Xiqiang Huang

Properties of nonstoichiometric Pr0.6−xSr0.4MnO3 as the cathodes of SOFCs

A series of samples Pr0.6-xSr0.4MnO3 (x = 0, 0.01, 0.05, 0.1, 0.15, 0.2) were synthesized by a solid state reaction method. Pr deficiency at the A site has a great effect on the properties of Pr0.6-xSr0.4MnO3 as the cathode of SOFCs (solid oxide fuel cells). Compared to the commonly used La0.6Sr0.4MnO3 and La0.55Sr0.4MnO3 cathode, Pr0.6-xSr0.4MnO3 is better in the properties of conductivity, overpotential and impedance. In all the samples, the one with x = 0.05, Pr0.55Sr0.4MnO3, revealed the best performance in the measured temperature range

THEORETICAL STUDY ON POTENTIAL-ENERGY SURFACE OF C2N2

B3LYP and CCSD(T) (single-point) calculations are performed on structures and interconversion transition states for five C2N2 isomers, i.e., the linear structures NCCN 1, CNCN 2, CNNC 3, and CCNN 4, and the NNC three-membered ring structure with exocyclic C–C bonding 5. A schematic potential-energy surface of the five C2N2 isomers is established. It is shown that the elusive and long searched for isomer 3 lies in a deep potential well against isomerization to the well-studied isomers 1 and 2, while the two transition states, which have been predicted to connect the isomers 1 and 3, are actually associated with the interexchange of the two cyano groups in isomer 2. It is also shown that the experimentally unknown but expectedly important isomer 4 may take an isomerization pathway to the isomer 1 via the intermediate 5, and the isomer 4 also lies in a deep potential well. Both the isomers 3 and 4 may be thermally as stable as the isomer 2. The results presented in this paper may provide useful information f...

A study on PrMnO3-based perovskite oxides used in SOFC cathodes

Two series of samples Pr1-xSrxMnO3 (x=0, 0.1, 0.2, 0.3, 0.4, 0.5) and Pr0.6-ySr0.4MnO3 (y=0, 0.01, 0.05, 0.1, 0.15, 0.2) were synthesized by a solid state reaction method. In the former series, the sample with x=0.4 exhibited the highest conductivity in the range of experimental temperature. Pr deficiency at the A site has a great effect on the properties of Pr0.6-ySr0.4MnO3 as a cathode of solid oxide fuel cells. Compared to the commonly used La0.6Sr0.4MnO3 cathode, Pr0.6-ySr0.4MnO3 has better properties of electrical conductivity, overpotential and impedance. Of all the samples, it is revealed that the one with y=0.05, Pr0.55Sr0.4MnO3 has the best performance in the measured temperature range

Anode-Supported Micro-SOFC Stacks Operated under Single-Chamber Conditions

A micro solid oxide fuel cell (SOFC) stack with two series-wound single fuel cells was fabricated and operated successfully under single-chamber conditions. In this stack, the single cells were based on Ni/yttria-stabilized zirconia (YSZ) anode-supported YSZ membrane and were arranged with an anode-facing-cathode configuration in diluted methane and oxygen mixture gas between 600 and 750 degrees C. The performances of the stack were affected by the flow rate, gas composition, and furnace temperature. The effects of the narrow path between two cells on the electrodes and cells were discussed in detail, according to the open-circuit voltages (OCVs) and impedance spectra of each cell. At 700 degrees C, the maximum OCV of the whole stack was larger than 2.0 V at CH4/O-2=1.75 and 2, while the maximum power output of stack was about 371 mW at CH4/O-2=1 with a mass specific power of 552 mW/g. The performance indicates that such microstacks have potential for portable applications. (c) 2007 The Electrochemical Society.

Study on new copper-containing SOFC anode materials

Abstract A series of new Ni–Cu–YSZ cermet made of oxide raw materials was employed as the anode of a SOFC. The reducing properties of these materials were first investigated. The open circuit voltage was over 1.1 V, and the output power density was about 33–43 mW/cm2 at 900°C. Altering the fuel gas between H2 and city coal gas shows that the output voltage and power are affected by fuel, and the response of fuel cell to the fuel gas is rapid. When pitch exists in the fuel gas, a tar-liked carbon is deposited on the Al2O3 tubes of the cell but not on the anode. It has been proved that the anode with Cu has a self-cleaning function.

