Memoria para optar al título de Ingeniero Civil Mecánico / De acuerdo a la necesidad de mitigar la variabilidad de producción de energía eléctrica mediante recursos renovables de naturaleza variable (energía solar y eólica), se analiza la factibilidad técnica de utilizar un sistema de almacenamiento de energía mediante bombeo de calor (Pumped Heat Energy Storage o PHES) utilizando CO2 como fluido de trabajo, lo que permite alcanzar altas eficiencias con bajo riesgo asociado al ciclo y un menor potencial de contaminación ambiental en comparación a otros fluidos de trabajo. El funcionamiento de un sistema PHES, consiste en el uso de bombas de calor para almacenar energía, en forma de calor (normalmente con sales fundidas tipo sal solar), a partir de superávit eléctrico, o bien en condiciones de bajo costo marginal en la red (alta generación de renovables - eólicas o fotovoltaicas). El calor almacenado es transformado nuevamente en energía eléctrica a través de un ciclo de potencia apropiado. Se establecen 6 distintas posibles configuraciones con distintos grados de viabilidad de acuerdo a tres factores: Las ventajas de utilizar el mismo fluido de trabajo en carga y descarga (Ciclo de descarga tipo Rankine de vapor o Brayton de CO2), la limitante tecnológica de la no existencia en el mercado de una turbina de CO2 apropiada (tipo de expansor en la bomba de calor: Turbina o válvula de expansión) y la limitante tecnológica-económica de los compresores de CO2 comerciales, los cuales no alcanzan temperaturas ideales para el uso de sales fundidas como medio de almacenamiento de calor (utilización o no de calentador eléctrico como complemento del compresor en la bomba de calor). Además se explora la posibilidad de utilizar 5 tipos distintos de sales fundidas, algunas de las cuales presentan potencial de ser producidas localmente. Se realizan modelos computacionales de cada configuración y se comparan eficiencias Round-Trip, eficiencia exergética de la bomba de calor y uso de sales fundidas principalmente. Se descartan combinaciones de sales fundidas con configuraciones que resultan inviables y se obtienen eficiencias Round-Trip entre 40 y 63% para aquellas viables, siendo la configuración con mayor eficiencia la con bomba de calor sin modificaciones y ciclo Rankine estándar (no considera restricciones), seguida por la configuración equivalente pero con calentador eléctrico (eficiencias 3-5% menores considerando restricción del compresor). Luego, las más prometedoras son aquellas con descarga Brayton, con eficiencias 4-7% inferiores que las con ciclo Rankine y presentando la posibilidad de utilizar los mismos equipos tanto en carga como descarga (ciclo Brayton reversible), aunque con mayores presiones de trabajo (asociado a mayores costos). Se considera necesario un estudio económico con mayor profundidad para determinar la conveniencia o no de este tipo de ciclos, así como también cuantificar las ventajas y desventaja de cada uno de los casos estudiados. Por último, de las 5 sales evaluadas, se detecta gran potencial en sales de litio (eficiencias 2-5% menores que sal solar con un requerimiento de flujo aproximadamente 40% menor) que podrían ser producidas en Chile dada la disponibilidad de materia prima.

