Scholarly Work - Chemistry & Biochemistry
Permanent URI for this collectionhttps://scholarworks.montana.edu/handle/1/8714
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Item Divergent Electrically Conductive Pathways in Yttrium-Based 2- and 3-Dimensional Metal–Organic Frameworks(American Chemical Society, 2024-07) Welty, Connor; Gormley, Eoghan L.; Oppenheim, Julius J.; Dincă, Mircea; Hendon, Christopher H.; Stadie, Nicholas P.Despite most porous framework solids exhibiting insulating character, some are known to conduct electrical charge. The peak performing conductive metal–organic frameworks are composed of redox-active hexasubstituted triphenylene linkers, but the impact of redox activity on material conductivity remains enigmatic because of limited availability of direct structure–function relationships. Here, we report a hexagonal yttrium-based conductive porous scaffold, comprising hexahydroxytriphenylene connected by Y-chains (YHOTP). In comparison to its known porous cubic counterpart (Y6HOTP2), this material features a 1000-fold increase in peak conductivity in polycrystalline samples (∼10–1 S cm–1). Furthermore, through a comparison of their electronic structures, we rationalize the origin of this difference and highlight the role of charge carrier concentration in dictating bulk electrical conductivity. Together, this work provides a design principle for the development of next-generation conductive porous frameworks.Item Hydrogen Adsorption in Ultramicroporous Metal–Organic Frameworks Featuring Silent Open Metal Sites(American Chemical Society, 2023-11) Chiu, Nan Chieh; Compton, Dalton; Gładysiak, Andrzej; Simrod, Scott; Khivantsev, Konstantin; Woo, Tom K.; Stadie, Nicholas P.; Stylianou, Kyriakos C.In this study, we utilized an ultramicroporous metal–organic framework (MOF) named [Ni3(pzdc)2(ade)2(H2O)4]·2.18H2O (where H3pzdc represents pyrazole-3,5-dicarboxylic acid and ade represents adenine) for hydrogen (H2) adsorption. Upon activation, [Ni3(pzdc)2(ade)2] was obtained, and in situ carbon monoxide loading by transmission infrared spectroscopy revealed the generation of open Ni(II) sites. The MOF displayed a Brunauer–Emmett–Teller (BET) surface area of 160 m2/g and a pore size of 0.67 nm. Hydrogen adsorption measurements conducted on this MOF at 77 K showed a steep increase in uptake (up to 1.93 mmol/g at 0.04 bar) at low pressure, reaching a H2 uptake saturation at 2.11 mmol/g at ∼0.15 bar. The affinity of this MOF for H2 was determined to be 9.7 ± 1.0 kJ/mol. In situ H2 loading experiments supported by molecular simulations confirmed that H2 does not bind to the open Ni(II) sites of [Ni3(pzdc)2(ade)2], and the high affinity of the MOF for H2 is attributed to the interplay of pore size, shape, and functionality.Item Prominent Structural Dependence of Quantum Capacitance Unraveled by Nitrogen‐Doped Graphene Mesosponge(Wiley, 2023-12) Tang, Rui; Aziz, Alex; Yu, Wei; Pan, Zheng‐Ze; Nishikawa, Ginga; Yoshii, Takeharu; Nomura, Keita; Taylor, Erin E.; Stadie, Nicholas P.; Inoue, Kazutoshi; Kotani, Motoko; Kyotani, Takashi; Nishihara, HirotomoPorous carbons are important electrode materials for supercapacitors. One of the challenges associated with supercapacitors is improving their energy density without relying on pseudocapacitance, which is based on fast redox reactions that often shorten device lifetimes. A possible solution involves achieving high total capacitance (Ctot), which comprises Helmholtz capacitance (CH) and possibly quantum capacitance (CQ), in high-surface carbon materials comprising minimally stacked graphene walls. In this work, a templating method is used to synthesize 3D mesoporous graphenes with largely identical pore structures (≈2100 m2 g−1 with an average pore size of ≈7 nm) but different concentrations of oxygen-containing functional groups (0.3–6.7 wt.%) and nitrogen dopants (0.1–4.5 wt.%). Thus, the impact of the heteroatom functionalities on Ctot is systematically investigated in an organic electrolyte excluding the effect of pore structures. It is found that heteroatom functionalities determine Ctot, resulting in the cyclic voltammetry curves being rectangular or butterfly-shaped. The nitrogen functionalities are found to significantly enhance Ctot owing to increased CQ.Item Hydrogen-Type Binding Sites in Carbonaceous Electrodes for Rapid Lithium Insertion(American Chemical Society, 2023-08) McGlamery, Devin; McDaniel, Charles; Xu, Wei; Stadie, Nicholas P.Direct pyrolysis of coronene at 800 °C produces low-surface-area, nanocrystalline graphitic carbon containing a uniquely high content of a class of lithium binding sites referred to herein as “hydrogen-type” sites. Correspondingly, this material exhibits a distinct redox couple under electrochemical lithiation that is characterized as intermediate-strength, capacitive lithium binding, centered at ∼0.5 V vs Li/Li+. Lithiation of hydrogen-type sites is reversible and electrochemically distinct from capacitive lithium adsorption and from intercalation-type binding between graphitic layers. Hydrogen-type site lithiation can be fully retained even up to ultrafast current rates (e.g., 15 A g–1, ∼40 C) where intercalation is severely hampered by ion desolvation kinetics; at the same time, the bulk nature of these sites does not require a large surface area, and only minimal electrolyte decomposition occurs during the first charge/discharge cycle, making coronene-derived carbon an exceptional candidate for high-energy-density battery applications.Item Stabilizing Effects of Phosphorus-Doped Silicon Nanoparticle Anodes in Lithium-Ion Batteries(ACS Publications, 2023-01) Gordon, Isabelle P.; Xu, Wei; Randak, Sophia; Jow, T. Richard; Stadie, Nicholas P.Phosphorus-doped silicon has been reported to exhibit improved cycling stability and/or higher capacity retention than pure silicon as the anode in lithium-ion batteries. However, crystallite size and particle morphology are difficult to decouple from compositional tuning during chemical modification. In this work, we explore direct solid-state routes to phosphorus doping of silicon powders relevant to electrochemical applications. A wide range of compositions are assessed, from 0.05 to 3.0 at % P, as well as a wide range of silicon starting materials of varying crystallinity, particle size, and particle morphology. Successful incorporation of phosphorus into the silicon lattice is best confirmed by X-ray diffraction; the Si(111) reflection shifts to higher angles as consistent with the known lattice contraction of 0.002 Å per 1 at % phosphorus. The addition of phosphorus to Si nanoparticles (100–500 nm) in the high doping regime causes grain coarsening and catalyzes an increase in crystallinity. On the other hand, dilute doping of phosphorus can be carried out without great alteration of the nanoparticulate morphology. The opposite effect occurs for very large microparticles (>10 μm), whereby the doping is concomitant with a disruption of the crystal lattice and reduction of the crystallite size. These effects are borne out in both the electrochemical stability over long-term cycling in a lithium-ion half-cell as well as in the thermal stability under high-temperature decomposition. By comparison across a wide range of pure and P-doped materials of varying particle and crystallite sizes, the independent effects of doping and structure on thermal and electrochemical stability are able to be decoupled herein. A stabilizing effect is most significant when phosphorus doping is dilute and heterogeneous (surface-enriched) within the silicon nanoparticles.