Degree Sign Research Articles

Improving the Sulphur Tolerance of Nickel Catalysts for Running Solid Oxide Fuel Cells on Waste Biogas

To explore the possibility of running Solid Oxide Fuel Cells (SOFC) on biogas, reactions of 2/1 CH4/CO2 gas mixtures over Ni/YSZ (yttria-stabilised zirconia) SOFC anode materials have been investigated using on-line quadrupole mass spectrometry in the temperature range 750-1000{degree sign}C. Carbon deposition has been analysed by post-reaction temperature programmed oxidation (TPO). Hydrogen sulphide (H2S) added to the reactant stream established the effect of sulphur containing gases on the reforming characteristics, carbon deposition and durability of nickel-based anodes. In addition to investigating the behaviour of a conventional Ni/YSZ anode, the performance of gold-, hafnia- and ceria-doped Ni/YSZ anodes were also studied in terms of their influence on the reforming activity, carbon deposition and sulphur tolerance.

Gating currents from neuronal KV7.4 Channels: General features and correlation with the ionic conductance

The KV7 (KCNQ) subfamily of voltage-gated K+ channels consists of five members (KV7.1- KV7.5) giving rise to non-inactivating, and slowly activating/deactivating currents mainly expressed in cardiac (KV7.1) and neuronal (KV7.2- KV7.5) tissue. In the present study, using the cut-open oocyte voltage clamp, we studied the relation of the ionic currents from homomeric neuronal Kv7 channels (KV7.2-KV7.5) with the gating currents recorded after K+ conductance blockade from the same channels. Increasing the recording temperature from 18{degree sign}C to 28{degree sign}C accelerated activation/deactivation kinetics of the ionic currents in all homomeric KV7 channels (activation Q10s at 0 mV were 3.8, 4.1, 8.3, and 2.8 for Kv7.2, Kv7.3, Kv7.4 and Kv7.5 channels, respectively), without large changes in currents voltage-dependence; moreover, at 28{degree sign}C, ionic currents carried by KV7.4 channels also showed a significant increase in their maximal value. Gating currents were only resolved in KV7.4 and KV7.5 channels; the size of the ON gating charges at +40 mV was 1.34 ± 0.34 nC for KV7.4, and 0.79 ± 0.20 nC for KV7.5. At 28{degree sign}C, KV7.4 gating currents had the following salient properties: 1) similar time integral of QON and QOFF, indicating no charge immobilization; 2) a left-shift in the V1/2 of the QON/V when compared to the G/V (≈ 50 mV in the presence of 2 mM extracellular Ba2+); 3) a QON decay faster than ionic current activation; and 4) a rising phase in the OFF gating charge after depolarizations larger than 0 mV. These observations suggest that, in KV7.4 channels, VSD movement is followed by a slow and/or low bearing charge step linking to pore opening, a result which may help to clarify the molecular consequence of disease-causing mutations and drugs affecting channel gating.

Atomic Layer Doping for Future Si Based Devices

The concept of atomic-level processing based on atomic-order surface reaction control is discussed. The main idea of the atomic layer approach is the control of the process by surface reactions at very low temperatures (even at room temperature). Results of B and P atomic layer doping of Si, Ge and SiGe are reviewed and discussed focussing on the control of the surface adsorption by changing temperatures and partial pressures of the dopant gases. For B atomic layer doping of SiGe and pure Ge using B2H6, high doping levels and steep doping profiles have been reached. The process was found to be self-limited at ~100{degree sign}C indicating preferred adsorption of B2H6 on Si and Ge sites and suppression of B cluster formation. In the case of B atomic layer doping of Si it is shown that the technique can be used for the selective deposition of polycrystalline Si. For P atomic layer doping of SiGe self-limitation of the process has been observed for temperatures between 200-550{degree sign}C allowing very precise dopant dose and location control.

Effect of Freezing Conditions on PEM-FC Components

For mobile applications, performance of polymer electrolyte membrane fuel cells (PEM-FCs) should be maintained with being exposed to subzero temperatures in winter time. To simulate such a situation, a single cell PEM-FC was operated at 70{degree sign}C, stopped, kept at -10{degree sign}C for 8 h, and heated to 80{degree sign}C for the next operation. The cell was unable to work. The degradation was attributed to freezing of water present inside the MEA, produced during operation, and remained in the PEMFC after the operation. To prevent the performance degradation, water was removed from the PEM-FC by supplying dry N2 to the PEM-FC before the cell temperature fell down to -10{degree sign}C. Several freezing/thawing cycles were operated to study the PEM-FC performance degradation. Effects of water freezing in the PEM-FC on the electrode structure were examined by SEM analysis.

