Search

A major challenge to overcome in demonstrating solid oxide fuel cells (SOFCs) to be suitable as efficient and environmentally friendly energy conversion devices capable of addressing pressing clean energy and environmental needs is to surmount chemical and thermo‐mechanical instabilities in their operational phase. To date, perovskite‐based mixed conducting cathodes, which include inherent Co and Sr elements for enhanced reactivity and conductivity, have been intensively studied. These Co/Sr‐based oxides, however, exhibit severe thermochemical expansion and suffer from Sr surface segregation, ultimately degrading the electrode performance. Here, high‐performance and durable SOFCs are demonstrated by employing a Co/Sr‐free fluorite‐based mixed conducting (Pr,Ce)O2‐δ (PCO) cathode eminently compatible with fluorite‐based solid electrolytes. The nanocolumnar PCO electrode developed in this study provides not only a remarkable low level of electrode resistance (e.g., ≈0.05 Ω cm2 at 600 °C) but also exceptional long‐term stability (e.g., a degradation rate 15 times slower compared to the state‐of‐the‐art La0.6Sr0.4CoO3‐δ perovskite). The competitive peak power densities of an anode‐supported single cell with the PCO cathode are also successively achieved, recording a value of 0.92 W cm−2 at 600 °C. These findings herald the development of new Co/Sr‐free electrodes for SOFCs at intermediate temperatures. [ABSTRACT FROM AUTHOR]

Fast oxygen-ion conductors for use as electrolyte materials have been sought for energy conversion and storage. Bi2O3-based ionic conductors that exhibit the highest known oxygen-ion conductivities have received attention for use in next-generation solid electrolytes. However, at intermediate temperatures below ~600 °C, their conductivities degrade rapidly owing to a cubic-to-rhombohedral phase transformation. Here, we demonstrate that physical manipulation of the grain structure can be used to preserve the superior ionic conductivity of Bi2O3. To investigate the effects of microstructural control on stability, epitaxial and nanopolycrystalline model films of Er0.25Bi0.75O1.5 were fabricated by pulsed laser deposition. Interestingly, in situ impedance and ex situ XRD analyses showed that the grain boundary-free epitaxial film significantly improved the stability of the cubic phase, while severe degradation was observed in the conductivity of its polycrystalline counterpart. Consistently, the cation interdiffusion coefficient measured by the Boltzmann–Matano method was much lower for the epitaxial thin film compared to the polycrystalline thin film. Furthermore, first-principles calculations revealed that the presence of grain boundaries triggered the structural resemblance between cubic and rhombohedral phases, as evidenced by radial distribution functions. Additionally, phase transition energetics predicted that the thermodynamic stability of the cubic phase with respect to the rhombohedral counterpart is reduced near grain boundaries. Thus, these findings provide novel insights into the development of highly durable superionic conductors via microstructural engineering.We, for the first time, reveal that manipulation of microstructure enables the suppression of phase transformation and enhancement of long-term stability of Bi2O3-based ionic conductors. To investigate the microstructural influence on the stability, thin films with precisely defined grain structures are prepared. The conductivity of polycrystalline thin film decreased by 94.6% after approximately 20 h of operation, while the initial conductivity of epitaxial thin film remained almost constant during annealing for up to 100 h. This study provides novel insights for the development of highly conductive and durable solid electrolytes for next-generation energy applications. [ABSTRACT FROM AUTHOR]

Cavitation occurs on objects that move underwater at high speeds, and it is accompanied by an increase in hull vibrations, a reduction in propulsion performance, and an increase in noise that is important for warships and submarines. Of the various types of cavitations, tip vortex cavitations (TVC) are the earliest occurring and are considered the most important in terms of cavitation inception speed (CIS). This study predicts the cavitation inception speed by conducting cavitation noise analyses. The trend of the noise according to the cavitation numbers before and after CIS was analysed, and the quantitative criteria to determine the CIS were presented through established procedures. The CIS value obtained through the analysis was verified by comparing it against the value obtained experimentally. The methods used to analyse the cavitation inception speed are developed using bubble dynamics for cavitation noises. First, flow-field information was obtained downstream of the wing to estimate the external force acting on the bubbles, and this was used to calculate the behaviour of the cavitation bubbles. The bubble dynamics analyses were performed for each cavitation nuclei by Lagrange approach to calculate the behaviour of the bubbles. The number of cavitation nuclei was calculated based on the density function with random placement upstream of the wing. The cavitation noise was analysed for various cavitation numbers, and the tendency of the noise generated for each case was investigated. The noise analysis results and the CIS predictions were compared and verified with the measured values in the Large Cavitation Tunnel (LCT) of the Korea Research Institute of Ship & Ocean Engineering (KRISO). Using these results, the effect of the tip vortex cavitation on the total flow noise was analysed, and CIS determination criteria using noise values was validated and established. [ABSTRACT FROM AUTHOR]

