The long-anticipated implementation of using renewable sources such as solar and wind to meet the world’s energy demand is still limited by not having appropriate grid-level energy storage systems on a global scale. When considering grid-scale energy storage solutions, environmental concerns, and techno-economic viability play a crucial role in the practical implementation of such technology. To address this, redox-active organic molecules (ROMs) have been explored for many uses including serving as redox-active molecules in redox flow batteries (RFBs) and providing overcharge protection in lithium-ion batteries (LIBs). Nevertheless, in order to be a major player in electrochemical energy storage, further optimization of ROMs with respect to performance and stability is required. Achieving optimum performance and stability mandates a molecular-level understanding of the interactions between chemical compounds, solvent molecules, and any other supporting solutes in the medium. Hence we approached this research question in the context of redox-active organic molecules for non-aqueous redox-flow batteries (NARFBs) by narrowing down the chemical space to a few classes of molecules. Herein, we extensively studied it from multiple perspectives such as; (1) Examining the correlation of molecular structure of redox-active organic molecules (ROMs) to solubility at different states of charge using quantitative structure-property relationships (QSPR), (2) Investigating the effect of electrolytes (counter-anions) on the solubility of ROMs using molecular dynamics (MD) simulations interfacing with experiments and multiple linear regression, (3) Exploring the concentration dependence of electrolytes with MD to explain experimental behavior at very high concentrations and to identify optimum concentration ranges for NARFBs, and (4) Probing Bulk and Interfacial Interactions of ROMs in complex solutions under an applied potential using classical MD simulations. This multi-approach endeavor has informed us of the strengths and limitations of predictive modeling in non-trivial molecular systems with limited data and high variability and boundaries related to improving the solubility of ROMs using structural modifications. Thus, in our continued efforts, we discovered that the solubility of these ROMs can be dramatically improved up to three-fold by switching the counter-anion due to the flexibility and size of the counter-anions. Our exploration of high-concentrated electrolytes implies that changes to supporting electrolyte concentration are significantly more impactful to the solution’s transport properties with the crowding of electrolytes leading to non-Newtonian fluid-like regimes. Expanding classical MD simulations to capture bulk and interfacial properties opens up a new paradigm of using computationally less-expensive methods for high-throughput simulations. To address the limitations we encountered in this effort, we also developed systems to automate similar MD simulations and analyses with the goal of producing large datasets that may pave the path to generating machine-learning models to predict different performance matrices efficiently in the future. In summary, the results and theoretical insights gained through these collective efforts would set the foundations for optimizing the performance and stability of ROMs thus helping experimentalists design better materials for electrochemical energy storage.

Conjugated polymers (CPs) are an emerging class of materials that are attractive for many applications due to their low cost, flexibility, and ease of processing. Both chemical and electrochemical doping of CPs is done to alter important properties such as their electrical conductivities and optical absorbances. This ability to tune their properties allows for their use in devices such as organic electrochemical transistors (OECTs) for biosensing and bioelectronics, electrochromic devices for color changing windows, as well as wearable thermoelectrics to use body heat to power wearable electronics. There are several factors that can influence the properties of doped CPs including doping level, film morphology, and the dopant or counterion used in the process. One disputed topic is what influence the ion size within the electrolyte has on the properties of electrochemically doped CPs. These ions balance the positive or negative charges on the backbones of doped CPs and their size can influence their interactions with the charge carriers and the overall morphologies of the films, therefore influencing their optical and electronic properties. This dissertation focuses primarily on understanding the influence of anion size on the properties of doped CPs as a function of their respective doping level. 

            The work presented here first focuses on the electrochemical doping ability of two benchmark CPs regioregular and regiorandom poly(3-hexylthiophene), rr- and rra-P3HT respectively, in electrolytes with anions of different sizes. Films of rr-P3HT are semicrystalline while those for rra-P3HT are amorphous allowing us to probe anion size as a function of CP morphology. Measured oxidation potentials and UV-vis data suggest that the larger anions are positioned further from the backbone of the polymer with two distinct polaron/bipolaron transitions apparent for rr-P3HT and only one for rra-P3HT. Further investigation into these materials as a function of doping level shows two distinct regimes that are important to consider. In the low doping regime, Coulombic interactions with the CP backbone and counterion largely contribute to the film’s properties with the larger anion having a higher electrical conductivity and lower Seebeck coefficient than the smaller and more Coulombically bound anion. Alternatively, in the high doping regime all charges are essentially “free” and CP morphology has the largest impact on film properties. In this case, the larger anion is more disruptive to the film morphology granting a lower electrical conductivity but higher Seebeck coefficient. At all measured doping levels, the films with the larger anions display higher thermoelectric power factors, proving that counterion size is an important consideration for these devices. 