Atomic Layer Deposition of Antimony Oxide on Hydrogen-terminated Silicon Substrates

Atomic layer deposition thin antimony oxide films on silicon substrates was investigated. Growth of small crystallites could be obtained by using triisopropylantimony (SbiPr3) and water. The deposition of thin continuous films succeeded after employing ozone and SbiPr3. The growth rate was significantly higher for the higher deposition temperature: 0.16 nm/cycle at 300 {degree sign}C compared to 0.06 nm/cycle at 200 {degree sign}C. X-ray photoelectron spectroscopy detected no impurities in the film other than adventitious carbon at surface. A composition ratio of antimony to oxide of 27/73 was found, suggesting the occurrence of the pentavalent oxide Sb2O5. The oxide is prone to sputter reduction during depth profiling. A chemical shift in the binding energy of the Sb photoemission peaks from the oxide to the Sb0 state clearly arises already after gentle argon sputtering. At temperatures up to 40 {degree sign}C the as-deposited films showed remarkably resistance to buffered oxide etch and nitric acid.

Electrodeposition of an Iron-Cobalt Phase Isostructural to α-Mn

Electrodeposition at elevated temperatures from a dibasic ammonium citrate-stabilized iron-cobalt electroplating solution is shown to promote the deposition of a metastable phase. The metastable phase is isostructural to α-Mn. XRD analysis indicated that the α-Mn-type phase begins to be deposited at temperatures between 30{degree sign}C and 40{degree sign}C. Below this the equilibrium BCC phase is deposited. Plating at 60{degree sign}C produced deposits composed completely of the α-Mn-type phase. TEM analysis indicated that increasing the plating temperature refined the deposit's grain structure and also led to regions with preferred orientation. Annealing of deposits composed of the α-Mn-type phase above its transformation temperature resulted in the formation of a textured BCC phase. The presence of the α-Mn-type phase led to high deposit coercivities. Annealing of deposits, which resulted in transformation of the α-Mn-type phase to the BCC phase, reduced their coercivities. The coercivities of these films, however, were not reduced to the level of those deposits which were plated as the BCC phase. In deposits completely composed of the BCC phase, either plated as such or transformed, annealing led to higher coercivities. This is attributed to coarsening of the deposit microstructure.

Low Temperature SOFC Cathode Layer Deposited by Reactive Spray Deposition Technology (RSDT)

Present work presents the results obtained by using a direct deposition technique to make SOFC cathode materials that either significantly reduce or eliminate the need for sintering. A reference composite cathode made of 75 wt.% Sm0.5Sr0.5CoO3 (SSC) and 25 wt.% Sm0.2Ce0.8O1.9 (SDC) has been applied on a cermet supported thin SDC electrolyte cell. Cell peak power performance was measured to be 0.49 W cm−2 operating at 600 {degree sign}C after firing at 1050 {degree sign}C. The measured total electrode polarization Rp(a + c) was 0.102 Ω cm2 at 600 {degree sign}C. In this study a thin (~5 μm) SSC cathode has been applied by Reactive Spray Deposition Technology (RSDT) and the total polarization was reduced to 0.079 Ω cm2, indicating over 20% reduction of losses compared to the traditional cathode processing route

Development of IT-SOFC Based on Lanthanum Gallate Electrolyte

The Kansai Electric Power Company, Inc. and Mitsubishi Materials Corporation started a joint research project for developing intermediate temperature (600{degree sign}C to 800{degree sign}C) solid oxide fuel cells (IT-SOFC) in 2001. High performance disk-type cells with lanthanum gallate-based electrolyte and a seal-less cell-stack design enable high efficiency operation at temperatures below 800{degree sign}C. The development of 10 kW-class CHP system under a project supported by NEDO (New Energy and Industrial Technology Development Organization) was started in FY2004. In 2007, the performance test of the 10 kW-class system using town gas as fuel has been undertaken. In this test, the electrical efficiency of 41%HHV on AC power output of 10 kW and the overall efficiency of 82%HHV by recovering 60åC hot water have been achieved. And the voltage degradation rate per 1,000 hours was 1.08% after 3,000 hours operation has been observed during the field test of the 10 kW-class system. Furthermore, after making some refinements to enhance the performance of 10 kW-class module, the second long-term stability test for 3,000 hours were carried out in 2008. Efforts to enhance cell and module durability have been made with 1 kW-class modules operated for 5,000 hours, and with the cell-stack units operated for 15,000 hours. The voltage degradation rates per 1,000 hours were 0.51 % for the 1 kW-class modules, and 0.23 - 0.48% for the cell-stack units.

A Wide Range Temperature Sensor Using SOI Technology

Silicon-on-insulator (SOI) technology is becoming widely used in integrated circuit chips for its advantages over the conventional silicon counterpart. The decrease in leakage current combined with lower power consumption allows electronics to operate in a broader temperature range. This paper describes the performance of an SOI-based temperature sensor under extreme temperatures and thermal cycling. The sensor comprised of a temperature-to-frequency relaxation oscillator circuit utilizing an SOI precision timer chip. The circuit was evaluated under extreme temperature exposure and thermal cycling between -190 {degree sign}C and +210 {degree sign}C. The results indicate that the sensor performed well over the entire test temperature range and it was able to re-start at extreme temperatures.

