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Urban, Jeffrey J. (ORCID:0000000349092869)

Publications and source records attributed to Urban, Jeffrey J. (ORCID:0000000349092869).

8 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Challenging thermodynamics: combining immiscible elements in a single-phase nano-ceramic

Abstract The Hume-Rothery rules governing solid-state miscibility limit the compositional space for new inorganic material discovery. Here, we report a non-equilibrium, one-step, and scalable flame synthesis method to overcome thermodynamic limits and incorporate immiscible elements into single phase ceramic nanoshells. Starting from prototype examples including (NiMg)O, (NiAl)O x , and (NiZr)O x , we then extend this method to a broad range of Ni-containing ceramic solid solutions, and finally to general binary combinations of elements. Furthermore, we report an “encapsulated exsolution” phenomenon observed upon reducing the metastable porous (Ni 0.07 Al 0.93 )O x to create ultra-stable Ni nanoparticles embedded within the walls of porous Al 2 O 3 nanoshells. This nanoconfined structure demonstrated high sintering resistance during 640 h of catalysis of CO 2 reforming of methane, maintaining constant 96% CH 4 and CO 2 conversion at 800 °C and dramatically outperforming conventional catalysts. Our findings could greatly expand opportunities to develop novel inorganic energy, structural, and functional materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Comparing Theoretical Salt Concentration Profiles in a Polymer Electrolyte with Experimental Measurements using Operando Raman Spectroscopy

Concentrated solution theory has furthered our understanding of ion transport in electrolytes. This theory can be used to predict salt concentration profiles under an applied current if the transport properties of the electrolyte (conductivity ( κ ), restricted diffusion coefficient ( D ), and the cation transference number with respect to the solvent velocity ( t + 0 )), and the thermodynamic factor ( T f ) are known. In this work, we provide the first study comparing the predicted salt concentration profiles with measurements based on operando Raman spectroscopy. Concentration polarization is asymmetrical; the increase in salt concentration near the positive electrode is a factor of two greater than the decrease in salt concentration near the negative electrode. We find qualitative agreement between theory and experiment. Further work is needed to resolve the quantitative differences.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Selective hydrogenation via precise hydrogen bond interactions on catalytic scaffolds

Abstract The active site environment in enzymes has been known to affect catalyst performance through weak interactions with a substrate, but precise synthetic control of enzyme inspired heterogeneous catalysts remains challenging. Here, we synthesize hyper-crosslinked porous polymer (HCPs) with solely -OH or -CH 3 groups on the polymer scaffold to tune the environment of active sites. Reaction rate measurements, spectroscopic techniques, along with DFT calculations show that HCP-OH catalysts enhance the hydrogenation rate of H-acceptor substrates containing carbonyl groups whereas hydrophobic HCP- CH 3 ones promote non-H bond substrate activation. The functional groups go beyond enhancing substrate adsorption to partially activate the C = O bond and tune the catalytic sites. They also expose selectivity control in the hydrogenation of multifunctional substrates through preferential substrate functional group adsorption. The proposed synthetic strategy opens a new class of porous polymers for selective catalysis.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Nanoscale insights into the structure of solution-processed graphene by x-ray scattering

Abstract Chemical exfoliation is an attractive approach for the synthesis of graphene due to its low cost and simplicity. However, challenges still remain in the characterization of solution-processed graphene, in particular with atomic resolution. Through this work we demonstrate the x-ray pair distribution function as a novel approach to study solution-processed graphene or other 2D materials with atomic resolution, directly in solution, produced by liquid-phase and electrochemical exfoliations. The results show the disappearance of long-range atomic correlations, in both cases, confirming the production of single and few-layer graphene. In addition, a considerable ring distortion has been observed as compared to graphite, irrespective of the solvent used: the normal surface angle to the sheet of the powder sample should be less than 6°, compatible with ripples formation observed in suspended graphene. We attribute this effect to the interaction of solvent molecules with the graphene nanosheets.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Spontaneous dynamical disordering of borophenes in MgB2 and related metal borides

Abstract Layered boron compounds have attracted significant interest in applications from energy storage to electronic materials to device applications, owing in part to a diversity of surface properties tied to specific arrangements of boron atoms. Here we report the energy landscape for surface atomic configurations of MgB 2 by combining first-principles calculations, global optimization, material synthesis and characterization. We demonstrate that contrary to previous assumptions, multiple disordered reconstructions are thermodynamically preferred and kinetically accessible within exposed B surfaces in MgB 2 and other layered metal diborides at low boron chemical potentials. Such a dynamic environment and intrinsic disordering of the B surface atoms present new opportunities to realize a diverse set of 2D boron structures. We validated the predicted surface disorder by characterizing exfoliated boron-terminated MgB 2 nanosheets. We further discuss application-relevant implications, with a particular view towards understanding the impact of boron surface heterogeneity on hydrogen storage performance.

36 MATERIALS SCIENCE↗