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Improving energy efficiency and reducing carbon emissions are crucial for the technological advancement of power systems. Various carbon dioxide (CO2) power cycles have been proposed for various applications. For high-temperature heat sources, the CO2 power system is more efficient than the ultra-supercritical steam Rankine cycle. As a working fluid, CO2 exhibits environmentally friendly properties. CO2 can be used as an alternative to organic working fluids in small- and medium-sized power systems for low-grade heat sources. In this paper, the main configurations and performance characteristics of CO2 power systems are reviewed. Furthermore, recent system improvements of CO2 power cycles, including supercritical Brayton cycles and transcritical Rankine cycles, are presented. Applications of combined systems and their economic performance are discussed. Finally, the challenges and potential future developments of CO2 power cycles are discussed. CO2 power cycles have their advantages in various applications. As working fluids must exhibit environmentally-friendly properties, CO2 power cycles provide an alternative for power generation, especially for low-grade heat sources.

Hydrogen as an energy carrier is critical for building a zero-carbon emission society. Solid oxide electrolysis cell (SOEC) is a feasible technology for hydrogen production with a high efficiency. Currently, the durability of SOEC systems still needs to be improved and technical issues need to be overcome. Reducing the working temperature is helpful for the lifetime. A good cell design to avoid delamination is also very important. In this study, the performance of a metal-supported intermediate-temperature SOEC is estimated using gadolinium doped ceria Gd0.1Ce0.9O2-δ (GDC) as the main electrolyte. First, a mathematical model is setup for the metal-supported SOEC. The effects of the porosity and tortuosity of the electrodes are analyzed. Subsequently, the influences of the working temperature, pressure, and steam concentration are estimated. Finally, the partial oxygen pressure inside the multi-layer electrolyte is determined and the risk of delamination is discussed. The results indicate that increasing the operation temperature can decrease the activation, concentration, and ohmic overpotentials simultaneously while increasing the pressure also can enhance the performance. Compared with the conventional design of Ceres Power, the new design using 10Sc1CeSZ as the barrier layer can increase the partial oxygen pressure of the GDC layer close to the cathode such that decomposition of GDC is avoided. Meanwhile, the partial oxygen pressure inside the multi-layer electrolyte close to the anode declines and the risk of delamination is reduced. Hence, the new design of the SOEC is beneficial for the durability of metal-supported SOEC.

A solid oxide fuel cell is a high-efficiency power device in hydrogen energy utilization. The durability and dynamic performance of metal-supported solid oxide fuel cells (MS-SOFCs) are superior to those of electrolyte- or electrode-supported cells, with many potential applications. Gadolinium-doped cerium (GDC) has a high oxygen ionic conductivity, making it suitable to act as the electrolyte in MS-SOFCs operating at 500–650 °C. However, the low-temperature sintering of GDC is difficult for MS-SOFCs. In this study, the factors affecting the low-temperature densification of GDC are analyzed based on an orthogonal experimental method. The shrinking rates of 16 experiments are determined. The effects of the particle diameter, pressure of the uniaxial press machine, sintering temperature, and fractions of aid and binder are estimated. The results of a range analysis indicate that the content of sintering aid has the greatest impact on the low-temperature densification of GDC, followed by the powder diameter and the uniaxial pressure. A maximum shrinking rate of 46.99% is achieved with a temperature of 1050 °C.