This work evaluates electrodeposited and differently treated Mn-Co catalysts for their oxygen evolution reaction activity. Catalysts are evaluated in the as-deposited and heat treated state: after 350 C and 600 C. Results show that the highest electrochemical activity is obtained for the as-deposited Mn-Co oxyhydroxide, which possibly possess a layered double hydroxide structure. After the heat treatment process, especially after 600 C, the electrochemical performance decreases considerably.
W publikacji przedstawiono motywację podjętych badań nad podstawianymi żelazem tytanianem strontu do zastosowań w wysokotemperaturowych ogniwach paliwowych oraz ukazano wstępne wyniki badań elektrycznych oraz elektrochemicznych.
The nanocrystalline compounds of Co and Cu co-doped ceria (with up to 20 mol.% of dopants) were fabricated by the reverse microemulsion synthesis method. They were deposited in a form of layers on the surface of SOFC anode in an aim to act as electrochemically active materials for biogas reforming process. Fourier Transformed Infrared Spectroscopy was used to analyze a composition of outlet gases simultaneously with the tests of electrical parameters of a fuel cell. It allowed comparing a catalytic activity of fabricated materials towards internal biogas reforming. It was found that Cu and Co ceria co-doping improves electrical parameters of a fuel cell and enhances its long-term stability when compared with mono-doped ceria. This type of a material gives also the highest conversion rate of methane and the highest yield of carbon monoxide.
Low-temperature deposition of electroceramic thin films allows the construction of new devices and their integration with existing large-scale fabrication methods. Developing a suitable low-cost deposition method is important to further advance the development of microdevices. In this work, we deposited a 1-lm-thick La0.6Sr0.4CoO3d (LSC) perovskite with high electrical conductivity on sapphire substrates at 400C and analyzed its electrical, morphological and structural properties as a function of temperature in the range of 400– 1100C. The results show that spray pyrolysis can be used to deposit highquality reproducible layers with the desired chemical and phase composition. Upon heating to around 600C, the residual C–O and C=O species are removed, and the deposited layers crystallize and become conducting. The dependence of electrical conductivity versus processing temperature has a complex character—the maximum conductivity is found for layers processed at 800C. An analytical model of stress distribution was used to predict stress to which the bi-layer material would be exposed to while being cooled down from the annealing temperature to room temperature. The high electronic conductivity and high-quality microstructure of the LSC layers, which can be adjusted with the appropriate heat treatment procedure, make them suitable for applications in electrochemical devices applied in integrated energy modules, including electrodes or contacts.
Doping of Na and K at La sites and of B at Si site in La10Si6O27 with oxyapatite structure and fabrication of their ceramics were made by the solid-state reaction method. It was found that partial substitution of Na+ and K+ on La sites decreased the sinterability of the La10Si6O27 based ceramics, whereas partial substitution of B3+ on the Si site improved the sinterability. Na+ and K+ substitutions in La10−xNaxSi6O27−x and La10−xKxSi6O27−x can suppress second-phase La2SiO5 formation, and, in this study, as the x value of the two substitutions reached 0.7 and 0.5, respectively, the La2SiO5 phase disappeared. Doping of Na+, K+, and B3+ all displayed the hindering effect of grain growth during sintering. Compositions of La9.3Na0.7Si6O26.3, La9.5K0.5Si6O26.5, and La10Si5.5B0.5O26.75 revealed the highest electrical conductivity in each system. La10Si5.5B0.5O26.75 ceramic sintered at 1575°C showed the highest electrical conductivity at temperatures above 600°C among all the apatite ceramics evaluated. The electrical conductivities of La10Si5.5B0.5O26.75 at 700°C and 800°C reported 0.011 S cm−1 and 0.024 S cm−1, respectively, which are superior or comparable to previous studies, and their activation energies for conduction were calculated to be 0.80 eV.
