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The electrochemical performance of solid oxide cells (SOCs) is investigated under both fuel cell and electrolyzer operations to understand their asymmetric behavior between the two operation modes. The current–voltage and electrochemical impedance characteristics of a hydrogen-electrode-supported cell are experimentally analyzed. Also, a numerical model is developed to reproduce the cell performance and to understand the internal resistances of the cell. Partial pressures of supplied gas and load current are varied to evaluate their effects on the cell performance. The gas partial pressures of hydrogen and steam supplied to the hydrogen electrode are kept equivalent so that the cell performance can be fairly compared between the two operation modes when the same current is applied. It is found that the origin of the asymmetry is mostly from the hydrogen electrode; both activation and concentration overpotentials show asymmetric behavior particularly at high current densities. A numerical experiment is also conducted by deliberately changing parameters in the model. Asymmetry in the activation overpotential is found to be originated from the non-identical charge-transfer coefficients in the Butler–Volmer equation and also from the non-uniform gas concentration formed in the hydrogen electrode under current-biased conditions. On the other hand, asymmetry in the concentration overpotential is associated with the non-equimolar counter diffusion of hydrogen and steam caused by the effect of Knudsen diffusion. Therefore, enhancing gas transport in the hydrogen electrode and reducing the contribution of Knudsen diffusion are effective approaches to reduce asymmetry not only in the concentration overpotential but also in the activation overpotential. • Performance of solid oxide cell is evaluated in fuel cell and electrolysis modes. • Numerical simulation is performed to understand the overpotential components. • Asymmetric behavior is observed between the two operation modes. • Asymmetry is caused by activation and diffusion resistances in hydrogen electrode. • Numerical experiment is conducted to identify physicochemical origin of asymmetry. [ABSTRACT FROM AUTHOR]

Reversible Solid Oxide Cells (RSOCs) are a transformative technology at the Hydrogen-Electricity Nexus, offering promising solutions for energy conversion and storage in renewable systems. However, challenges such as achieving stable and efficient reversible operations limit their widespread adoption. This work critically analyzes recent advancements in RSOC technology, focusing on reversible mode switching and its integration with renewable energy sources. Key topics include transient dynamics, such as current density overshoot and thermal management, along with advanced control strategies to optimize RSOC performance and extend lifespan. We also explore material innovations, particularly in electrode design, to enhance durability during reversible operations. Additionally, we discusse scale-up demonstrations and engineering applications, bridging the gap between research and real-world implementation. This work serves as a valuable resource for advancing RSOC technology, providing insights and guidance for future research and development efforts. [Display omitted] ● Explores core RSOC principles and intricacies of reversible mode switching for efficient operation. ● Analyzes transient dynamics and their impact on RSOC performance, stability, and longevity. ● Presents advanced control strategies for optimizing temperature, current, and gas flow in RSOCs. ● Emphasizes material innovations, focusing on durability and performance in reversible operations. ● Discusses RSOC potential and challenges in large-scale renewable energy and hydrogen systems. [ABSTRACT FROM AUTHOR]

Reversible solid oxide cell (RSOC) has attracted significant attention due to its multi-functionalities for energy conversion and storage. This device works as a fuel cell (FC) or an electrolyzer cell (EC) with superior efficiency. However, its dynamic response is complex and may cause a large overshoot of current operated in reversible cell mode, which impairs the long-term stability of RSOC. Although several works report the overshoot phenomenon, the mechanism and effects on cell performance are still unclear so far. In this work, we build a 3D dynamic planar RSOC model to investigate the detailed behavior of overshoot. The results show that the overshoot of current for RSOC can be caused under switching mode conditions. Especially a larger overshoot of current can be observed within switching mode from EC to FC. The overshoot of current is mainly caused by the load change, slower gas diffusion, and differentiated temperature distribution in RSOC. [Display omitted] • The mode-changing can cause a large overshoot of current in RSOCs. • A dynamic model of RSOCs is developed to elevate the overshoot and response time. • Load sizes, switching time and temperature effect on the dynamic performance. • The current overshoot is proportional to the variation of load change. [ABSTRACT FROM AUTHOR]

