New Electrolytic Media and Methods for Energy Storage and

Introduction: An Overview of Relevant Techniques and Concepts

Overview

Given the scope and breadth of information covered in this dissertation, this introduction is intended to provide an overview of relevant concepts, techniques, and areas of chemistry discussed or used in this document. The unifying theme in this thesis is the generation of new electrolytic media capable of electrochemical conversion or energy storage, seen through the lens of a physical-inorganic chemist.

Ionic Liquids: Extreme Electrolyte Concentrations

This study also established the non-additivity of the Faradaic current and a clear disparity in diffusion coefficients between oxidized and reduced species, a consequence of the high ionic concentration of ionic liquids.2. This advance demonstrated the role of ionic liquids in minimizing the overpotential of reduction through cation stabilization.12.

Table 1.1. Water content of atmospheric and vacuum-dried, room- room-temperature ionic liquids, as well as their Gutmann donor numbers and electrochemical solvent windows when vacuum-dried

CO 2 Reduction: Current Status and Trends

Another difficulty in investigating CO2 reduction to higher order products is that the intermediates and mechanistic information involved in, for example, a six-to-twelve-step mechanism are quite difficult to explain, making the rational design of catalysts for CO2 reduction hindered. In this mechanism, two-electron reduction of 1 and loss of chloride is followed by binding of CO2.

Table 1.2. Reactions and standard reduction potentials of CO 2 to C 1 products. The formal potential of hydrogen production is shown for comparison

Lewis Acid-Base Interactions in Organometallic Chemistry: History and

An approximately linear correlation with small variations due to dielectric constant and solvation effects is found for the formal redox potential of the Fe(III/II) couple and the acceptor number of the solvent. These studies laid the foundation for a more definitive understanding of the effects of both dielectric constant and donor–acceptor interactions on the fundamental electronic properties of cyanometalates and provided a unified theory for the effects of solvent donor–acceptor interactions on solvent reactivity. small molecules.

Table 1.3. Formal potentials for (TBA) 3 [Fe(CN) 6 ] in aprotic and protic solvents with varying dielectric constants and acceptor numbers

Redox Flow Batteries: From Aqueous to Non-Aqueous

15 current state of the art, mainly aqueous all-vanadium or zinc-bromine flow batteries.55 However, these systems exhibit low volumetric energy densities and require expensive ion exchange membranes.56 Despite major advances in flow battery technology, greater energy densities and longer cycle life are needed to to make these batteries commercially viable. Current non-aqueous redox flow battery technology is plagued by a variety of problems including charge carrier decomposition (ligand dissociation, reaction with solvent), speciation at the electrode surface due to a solubility mismatch in the charged or discharged state of the battery, species crossover at the membrane,58 and low voltage efficiency due to high overpotentials arising from resistance at ion exchange membrane interfaces.59 Apart from technical challenges of stability and scalability, there are a limited number of non-aqueous solvents useful for flow -batteries due to flammability, recyclability and ecotoxicity.60,61.

Chapter Summaries

17 Chapter 5 extends the unique reactivity of borane adducts to the characterization of a full series of hexaisocyanoboratometalates (Cr, Mn, Fe, Ru, Os), compounds that demonstrate the concept of cyanide as a "variable field" ligand, including circular magnetic . dichroism spectroscopy, electron paramagnetic spectroscopy, luminescence studies, excited state lifetime studies and electrochem. These species are shown to be powerful excited-state reductants and oxidants, strong and long-lived phosphors, and promising electrolytes for symmetric, non-aqueous redox flow batteries.

With an understanding of the electrochemical behavior of Re(bpy)(CO) 3Cl in IL media, CO2 reduction studies were performed to determine whether Re(bpy)(CO) 3Cl exhibited catalytic behavior in ion gel electrolytes. This reduction is 2.14 V positive of the formal potential for MnIII/II for [Mn(CN)6]3-, consistent with our previous studies on [Fe(CN)6]4-.

Electrochemistry in Ionic Liquids: Case Study of a Manganese Corrole

Summary

We found that MnIV/III formal potentials depend on IL counteranion: OTf- < EtOSO3- < TFSI- < TCB-. In EMIm-TCB and BMIm-TFSI, reversible, diffusion-controlled MnIV/III reactions occurred, as evidenced in each case by the ratio of anodic to cathodic diffusion coefficient over a range of scan rates.

Introduction

Results and Discussion

Cyclic voltammograms of MnIV/III and MnIII/II redox couples of (tpfc)Mn are shown in Figure 2.2 (formal potential values ​​for MnIV/III oxidation and MnIII/II reduction of (tpfc)Mn in four ILs are given in Table 2.1 ). To address this question, UV-vis absorption spectra for (tpfc)Mn in four different ionic liquids were obtained and are shown in Figure 2.5.

