Influence of Mg-substitution on structural and electrical properties of ion-conducting Ca-doped tri-yttrium gallate

The signature of oxide ion conductivity was perceived in acceptor-doped (alkaline-earth metals) Y₃GaO₆. An acceptor doping of 2%Ca in Y₃GaO₆ (i.e., Y_2.94Ca_0.06GaO₆) has been found to exhibit a remarkable conductivity. The present work examines the conductivity behavior of 2% Ca-doped tri-yttrium gallate (Y_2.94Ca_0.06GaO₆) and also the effect of Mg-substitution on the phase formation and electrical conductivity of Y_2.94Ca_0.06GaO₆ for its possible application as a solid electrolyte. Polycrystalline dense ceramic samples of Y_2.94Ca_0.06Ga_1−xMg_xO_6−δ (with x = .00–.04) were fabricated using the conventional solid-state reaction route. The X-ray diffraction patterns were recorded to confirm the phase formation. The solid solubility limit of Mg²⁺ at Ga³⁺ site was found for x < .03. All the samples were observed to exhibit orthorhombic structure with Cmc21 symmetry (ICSD no.: 155086). Scanning electron microscopy (SEM) morphology reveals dense polygonal grains with vibrant grain boundaries. A significant increase in the conductivity is observed by substituting 1 mol% of Mg²⁺ at the Ga³⁺ site of Y_2.94Ca_0.06Ga_1−xMg_xO_6−δ. However, a further addition of higher dopant concentration of Mg²⁺ leads to a decline in the electrical conductivity. A relationship between the dopant concentration, phase formation, and structural characterizations has been established to analyze the conductivity behavior.     

Polymer electrolyte membrane modification in direct ethanol fuel cells: An update

Direct ethanol fuel cells (DEFCs) offer a high degree of design flexibility, ranging from a single cell to a massive multi-cell that can be used in various applications, including portable devices, transportation, and stationary applications. Unfortunately, the most significant barrier to the commercialization of DEFCs is getting low-cost and ethanol permeability, high conductivity performance, and extended durability of polymer electrolyte membranes, as key components that highly influence the overall performance. In this paper, the recent progress in developing the polymer electrolyte membrane for the application of DEFCs has been comprehensively reviewed. Focusing on an updated modification of polymeric materials in the last 5 years, including Nafion-based membrane, polyvinyl alcohol-based membrane, polybenzimidazoles-based membrane, chitosan-based membrane, and sodium alginate-based membrane, as well as factors and challenges that affected the performance of polymer electrolyte membranes have been discussed, including the main characterization, catalyst selection, cell design, and work in membrane and cell performance of DEFCs. All discussion addresses the strategy to improve the performance of polymer electrolyte membranes in DEFCs in order to penetrate the commercialization stages.     

Microstructure optimization of fuel electrodes for high-efficiency reversible proton ceramic cells

Reversible protonic ceramic cells (R-PCCs) are efficient energy storage and conversion devices that can operate in two modes, namely, in the fuel cell mode for the conversion of fuel to electricity, and in the electrolysis (EC) mode for the EC of water into hydrogen and oxygen. Fuel electrode is a critical component of fuel-electrode-supported R-PCCs, and its pore structure directly affects the electrochemical performance of the R-PCCs, but it has not been fully studied yet. Herein, the pore structure of Ni–BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3−δ (Ni–BZCYYb) fuel electrodes was systematically modulated by varying the weight ratio (0, 5, 10, and 15 wt.%) of the pore-former added to Ni–BZCYYb, and the electrochemical performance characteristics in the fuel cell and EC modes were investigated. The cell with 10 wt.% pore-former in the Ni–BZCYYb electrode achieved a remarkable peak power density of 540.7 mW cm⁻² and a high current density of –2.28 A cm⁻² at 1.3 V at 700°C in the fuel cell and EC modes, respectively, and showing excellent durability for over 100 h. These results further highlight the critical role of the microstructure of fuel electrodes, which can be modified to achieve exceptional performance, particularly in EC operations.     

Photoelectronic and transport properties of polypyrrole doped with a dianionic dye

Polypyrrole (PPy) doped with dodecylsulfate (DS) and an organic dye (indigo carmine, IC) was electrochemically prepared and characterized by Raman spectroscopy and X-ray diffraction (XRD). The photoelectrochemical properties of PPy-DS and PPy-DS-IC in contact with an electrolytic solution containing a redox couple were studied using the theories for the semiconductor ∣ electrolyte interface. Results indicate that the system containing IC presents a higher photocurrent density under polychromatic illumination and faster response time when compared with PPy-DS. This fact was assigned to the formation of molecular-scale paths in PPy-DS-IC. The IC molecules lying perpendicularly between PPy chains, as confirmed by the X-ray analysis, could facilitate the mass transport at the interface and increase the ordering degree to provide better electronic charge transfer in the bulk. Although the photoelectrochemical devices presented here do not present all the properties of inorganic-based devices, we discuss some strategies to enhance the photoelectrochemical properties and response time of conducting polymers used in these type of systems.     

Production of hydrogen for fuel cells by reformation of biomass-derived ethanol

The reformation of biomass-derived ethanol to a hydrogen-rich gas stream suitable for feeding fuel cells is investigated as an efficient and environmentally friendly process for the production of electricity for mobile and stationary applications. Steam reforming of ethanol is investigated over Ni catalysts supported on La₂O₃, Al₂O₃, YSZ and MgO. The influence of several parameters on the catalytic activity and selectivity is examined including reaction temperature, water-to-ethanol ratio and space velocity. Results reveal that the Ni/La₂O₃ catalyst exhibits high activity and selectivity toward hydrogen production and, most important, long term stability for steam reforming of ethanol. The enhanced stability of this catalyst may be due to scavenging of coke deposition on the Ni surface by lanthanum oxycarbonate species which exist on top of the Ni particles under reaction conditions.     