The successful market introduction of the solid oxide fuel/electrolysis cell technology for power‐to‐gas applications requires the reduction of the degradation rates and the better understanding of the degradation mechanisms of the stacks. Therefore, the paper reports and compares the long‐term behavior of a solid oxide cell stack in electrolysis and reversible fuel cell/electrolysis operation. The 30‐cell stack with electrolyte supported cells was supplied by Sunfire GmbH (Dresden/Germany) in the German funded RSOC Project. The stack was operated for 3,370 h in electrolysis and afterwards for 2,500 h in reversible fuel cell/electrolysis mode, each at 70% gas conversion. In the beginning of the test, the stack showed high gas tightness, good performances and high efficiencies in both SOEC and SOFC operations. During 3,370 h of SOEC operation a low degradation of +0.5%/1,000 h was measured. During 2,500 h of reversible fuel cell/electrolysis cycling, the gas tightness of the stack slightly decreased, which led to a temperature increase, and higher degradation rates were observed. The increase of the ohmic resistance contributed mostly to the degradation. Optimized operating conditions for reversible cycling and increasing the purity of the supplied water are foreseen in order to minimize stack degradation in reversible operation. [ABSTRACT FROM AUTHOR]

Reversible solid oxide cells (ReSOCs) can provide significant value by playing different roles – electrical generation or electricity storage – depending on the prevailing electrical grid requirements. Relatively few studies have focused on the life testing of solid oxide cells in this mode-switching operation, and much of that work has focused on small "button" cells. The present study describes electrochemical characterization and post-test characterization from an ∼2600 h life test of a 10 cm × 10 cm fuel-electrode-supported cell operated with periodically reversing current. The cell performance gradually decreased for the first ∼1000 h and then stabilized with low degradation rate until an abrupt test-ending gas crossover failure that resulted in open circuit voltage drop. Post-test characterization of the (La,Sr)CoO 3-δ air-electrode showed evidence of Cr vapor contamination from stainless-steel manifolds and Ag contamination from current collection contacts. Partial delamination of the air-electrode and Gd-doped ceria interlayer was observed, along with fractures in the electrolyte near the fuel inlet that probably caused a drop in open circuit voltage near the end of the test. Ni Ni connectivity was reduced in both the functional and support layers accompanied by Ni particle coarsening, especially at the fuel outlet. [Display omitted] • A ∼ 2600 h life-test of a large-area ReSOC showed little degradation dependence on current density and cycle period. • Ni coarsening and isolated Ni particles were evident mostly at the fuel outlet. • Nano-pores developed in the air electrode likely due to Cr contamination. • Co, La, Cr, and Ag contaminated the GDC interlayer resulting in contact loss. • Fractures and incursion of Ag in YSZ electrolyte at the air outlet. [ABSTRACT FROM AUTHOR]

Increasing global energy demands have been accelerating the research and development of reversible electrochemical systems that can realize an efficient use of the intermittent renewable energy resources. This paper thus describes a numerical investigation of reversible solid oxide cells (RSOCs), for their high energy efficiency delivered from the high operating temperatures ranging from 600 to 1000 °C. Unlike the previous studies, a model-based strategy is applied for the simultaneous integration of different operating modes (namely, fuel cell and electrolysis cell modes) to enable more realistic predictions on the trade-off behavior of the effects of electrode design parameters on the cell performance. This approach was taken to investigate the effects of various geometric designs and operating parameters (electrode backing layer thickness; interconnector rib size; fuel gas composition) on the current-potential characteristic and the round-trip efficiency. The cell performance was significantly affected by the rib size, particularly when the backing layer was thin, because of the uneven distribution of the reactant species. Overall, this study provides insights into key geometric design parameters that dominate the performance of dual-mode RSOCs. [ABSTRACT FROM AUTHOR]