Figure 2.3. Scan rate dependence of the three redox couples of (tpfc)Mn in BMIm-TFSI

Conclusions

Experimental

Microelectrode experiments were performed with an 11 µm carbon fiber disc electrode, a 0.01 M Ag+/0in 0.1 M TBAPF6 in MeCN quasi-reference electrode (BAS, Inc.), and platinum wire counter electrode.

The contraction of the M-CN bond in (TEA)4[Fe(CN-BPh3)6] is therefore negligibly small. The increased number of bands observed in the low-energy region of the spectrum corresponds to the increased spin-orbit coupling.

Electrocatalysis of CO 2 Reduction in Brush Polymer Ion Gels

Summary

Electrochemical characterization of brush polymer ionic gels composed of polystyrene-polyethylene oxide-polystyrene (PS-PEO-PS) triblock brush polymer, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIm-TFSI) and some combinations of ferrocene (Fc). cobaltocenium (CoCp2+) and Re(bpy)(CO)3Cl. Small-angle X-ray scattering results show that no change in gel morphology occurs on the microscopic length scale between blank gels and gels with added redox-active species.

Introduction

Significance

Results and Discussion

To confirm that the redox behavior of the Fc+/0 and CoCp2+/0 redox couples in the ion gel is consistent with non-aqueous behavior, diagnostic plots were obtained using Nicholson and Shain metrics. The maximum cathodic potential versus the logarithm of the scan rate in EMIm-EtSO4 for the proposed EqCi redox process of Re(bpy)(CO)3Cl. Due to the diffusion limitations of the gel, the thickness of the gel, and the lack of agitation for the gel, the amount of charge passing to CO2 reduction in the gel electrolyte is less than in BMIm-TFSI.

Figure 3.3. Macroscopic and molecular views of ion gel electrolytes with Re(bpy)(CO) 3 Cl

Conclusions

Based on the CO peak area in the GC trace and the charge passed during electrolysis, Faradaic efficiencies were calculated. Any loss in product can be attributed to the viscosity of the pure IL and gel electrolyte, which prevents complete escape of the product (time constraint) prior to headspace sampling. Extraction of electrochemical reaction products, reformulation of composition, and macroscopic shape tuning should thus be possible, making this a promising medium for CO2.

Future Directions

Scan rate dependence of Fc (8.4 mM) in chemically cross-linked, PEO homopolymer ion gel electrolyte. First, as depicted in Figure 3.20, the triblock brush polymer ion gel electrolyte can be used as a thin layer scaffold to generate CO or CH4 in air or with a positive pressure of CO2 transported across the surface of the gel, provided a suitable catalyst is found to carry out these transformations selectively. Cell schematic of a thin membrane ion gel electrolyte layer used to overcome diffusion limitations of CO2 reduction in aqueous media.

Figure 3.19. Scan rate dependence of Fc (8.4 mM) in chemically cross- cross-linked, PEO-homopolymer ion gel electrolyte

Experimental

Electrode cell 63 containing a 3 mm diameter glassy carbon working electrode (CH Instruments), silver wire pseudo-reference electrode (CH Instruments), and platinum wire counter electrode (Kurt J. Lesker). Ultramicroelectrode experiments were performed with an 11 μm carbon fiber disc microelectrode, Ag pseudoreference electrode, and platinum wire counter electrode. The curve was obtained by injecting different ratios of CO2 to CO with a gas-tight syringe.

Figure 3.21. Calibration curve for CO detection on Agilent 7890a gas chromatograph. The curve was obtained by injecting different ratios of CO 2 to CO with a gas-tight syringe

The NIR spectrum of 60 mM tetraphenylphosphonium chloride showed no measurable absorbance in the NIR region of the spectrum. This energy difference (2190 cm-1) is consistent with vibronic coupling to the stretching mode of the isocyanoborate ligand occurring at 2204 cm-1. Comparison of the first two LMCT transitions in borated cyanometallics and the energy change during boration.

Tuning the Formal Potential of Ferrocyanide Over a >2.1 V Range

Summary

Borane coordination changes d-d transitions, metal-to-ligand charge transfer, and cyanide IR and Raman frequencies. Coordination by Lewis acids provides a route for selectively modifying the electronic structures and electrochemical properties of cyanometalates. While previous studies have hinted at the effects of Lewis acids on the electronic structure of homoleptic cyanometalates, the studies presented here unequivocally identify the effects of boronation on the energies of ligand- and metal-ligand-field charge transfer transitions, as well as Ground-state electronic structure as evidenced by the electrochemical responses of iron-based cyanometalates.