According to the center for disease control (CDC), an estimated 1.7 to 2.2 million persons die from waterborne diseases annually. The majority of individuals dying from diseases resulting from unsafe drinking water, such as diarrhea and gastroenteritis, are children. This has in turn created a global water crisis. Different methods have been developed to treat contaminated water in response to the global water crisis such as adsorption, filtration, ozonolysis, catalysis, etc. Of the methods available, filtration via polymeric membranes has been one of the most successfully applied. A membrane is a thin semi-permeable barrier (often made of a polymer) used to separate differing phases in a media under pressure. Membrane filtration is ideal for water treatment due to high rejection and throughput, as well as ease of integration into other water treatment systems. Unlike other methods of water treatment, membrane filtration can be easily tuned to target specified contaminant at different size and pressure levels.

Syed Joy will be presenting his doctoral thesis, "Understanding of Processing Additives Influence in Tin Halide Perovskites: Chemistry, Defect, and Photovoltaic Performance."

Perovskites have emerged as a promising candidate for low-cost production of solar cells. However, the most critical barrier for commercialization of perovskite solar cells (PSCs) is the inadequate stability of the organic metal halide perovskites (OMHPs). The degradation of OMHPs is induced by light, heat, air, and electrical bias. The known degradation pathways involve the oxidation of I^- and Sn²⁺, dissolution of perovskites by moisture, irreversible reactions with water, ion migration, and ion segregation. To improve the stability of OMHPs various methods are adopted, such as additive engineering, perovskite surface treatment, and composition engineering. Surface ligands are used on top of perovskite thin films to passivate the undercoordinated ions leading to improved charge collection efficiency and stability of PSCs. However, not all surface ligands stay at the surface of the perovskite. Some of them penetrate the perovskite layer forming reduced dimensional phases at the surface. This kind of behavior not only alters the electronic nature at the interface, but also negatively affects the stability of the OMHPs compared to surface ligands that remain only at the surface. On the other hand, additives are commonly used to reduce defects in bulk of the perovskites and thus improve their stability. They improve the stability of OMHPs by controlling the morphology of OMHP thin films, improving the thermodynamic stability of Sn²⁺ and I^-, and lowering the ion migration and ion segregation. The stability of OMHPs is also significantly improved by incorporating bulky organic cations into the perovskite composition. Although these routes for improving the stability are optimistic, it is not clear how the surface chemistry of OMHPs and chemical nature of additives or organic cations affects stability.

Surface chemistry of OMHPs can be tuned to control the extent of ligand penetration by changing the composition and processing conditions of OMHPs. To this end, it is important to find out what affects the extent of ligand penetration. We find that the perovskite compositions used in this study have little or no effect on ligand penetration. However, the perovskite film processing conditions have a greater effect on ligand penetration. Using a family of phenethylammonium iodide (PEAI) with different substituents on the benzene ring, we show that the ligand penetration can be affected by type of substituents as well. Stabilizing the perovskite precursors is also important as degraded precursors lead to defective perovskites with poor stability. Here, we show that additives influence the thermodynamic stability of Sn²⁺ and I^- by changing the acidity of the precursor solutions. Using additives with a range of pKa we find that additives with higher pKa provide a more stabilizing chemical environment for Sn²⁺ and I^-. 

It is known that bulky organic cations improve the stability of OMHPs by shielding the metal-halide octahedra from air. However, how the structure of the organic cations affect the air, oxygen, and moisture stability of the OMHPs is not well understood. Using twelve different organic cations we show that the stronger the attractive interactions between the organic cations in two dimensional (2D) OMHPs the higher is the stability. The stability of 2D-OMHP thin films decreases as the orientation of the 2D sheets deviates from planarity with respect to the substrate plane.