65nm Low Power (LP) SOI Technology on High Resistivity (HR) Substrate for WLAN and Mmwave SOCs

We present a 65nm RF SOI CMOS technology, targeted as Low Power (LP) to serve mobile applications. The integration has been made on High Resistive (HR) back substrate 300mm SOI wafers from SOITEC to improve performances in high frequency range, compared to bulk [1, 2]. For the first time, low leakage SRAM (Isb< 10pA at 0.9V, 25{degree sign}C, for 0.62µm2 and 0.52µm2 cells) are integrated on these HR wafers, and the paper reports a 30% power reduction in operation for a given maximum speed, compared to similar SRAM design on bulk. Furthermore, we have demonstrated a 21% measured power-delay product reduction compared to bulk, at 125{degree sign}C, on loaded ring oscillators.

Stress Changes in Silicon Nitride Thin Films on Thermal Cycling and Deconvolution of Separate Contributions

A correlation between stress in amorphous silicon nitride films and their composition has been established. This has led to the deposition of low-stressed films at low temperatures. The density of the films calculated from the results of Rutherford Backscattering Spectroscopy and Nuclear Reaction Analysis techniques is high, around 2.4 g/cm3, indicating a dense network. The films exhibit relatively high coefficient of thermal expansion, around 3.2 ppm/{degree sign}C, indicating a fairly short-range order in the film. Furthermore, a reversible thermally induced stress, i. e., a negligible stress hysteresis upon thermal cycling between room temperature and 400{degree sign}C has been observed in the film. From the stress response of the films to the thermal cycling separate contributions from the thermal and athermal components to the net room temperature stress have been deconvoluted.

Humidity Standard of Compressed Oxygen for Future Generation PEM Fuel Cells

Compressed oxygen is one of the most important needs for future generation PEM fuel cells. For the measurement and control as well as the design of humidification equipment, knowledge of the equilibrium water content of oxygen as a function of temperature and pressure is desirable. A simple presentation in chart form is usually adequate for most fuel cell applications and such a chart has been prepared based on the information on the water vapor content of a oxygen-water mixture. Absolute humidity of grams of water vapor per kilogram of dry oxygen is determined as a function of pressure up to 20 atmospheric pressures for various dew-point temperatures in the range of 0 {degree sign}C to 100 {degree sign}C. The maximum expanded uncertainty at a 95 percent confidence level is determined to be 2 percent of the value for this temperature range.

Startup-Procedures for a HT-PEMFC Stack

Up to now, the startup of HT-PEMFC is either requiring starting temperatures of 80 {degree sign}C or more, or will result in a significant cell degradation. In this contribution, investigations on low temperature startup and shutdown procedures are presented. These procedures allow the reduction of the startup temperature down to levels in the range of 60 {degree sign}C without permanently damaging the cell, thus allowing to strongly reduce time and auxiliary energy demand for cell startup. The startup procedure is derived from water vapour pressure data of H3PO4 and is investigated using modelling techniques. The results were experimentally confirmed by repeated startup cycles for different operation parameter sets.

Degradation Study of PFSA Polymer Electrolytes: Approach from Decomposition Product Analysis

Fuel cell operation tests (I) and hydrogen peroxide vapor exposure tests with PFSA (perfluorosulfonic acid) polymer membranes (II) were carried out, and the decomposition products of PFSA polymer during the tests were examined mainly by NMR. (I) After OCV-hold and load cycling tests, we analyzed extracts from electrodes separated from a single cell, identifying six decomposition products in the extracts. The total amount generated from the OCV-hold test exceeded that generated from the load cycling test, as well as fluoride ion release rate (FRR). (II) Hydrogen peroxide vapor exposure tests at 90 and 100{degree sign}C under 3 humidity conditions were carried out with Nafion® 112 and Nafion® NRE-212. Decomposition products other than fluoride ions accounted for a significant portion of degradation weight loss, and their generation rates were not proportional to FRR, suggesting the presence of multiple PFSA degradation mechanisms.

Direct Fuel Cell Materials Experience

The Direct Fuel Cell® (DFC®) power plant is an emerging high efficiency, ultra-clean electric power generation system. The power-producing block is the carbonate fuel cell, which uses alkali carbonate electrolyte and operates at ~550-650{degree sign}C. Its internal reforming process results in a simpler, more efficient and cost-effective energy conversion system. Since 2000, FCE has placed around the world approximately 85 units ranging from 250kW to 2.4 MW, accumulating extensive materials experience (up to >30,000h). Consistent DFC stack durability and performance improvement, and substantial cost reduction have been demonstrated. This paper describes status of DFC field products, stack material durability, power output increase, and cost reduction.