This paper presents the annual performance of a proposed reversible water/LiBr absorption heat pump connected to a district heating network for space cooling, heating, and domestic hot water (DHW) applications. A typical small-office building located in two cities (Barcelona and Berlin) with different climate zones was considered in this study. The absorption heat pump operated in heating and cooling modes of operation depending on the needed demand type in the building. The dynamic modelling and simulation of the absorption heat pump driven by the district heating network were carried out for each operational mode. The obtained simulation results are seasonal COP in heating and cooling mode as well as the amount of potential DHW production throughout the year. Moreover, the annual operation time and primary energy ratio of the proposed system were obtained. Then, the primary energy ratio is compared with conventional buildings' cooling and heating systems. It is found that the proposed system has an increasing operation time up to 63% and consumes less primary energy with a reduction of up to 30%. Thus, the development of this type of system contributes towards the reduction of fossil fuel consumption for the space cooling and heating sector of non-residential buildings. • District-heat-driven reversible water/LiBr AHP system is proposed. • Annual performance of district-heat-driven water/LiBr AHP is investigated. • Seasonal cooling and heating COPs of AHP are obtained in warm and cold climates. • Reversible operation of the AHP increased its annual operational time up to 63%. • Primary energy consumption is reduced by up to 30% using the proposed system. [ABSTRACT FROM AUTHOR]

High-temperature solid oxide cells (SOCs) are attractive for storage and conversion of renewable energy sources by operating reversibly in solid oxide fuel cell and solid oxide electrolysis cell modes. Solid oxide fuel cell is the most efficient energy conversion device for the electricity generation by electrochemically direct conversion of chemical energy of fuels such as hydrogen, methanol and methane, while under solid oxide electrolysis cell operation mode, hydrogen or syngas can be produced as fuels or feedstock for liquid fuels such as methanol, gasoline and diesel using electricity from renewable energy sources. This mini review will introduce briefly the principle, status and progress in the electrochemical energy conversion and storage process by reversible operation of high temperature SOCs. The challenges in key material and performance degradation issues associated with high-temperature fuel cell and electrolysis operation of SOCs will be concisely reviewed and discussed. Copyright © 2016 Curtin University of Technology and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Electrical energy storage is expected to be a critical component of the future world energy system, performing load-leveling operations to enable increased penetration of renewable and distributed generation. Reversible solid oxide cells, operating sequentially between power-producing fuel cell mode and fuel-producing electrolysis mode, have the capability to provide highly efficient, scalable electricity storage. However, challenges ranging from cell performance and durability to system integration must be addressed before widespread adoption. One central challenge of the system design is establishing effective thermal management in the two distinct operating modes. This work leverages an operating strategy to use carbonaceous reactant species and operate at intermediate stack temperature (650 °C) to promote exothermic fuel-synthesis reactions that thermally self-sustain the electrolysis process. We present performance of a doped lanthanum-gallate (LSGM) electrolyte solid oxide cell that shows high efficiency in both operating modes at 650 °C. A physically based electrochemical model is calibrated to represent the cell performance and used to simulate roundtrip operation for conditions unique to these reversible systems. Design decisions related to system operation are evaluated using the cell model including current density, fuel and oxidant reactant compositions, and flow configuration. The analysis reveals tradeoffs between electrical efficiency, thermal management, energy density, and durability. [ABSTRACT FROM AUTHOR]

Radiation reservoirs are more complex than heat reservoirs. They depend on the intensive thermodynamic parameters (such as temperature, pressure, and chemical potential) as well as on other state parameters (such as the geometric factors). The paper refers to work extraction from a high temperature radiation reservoir (the pump), the sink being a heat reservoir, respectively a radiation reservoir. The simplest case of radiation reservoir (i.e. blackbody isotropic radiation) is considered. Reversible and endoreversible conversion is analyzed. The upper bound for reversible work extraction is not Carnot efficiency. All upper bound efficiencies obtained here depend on the pump geometric factor. [ABSTRACT FROM AUTHOR]

