2019 Eilers Scholars
Electricity Market Design to Increase Integration of Renewables in the Power Grid
Department of Electrical Engineering
Faculty Advisor: Vijay Gupta
Reliable on-demand electricity supply is a fundamental requirement for ensuring public safety, health and welfare, as well as for developing a nation's economy and standard of living. Growing concern about the negative effects of burning fossil fuels has made increasing renewable energy penetration in the electricity grid a major social and policy goal. However, renewable sources such as wind and solar are inherently intermittent and unpredictable, making the goal of reliable on-demand electricity difficult to achieve at high levels of renewable penetration. The proposed project addresses that challenge by developing a grid that can deliver reliable on-demand electricity inexpensively, while increasing renewable participation. This goal will be achieved through the design and analysis of new structures for electricity markets which promote collaboration among different energy sources. With that, despite renewable variability, the total energy supply will equal the total demand at all times. The flexibility of a power grid refers to the ability to modify electricity production or consumption to counterbalance mismatches between supply and demand. Developing a flexible grid that reliably accommodates the variability and uncertainty of renewable energy sources has been recognized as a major challenge in the transition towards higher renewable usage. To achieve that goal, some other source should consume energy when renewables produce more than the demand and provide energy when renewables produce less, so that the total energy supply equals the total demand at every time. Such flexibility may be provided by batteries, flexible demand, or even natural gas power plants that can ramp up or down their supply quickly. However, flexible sources are not yet available at a grid scale at the efficiency-cost points required for large scale integration of renewables. Current practices do not provide enough economic incentives for innovation and development of such sources. Energy markets currently pay for quantity of electricity supplied and do not price flexibility, except ad hoc fixes that have failed to provide adequate motivations for investors. For instance, a battery that provides no net electricity will gain limited revenue in current markets even though it can be crucial for accommodating renewable variability and uncertainty. In my preliminary work, I proposed the design of a market in which flexible power sources offer to reserve some fuel to be used in case of renewable shortage, while renewable generators purchase the right to ask those sources to use that reserve if needed. Using optimization and economics theories, I derived expressions for the optimal pricing and size of such trades. I validated my analytical results through numerical simulations of a case study, and I showed that such mechanism stimulates the participation of renewables in the market. Furthermore, it provides adequate payment for flexibility providers and does not increase the energy price paid by consumers.
Compositionally Insensitive Size-Dependent Stokes Shifts in CsPbX3 (X = Cl, Br, I) Nanocrystals
Department of Chemistry and Biochemistry
Faculty Advisor: Masaru (Ken) Kuno
CsPbX3 (X = Cl, Br, I) nanocrystals are highly attractive materials to be implemented in next-generation light-emitting/harvesting applications due their tunable bandgaps, high photoluminescence quantum yields and narrow emission linewidths. Full elucidation of their size-dependent electronic/optical properties is critical to their successful implementation into working, efficient solar cells. In the proposed work, size-dependent Stokes shifts will be demonstrated to be universal features of colloidal all-inorganic lead halide perovskite (CsPbX3; X = Cl, Br, I) nanocrystals. We previously demonstrated size-dependent Stokes shifts exists in CsPbBr3 nanocrystals and have proposed a model so as to explain the phenomena’s origin (Brennan, M.C.; Herr, J.E.; et al. J. Am. Chem. Soc. 2017, 139, 12201-12208.; Brennan M.C.; et al. ACS Energy Lett. 2017, 2, 1487- 1488.) Our modeling predicts size-dependent Stokes shifts will exist in CsPbX3 irrespective of their halide composition. This will be done by first synthesizing a size-series of high quality, monodisperse CsPbCl3, CsPb (Cl0.5Br0.5)3, CsPbI3 and CsPb(I0.5Br0.5)3 nanocrystals and subsequently measuring absorption/emission to determine Stokes shift values. Subsequent modeling of all aforementioned halide composition will accompany the experimental data. At a broader level, proving this phenomena is a general feature of all perovskite NCs will allow it to be tuned via NC size to influence their response within photovoltaic or light-emitting applications.
