Advanced Materials Research Vols. 287-290

Abstract: Pb_0.97La_0.02Zr_0.95Ti_0.05O₃ (PLZT) antiferroelectric thin films were prepared on Pt (111)/ Ti/SiO₂/Si (100) substrates by a sol-gel process. The influences of annealing temperature on the structures and dielectric properties of the PLZT antiferroelectric thin films were investigated. And the phase structure and crystal orientation were studied by X-ray diffraction analyses (XRD). The antiferroelectric characterization of the PLZT thin films annealed at different temperature was demonstrated by P(polarization)-E(electric field) and C(capactitance)-E(electric field) curves. The maximum polarizations for the films annealed at 650°C, 700°C and 750°C were 35μC/cm², 42μC/cm² and 47μC/cm², respectively. The temperature dependent of the dielectric constant and loss was measured under the frequency 1, 10, 100 and 1000 kHz. The films annealed at 700°C have high (100)-preferred orientation and excellent dielectric properties.

Abstract: Different kinds of dopants were selected to dope polyaniline by chemical oxidative polymerization in this paper. Major characteristic peaks and microstructure of the doped polyaniline were analyzed by Fourier transform infrared spectra (FTIR) and scanning electron microscope (SEM). Measurement of membrane potential indicated that polyaniline doped with protonic acid such as sulfosalicylic acid (SSA) and hydrochloric acid (HCl) had characteristic of anionic selectivity, and polyaniline doped with cationic surfactant hexadecyl trimethyl ammonium bromide (CTAB) had characteristic of cationic selectivity. Doped polyaniline was added to the epoxy resin to obtain different ions selective coatings, such as anionic coating, cationic coating and bipolar coating. Results of electrochemical test in 5% potassium chloride (KCl) solution (at 60 °C) showed that anti-corrosion performance of the bipolar coating is better than that of cationic coating, and performance of the cationic coating is better than that of anionic coating. And the coatings contained HCl-doped polyaniline had better protection performance than those of SSA-doped because of its micro appearance and distribution.

Abstract: In this paper，PANI/SSA thin films were deposited by MAPLE technique with different lasers. The structures and composition of films were characterized by XPS. The XPS results showed that because of the protection of matrix, the main structures and composition of films were protected effectively during deposition. While different lasers bring different influence to film structures. To short-wave laser, photochemical effect is obvious, the structures related to doping showed obvious change. To long-wave laser, photochemical effect did not bring obvious change to related structures, the XPS peaks showed no difference to that of PANI/SSA powder.

Abstract: Proton exchange membrane (PEM) fuel cell is a clean electrochemical device with great prospect of application. Performance plays an important role in the application of PEM fuel cell. In this paper, a voltage characteristics model of PEM fuel cell is established, its performance curves is simulated, and the influence of the operating parameters on its performance is analyzed. The results show that the simulated performance curves of PEM fuel cell and its experimental performance curves have a high degree of agreement; when the cell temperature is lower than the gas humidification temperature, the drooping extent in the high current density section of performance curve increases with the increase of the gas humidification temperatures. When the cell temperature is equal to or higher than the gas humidification temperature, the slope of the straight line section of the performance curve decreases with the increase of the gas humidification temperatures. The performance curve of the PEM fuel cell goes up with the increase of reaction gas pressure. The results are very helpful to optimization and application of PEM fuel cell.

Abstract: In plant, the main factor affecting power unit is the boiler, which mainly has the problem as unplanned outage caused by the leakage of water-cooled wall, superheater, reheater, economizer. So it is very meaningful and important to discover the problem of weak leakage of compression and heating surface of boiler and give the alarm in an early phase so as to figure out recondition method and reduce the recondition time. In this paper the deep research on acoustic features of background noise produced by boiler tube leakage and spectrum features of leak noise are presented to provide assistance for accurate location of the boiler leakage in the future.

Abstract: Development of a solid oxide fuel cell anode by impregnating catalytic Ni and Ni-CeO₂ nano-particles on 8YSZ fiber structure was carried out in this work. The nano-scale 8YSZ fibers were successfully fabricated by the electrospinning process and were well matched with the 8YSZ electrolyte. The experimental results demonstrated that the Ni/8YSZ anode with nano-8YSZ fibers, which impregnated with 3M nickel nitrate, decreases the polarization resistance and increases the exchange current density. However, the lowest polarization resistance and the highest exchange current density are observed in Ni/8YSZ fibers anode by adding nano-ceria particle from 5 wt.% to 10 wt.%. It is attributed to that the grain growth of Ni particle has been constrained by modifying appropriate amount of ceria particle to reduce the obstruction of diffusion path of fuel gas and to enhance the amount of triple phase boundary (TPB). On the other hand, 8YSZ nano-fibers provide a stabilized porous structure of the anode. Accordingly, nano-CeO₂ particle provides storing and releasing of oxygen ion to improve the catalytic performance of nano-Ni modified 8YSZ fiber anode