Introduction

Significance

Results and Discussion

However, this is likely a combination of both the increased Lewis acidity and the increased net positive charge of the species. Comparison of the 1A1g → 1T1g absorption bands in borane adducts of hexacyanoferrate in dichloromethane, highlighting the blue-shifted absorption of boronated cyanometallates. Comparison of the charge transfer transitions in bare hexacyanoferrate and borane adducts of hexacyanoferrate in dichloromethane, highlighting the blue-shifted absorption of MLCT transitions in boronated cyano metallates.

Figure 4.1. (Left) Molecular structure of (TEA) 4 [Fe(CN-BPh 3 ) 6 ]. Thermal ellipsoids set at 50% probability

Conclusions

Experimental

The isotropic displacement parameters of all hydrogen atoms were fixed at 1.2 times the Ueq value of the bound atom. All M(III) species were crystallized from a concentrated solution of the compound in DCM at -20 oC. 153 A particularly unique feature of the electronic structure of Os(III) complexes are the interconfigurational transitions observed in the NIR energy region of the spectrum.

A plot of the peak current ratio versus the logarithm of the scan rate supports this interpretation (Figure 5.24). To our knowledge, this is the first example of using HYSCORE spectroscopy to identify the primary ligand domain surrounding Cr3+.

Table 4.2. Rate constants of for the oxidative quenching of Ru(III) with different concentrations of (TBA) 4 [Fe(CN-BCF) 6 ] estimated from MatLab modeling

Summary

Boronation results in an anodic shift of V to the MIII/II formal potential for all species while simultaneously maintaining or improving the electrochemical reversibility. UV-vis spectroscopy, magnetic circular dichroism spectroscopy, and density functional theory calculations suggest that the first LMCT in all M(III) species is a t2u → t2g transition, meaning that the extended pi bond affects the negligible in the t2u ligand orbitals. Based on this assignment, the energy shift of the t2u level is very close to the formal potential change for all complexes.

Introduction

According to self-consistent molecular orbital calculations, the coordination of an electron-deficient species with nitrogen results in a reduction of all molecular orbital energy levels of one electron, but not to the same extent. Furthermore, many of these changes cause charge transfer states to be so high energy that the lowest energy transition is now ligand-centered.5 The molecular orbital interpretation of boronation on cyano metallates is shown in Figure 5.2. These species exhibit unique structural and electronic features that provide an opportunity to improve our understanding of the electronic structure and energy levels of molecular materials.

Figure 5.2 Effect of boronation on the electron density of metal isocyanoborates

Results and Discussion

Electrochemical impedance spectroscopy was used to obtain the uncompensated resistance of the cell via the Nyquist plot. The shift in the formal potential for redox pairs is correlated with the Gutmann-Beckett acceptor number of the solvent and consequently with the acceptor number of borane. IC junctions can also couple to asymmetric vibrational modes of the complex to create spurious origins.

Left) Voltammetry at room temperature and low temperature (−25, oC) and peak current ratio versus the logarithm of the scan rate (right) for [Cr(CN-B(C6F5)3)6]3-. This behavior arises from the ability of the metal center to participate in covalent interactions, namely pi backbonding.

Figure 5.3. General synthetic scheme for M(II) and M(III) boronated cyanometallates.

Conclusions

Synthesis and Experimental

Borane Adducts of Heteroleptic Cyanometallates: Electronic Structure

Summary

Introduction

Results and Discussion

Conclusions

Synthesis and Experimental

Cobalt(II) and Cobalt(III) Boronated Cyanometallates: Synthesis,

Summary

Introduction

Results and Discussion

Conclusions

Synthesis and Experimental

27 Figure 2.3 Dependence of the scanning rate of the three redox couples of (tpfc)Mn in BMIm-TFSI. 28 Figure 2.4 Peak current versus square root of scan rate plots for the anodic and cathodic components of the MnIV/III redox couple in various ionic liquids. 29 Table 2.3 Anodic and cathodic diffusion coefficients of the MnIV/III redox couple in each ionic liquid and their ratios.

163 Table 5.13 Comparison of the first two LMCT transitions in boronated cyanometallates and the change in transition energy upon boronation. Outer-sphere coordination effects on the redox behavior of the Fe(CN)63−/ Fe(CN)64− pair in nonaqueous solvents. In particular, 1 dissolves homogeneously in the interpenetrating matrix domain of the ion gel, and exhibits electrocatalytic CO2 reduction to CO in the gel.

Due to the small surface area of ​​the working electrode, PEIS methods for the determination of Ru are valid.

F (blue) overlaid