(La,Sr)MnO3−δ has received a great deal of attention as an oxygen carrier that can replace the state-of-the-art carrier CeO2 for solar-driven thermochemical fuel production. Despite the many relevant studies, however, the redox reaction kinetics of this material, which determines the fuel production rate, has rarely been reported. Here, we investigate the surface reaction rate of reduced Sr-doped lanthanum manganite thin films, as a model for a gas/solid interface of a perovskite-structured oxygen carrier under a condition, in which carbon monoxide is produced from CO2 in a two-step thermochemical cycling process. Thin films of La1−xSrxMnO3−δ (x = 0.1, 0.2, 0.3, 0.4) with dense and flat surfaces are fabricated via pulsed laser deposition, and their surface oxygen exchange rates are then characterized via electrical conductivity relaxation under actual operating conditions (T = 650 to 800 °C and pO2 = 2.9 × 10−19 to 9.0 × 10−13 atm). As the Sr content increases, the oxygen exchange greatly decelerates. On the other hand, for a given Sr content, the oxygen exchange does not vary much over a wide range of pO2 near the target temperature of 800 °C. We also observe the surface oxygen exchange rate has a direct impact on the CO production rate. These observations can guide the selection of an ideal oxygen carrier composition for high-performance fuel production. [ABSTRACT FROM AUTHOR]

High-Performance and Durable Fuel Cells using Co/Sr-Free Fluorite-Based Mixed Conducting (Pr,Ce)O2- Cathode (Adv. (Pr,Ce)O2, Co/Sr-free mixed conducting oxides, nanocolumnar structures, oxygen reduction reaction, solid oxide fuel cells Keywords: (Pr,Ce)O2; Co/Sr-free mixed conducting oxides; nanocolumnar structures; oxygen reduction reaction; solid oxide fuel cells EN (Pr,Ce)O2 Co/Sr-free mixed conducting oxides nanocolumnar structures oxygen reduction reaction solid oxide fuel cells 1 1 1 11/21/22 20221117 NES 221117 B Fuel Cells b In article number 2202101, Ji-Won Son, WooChul Jung, and co-workers demonstrate high-performance and durable solid oxide fuel cells by employing a Co/Sr-free fluorite-based mixed conducting (Pr,Ce)O SB 2- sb cathode, delivering outstanding oxygen reduction reaction activity, importantly, together with a much extended long-term stability. [Extracted from the article]

Stabilized Bi 2 O 3 has gained a considerable amount of attention as a solid electrolyte material for low-temperature solid oxide fuel cells due to its superior oxygen-ion conductivity at the temperature of relevance (≤500 °C). Despite many research efforts to measure the transport properties of stabilized Bi 2 O 3 , the effects of grain boundaries on the electrical conductivity have rarely been reported and their results are even controversial. Here, we attempt quantitatively to assess the grain boundary contribution out of the total ionic conductivity at elevated temperatures (350-500 °C) by fabricating epitaxial and nano-polycrystalline thin films of yttrium-stabilized Bi 2 O 3 . Surprisingly, both epitaxial and polycrystalline films show nearly identical levels of ionic conductivity, as measured by alternating current impedance spectroscopy and this is the case despite the fact that the polyfilm possesses nanosized columnar grains and thus an extremely high density of the grain boundaries. The highly conductive nature of grain boundaries in stabilized Bi 2 O 3 is discussed in terms of the clean and chemically uniform grain boundary without segregates, and the implications for device application are suggested.