Publications

55 Results
Skip to search filters

Enhanced alkaline stability in a hafnium-substituted NaSICON ion conductor

Journal of Materials Chemistry A

Small, Leo J.; Wheeler, Jill S.; Ihlefeld, Jon F.; Clem, Paul G.; Spoerke, Erik D.

We present here a multi-length scale integration of compositionally tailored NaSICON-based Na+ conductors to create a high Na+ conductivity system resistant to chemical attack in strongly alkaline aqueous environments. Using the Pourbaix Atlas as a generalized guide to chemical stability, we identify NaHf2P3O12 (NHP) as a candidate NaSICON material for enhanced chemical stability at pH > 12, and demonstrate the stability of NHP powders under accelerated aging conditions of 80 °C and pH = 13-15 for a variety of alkali metal cations. To compensate for the relatively low ionic conductivity of NHP, we develop a new low temperature (775 °C) alkoxide-based solution deposition chemistry to apply dense NHP thin films onto both platinized silicon wafers and bulk, high Na+ conductivity Na3Zr2Si2PO12 (NZSP) pellets. These NHP films display Na+ conductivities of 1.35 × 10-5 S cm-1 at 200 °C and an activation energy of 0.53 eV, similar to literature reports for bulk NHP pellets. Under aggressive conditions of 10 M KOH at 80 °C, NHP thin films successfully served as an alkaline-resistant barrier, extending the lifetime of NZSP pellets from 4.26 to 36.0 h. This integration of compositionally distinct Na+ conductors across disparate length scales (nm, mm) and processing techniques (chemically-derived, traditional powder) represents a promising new avenue by which Na+ conducting systems may be utilized in alkaline environments previously thought incompatible with ceramic Na+ conductors.

More Details
TYPE Journal Article YEAR 2018
ScopusOSTIDOI

MOF-Sensitized Solar Cells Enabled by a Pillared Porphyrin Framework

Journal of Physical Chemistry C

Spoerke, Erik D.; Small, Leo J.; Foster, Michael E.; Wheeler, Jill S.; Ullman, Andrew M.; Stavila, Vitalie S.; Rodriguez, Mark A.; Allendorf, Mark D.

Metal-organic frameworks (MOFs) are highly ordered, functionally tunable supramolecular materials with the potential to improve dye-sensitized solar cells (DSSCs). Several recent reports have indicated that photocurrent can be generated in Grätzel-type DSSC devices when MOFs are used as the sensitizer. However, the specific role(s) of the incorporated MOFs and the potential influence of residual MOF precursor species on device performance are unclear. Herein, we describe the assembly and characterization of a simplified DSSC platform in which isolated MOF crystals are used as the sensitizer in a planar device architecture. We selected a pillared porphyrin framework (PPF) as the MOF sensitizer, taking particular care to avoid contamination from light-absorbing MOF precursors. Photovoltaic and electrochemical characterization under simulated 1-sun and wavelength-selective illumination revealed photocurrent generation that is clearly ascribable to the PPF MOF. Continued refinement of highly versatile MOF structure and chemistry holds promise for dramatic improvements in emerging photovoltaic technologies. (Figure Presented).

More Details
TYPE Journal Article YEAR 2017
ScopusOSTIDOI

Isomer-sensitive deboronation in reductive aminations of aryl boronic acids

Tetrahedron Letters

Jones, Brad H.; Wheeler, David R.; Wheeler, Jill S.; Miller, Lance L.; Alam, Todd M.; Spoerke, Erik D.

Deboronation is observed during the reductive amination of formylphenylboronic acid (FPBA) to the amine termini and side chains of peptides. This deboronation is sensitive to the isomerism of the boronic acid (BA), with ortho-FPBA yielding complete deboronation in the preparation of an N-terminally-modified dipeptide. The observed behavior is also clearly mediated by the chemical identity of the amine substrate. These results reveal a previously undocumented subtlety of BA functionalization and highlight the importance of thorough spectroscopic characterization in the preparation of peptide and small molecule BAs.

More Details
TYPE Journal Article YEAR 2015
ScopusOSTIDOI

A multi-stimuli responive, self-assembling, boronic acid dipeptide

ChemComm

Jones, Brad H.; Martinez, Alina M.; Wheeler, Jill S.; McKenzie, Bonnie B.; Miller, Lance L.; Wheeler, David R.; Spoerke, Erik D.