A Critical Assessment of the Synthesis of Diameter and Chirality Controlled CNTs in Zeolites

We here present the controlled synthesis of ultra-small diameter nanotubes in well-defined subnanometer sized confined space within zeolites. A critical view on the zeolite occluded nanotube growth is presented. Thermogravimetric analysis and optical techniques are evaluated for nanotube characterization. The introduction of Bro̸nsted acid sites in the zeolite framework leads to optimized yields. As temperatures below 500{degree sign}C are envisioned for nanotube synthesis, zeolite occluded nanotubes are compatible with current CMOS technology platform, in densities in accordance with ITRS standards for future interconnects, making zeolites a viable pathway for integration of SWCNTs in the chip of the future.

Effect of Surface Adsorbates on Graphene Probed by Hall-Effect and Raman Spectroscopy

The impact of adsorbed gases on graphene layers grown by SiC sublimation is investigated by temperature-dependent Hall-effect and Raman spectroscopy. For samples stored in ambient laboratory conditions, irreversible changes are seen in sheet resistance (\\rho\ extsubscript{sh}), mobility, and carrier concentration after heating to 400 K in vacuum. Subsequent heating to 400 K produces no additional changes in \\rho\ extsubscript{sh}, mobility or carrier concentration. Re-exposure of this 'clean' surface to air produces only minor changes in the electrical characteristics of the film. These kinetics suggest chemisorbed species produce a larger impact on electrical transport in graphene layers than do physisorbed species. The graphene Raman 2D peak is shifted ~15 cm\ extsuperscript{-1} at 500 {degree sign}C in vacuum, while the room temperature Raman 2D frequency is unchanged after heating.

Development of Solid Oxide Fuel Cells at Versa Power Systems

Versa Power Systems (VPS) is a developer of solid oxide fuel cells (SOFCs) for clean power generation. VPS has been working with its development partner FuelCell Energy within the U.S. Department of Energy (DOE) Office of Fossil Energy's Solid State Energy Conversion Alliance (SECA) program to apply SOFC technology in large-scale, multi-megawatt power plant systems that utilize coal in a clean and efficient manner. As a result, new initiatives such as widening the temperature of operation (600-800{degree sign}C) and scale-up of the cell and stack are now being actively pursued for these applications.

Ultra-Shallow Junction Formation by Plasma doping and Excimer Laser Annealing

Plasma doping (PLAD) process using PH3 plasma is presented to fabricate n+/p ultra shallow junction at room temperature. Directly after the PLAD, a pre-annealing has been conducted for 5 min at 500 {degree sign}C in thermal furnace. ArF excimer laser annealing (ELA) process was then followed with an increment of 20 mJ/cm2 in the laser energy ranging from 400 to 500 mJ/cm2. When the laser energy density was larger than 460 mJ/cm2, a reduced sheet resistance was observed. In order to examine the crystalline defects generated during PLAD, the transmission electron microscopy (TEM) and double crystal X-ray diffraction (DXRD) measurements have been made. With optimized PLAD and ELA conditions, junction depth of 30 nm and sheet resistance of 151.6 Ω/□ could be obtained.

Photoelectrochemical Splitting of Water to H2 and O2 at n-Fe2O3 Nanowires and Nanocrystalline Carbon-Modified (CM)-n-Fe2O3 Thin Films

Iron oxide n-Fe2O3 nanowire thin films were synthesized by thermal oxidation of Fe metal sheet (Alfa Co. 0.25 mm thick) in an electric oven then tested for their photoactivity. The photoresponse of the n-Fe2O3 nanowires was evaluated by measuring the rate of water splitting reaction to hydrogen and oxygen, which was found to be proportional to photocurrent density, jp. The optimized electric oven-made n-Fe2O3 photoelectrodes showed photocurrent densities of 1.32 mA cm-2 at measured potential of 0.0 V/SCE with photoconversion efficiency of 1.69 % at applied potential of 0.70 V vs Eaoc (electrode potential at open circuit conditions) under illumination intensity of 100 mW cm-2 from a Solar simulator with a global AM 1.5 filter. The photoactivity was improved upon incorporation of carbon into the lattice of n-Fe2O3 by flame oxidation at 850{degree sign}C. The carbon modified (CM)-n-Fe2O3 showed enhanced photocurrent response to 3.14 mA cm-2 at a measured potential of 0.0 V/SCE with an efficiency of 2.23% at applied potential of 0.52 V vs Eaoc. The nanocrystalline CM-n- Fe2O3 and n-Fe2O3 nanowires thin films were characterized using photocurrent density measurements under monochromatic light illumination, UV-Vis spectra, X-ray diffraction (XRD) and scanning electron microscopy (SEM).