The rapid influx of solar energy and the desire to utilize carbon dioxide (CO2) will require large-scale energy storage and CO2 conversion technologies. Electrocatalytic devices can substantially impact both challenges, but improvements to electrocatalyst cost, activity, and selectivity are needed. Transition metal carbides provide a unique framework to reduce the loading of expensive catalyst metals while tuning the electrocatalytic activity and selectivity. Transition metal nitrides have many similar properties as carbides, and their synthesis inherently avoids the unwanted carbonaceous overlayer associated with carbide synthesis. Here it is shown that carbides and nitrides enable lower platinum-group metal (PGM) loadings and improve the activity and selectivity of electrocatalysts for reactions of water electrolysis and electrochemical CO2 reduction. Atom-thick layers of Pt were deposited onto niobium carbide (NbC) thin films to assess hydrogen evolution reaction (HER) activity. The Pt/NbC thin film, with one monolayer of Pt on NbC, performed similarly to bulk Pt. This correlated well with density functional theory (DFT) calculations of the hydrogen binding energy on the Pt/NbC surface. Potential applications of transition metal nitrides as electrocatalyst support materials were explored by synthesizing thin film nitrides of niobium and tungsten. The stability of each nitride was evaluated across broad potential-pH regimes to create a pseudo-Pourbaix diagram for each one. The films were each modified with atom-thick layers of Pt and were evaluated for HER performance in acid and alkaline electrolyte. Thin layers of Pt on WN and NbN showed Pt-like HER performance in acid and are promising candidates for high-surface area catalysts. To address the issue of high iridium (Ir) loading for the oxygen evolution reaction (OER) at the water electrolyzer anode, core-shell Ir-metal nitride particles were synthesized that contained 50% of the Ir mass loading of benchmark IrO¬2 particles. Iridium-iron nitride (Ir/Fe4N) showed increased activity on a mass-Ir basis and on a per-site basis, compared to IrO2. The core-shell morphology and stability under reaction conditions were confirmed with electron microscopy and in-situ X-ray absorption spectroscopy. Electrochemical reduction of CO2 to a mixture of CO and H¬2 (synthesis gas) was achieved on the palladium hydride (PdH) electrocatalyst. The product mixture can then be used as feedstock for the Fischer–Tropsch process and methanol synthesis. The syngas production performance was optimized by evaluating shape controlled PdH particles, bimetallic PdH, and PdH supported on transition metal carbides. At each step, the phase transition from Pd to PdH was monitored under reaction conditions with synchrotron-based X-ray absorption spectroscopy and X-ray diffraction. We also performed an overall carbon balance for catalytic transformation of CO2 to methanol via four reaction schemes, including one relying on electrocatalytic syngas production. The analysis revealed that hybrid electrocatalytic/thermocatalytic processes are most promising for resulting in overall CO2 reduction, but current densities of recently reported electrocatalysts need to increase to make the process economically feasible.

Current demands on lithium ion battery (LIB) technology include high capacity retention over a life time of many charge and discharge cycles. Maximizing battery longevity is still a major challenge partly due to electrode degradation as a function of repeated cycling. The intercalation of lithium ions into an active material causes the development of stress and strain in active electrode materials which can result in fracture and shifting that can in turn lead to capacity fade and eventual cell failure. The processes leading to active material degradation in cycling LIBs has been studied using a combination of acoustic emission (AE) and in situ X-ray diffraction (XRD) techniques. Safe, low cost custom electrochemical cells were designed and developed for use in battery AE and XRD experiments. These tools were used to monitor the time of material fracture through AE and link these events to lattice strain and phase composition as determined by XRD. Both anode and cathode materials were studied with an emphasis on graphite, silicon, and Li(Mn1.5Ni0.5)O4, and tin. A thermal analogy model for lithiation/delithiation induced fracture of spherical particles capable of predicting when AE should be detected in a cell containing a composite silicon electrode. The results of this work were used to develop an understanding of when and how active materials are degrading as well as to suggest methods of improving their performance and operational longevity.