The Role of Morphology and Electrochemical Interface on the Electrodeposition/Dissolution Efficiency of Magnesium Batteries
Department of Chemical and Biomolecular Engineering
Faculty Advisor: Jennifer L. Schaefer
The environmental impact of fossil fuels, including difficulties with CO2 capture, has led to the development of hybrid and electric vehicles. Rechargeable batteries are an integral part to the success of these technologies, and lithium-ion batteries are dominating the field of electrochemical energy storage. Despite the decrease in fossil fuel usage, electric vehicles are not necessarily environmentally friendly nor sustainable for the long-run given the current state-of-art of battery technologies. Lithium-ion batteries rely on materials that are not readily abundant nor easily recyclable. The majority of lithium reserves are contained in seawater and brine; exacting lithium from seawater is energy intensive and the projected amount needed would rely on improvement of current technologies. Recycling lithium would lower the demand of raw materials, but there is currently only one commercial lithium recycling site in the United States. Common Li-ion intercalation cathodes contain materials such as cobalt. However the world’s main supplier, the Democratic Republic of the Congo, has faced many health and environmental problems since the rise of electronic devices, due to unsafe working conditions and water contamination. To mitigate these environmental risks, alternatives to intercalation electrodes and lithium-based batteries are under development. Magnesium metal is of interest for use as an anode material due to its large volumetric capacity (3833 mAh/cm3 versus 2026 mAh/cm3 for lithium) and widespread abundance. Magnesium can be recovered from a wide range of resources and is considered to be “virtually unlimited” by the US Geological Society. Because of magnesium’s abundance and widespread use, it is readily recyclable. However, magnesium metal cannot be used in place of lithium in an analogous battery system. Magnesium metal anodes are very sensitive and form a passivating layer in the presence of common salts, solvents, and trace impurities (water), which renders the battery nonrechargeable. Common electrolytes that enable highly reversible magnesium electrodeposition (charge, deposition; discharge, dissolution) use highly flammable compounds such as THF and Grignard reagents. Research efforts have focused on developing electrolytes with increased thermal stability and decreased corrosiveness in order to lead to the eventual application of magnesium batteries; despite these efforts, the magnesium deposition efficiencies are often compromised (< 80 %). My research project addresses the electrolyte/anode interface and altering the electrolyte chemistry to study the effect on battery operation. The emphasis of my research is on developing electrolytes that can maintain high electrochemical performance (measured by parameters such as electrochemical stability and electrodeposition/dissolution efficiency), while focusing on changing the corrosiveness and thermal properties of the electrolyte to make it more suitable for practical application. Recently, we demonstrated that a solvent mixture of butyl sulfone and THF can significantly increase the thermal stability of an electrolyte while maintaining efficiencies above 90 %. However, the deposition quality and interfacial chemistry between the solvent and the substrate are hypothesized to impact the efficiency of magnesium electrodeposition/dissolution. Furthermore, due to the reactivity of the magnesium surface, the library of solvents that can be used with high efficiency is limited. Therefore, we are also pursuing work on engineering an interphase on the magnesium anode that prevent decomposition on the electrode surface thus leading to increased efficiencies.
Intercalation of Uranyl Peroxide Nanoclusters into Synthetic Layered Double Hydroxide Clays
Department of Civil and Environmental Engineering and Earth Sciences
Faculty Advisor: Peter C. Burns
The scope of this work will involve several phases of laboratory scale reactions of gram and microgram quantities of synthetic forms of the anionic clays based on the mineral hydrotalcite. The hydrotalcites are commonly referred to as the layered double hydroxides (LDHs) owing to their sheet structures. Parts per million (ppm) concentrations of select species of uranium based polyoxometalates, referred to as uranyl peroxide nanoclusters for their interaction between the uranyl ion and peroxide, will be reacted with these clays. The first phase will focus on developing the optimal combination of LDH-type and uranyl peroxide nanocluster species for maximum U removal from an aqueous solution. The second phase of research will involve adding ppm concentrations of non-radioactive isotopes of fission products (FPs) into the reactions of the LDHs and uranyl peroxide nanoclusters and tracking the concentration trends of the FPs during these interactions. The next phase will involve introducing simulated seawater into the reactions, to have a laboratory scale experiment replicating similar conditions to the Fukushima Daiichi disaster.