Abstract: The need for electrical energy storage (EES) is being driven by the deployment of increasing amounts of intermittent renewable energy resources. In addition to their fuel flexibility, high efficiency, scalability, and long-term cost outlook, reversible (regenerative) solid oxide cell (rSOC) systems have the potential for round-trip efficiencies competitive with the other available energy storage technologies. Accordingly, the focus of the current study is to investigate modeling methods for high temperature rSOCs in order to facilitate future endeavors related to establishing optimal operating conditions and system designs. Previously developed solid oxide fuel cell (SOFC) and solid-oxide electrolytic cell (SOEC) models are integrated to form a general rSOC model. The model is first calibrated and validated based on the available experimental data in the extant literature. The validation results show that the fitting parameters extracted from the calibration study can precisely simulate the cell behavior under various operating conditions. The effects of key operating parameters, such as temperature, gas composition and fuel utilization, on the voltage–current density performance characteristic and thermoneutral voltage are then investigated. It is also observed that the total electrochemical losses of the cell can be significantly different in each operating mode (fuel cell and electrolyzing) under certain operating conditions. Advantages of pressurized operation on thermal management are also discussed. [Copyright &y& Elsevier]

Abstract: Two kinds of maps that describe evolution of states of a subsystem coming from dynamics described by a unitary operator for a larger system, maps defined for fixed mean values and maps defined for fixed correlations, are found to be quite different for the same unitary dynamics in the same situation in the larger system. An affine form is used for both kinds of maps to find necessary and sufficient conditions for inverse maps. All the different maps with the same homogeneous part in their affine forms have inverses if and only if the homogeneous part does. Some of these maps are completely positive; others are not, but the homogeneous part is always completely positive. The conditions for an inverse are the same for maps that are not completely positive as for maps that are. For maps defined for fixed mean values, the homogeneous part depends only on the unitary operator for the dynamics of the larger system, not on any state or mean values or correlations. Necessary and sufficient conditions for an inverse are stated several different ways: in terms of the maps of matrices, basis matrices, density matrices, or mean values. The inverse maps are generally not tied to the dynamics the way the maps forward are. A trace-preserving completely positive map that is unital cannot have an inverse that is obtained from any dynamics described by any unitary operator for any states of a larger system. [ABSTRACT FROM AUTHOR]

The continuous increase of energy demand with the subsequent huge fossil fuel consumption is provoking dramatic environmental consequences. The main challenge of this century is to develop and promote alternative, more eco-friendly energy production routes. In this framework, Solid Oxide Cells (SOCs) are a quite attractive technology which could satisfy the users' energy request working in reversible operation. Two operating modes are alternated: from "Gas to Power", when SOCs work as fuel cells fed with hydrogen-rich mixture to provide both electricity and heat, to "Power to Gas", when SOCs work as electrolysers and energy is supplied to produce hydrogen. If solid oxide fuel cells are an already mature technology with several stationary and mobile applications, the use of solid oxide electrolyser cells and even more reversible cells are still under investigation due to their insufficient lifetime. Aiming at providing a better understanding of this new technological approach, the study presents a detailed description of cell operation in terms of electrochemical behaviour and possible degradation, highlighting which are the most commonly used performance indicators. A thermodynamic analysis of system efficiency is proposed, followed by a comparison with other available electrochemical devices in order to underline specific solid oxide cell advantages and limitations. [ABSTRACT FROM AUTHOR]

With the advancement of computer and communication technologies in data processing, storage, and increasing bandwidth of data transmission, the amount of multimedia data generation and sharing has increased exponentially. Therefore, the security of multimedia data becomes more important in transmission, processing, and storing the day-to-day. Cryptography is one of the important mechanisms in preserving the confidentiality, integrity, and availability of multimedia data such as images. In this research, a digital encryption method is presented based on Galois fields, consisting of two main stages of diffusion and permutation. At the Diffusion stage, using matrix multiplication operations in the GF (256), the overlapping rows and columns of image pixels are mixing. The permutation stage changes image pixels position by using The 2D chaotic map in GF (2n) or The 3D chaotic map in the GF field (2k). The proposed method, with a maximum of two rounds repetition of the main steps, reaches the optimal values of the parameters of the performance evaluation. By performing standard security tests, the proposed method is resistant to differential and statistical attacks and has yielded relatively good performance compared to similar digital image encryption methods. [ABSTRACT FROM AUTHOR]