To meet the predicted increase in demand for energy storage in tomorrow's society, the development of inexpensive, flexible, lightweight and sustainable energy-storage materials is essential. In this respect, devices based on electroactive organic molecules, such as conducting polymers, are highly interesting. The aim of this thesis was to evaluate the use of nanocellulose as a matrix material in composites of cellulose and the electroactive polymer polypyrrole (PPy), and the use of these composites in all-polymer paper-based energy-storage devices.   Pyrrole was polymerized using FeCl3 onto cellulose nanofibers in the form of a hydrogel. The resulting PPy-coated fibers were washed with water and dried into a high surface area, conductive paper material. Variations in the drying technique provided a way of controlling the porosity and the surface area of wood-based cellulose nanofibers, as the properties of the cellulose were found to have a large influence on the composite structure. Different nanocellulose fibers, of algal and wood origin, were evaluated as the reinforcing phase in the conductive composites. These materials had conductivities of 1–6 S/cm and specific surface areas of up to 246 m2/g at PPy weight fractions around 67%.   Symmetrical supercapacitor devices with algae-based nanocellulose-PPy electrodes and an aqueous electrolyte showed specific charge capacities of around 15 mAh/g and specific capacitances of around 35 F/g, normalized with respect to the dry electrode weight. Potentiostatic charging of the devices was suggested as a way to make use of the rapid oxidation and reduction processes in these materials, thus minimizing the charging time and the effect of the IR drop in the device, and ensuring charging to the right potential. Repeated charging and discharging of the devices revealed a 10–20% loss in capacity over 10 000 cycles. Upon up-scaling of the devices, it was found that an improved cell design giving a lower cell resistance was needed in order to maintain high charge and discharge rates.   The main advantages of the presented concept of nanocellulose-PPy-based electrical energy storage include the eco-friendly raw materials, an up-scalable and potentially cost-effective production process, safe operation, and the controllable porosity and moldability offered by the nanocellulose fiber matrix. Integrating energy storage devices into paper could lead to un- precedented opportunities for new types of consumer electronics. Future research efforts should be directed at increasing the energy density and improving the stability of this type of device as well as advancing the fundamental understanding of the current limitations of these properties.

The objective of this study is to synthesize nanomaterials by mixing molten salt (alkali nitrate salt eutectics) with inorganic nanoparticles. The thermo-physical properties of the synthesized nanomaterials were characterized experimentally. Experimental results allude to the existence of a distinct compressed phase even for the solid phase (i.e., in the nanocomposite samples). For example, the specific heat capacity of the nanocomposites was observed to be enhanced after melting and re-solidification - immediately after their synthesis; than those of the nanocomposites that were not subjected to melting and re-solidification. This shows that melting and re-solidification induced molecular reordering (i.e., formation of a compressed phase on the nanoparticle surface) even in the solid phase - leading to enhancement in the specific heat capacity. Numerical models (using analytical and computational approaches) were developed to simulate the fundamental transport mechanisms and the energy storage mechanisms responsible for the observed enhancements in the thermo-physical properties. In this study, a simple analytical model was proposed for predicting the specific heat capacity of nanoparticle suspensions in a solvent. The model explores the effect of the compressed phase – that is induced from the solvent molecules - at the interface with individual nanoparticles in the mixture. The results from the numerical simulations indicate that depending on the properties and morphology of the compressed phase – it can cause significant enhancement in the specific heat capacity of nanofluids and nanocomposites. The interfacial thermal resistance (also known as Kapitza resistance, or “Rk”) between a nanoparticle and the surrounding solvent molecules (for these molten salt based nanomaterials) is estimated using Molecular Dynamics (MD) simulations. This exercise is relevant for the design optimization of nanomaterials (nanoparticle size, shape, material, concentration, etc.). The design trade-off is between maximizing the thermal conductivity of the nanomaterial (which typically occurs for nanoparticle size varying between ~ 20-30nm) and maximizing the specific heat capacity (which typically occurs for nanoparticle size less than 5nm), while simultaneously minimizing the viscosity of the nanofluid. The specific heat capacity of nitrate salt-based nanomaterials was measured both for the nanocomposites (solid phase) and nanofluids (liquid phase). The neat salt sample was composed of a mixture of KNO3: NaNO3 (60:40 molar ratio). The enhancement of specific heat capacity of the nanomaterials obtained from the salt samples was found to be very sensitive to minor variations in the synthesis protocol. The measurements for the variation of the specific heat capacity with the mass concentration of nanoparticles were compared to the predictions from the analytical model. Materials characterization was performed using electron microscopy techniques (SEM and TEM). The rheological behavior of nanofluids can be non-Newtonian (e.g., shear thinning) even at very low mass concentrations of nanoparticles, while (in contrast) the pure undoped (neat) molten salt may be a Newtonian fluid. Such viscosity enhancements and change in rheological properties of nanofluids can be detrimental to the operational efficiencies for thermal management as well as energy storage applications (which can effectively lead to higher costs for energy conversion). Hence, the rheological behavior of the nanofluid samples was measured experimentally and compared to that of the neat solvent (pure molten salt eutectic). The viscosity measurements were performed for the nitrate based molten salt samples as a function of temperature, shear rate and the mass concentration of the nanoparticles. The experimental measurements for the rheological behavior were compared with analytical models proposed in the literature. The results from the analytical and computational investigations as well as the experimental measurements performed in this proposed study – were used to formulate the design rules for maximizing the enhancement in the thermo-physical properties (particularly the specific heat capacity) of various molten salt based inorganic nanomaterials. The results from these studies are summarized and the future directions are identified as a conclusion from this study.

