on altering the additive concentrations and combinations for developing high-performing EMD materials. This Ph.D. work also highlighted the opportunities to valorize the biomass waste to produce AC with desired characteristics of hierarchical pore structure, larger surface area, etc., to replace the conventional AC electrodes. Finally, the electrochemical performance of the hybrid capacitor fabricated using best performed EMD material (EMD/B-AB30) and biomass-waste derived AC (MS-AC 1100) surpassed the energy density values of the existing supercapacitors, proving its potential development in commercial applications

Reaction mechanisms for catalytic partial oxidation systems : application to ethylene epoxidation

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2005.Includes bibliographical references.With the rapid advances in kinetic modeling, building elementary surface mechanisms have become vital to understand the complex chemistry for catalytic partial oxidation systems. Given that there is selected experimental knowledge on surface species and a large number of unknown thermochemical, rate parameters, the challenge is to integrate the knowledge to identify all the important species and accurately estimate the parameters to build a detailed surface mechanism. This thesis presents computational methodology for quickly calculating thermodynamically consistent temperature/coverage-dependent heats of formation, heat capacities and entropies, correction approach for improving accuracy in heats of formation predicted by composite G3- based quantum chemistry methods, and detailed surface mechanism for explaining selectivity in ethylene epoxidation. Basis of the computational methodology is the Unity Bond Index- Quadratic Exponential Potential (UBI-QEP) approach, which applies quadratic exponential potential to model interaction energies between atoms and additive pairwise energies to compute total energy of an adsorbed molecule. By minimizing the total energy subject to bond order constraint, formulas for chemisorption enthalpies have been derived for surface species bound to on-top, hollow and bridge coordination sites with symmetric, asymmetric and chelating coordination structures on transition metal catalysts. The UBI-QEP theory for diatomics has been extended for polyatomic adsorbates with empirical modifications to the theory.(cont.) Formulas for activation energies have been derived for generic reaction types, including simple adsorption, dissociation-recombination, and disproportionation reactions. Basis of the correction approach is the Bond Additivity Correction (BAC) procedures, which apply atomic, molecular and bond- wise modifications to enthalpies of molecules predicted by G3B3 and G3MP2B3 composite quantum chemistry methods available in Gaussian® suite of programs. The new procedures have improved the accuracy of thermochemical properties for open and closed shell molecules containing various chemical moieties, multireference configurations, isomers and degrees of saturation involving elements from first 3 rows of the periodic table. The detailed mechanism explains the selectivity to ethylene oxide based on the parallel branching reactions of surface oxametallacycle to epoxide and acetaldehyde. Using Decomposition Tree Approach, surface reactions and species have been generated to develop a comprehensive mechanism for epoxidation. As a result of these developments in the thesis, chemisorption enthalpies can now be estimated within 3 kcal/mol of experimental values for transition metal catalysts and enthalpies predicted by G3B3 and G3MP2B3 Gaussian methods can be corrected within 0.5 kcal/mol. Examples of heterogeneous reaction systems involving silver-catalyzed ethylene epoxidation demonstrate the effectiveness of the methodologies developed in this work.by Bharthwaj Anantharaman.Ph.D

Nanoparticle-based electrochemical sensors for the detection of lactate and hydrogen peroxide

In the present study, electrochemical sensors for the detection of lactate and hydrogen peroxide were constructed by exploiting the physicochemical properties of metal ad metal oxide nanoparticles. This study can be divided into two main sections. While chapter 2, 3, and 4 report on the construction of electrochemical lactate biosensors using CeO2 and CeO2-based mixed metal oxide nanoparticles, chapter 5 and 6 show the development of electrochemical hydrogen peroxide sensors by the decoration of the electrode surface with palladium-based nanoparticles. First generation oxidase enzyme-based sensors suffer from oxygen dependency which results in errors in the response current of the sensors in O2-lean environments. To address this challenge, the surface of the sensors must be modified with oxygen rich materials. In this regard, we developed a novel electrochemical lactate biosensor design by exploiting the oxygen storage capacity of CeO2 and CeO 2-CuO nanoparticles. By the introduction of CeO2 nanoparticles into the enzyme layer of the sensors, negative interference effect of ascorbate which resulted from the formation of oxygen-lean regions was eliminated successfully. When CeO2-based design was exposed to higher degree of O2 -depleted environments, however, the response current of the biosensors experienced an almost 21 % decrease, showing that the OSC of CeO2 was not high enough to sustain the enzymatic reactions. When CeO2-CuO nanoparticles, which have 5 times higher OSC than pristine CeO2, were used as an oxygen supply in the enzyme layer, the biosensors did not show any drop in the performance when moving from oxygen-rich to oxygen-lean conditions. In the second part of the study, PdCu/SPCE and PdAg/rGO-based electrochemical H2O2 sensors were designed and their performances were evaluated to determine their sensitivity, linear range, detection limit, and storage stability. In addition, practical applicability of the sensors was studied in human serum. The chronoamperometry results showed that the PdCu/SPCE sensors yielded a high sensitivity (396.7 µA mM -1 cm-2), a wide linear range (0.5 -11 mM), and a low limit of detection (0.7 µM) at the applied potential of -0.3 V. For PdAg/rGO sensors, a high sensitivity of 247.6 ± 2.7 µA˙mM -1˙cm-2 was obtained towards H2O 2 in a linear range of 0.05 mM to 28 mM