Proton Conductivity Measurements in Yttrium Barium Cerate by Impedance Spectroscopy

Proton-conducting solid-electrolyte perovskite ceramics based on acceptor-doped barium and strontium cerates have become the focus of extensive investigations as candidate materials for fuel cells that operate at moderate temperatures. To assess the suitability of a material for this application, it is necessary that bulk electrolyte conductivity be measured at the operating temperature. However, very little reliable published conductivity data exist above 600°C. Protonic conductivity in yttrium-doped barium cerate has been observed to be less at high temperatures than would be expected, based on the activation energy and preexponential for hydrogen transport at temperatures <300°C. Conductivity data obtained from impedance spectroscopy on BaCe_0.9Y_0.1O_3–α over the extended temperature range of 100°–900°C are presented. An Arrhenius plot of the data shows two distinct linear regions, suggesting that two different rate-limiting processes occur in series with a break-over transition at ∼250°C. The decrease in conductivity is apparently not due to dehydration. An activation energy for protonic transport of 0.26 eV, about one-half of the low-temperature value, is proposed, based on curve fitting of the high-temperature data.     

Properties of CuMn1.5Ni0.5O4 spinel as high-performance cathode for solid oxide fuel cells

Spinel oxide cathode has made great progress in solid oxide fuel cells (SOFCs) because of its special characteristics different from perovskite. In this study, a spinel-structured SOFC cathode, CuMn_1.5Ni_0.5O₄ (CMN), is proposed. Rietveld refinement shows that CMN takes the cubic structure of the space group of P4₃32. CMN shows a high conductivity of about 70.0–91.2 S cm⁻¹ at 600–800 ºC in the air and exhibits good catalytic activity for oxygen. A symmetric cell with CMN-GDC composite cathode demonstrates a low Rp of 0.047 Ω cm² at 800 ºC. The charge transfer of oxygen is the rate-limiting process at lower temperatures. The performance test results of the button cell with CMN-GDC composite cathode are excellent, with high power densities of 1342.4 mW cm⁻² at 800 ºC. After a110h long-term test, the cell runs stably, and no microstructure damage is observed.     

A high-performance fuel electrode-supported tubular protonic ceramic electrochemical cell

Protonic ceramic electrochemical cells (PCECs) have received extensive attention for encouraging energy conversion and storage efficiencies. One of the key obstacles hindering the development of PCECs is the time-consuming and costly fabrication processes. In this study, we have fabricated fuel electrode-supported tubular PCECs via a facile and well-controlled phase inversion methhod combined with a dip-coating process. When operated in a fuel cell (FC) mode, single cells exhibit excellent peak power densities of 0.48, 0.91, 1.50, and 2.62 W cm^-2 at 550–700 ℃, respectively. While in electrolysis cell (EC) mode, these tubular cells achieve high electrolysis current densities of − 0.61, − 1.59, − 3.03, and − 4.67 A cm^-2 with reasonable Faradaic efficiencies at 550–700 ℃ and an applied voltage of 1.3 V, respectively. Additionally, cells can be stably operated at 0.5 A cm^-2 for 120 h in FC mode and − 0.5 A cm^-2 for 110 h in EC mode at 650 °C.     

FLUID-MECHANICAL DAMAGE OF FREELY-SUSPENDED ANIMAL CELLS IN AGITATED BIOREACTORS: EFFECTS OF DEXTRAN, DERIVATIZED CELLULOSES AND POLYVINYL ALCOHOL

Different media additives were used to analyze cell damage and “shear protection” characteristics of freely suspended animal cells (CRL-8018) cultured in stirred tank bioreactors. The additives used included dextran, polyvinyl alcohol (PVA), and methylcellulose, which are viscosity enhancers, surface active agents or combinations of these, respectively. We used these additives to study the effects of bulk viscosity and interfacial properties on cell damage or protection under conditions whereby bubble-induced cell damage becomes inhibitory to cell growth if the medium is not supplemented with a protective additive. Dextran (229 kDa, 1-3% w/v) was used to analyze the effects of increased bulk viscosity on cell damage or protection. It was found that the presence of dextran increased cell death under intense agitation. Several grades and types of derivatized methylcelluloses including Methocel A15LV (15 kDa, 0.1-0.5 w/v%), Methocel E50LV (50 kDa, 0.1% w/v), and Methocel H100LV (100 kDa, 0.25% w/v), provided shear protection. PVA (10 kDa, 0.1% w/v), which is an effective shear protectant, was used in combination with dextran and the results suggest that the interfacial properties it imparted were capable of overcoming the negative effect of dextran. We also found that in the absence of a gas-liquid interface at the surface of a sparged, stirred tank bioreactor, animal cells grown in medium that does not include additives can be agitated at rates in excess of 400 rpm without being damaged by turbulent cell-bubble interactions in the bulk.     

固定化紫草细胞生产紫草宁衍生物

用海藻胶包埋紫草细胞,在紫草色素生产培养基M_9中,常温、黑暗下培养不同时间,收集培养液并提取色素,进行紫外—可见全波长分光光度扫描和TLC分析。结果表明:固定化紫草细胞可连续分泌紫草色素,其主要成分与天然成分基本相同,产量已达到一定水平。此外对海藻胶包埋条件、固定化珠粒的稳定性以及1L固定化植物细胞反应器生产紫草色素工艺进行了讨论。