The performances of current electrical energy storage systems (both batteries and electrochemical capacitors) are not capable of meeting the ever-increasing demands of emerging technologies. This is because batteries often suffer from slow power delivery, limited life-time, and long charging time whereas electrochemical capacitors suffer from low energy density. While extensive efforts have been made to the development of novel electrode materials, progress has been hindered by the lack of a profound understanding on the complex charge storage mechanism. Therefore, the main objective of this research is to develop novel electrode materials which can exhibit both high energy and power density with prolonged life-time and to gain a fundamental understanding of their charge storage mechanism. First, nanostructured, thin, and conformal coatings of transition metal oxides have been deposited onto three-dimensional porous substrates of current collectors to form composite electrodes. The structures and compositions of the oxide coatings are further altered by a controlled annealing process and characterized by electron microscopy and spectroscopy, laboratory X-ray diffraction, gas adsorption analysis, and in-situ and ex-situ synchrotron-enabled X-ray diffraction and absorption spectroscopy. The structural features have also been correlated with the electrochemical behavior of the transition metal oxides as an electrode in an electrochemical capacitor. It is found that the electrochemical performance of the composite electrodes depends sensitively on the composition, nanostructure, and morphology of the oxide coatings. When optimized, the electrodes displayed the highest energy and power density with excellent cycling life among all materials reported for electrochemical capacitors. Finally, new charge storage mechanisms have also been proposed for the novel electrode materials based on insights gained from in-situ synchrotron-based X-ray absorption spectroscopy.

This dissertation investigates the distribution and transmission systems reliability and economic impact of energy storage and renewable energy integration. The reliability and economy evaluation framework is presented. Novel operation strategies of energy storage and renewable energy are proposed. The method for optimizing the energy storage sizing and operation strategy in order to achieve optimal reliability and economy level is developed. The objectives of the movement towards the smart grid include making the power systems more reliable and economically efficient. The rapid development of the large scale energy storage technology makes it an excellent candidate in achieving these goals. A novel Model Predictive Control (MPC)-based operation strategy is proposed to optimally manage the charging and discharging operation of energy storage in order to minimize the energy purchasing cost for a distribution system load aggregator in power markets. Different operation strategies of energy storage have different reliability and economic impact on power systems. Simulation results illustrate the importance of the energy storage operation strategies. A hybrid operation strategy which combines the MPC-based operation strategy and the standby backup operation strategy is proposed to flexibly adjust the reliability and economic improvement brought by energy storage. A particle swarm optimization approach is developed to determine the optimal energy storage sizing and operation strategy while maximizing reliability and economic improvement. A reliability and economy assessment framework based on sequential Monte Carlo method integrated with the operation strategies is proposed. The impact on the transmission systems reliability brought by energy storage and renewable energy with the proposed operation strategies is investigated. Case studies are conducted to demonstrate the effectiveness of the proposed operation strategies, optimization approach, and the reliability and economy evaluation framework. Insights into how energy storage and renewable energy affect power system reliability and economy are obtained.