Toward a better understanding of iptycene-based polyimide membranes: structure, microporosity and gas separation performance
Department of Chemical and Biomolecular Engineering
Faculty Advisor: Ruilan Guo
Membrane technology for gas separation has been commercialized for more than 30 years and can be applied in many industries, such as removal of carbon dioxide from natural gas and biogas (CO2/CH4), production of nitrogen from air (N2/O2) and hydrogen recovery from petrochemical plants (H2/CH4, H2/ N2). Membrane separation shows strong growth potential due to its high energy-efficiency, low operating cost and small footprint comparing to conventional gas separation processes . Ideally, the membranes for industrial application should have both high permeability (P) and high selectivity (α). High permeability allows small membrane area for reduced cost, while high selectivity improves purity of desired products. However, there is an intrinsic trade-off between permeability and selectivity for polymeric membranes, where highly permeable membranes always show low selectivity and vice versa. The trade-off has been illustrated by Robeson in permeability-selectivity upper bound plots and is now used as an empirical criterion to gauge performance of membranes . Majority of current gas separation membrane studies have been directly to explore new rigid polymer structures that show high permeability-selectivity combinations to overcome the limitation. Among all these works, polyimides are drawing lots of attention because of their good thermal and chemical stability, as well as their decent gas separation performance. The rigid aromatic polyimide backbones can pack tightly to create small interchain spacing, i.e., fractional free volume (FFV), delivering moderate to high selectivity. However, the permeability of existing polyimides is still relatively low making them less desirable for industrial implementation. In this regard, it is in pressing need to explore new macromolecular design of polyimide structure that features high chain rigidity with large fractional free volume for fast gas diffusion, and narrow free volume size distribution to maintain high selectivity . Introducing bulky, shape-persistent building block, such as iptycene moieties, into polymer backbone represents a promising macromolecular design to produce high performance membrane materials. Iptycenes are a family of rigid, three-dimensional molecules with phenyl rings attached to the central hinge, where triptycene and pentiptycene are the simplest members of the family with three and five phenyl rings, respectively . In our group’s previous research on iptycene-based polyimides, it has been shown that the incorporation of rigid iptycene moieties in polymer backbone can effectively enhance the fractional free volume as well as control the molecular cavity architecture, leading to much improved separation performance relative to commercial Matrimid® polyimide [5,6]. However, the ether bond in these custom-synthesized iptycene-based monomers prevents further improvement in gas permeability of these iptycene-based polyimides . In this project, a new triptycene diamine is designed wherein the polymerizable amine groups are directly positioned on triptycene skeleton without using spacer moieties containing ether bond. This new monomer design will significantly improve the backbone rigidity and introduce non-planar, contorted structure as the heterocylic imide rings are directly connected to triptycene building block. As a result, high gas permeability is expected for the polyimides prepared from this new triptycene diamine due to the large fractional free volume induced by inefficient chain packing. Based on this new triptycene diamine, a series of novel iptycene-containing polyimides will be prepared by condensation reaction using various commercial and custom synthesized dianhydrides. The choice of the dianhydride monomers is carefully made to finely tune the size and size distribution of free volume-based microcavities of the membranes. Custom-synthesized dianhydride monomers containing bulky units, such as triptycene and pentiptycene, are of particular interest which tend to restrict the chain packing and further enhance the gas transport performance. More importantly, the iptycene units in polyimide backbone can potentially construct “hourglass”-like ultrafine micropores in membranes to boost size sieving effect, enhancing selectivity without sacrifice permeability . Membranes of the comparable polymers will be fabricated and characterized to estalish the property-structure relationships for this new family of polyimide membranes. Overall, this study will deliver a broad set of polyimides with varied iptycene-containing diamine-dianhydride pairs to examine the effect of iptycene units on physical properties, gas transport properties and separation efficiency of the membranes. This in turn can contribute to a better understanding of the role of iptycene moieties in manipulating free volume architecture and affecting gas separation performance.
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