Abstract: Over the years, nanomaterials research has advanced towards discovering versatile and readily accessible materials tailored for a diverse range of applications. A comprehensive understanding of materials’ phases and their transformations are integral to this effect to enable better synthetic control as well as the functionalization of nanomaterial properties. Among advanced characterization techniques, the transmission electron microscope (TEM) is a powerful tool that provides direct access to the nanoscale and, therefore, an indispensable tool in studying fundamental materials problems. This dissertation discusses several nanomaterial systems where TEM tools and techniques are utilized to gain a deep understanding of their chemistry. 

This dissertation focuses on structural and phase transformations of nanomaterials using in situ heating in the TEM, which allows direct observation of these dynamic processes. Reported here are studies of the phase transformation and stabilization of the mackinawite phase of iron(II) sulfide nanoplatelets, the structural transformation of gold-catalyzed tin(IV) oxide nanowires into gold core/tin(IV) oxide shell nanowire heterostructures, and finally the interaction between aluminum oxide and lead (at. 17%) lithium alloy proposed for use as a coolant in nuclear fusion reactors. These studies showcase the significance of knowledge of the mechanistic details of phase transformations, with the eventual goal of being able to determine and control structure-property relationships. 

KEYWORDS: phase transformations, nanomaterials, transmission electron microscopy (TEM), in situ TEM

Abstract: The principal concept behind biorefining involves the transformation of lignocellulosic biomass into valuable products and energy resources. Historically, biorefinery strategies for lignocellulosic biomass have primarily focused on improving the conversion of cellulose into ethanol, often neglecting the underutilized lignin component. Lignin consists of phenolic subunits, from which it follows that value-added products can be obtained from lignin depolymerization. Unfortunately, lignin utilization is particularly challenging due to its high structural irregularity and recalcitrance. The goal of this study was to develop an AuPd/Li-Al layered double hydroxide (LDH) bimetallic catalyst for efficient lignin depolymerization, resulting in the production of high-value aromatic compounds. The structural complexity of lignin renders the study of individual reactions in lignin difficult. Therefore, model compounds were used to evaluate catalyst performance. Initially, we prepared AuPd bimetallic nanoparticles with varying molar ratios supported on a basic Li-Al LDH using a sol-immobilization method. Subsequently, we characterized the synthesized catalysts and evaluated them in aerobic oxidation reactions of 1-phenylethanol and simple benzylic alcohols at atmospheric pressure to identify the most effective catalyst configurations. Those catalysts demonstrating promising performance were further examined in the aerobic oxidation of lignin model dimers containing ß-O-4 linkages. Remarkably, these model compounds underwent sequential oxidation, ultimately leading to the cleavage of the ß-O-4 bonds. Subsequently, we evaluated the catalysts in the oxidative deconstruction of ?-valerolactone (GVL) extracted from maple lignin at 120 °C, again using O2 as the oxidant. These results highlight the potential of the AuPd/Li–Al LDH catalyst system as an eco-friendly approach for lignin depolymerization under mild conditions, offering a promising avenue for valorizing lignin in biorefining processes.

Abstract: Understanding materials at their atomic level is important given that the macroscopic properties of a material are intricately linked to its nanoscale structure. This plays a pivotal role in advancing structural materials since their performance is significantly influenced by factors such as composition, and microstructure which consist of different interfaces, crystalline phases, and defects. 

In the automotive and aerospace industries reducing the weight of materials is critical to enhance fuel efficiency without compromising safety and performance. Lightweight aluminum alloys are extensively studied to replace heavier materials in these sectors. This work offers a comprehensive characterization of the evolution of various precipitates within aluminum alloys under laser treatment conditions, aiming to enhance their mechanical properties.

The thesis also delves into understanding the diffusion and dissolution mechanisms of metal nanoparticles on or into metal oxides. Metals like gold, in their bulk form, are traditionally considered chemically inert and inefficient as catalysts. At the nanoscale, however, as the particle size decreases, their catalytic activity towards various reactions significantly increases. Our exploration of these systems under in situ TEM heating has provided valuable insights into the structure-function relationships of these interfaces. This knowledge can be employed in optimizing the production of nanomaterials with enhanced interface properties.

KEYWORDS: Aluminum alloys, precipitate hardening alloys, SLV, TEM, in situ TEM