This work evaluates porous Sr0.86Ti0.65Fe0.35O3 (STF35) as a possible oxygen electrode material for Solid Oxide Cells. The powder synthesis was performed by solid state method. Characterization included DC electrical conductivity study of sintered bulk samples and impedance spectroscopy study of symmetrical electrodes deposited on gadolinium doped ceria substrates. Measurements were carried out in atmospheres with different pO2 levels: 0.1%–20% O2. Detailed equivalent circuit analysis was carried out in order to clarify the reaction pathway on porous electrode, which extends knowledge available for dense model electrodes. At 800 °C in 21% O2, the DC electrical conductivity of STF35 pellet was 0.6 S cm−1 and the polarization resistance of the electrode in the symmetrical cell was ∼100 mΩ cm2. Detailed impedance spectroscopy studies revealed that the largest contribution (∼80%) towards the polarization resistance is due to oxygen adsorption, which is limiting the oxygen reduction performance of the porous STF35 electrode. These results show the applicability of advanced impedance analysis methods (e.g. Distribution of Relaxation Times - DRT) for description of complex impedance electrode phenomena of porous electrodes.
The 430L stainless steel powder with a mean particle size of 95 μm was studied to determine its high-temperature oxidation properties. Continuous thermogravimetric measurements were carried out for 100 h in air at temperatures in the range of 600–850 °C. Even though a considerable amount of Cr (up to ˜5 wt.% Cr) inside the grains was depleted – especially inside small grains – no breakaway oxidation was observed. This indicates that both the remaining Cr and the formed chromia scale remained protective with regard to the metallic core until the Cr concentration reached very low levels.
The purpose of this study was to develop a method and software based on the Fourier Transform Infrared Spectroscopy for the in-situ, quantitative analysis of the composition of outlet gases from Solid Oxide Fuel Cell (SOFC). The calibration procedure performed at the beginning of the experiment indicated a polynomial dependence between the concentration of a calibrating gas (CO, CO2, CH4) and the corresponding integrated absorbance in particular wavenumber ranges. Further, it allowed determining a concentration of CO2, CO, CH4 and H2 in the outlet gas stream of the Ni-YSZ anode supported Direct Internal Reforming-SOFC fuelled by synthetic biogas (mixture of CO2 and CH4 in a volume ratio 2:3). The analysis was performed for over 90 h. Based on calculated concentration the conversion rates for both CH4 and CO2 gases were calculated, as well as the yields and selectivities of CO and H2. Also, the carbon balance was determined. In order to predict the direction of particular reforming reactions, a non-equilibrium analysis was performed. Namely, a thermodynamic probability of solid carbon formation was determined based on calculations of carbon activity coefficients. Obtained results indicated degradation of a fuel cell and corresponded well with electrical measurements where a decrease of power density in wet synthetic biogas was observed.
In this work, the spontaneous release of anti-inflammatory salicylate from polypyrrole (PPy) coated iron has been studied during degradation of the material in phosphate buffer saline at 37 C. The sodium salicylate was incorporated into PPy in a one-step electropolymerization process. The influence of the synthesis conditions such as sodium salicylate concentration, pyrrole concentration and deposition charge on drug release profile has been investigated. The morphology, surface roughness and redox properties of PPy/Fe have been also studied. The drug release was studied by UV-Vis spectrophotometer with flow cuvette connected to the electrochemical cell, which provided continuous study of the released dopant. As a result, reliable and quantitative study of salicylate release from PPy coated iron was attained.Depending on the synthesis conditions the concentration of the salicylate released was in the range of 83-183 mM/cm2 after 21 h of immersion. The rate of drug release of 10-11mM/h was the highest at the beginning after immersion (1-2 h), then it gradually decreased and finally it reached the lowest value of approximately 0.3 mM/h at the end of the process.
Non-conducting BaO-B2O3-Al2O3-SiO2 parent glasses designed for solid oxide fuel cell (SOFC) sealing applications were prepared using the melt-quenching technique. The glass formation region was determined according to phase equilibrium relations and was found to be in the composition range 70BaO-(x)Al2O3-(10−x)B2O3-20SiO2 where 3.0 < x < 6.0 wt%. The conductivity values obtained conductivity ranged from 10−5 to 10−10 S/cm at temperatures between 600 and 850 °C. The batch compositions presented a threshold of dc conductivity near 70BaO wt% with a quasi linear behavior with the decrease of the BaO content. Different values of conduction activation energy were observed at temperatures above the glass transition temperature (Tg) (up to 700 °C), which were attributed to the thermal bond-breaking of non-bridging oxygen (NBO) defects. The experimental results of the electrochemical characterization by impedance spectroscopy of glass–ceramic interfaces with yttria-stabilized zirconia (YSZ) acting as solid ionic conductor electrolyte are presented and discussed.