Abstract: Fabrication of a fiber anode with a mixture of the Gd₂O₃ and SrO co-doped ceria fibers and the Ni nano-catalyzer by using electrospinning and impregnated process were carried out for application in an intermediate temperature fuel cell (ITFC). Experimental results demonstrate that a uniform co-doped ceria fiber of 100 nm diameter could be spun at the concentration of PVP approximately 11.32 wt.% and electric field of 20 kV. The anodic films were prepared via a nickel wet dipping process and sintered at different temperatures. The micrograph of the anode sintered at 1200°C for1hr has a well defined microstructure in terms of electrolyte area covered with nickel and the triple phase boundary (TPB) between electrolyte, electrode and gas phase. Fiber anode exhibits low polarization resistance and high exchange current density due to formation of the reticular nano-fiber structure. Accordingly, using a new concept of combination of the nano-ceramic fiber and the Ni nano-particle for increasing the catalytic properties of anode is successfully proved, it is found that nano-fiber substituting to powder in anode could decrease the processing temperature of cell and maintain the porous structure of anode to increase the amount of TPB and restrain formation of agglomerates of nickel particles.

Abstract: In this paper, NiO-YSZ composite powder was synthesized via in situ urea combustion method to prepare high homogeneity cathode. Sm_0.2Ce_0.8O_1.9 (SDC) is used as a barrier interlayer between Ba_0.5Sr_0.5Co_0.8Fe_0.2O3-δ (BSCF) anode and 8YSZ electrolyte to avoid solid state interaction for high temperature application. The crystal structure and surface morphologies of NiO, YSZ, BSCF and SDC powders were characterized, respectively. The optimization of technological conditions for the synthesis was investigated. The adding amount was calculated by the combustion reaction equation. BSCF-SDC/YSZ/Ni-YSZ single button cells were prepared and the related electrochemical performances were test at 850°C. The research results showed that the products were well crystallized with NiO coating on YSZ particles. The optimized addition of CO(NH₂)₂ to Ni(NO₃)₂ was 2:1. A SOEC single cell made from NiO-YSZ with the molar ratio of 2:1 composite powder exhibited better performance than the other samples with the electrolytic voltage of 0.98V and showed excellent durability under the electrolytic currency of 0.33 A/cm², the input stream of 90%H₂O+10%H₂. The hydrogen production rate of the single SOEC using BSCF/SDC can be up to 196.6 mL·cm^-2h^-1, which indicates that it could be a potential candidate for the future application of SOEC technology.

Abstract: The internal mass transfer and the distribution of each component in proton exchange membrane fuel cell (PEMFC), including the hydrogen-oxygen proton exchange membrane fuel cell (H₂-O₂ PEMFC) and direct methanol fuel cell (DMFC), have great effects on the life and performance of cell. Simulation with software is one of the most important research methods. In this paper, the recent researches on the working conditions of PEMFC modeled with commercial software ANSYS / FLUENT are summarized, and on the basis, new visions for further study about abnormal fuel cells are brought forward.

Abstract: High temperature steam electrolysis (HTSE) through solid oxide electrolysis cells (SOEC), a promising high-efficiency and zero-emission way to large-scale hydrogen production, has been received increasingly international interest. The hydrogen production efficiency of HTSE is more than 50%. In this paper, the electrochemical performance and microstructure change of single button cells operating in both fuel cell (SOFC) and electrolysis modes (SOEC) were studied at 850°C. Also, the degradation mechanisms of hydrogen electrodes were investigated. The results showed that OCV decreased from 0.944 V to 0.819 V when the steam content increased from 20% to 80%. The voltage began to increase rapidly at relatively higher current density for lower steam content because of steam starvation; however, steam starvation did not occur at higher steam content. The ASR data decreased from 1.68 to 0.645Ωcm² with the increase of steam contents, while steam content had little effect on ASR data in SOFC mode. The polarization loss of the single cell was higher in electrolysis mode than that in fuel cell mode. The microstructure of the hydrogen electrode changed obviously after electrolysis process. Furthermore, the performance degraded at high steam partial pressure due to the oxidation of Ni grains at the interface of hydrogen electrode.