Maxwell A. T. Marple

Nanocrystalline diamond (NCD) targets have recently enabled inertial confinement fusion (ICF) ignition at the National Ignition Facility (NIF), with gains exceeding the input laser energy. Achieving ignition requires NCD targets with carefully tuned density profiles and high material uniformity to minimize fuel‐ablator mix. Here, we report on the fabrication of high‐isotopic‐purity ¹³ C‐NCD capsules with a ¹³ C/ ¹² C ratio greater than 100 and a density of 3.64 g cm ⁻³ , 8% higher than comparable ¹² C‐NCD coatings. The higher density shortens shock transit times, offering symmetry control advantages and enabling density gradient tuning across NCD/W‐NCD interfaces for improved implosion stability. ¹³ C‐NCD also opens a new diagnostic platform for studying fuel‐ablator mix and yield in NIF ICF experiments through ¹³ N production via the ¹³ C(p,n) ¹³ N reaction. Leveraging high isotopic purity of ¹³ C‐NCD coatings, we perform quantitative characterization of non‐diamond carbon phases using solid‐state direct‐polarization nuclear magnetic resonance (NMR) spectroscopy. This reveals the presence of hydrogenated carbon (2.9 at.%), graphitic carbon (0.5 at.%), and tetrahedral amorphous carbon (0.4 at.%), yielding previously unavailable insight into NCD ablator composition and structure. This work clarifies the nature of NCD ablator shells and lays the foundation for new target designs that exploit ¹³ C‐NCD's higher density and enable diagnostics for ICF experiments.

Nanoconfinement of metastable hydrides such as alane (AlH₃) in functionalized porous frameworks represents a promising yet largely untapped strategy for high-capacity energy storage. Despite its potential, the underlying mechanisms responsible for the thermodynamic stabilization of metastable hydrides are poorly understood. Here, concepts from solution Lewis acid-base chemistry were applied to a crystalline metal-organic framework (MOF) to stabilize AlH₃. The long-range order and synthetically versatile pore chemistry enabled us to reveal the intimate details of the hydride-host interactions. Powder X-ray diffraction (PXRD) of AlH₃-infiltrated UiO-67bpy (Zr₆O₄(OH)₄(bpydc)₆; bpydc^2- = 2,2'-bipyridine-5,5'-dicarboxylate) confirms that the framework maintains its crystallinity up to 250 °C and is stable under 70 MPa H₂ pressure. We find that thermodynamic stabilization arises from coupled single-electron and hydrogen-atom transfer from AlH₃ to bipyridine-containing linkers. Electron paramagnetic resonance detects a bipyridyl radical with an anisotropic g-tensor (g values of 2.00132, 2.00215, and 2.00275), consistent with Bader charge analysis predicting 0.82 e^- transferred from the hydride to the MOF. These findings establish critical structure-property relationships underpinning AlH₃ stabilization and suggest general strategies for tuning the thermodynamics and kinetics of metastable materials.

Aminopolymer‐based adsorbents are a prominent class of materials being used for direct air capture of CO ₂ at the industrial scale. However, improving their working lifetime, specifically by increasing their resilience to oxidative degradation, remains an ongoing challenge. Toward this end, functionalization of aminopolymers with non‐amine functionalities such as hydroxyls has emerged in recent years as a promising strategy toward improving adsorbent lifetime. Although there is a growing body of work demonstrating the effectiveness of this approach and investigating the origin of this improved stability, studies to date have primarily focused on branched aminopolymer systems such as branched poly(ethylenimine). In this work, hydroxyl‐functionalized linear poly(ethylenimine) is used to continue to probe the underlying protective mechanism of this strategy. A combination of thermogravimetric analysis, NMR relaxometry, differential scanning calorimetry, and computational simulations is used to better understand the relationship between the extent of chemical functionalization, physical properties, and adsorbent performance.

Aminopolymer-based adsorbents are a prominent class of materials being used for direct air capture of CO2 at the industrial scale. However, improving their working lifetime, specifically by increasing their resilience to oxidative degradation, remains an ongoing challenge. Towards this end, functionalization of aminopolymers with non-amine functionalities such as hydroxyls has emerged in recent years as a promising strategy towards improving adsorbent lifetime. Although there is a growing body of work demonstrating the effectiveness of this approach and investigating the origin of this improved stability, studies to date have primarily focused on branched aminopolymer systems such as branched poly(ethylenimine). In this work, we use hydroxyl-functionalized linear poly(ethylenimine) to continue to probe the underlying protective mechanism of this strategy. A combination of thermogravimetric analysis, NMR relaxometry, differential scanning calorimetry, and computational simulations is used to better understand the relationship between extent of chemical functionalization, physical properties, and adsorbent performance.

Elevated thermal treatments increase the CO₂ capacity of aminosilane-grafted SBA-15 sorbents through freeing up additional surface hydroxyls and favoring CO₂ binding as carbamic acid.

Aminopolymer‐based adsorbents are commonly investigated for CO₂ direct air capture (DAC). In the presence of high temperature and oxygen, which can occur during adsorption‐regeneration cycles, oxidative degradation can significantly reduce adsorbent lifetime. Degradation is typically measured using adsorption performance metrics or chemical characterization. This work demonstrates that the polymer's physical properties, as measured via nuclear magnetic resonance (NMR) relaxometry and differential scanning calorimetry, can be used to quantitatively track degradation. The extent of oxidation of an alumina‐poly(ethylenimine) sample, measured by reductions in amine efficiency (A.E.), is correlated with proton T₂ relaxation times. This work hypothesizes that T₂ relaxation accurately tracks oxidative degradation in aminopolymers due to the reduction in polymer mobility occurring during the oxidation process. The ability to use NMR relaxometry as a noninvasive technique to probe degradation is demonstrated on a 1‐inch square‐channel monolith adsorbent exposed to actual DAC service conditions. This highlights the potential for relaxometry to evaluate the state of the adsorbent accurately and rapidly compared to typical analytical methods.

The production of ceramics from uranium coordination compounds can be achieved through thermal processing if an excess amount of the desired atoms (i.e., C or N), or reactive gaseous products (e.g., methane or nitrogen oxide) is made available to the reactive uranium metal core via decomposition/fragmentation of the surrounding ligand groups. Here, computational thermodynamic approaches were utilized to identify the temperatures necessary to produce uranium metal from some starting compounds-UI4(TMEDA)(2), UCl4(TMEDA)(2), UCl3(pyridine)(x) , and UI3(pyridine)(4). Experimentally, precursors were irradiated by a laser under various gaseous environments (argon, nitrogen, and methane) creating extreme reaction conditions (i.e., fast heating, high temperature profile >2000 degrees C, and rapid cooling). Despite the fast dynamics associated with laser irradiation, the central uranium atom reacted with the thermal decomposition products of the ligands yielding uranium ceramics. Residual gas analysis identified vaporized products from the laser irradiation, and the final ceramic products were characterized by powder X-ray diffraction. The composition of the uranium precursor as well as the gaseous environment had a direct impact on the production of the final phases.

Combined modeling and experiments uncover the influence of epoxide-functionalization on hydrogen bonding and mobility within poly(ethylenimine) CO ₂ sorbents, rationalizing the antidegradation benefits conferred by functionalization.