Modification of the dipeptide of phenylalanine, FF, with a boronic acid (BA) functionality imparts unique aqueous self-assembly behavior that responds to multiple stimuli. Changes in pH and ionic strength are used to trigger hydrogelation via the formation of nanoribbon networks. Thus, we show for the first time that the binding of polyols to the BA functionality can modulate a peptide between its assembled and disassembled states.

More Details
TYPE Journal Article YEAR 2015
OSTIDOI

Surfactant-induced assembly of enzymatically-stable peptide hydrogels

Soft Matter

Jones, Brad H.; Martinez, Alina M.; Wheeler, Jill S.; Spoerke, Erik D.

The secondary structure of peptides in the presence of interacting additives is an important topic of study, having implications in the application of peptide science to a broad range of modern technologies. Surfactants constitute a class of biologically relevant compounds that are known to influence both peptide conformation and aggregation or assembly. We have characterized the secondary structure of a linear nonapeptide composed of a hydrophobic alanine/phenylalanine core flanked by hydrophilic acid/amine units. We show that the anionic surfactant sodium dodecyl sulfate (SDS) induces the formation of β-sheets and macroscopic gelation in this otherwise unstructured peptide. Through comparison to related additives, we propose that SDS-induced secondary structure formation is the result of amphiphilicity created by electrostatic binding of SDS to the peptide. In addition, we demonstrate a novel utility of surfactants in manipulating and stabilizing peptide nanostructures. SDS is used to simultaneously induce secondary structure in a peptide and to inhibit the activity of a model enzyme, resulting in a peptide hydrogel that is impervious to enzymatic degradation. These results complement our understanding of the behavior of peptides in the presence of interacting secondary molecules and provide new potential pathways for programmable organization of peptides by the addition of such components.

More Details
TYPE Journal Article YEAR 2015
ScopusOSTIDOI

Direct-write, chemically-prepared temperature insensitive dielectrics

Hernandez-Sanchez, Bernadette A.; Lu, Ping L.; Garino, Terry J.; Sipola, Diana L.; Bell, Nelson S.; Wheeler, Jill S.

Development of high energy density dielectrics with low temperature coefficients of capacitance that are systems integrable are needed for extreme environment, defense and automotive applications. The synthesis of high purity chemically prepared Ca(Zr,Ti)O3 powders is described and has resulted in the lowering of conventional firing temperatures by over 100 C. Direct write aerosol spray deposition techniques have been used to fabricate high quality single layer and multilayer capacitors from these powders. The dielectric constants of the direct write capacitors are equivalent to those of fired bulk ceramics. Our presentation emphasizes the synthesis, phase evolution and microstructure development that has resulted in dielectrics with energy densities in excess of 3 J/cm3 with less than 1% change in dielectric constant over a 200 C temperature range.

More Details
TYPE Conference YEAR 2010
OSTI

Lightning arrestor connector lead magnesium niobate qualification pellet test procedures

Wheeler, Jill S.; Mahoney, Patrick M.

Enhanced knowledge preservation for DOE DP technical component activities has recently received much attention. As part of this recent knowledge preservation effort, improved documentation of the sample preparation and electrical testing procedures for lead magnesium niobate--lead titanate (PMN/PT) qualification pellets was completed. The qualification pellets are fabricated from the same parent powders used to produce PMN/PT lightning arrestor connector (LAC) granules at HWF&T. In our report, the procedures for fired pellet surface preparation, electrode deposition, electrical testing and data recording are described. The dielectric measurements described in our report are an information only test. Technical reasons for selecting the electrode material, electrode size and geometry are presented. The electrical testing is based on measuring the dielectric constant and dissipation factor of the pellet during cooling from 280 C to 220 C. The most important data are the temperature for which the peak dielectric constant occurs (Curie Point temperature) and the peak dielectric constant magnitude. We determined that the peak dielectric constant for our procedure would be that measured at 1 kHz at the Curie Point. Both the peak dielectric constant and the Curie point parameters provide semi-quantitative information concerning the chemical and microstructural homogeneity of the parent material used for the production of PMN/PT granules for LACs. Finally, we have proposed flag limits for the dielectric data for the pellets. Specifically, if the temperature of the peak dielectric constant falls outside the range of 250 C {+-} 30 C we propose that a flag limit be imposed that will initiate communication between production agency and design agency personnel. If the peak dielectric constant measured falls outside the range 25,000 {+-} 10,000 we also propose that a flag limit be imposed.

More Details
TYPE SAND Report YEAR 2009
OSTIDOI
55 Results
55 Results