Harry Abernathy

Chemical reduction of three-dimensional silica micro-assemblies into microporous silicon replicas

The carbothermal reduction of silica into silicon requires the use of temperatures well above the silicon melting point (≥2,000 °C). Solid silicon has recently been generated directly from silica at much lower temperatures (≤850 °C) via electrochemical reduction in molten salts. However, the silicon products of such electrochemical reduction did not retain the microscale morphology of the starting silica reactants. Here we demonstrate a low-temperature (650 °C) magnesiothermic reduction process for converting three-dimensional nanostructured silica micro-assemblies into microporous nanocrystalline silicon replicas. The intricate nanostructured silica microshells (frustules) of diatoms (unicellular algae) were converted into co-continuous, nanocrystalline mixtures of silicon and magnesia by reaction with magnesium gas. Selective magnesia dissolution then yielded an interconnected network of silicon nanocrystals that retained the starting three-dimensional frustule morphology. The silicon replicas possessed a high specific surface area (>500 m2 g-1), and contained a significant population of micropores (≤20 Å). The silicon replicas were photoluminescent, and exhibited rapid changes in impedance upon exposure to gaseous nitric oxide (suggesting a possible application in microscale gas sensing). This process enables the syntheses of microporous nanocrystalline silicon micro-assemblies with multifarious three-dimensional shapes inherited from biological or synthetic silica templates for sensor, electronic, optical or biomedical applications.

GDC-Based Low-Temperature SOFCs Powered by Hydrocarbon Fuels

The critical issues facing the development of economically competitive solid oxide fuel cell (SOFC) systems include lowering the operation temperature and creating novel anode materials and microstructures capable of efficiently utilizing hydrocarbon fuels. In this paper, we report our recent progress in developing more efficient anodes for direct utilization of methane and propane in low-temperature SOFCs. Anode-supported SOFCs with an electrolyte of 20 μm thick Gd-doped ceria (GDC) were fabricated by copressing, and both Ni- and Cu-based anodes were prepared by a solution impregnation process. Results indicate that both microstructure and composition of the anodes, as fabricated using a solution impregnation technique, greatly influence fuel cell performance. At 600°C, SOFCs fueled with humidified H 2 , methane, and propane reach peak power densities of 602, 519, and 433 mW/cm 2 , respectively.

Synthesis and properties of phosphonic acid-grafted hybrid inorganic–organic polymer membranes

A class of phosphonic acid-grafted hybrid inorganic–organic polymer membranes was synthesized using a sol–gel process. Their thermal stability, water uptake, and proton conductivity were investigated. TGA–DSC analysis indicated that these membranes are thermally stable up to at least 220 °C in dry air. The proton conductivities of the new membranes increase with –PO3H2 group content and relative humidity, reaching 6.2 × 10−2 S cm−1 at 100 °C with ∼100% relative humidity, comparable to those of Nafion® under similar conditions. These new membranes have high proton conductivity at low relative humidity and thus have great potential to be used as electrolytes for high-temperature, low-humidity PEM fuel cells and other electrochemical applications. The proton conductivity of the membranes in the anhydrous state was enhanced by substitution of –CH2–PO3H2 groups with –CF2–PO3H2 groups owing to the large electron-withdrawing effect of C–F bonds. However, it was found that the concentration of –PO3H2 groups and the molecular structures of the new membranes are the key factors for the proton transport process in a humidified environment.

Raman spectroscopic monitoring of carbon deposition on hydrocarbon-fed solid oxide fuel cell anodes

Solid oxide fuel cells (SOFCs) are potentially the most efficient and cost-effective solution for the utilization of a wide variety of fuels beyond hydrogen. One of the chief obstacles to true fuel flexibility lies in anode deactivation by coking as well as a limited mechanistic understanding of coking and its prevention. Here we report Raman spectroscopic mapping and monitoring of carbon deposition on SOFC anode surfaces under both ex situ and in situ conditions. Carbon mapping was successfully demonstrated with a model Ni–YSZ electrode exposed to a CH4-containing atmosphere at high temperature (625 °C), while carbon deposition over time in a wet C3H8 atmosphere was directly monitored on a similar anode system as well as a BaO-modified system. This spectroscopic technique provides valuable insight into the mechanism of carbon deposition, which is vital in achieving rational design of carbon-tolerant anode materials.

Effect of Sr-Doped LaCoO3 and LaZrO3 Infiltration on the Performance of SDC-LSCF Cathode

The effects on performance of commercially produced solid oxide fuel cell (SOFC) were evaluated for two types of cathode infiltration: a mixed ionic-electronic conductor and an electronic insulator. The bi-layered cathode backbone consists of a thin, dual-phased functional layer containing Sm 2 O 3 -doped CeO 2 (SDC) and La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3―δ (LSCF) and a thick current collecting layer of LSCF. The backbone was infiltrated with either La 0.6 Sr 0.4 CoO 3 (LSCo) or La 1.97 Sr 0.03 Zr 2 O 7 (LSZ) using nitrate solution precursors, followed by calcination at 850 or 950°C, respectively. LSCo infiltration decreased the measured full cell overpotential by 28―40% after 6 wt % loading, and no further effect was observed with higher loading. The LSCo-infiltrated cells demonstrated stable performance for over 200 h of operation at 0.25 A/cm 2 and 750°C. Conversely, cathode infiltration with electrically insulating LSZ pyrochlore had a negative influence on the cathode performance that became substantial with increased infiltrate loading. Characteristic wetting behavior of the two infiltrates on the composite backbone affects the dependency of infiltrate amounts on cathode performance. The results imply that the composite cathode reaction is primarily under the control of the surface exchange reaction rate. This comparative study demonstrates that the cathode performance of a commercially produced SOFC can be influenced by applying infiltrates in a simple process, and indicates that the infiltrates electrocatalytic activity and conductivity must be carefully considered when infiltrating a standard SDC-LSCF cathode.

FTIR STUDY OF THE OXYGEN REDUCTION REACTIONS ON Sm0.5Sr0.5CoO3

The oxygen reduction on solid oxide fuel cell cathode electrode, Sm0.5Sr0.5CoO3, was studied by using emission Fourier transform infrared spectroscopy (FTIR). Superoxide

Characterization of O2–CeO2 Interactions Using In Situ Raman Spectroscopy and First-Principle Calculations

(O_{2}^{-})

Raman Spectroscopy of Nickel Sulfide Ni3S2

species was detected with appearance of an IR peak at wavenumber about 1124 cm-1. Moreover, we interpreted for the first time that there would be a close relationship between the baseline shift of IR spectra and the oxygen vacancy concentration (OVC) of the samples. The downward baseline shift of IR spectra is due to the decrease of OVC in the bulk, while, the increase of the OVC in the bulk would cause the upward baseline shift.