V. Sara Thoi

The first conjugated polymers with functional Si–Si crosslinks are reported. In addition to complete structural characterization using solid-state NMR techniques, the electronic structure of the polymers are supported by electrochemical studies.

PolyMOFs, a class of metal–organic frameworks composed of polymeric linkers and metal ion nodes, are used as quasi-solid-state electrolytes for Li ⁺ transport. Oxidic donors in the polymeric linker are found to facilitate Li ⁺ conduction.

Highly concentrated electrolytes (HCEs) have been shown to hinder dendrite formation and improve cyclability in Li-based batteries. Herein, we developed a novel strategy to use an electrolyte matrix composed of gel metal-organic frameworks (g-MOFs) and an HCE consisting of 4.5 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in acetonitrile. The addition of Zr-based g-MOFs into the HCE creates a "sandy-slurry" electrolyte with higher ion conductivity and Li⁺ transference number (i.e., g-MOF-808: σ = 16.0 mS cm^-1, t_Li+ = 0.800) compared to the HCE alone (σ = 8.52 mS cm^-2, t_Li+ = 0.511). Li-symmetric cells containing g-MOF electrolyte have stable symmetric cell cycling at high charge/discharge rates. X-ray photoelectron spectroscopy and scanning electron microscopy show that the g-MOF changes the composition of the solid-electrolyte interface of the Li electrode compared with control samples. In a series of Zr g-MOFs with varying porosity, we discovered that cells containing g-MOF-808 can be symmetrically cycled with low overpotential values compared to the control Li-symmetric cells under similar conditions. To the best of our knowledge, this study is the first to implement g-MOFs in Li-based batteries and demonstrates the potential of porous framework materials as gel electrolyte components for high-density energy storage devices.

Lithium-sulfur batteries are a promising energy storage system with a high theoretical energy density. A significant challenge in realizing this energy density is the polysulfide shuttle effect, where soluble polysulfides migrate between the two electrodes during cycling, which ultimately leads to reduced sulfur utilization and poor capacity retention. To mitigate these issues, metal-organic frameworks (MOFs) have been utilized as cathode additives to create tunable pore environments for capturing polysulfides and facilitating their redox reactions. However, an often-overlooked aspect of MOFs beyond pore dimensions is the confluence of particle size and porosity on the Li-S battery performance. Herein, we investigate two isoreticular Zr-based MOFs, MOF-801 and UiO-66, with varied particle sizes to understand the interplay of these parameters. At lower charge rates, we found that the high external surface area of small particles provided the best battery performance. However, at higher charge rates, porosity tips the scale as UiO-66 outperforms MOF-801 even at the smallest particle sizes. This study highlights the critical balance between the external surface area and internal porosity, where optimizing particle size can be as crucial as tailoring pore dimensions for effective polysulfide confinement and redox.

A new pentadentate-fluorinated N₄S(thiolate) ligand was synthesized. Reaction with Fe(BF₄)₂·6H₂O gives a new thioether complex, [Fe^II(CH₃CN)(N3Py^pFSEtCN)][BF₄]₂ (1), and on-metal deprotection gives the thiolate complex, [Fe^II(CH₃CN)(N3Py^pFS)][BF₄] (2). Reaction of 2 with NO forms a low-spin ground state (S = 1/2) {FeNO}⁷ complex (3). Chemical reduction of 3 with cobaltocene gives a metastable intermediate spin S = 1 {FeNO}⁸ complex (4). Protonation of 4 releases nitroxyl (HNO), as observed by ESI-MS and ³¹P NMR trapping experiments with PPh₃. Complexes 1 and 2 were characterized by single-crystal X-ray crystallography, complexes 2-4 were characterized by EPR and FT-IR spectroscopies, and all iron complexes were characterized by ¹⁹F NMR, UV-vis, and ⁵⁷Fe Mössbauer spectroscopies. These results show that a nonheme iron complex can generate and release HNO, suggesting that nonheme iron centers could be endogenous or exogenous sources of HNO in biological systems. Additionally, the fluorine-substituted N₄S(thiolate) ligand provides a unique spectroscopic handle to monitor the reactivity of the iron center several bonds away from the fluorine substituent.

The electrochemical reduction of carbon dioxide (CO₂) to carbon monoxide (CO) is challenged by a selectivity decline at high current densities. Here we report a class of indigo-based molecular promoters with redox-active CO₂ binding sites to enhance the high-rate conversion of CO₂ to CO on silver (Ag) catalysts. Theoretical calculations and in situ spectroscopy analyses demonstrate that the synergistic effect at the interface of indigo-derived compounds and Ag nanoparticles could activate CO₂ molecules and accelerate the formation of key intermediates (*CO₂^– and *COOH) in the CO pathway. Indigo derivatives with electron-withdrawing groups further reduce the overpotential for CO production upon optimizing the interfacial CO₂ binding affinity. By integrating the molecular design of redox-active centres with the defect engineering of Ag structures, we achieve a Faradaic efficiency for CO exceeding 90% across a current density range of 0.10 − 1.20 A cm^–2. The Ag mass activity toward CO increases to 174 A mg^–1_Ag. This work showcases that employing redox-active CO₂ sorbents as surface modification agents is a highly effective strategy to intensify the reactivity of electrochemical CO₂ reduction.

The direct synthesis of Si–Si dimeric 9-dimethylsilafluorene, structural characterization via single crystal X-ray diffraction studies, and electrochemical redox chemistry with DFT electronic structural analysis is reported herein.

Intermetallic AuCu alloy thin films were grown electrochemically onto Ti foil substrates and exhibited enhanced selectivity and activity for electrochemical C–N coupling to form urea (CO(NH₂)₂) compared to their parent metals. Varying the Au and Cu stoichiometry provided a synthetic handle to tune the film electronics (i.e., d-band position, oxophilicity) while maintaining overall film stability. The AuCu alloy with the highest Au loading of 75% proved to be the most electrochemically stable and possessed the highest selectivity (∼68%) for urea formation. X-ray absorption spectroscopy (XAS) revealed that the Cu in alloys with more Au content maintained a higher oxidation state (in the form of Cu–O) under electrochemically relevant conditions. This observation suggests enhanced anion (NO₃ ⁻/NO₂ ⁻) adsorption and retention at the surface. This work highlights the utility of using intermetallic alloys to enable complex electrochemical coupling reactions by finely tuning material properties.