Fabrication of dense YSZ electrolyte membranes by a modified dry-pressing using nanocrystalline powders

A simple and cost-effective method for synthesizing yttria-stabilized zirconia (YSZ) electrolyte membranes is described that is based on a modified dry-pressing process using nanocrystalline powders. The thickness of the YSZ electrolyte membranes was easily controlled by controlling the mass of nanocrystalline YSZ powders. Good adhesion of the dense electrolyte membranes to the anode substrates without cracking or delamination could be readily obtained. The studied single cell possessed much higher open circuit voltage (OCV) and higher output performance than a cell whose electrolyte thick film was made from a traditional dry-pressing method using commercially microcrystalline powders. The good performance in this study was attributable to the successful fabrication of the electrolyte membrane by the uniquely modified dry-pressing process using loose nanocrystalline YSZ powders. The implementation of the modified dry-pressing process using nanocrystalline YSZ powders to fabricate electrolyte membranes exhibits a significant potential to greatly reduce the fabrication cost of solid oxide fuel cells (SOFCs).

Direct Flame SOFCs with La(0.75)Sr(0.25)Cr(0.5)Mn(0.5)O(3-delta)/Ni Coimpregnated Yttria-Stabilized Zirconia Anodes Operated on Liquefied Petroleum Gas Flame

In the present study, the performances of a single solid oxide fuel cell (SOFC) and a micro-SOFC stack fueled with flame of combusting liquefied petroleum gas (LPG) were studied. La(0.75)Sr(0.25)Cr(0.5)Mn(0.5)O(3-delta) and Ni coimpregnated yttria-stabilized zirconia were used as the anode material of the direct-flame SOFC. The operation temperature of the cell can be sustained at 500-700 degrees C for the combustion of LPG. With the anode facing the LPG flame and the La(0.8)Sr(0.2)MnO(3-delta) cathode freely exposing to ambient air, the single cell exhibited an open-circuit voltage (OCV) of more than 0.85 V and the maximum power density (P(max)) of 238 mW/cm(2). The micro-SOFC stack with three single cells connected in series demonstrated an OCV of 2.5 V and the maximum power output of 64 mW (corresponding to a P(max) of 139 mW/cm(2)). The cell performance was found to be strongly influenced by the cell temperature. And the temperature is determined by cell position and gas composition. Additionally, the cell stability and carbon deposition after operation on the diffusion flame of the LPG were also tested

Effect of the Cell Distance on the Cathode in Single Chamber SOFC Short Stack

Two-cell solid oxide fuel Cell (SOFC) stacks with an anode-facing-cathode configuration were operated in single chamber conditions, i.e., oxygen, methane, and nitrogen mixture. The effect of the distance between two cells on the cell performance was investigated. A single cell consisted of a porous NiO/8 mol % Y(2)O(3)-stabilized ZrO(2) (YSZ) anode support, a YSZ electrolyte membrane, and a Ce(0.8)Sm(0.2)O(1.9)-impregnated La(0.7)Sr(0.3)MnO(3) cathode. The experimental result demonstrated that the effect of the distance on the cathode was quite distinct when the distance (D) was equal to 2 mm. The distance effect could be negligible when D was larger than 4 mm. The effects were also varied with the ratio of methane and oxygen (M). An acceptable value of the distance was critical for the operation and performance of the stack

Calculated properties of cationic phosphorus clusters P2n+1+ with n = 3, 4, 5, and 6

Abstract An attempt has been made to predict the most stable structures of the clusters P 2 n +1 + with n = 3,4,5, and 6 by using the ab initio molecular orbital method at the 6-31G∗ basis set level. The chemical activities of the clusters P 2 n +1 + have been discussed by means of Mulliken atomic charges. As an extension, the clusters P 2 n S with n = 3, 4, 5, and 6 have been investigated as well.

A preliminary study of the pseudo-capacitance features of strontium doped lanthanum manganite

The intrinsically poor electrical conductivity of transition metal oxides is a critical challenge to obtain high electrochemical performance when these materials are used as the electrode of supercapacitors. In this study, the pseudo-capacitance features of perovskite (La0.75Sr0.25)0.95MnO3−δ (LSM) having a high electric conductivity of 44.9 S cm−1 at room temperature was preliminarily investigated. The easily prepared LSM electrode was characterized by cyclic voltammetry and galvanostatic charge–discharge method to evaluate its electrochemical performances. The results show that LSM has pseudo-capacitance features and the specific capacitance is 56 F g−1 at a scanning rate of 2 mV s−1. This is the first report on the pseudo-capacitance value of LSM. Furthermore, the electrodes show no obvious capacitance degradation after 1000 cycles.