Porous carbons are versatile materials with applications in different fields. They are used in filtration, separation and sequestration of fluids and gases, as conductive additives in many energy storage materials, as coloring agents, as pharmaceutical and food additives, and in many other vital technologies. Porous carbons produced by pyrolysis and activation of organic precursors commonly suffer from poorly controlled morphology, microstructure, chemistry, and pore structure. In addition, the poorly controlled parameters of porous carbons make it challenging to elucidate the underlying key physical parameters controlling their performance in energy storage devices, including electrochemical capacitors (ECs) and lead-acid batteries (LABs). Zeolite-templated carbons (ZTCs) are a novel class of porous carbon materials with uniform and controllable pore size, microstructure, morphology, and chemistry. In spite of their attractive properties, they have never been explored for use in LABs and their studies for ECs have been very limited. Here I report a systematic study of ZTCs applications in ECs operating at temperatures as low as - 70 C and in LABs. Greatly improved power and energy performance, compared to state of the art devices, has been demonstrated in the investigated ECs. Moreover, the application of ZTCs in LABs has resulted in a dramatic enhancement of their cycle life and power and energy densities.

A method has been developed, Physical Hybrid Model, to investigate the physical large scale electrical effects of a Battery Energy Storage System (BESS) on a distribution grid by scaling the response from a small size Research Development and Demonstration (RD&D) platform. In order to realize the model the control system of an existing RD&D platform was refurbished and stability of components ensured. The Physical Hybrid Model proceeds as follows: Data from a distribution grid are collected. A BESS cycle curve is produced based on analyzed measurements. Required BESS power and capacity in investigated grid is scaled down by factor k to that of the physical test installation of the RD&D platform. The scaled BESS cycle is sent as input to control of the battery cycling of the RD&D platform. The response from the RD&D platform is scaled – up, and used in simulation of the distribution grid to find the impact of a BESS. The model was successfully implemented on a regional distribution grid in southern Sweden.

At the time of this writing, increasing pressure for fuel efficient passenger vehicles has prompted automotive manufactures to invest in the research and development of electrically propelled vehicles. This includes vehicles of strictly electric drive and hybrid electric vehicles with internal combustion engines. To investigate some of the many technological innovations possible with electric power trains, the AUTO21 network of centres of excellence funded project E301-EHV; a project to convert a Chrysler Pacifica into a hybrid electric vehicle. The converted vehicle is intended for use as a test-bed in the research and development of a variety of advances pertaining to electric propulsion. Among these advances is hybrid energy storage, the focus of this investigation. A key difficulty of electric propulsion is the portable storage or provision of electricity, challenges are twofold; (1) achieving sufficient energy capacity for long distance driving and (2) ample power delivery to sustain peak driving demands. Where gasoline is highly energy dense and may be burned at nearly any rate, storing large quantities of electrical energy and supplying it at high rate prove difficult. Furthermore, the demands of regenerative braking require the storage system to undergo frequent current reversals, reducing the service life of some electric storage systems. A given device may be optimized for one of either energy storage or power delivery, at the sacrifice of the other. A hybrid energy storage system (HESS) attempts to address the storage needs of electric vehicles by combining two of the most popular storage technologies; lithium ion batteries, ideal for high energy capacity, and ultracapacitors, ideal for high power discharge and frequent cycles. Two types of HESS are investigated in this study; one using energy-dense lithium ion batteries paired with ultracapacitors and the other using energy-dense lithium ion batteries paired with ultra high powered batteries. These two systems are compared against a control system using only batteries. Three sizes of each system are specified with equal volume in each size. They are compared for energy storage, energy efficiency, vehicle range, mass and relative demand fluctuation when simulated for powering a model Pacifica through each of five different drive cycles. It is shown that both types of HESS reduce vehicle mass and demand fluctuation compared to the control. Both systems have reduced energy efficiency. In spite of this, a battery-battery system increases range with greater storage capacity, but battery-capacitor systems have reduced range. It is suggested that further work be conducted to both optimize the design of the hybrid storage systems, and improve the control scheme allocating power demand across the two energy sources.