Alexander Travis Brown

In prior work, porous nickel foams have been investigated to enhance the performance of proton exchange membrane fuel cells (PEMFCs) by improving mass transport and water management when used in place of bipolar plates with conventional flow fields. This work simplifies PEMFC cathodes by replacing the conventional flow field (FF), gas diffusion layer (GDL), and microporous layer (MPL) with nickel foam. We compare the cell-level performance of a PEMFC with a conventional serpentine flow field to three cells utilizing nickel foam. Electrochemical impedance spectroscopy shows nickel foam reduces the charge transfer and mass transport resistances, although it can also increase interfacial contact resistance. Parasitic pump power consumption was estimated using the cathode side pressure drop as a function of air flow rate. When system-level pump power is considered, cells utilizing nickel foam have net power output comparable to a conventional fuel cell. These simple nickel foam-based fuel cells demonstrate an alternative, simpler design that eliminates the need for expensive bipolar plates with complex flow fields. Ultimately, the highest performing cathode examined in this study, a wet-laid MPL on nickel foam, is shown to yield peak power density of 1531 mW·cm-2 under optimized conditions.

There is a need to develop new solid-phase adsorbents to extract elements from the coal ash. High surface area carbon adsorbents are remarkably good at adsorption of rare earth elements and have good stability in acidic media. A high surface area (1162 m²/g), surface-oxidized microsphere flower carbon (MFC-O) has been prepared for the extraction of rare earth elements as well as thorium and uranium. MFC-O exhibits outstanding distribution coefficients up to k_d = 1.2 × 10⁶ for thorium, uranium, and rare earth elements. It was found that thorium and uranium can be separated from the rare earth elements by adjusting the pH. The maximum extraction capacity (71.3 mg/g) was performed up to 88 ppm with 18 competitive elements (Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Th, and U), and element recovery was >85%. A coal ash sample (NIST SRM 1633c) with a known concentration of elements (Na, Ca, Al, Si, Fe, Sc, La, Ce, Nd, Sm, Eu, Tb, Dy, Yb, Lu, Th, and U) was leeched resulting in 45% Ce recovery. The leeched solution from NIST 1633c was then mixed with MFC-O for Ce extraction of 74%, Na (17%), Ca (13%), Al (24%), Si (41%), and Fe (17%). The binding properties of MFC-O show that it is an attractive material for the selective extraction of rare earth elements from coal ash.

The biological response of multi-walled carbon nanotubes (MWNTs) is related to their physicochemical properties and a thorough MWNT characterization should accompany an assessment of their biological activity, including their potential toxicity. Beyond characterizing the physicochemical properties of MWNTs from different sources or manufacturers, it is also important to characterize different production lots of the same MWNT product from the same vendor (i.e., lot-to-lot batch consistency). Herein, we present a comprehensive physicochemical characterization of two lots of commercial pristine MWNTs (pMWNTs) and carboxylated MWNTs (cMWNTs) used to study the response of mammalian macrophages to MWNTs. There were many similarities between the physicochemical properties of the two lots of cMWNTs and neither significantly diminished the 24-h proliferation of RAW 264.7 macrophages up to the highest concentration tested (200 μg cMWNTs/mL). Conversely, several physicochemical properties of the two lots of pMWNTs were different; notably, the newer lot of pMWNTs displayed less oxidative stability, a higher defect density, and a smaller amount of surface oxygen species relative to the original lot. Furthermore, a 72-h half maximal inhibitory concentration (IC-50) of ~90 µg pMWNTs/mL was determined for RAW 264.7 cells with the new lot of pMWNTs. These results demonstrate that subtle physicochemical differences can lead to significantly dissimilar cellular responses, and that production-lot consistency must be considered when assessing the toxicity of MWNTs.

Liquid fluoride thorium reactors have been considered as replacements for uranium-based nuclear reactors, having many economic and environmental advantages. The production of thorium is usually accompanied by the separation of thorium from rare earth elements since the major thorium production mineral, monazite, contains other rare earth elements. The conventional manufacturing process involves a liquid–liquid extraction with organic ligands. There is a need to develop solid state absorbents with good reusability for metal ion separation processes. Porous carbon is particularly interesting due to acid/base resistance. A new absorbent, surface-oxidized wrinkled mesoporous carbon (WMC-O), has been prepared for the selective extraction of thorium ions from rare earth ions. WMC-O shows high selectivity for thorium adsorption due to the 4+ oxidation state of thorium. The distribution coefficient (K_d) of the WMC-O for thorium from all rare earth elements is 2 orders of magnitude larger than that of surface-oxidized activated carbon (13 × 10⁴ vs 35 × 10² at pH 2.15). WMC-O also shows a high adsorption capacity for pure rare earth ions (K_d > 3 × 10⁵). These features make WMC-O a promising absorbent for thorium extraction and rare earth ion recovery.

Motivated by the complex structure and properties of giant unit cell intermetallic compounds, a new isostructural Fe analogue of the Dy₁₁₇Co₅₇Sn₁₁₂ structure type was synthesized. Single crystals of Dy₁₂₂Fe₅₅Sn₁₀₁ were grown at 1260 °C via a Dy–Fe eutectoid flux. The Fe analogue also adopts the space group Fm3m with lattice parameters a = 29.914(9) Å, V = 26769(23) ų, and Z = 4. Dy₁₂₂Fe₅₅Sn₁₀₁ has a large cell volume, structural complexity, and consists of seven Dy, eight Fe, and ten Sn unique crystallographic sites. There are fifteen fully occupied atomic positions, three unique pairs of alternating atomic positions with positional disorder, and seven partially occupied atomic sites. Within this complex unit cell, only approximately half the unique atomic positions are fully occupied with the remainder of the atoms either positionally or occupationally disordered. X‐ray photoelectron spectroscopy indicates that the compound contains Dy³⁺, Fe⁰, Fe²⁺, Sn⁰, and Sn⁴⁺.