The world is recently witnessing an explosive development of novel electronic and optoelectronic devices that demand more-reliable power sources that combine higher energy density and longer-term durability. Supercapacitors have become one of the most promising energy-storage systems, as they present multifold advantages of high power density, fast charging-discharging, and long cyclic stability. However, the intrinsically low energy density inherent to traditional supercapacitors severely limits their widespread applications, triggering researchers to explore new types of supercapacitors with improved performance. Asymmetric supercapacitors (ASCs) assembled using two dissimilar electrode materials offer a distinct advantage of wide operational voltage window, and thereby significantly enhance the energy density. Recent progress made in the field of ASCs is critically reviewed, with the main focus on an extensive survey of the materials developed for ASC electrodes, as well as covering the progress made in the fabrication of ASC devices over the last few decades. Current challenges and a future outlook of the field of ASCs are also discussed.

Electrochemical capacitors or supercapacitors have achieved great interest in the recent past due to their potential applications ranging from microelectronic devices to hybrid electric vehicles. Supercapacitors can provide high power densities but their inherently low energy density remains a great challenge. The high-performance supercapacitors utilize large electrode surface area for electrochemical double-layer capacitance and/or pseudocapacitance. To enhance the performance of supercapacitors, various strategies have been adopted such as electrode nanostructuring, hybrid electrode designs using nanocomposite electrodes and hybrid supercapacitor (HSC) configurations. Nanoarchitecturing of electrode-active materials is an effective way of enhancing the performance of supercapacitors as it increases the effective electrode surface area for enhanced electrode/electrolyte interaction. In this review, we focus on the recent developments in the novel electrode materials and various hybrid designs used in supercapacitors for obtaining high specific capacitance and energy density. A family of electrode-active materials including carbon nanomaterials, transition metal-oxides, transition metal-nitrides, transition metal-hydroxides, electronically conducting polymers, and their nanocomposites are discussed in detail. The HSC configurations for attaining enhanced supercapacitor performance as well as strategies to integrate with other microelectronic devices/ wearable fabrics are also included.

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In this paper, two configurations of the S-CO2 Brayton cycles (i.e., the single-recuperated and recompression cycles) are thermodynamically modeled and optimized through a multi-objective approach. Two semi-conflicting objectives, i.e., cycle efficiency (ηc) and cycle specific power (Φsp) are maximized simultaneously to achieve Pareto optimal fronts. The objective of maximum cycle efficiency is to have a smaller and less expensive solar field, and a lower fuel cost in case of a hybrid scheme. On the other hand, the objective of maximum specific power provides a smaller power block, and a lower capital cost associated with recuperators and coolers. The multi-objective optimization is carried out by means of a genetic algorithm which is a robust method for multidimensional, nonlinear system optimization. The optimization process is comprehensive, i.e., all the decision variables including the inlet temperatures and pressures of turbines and compressors, the pinch point temperature differences, and the mass flow fraction of the main compressor are optimized simultaneously. The presented Pareto optimal fronts provide two optimum trade-off curves enabling decision makers to choose their desired compromise between the objectives, and to avoid naive solution points obtained from a single-objective optimization approach. Moreover, the comparison of the Pareto optimal fronts associated with the studied configurations reveals the optimum operational region of the recompression configuration where it presents superior performance over the single-recuperated cycle.