Spectral beam split is attracting more attention thanks to the efficient use of whole spectrum solar energy and the cogenerative supply for electricity and heat. Nanofluids can selectively absorb and deliver specific solar spectra, making various nanofluids ideal for potential use in hybrid photovoltaic/thermal (PV/T) systems for solar spectrum separation. Clarifying the effects of design parameters is extremely beneficial for optimal frequency divider design and system performance enhancement. The water-based SiO2 nanofluid with excellent thermal and absorption properties was proposed as the spectral beam splitter in the present study, to improve the efficiency of a hybrid PV/T system. Moreover, a dual optical path method was applied to get its spectral transimissivity and analyze the impact of its concentration and optical path on its optical properties. Furthermore, a PV and photothermal model of the presented system was built to investigate the system performance. The result indicates that the transimissivity of the nanofluids to solar radiation gradually decreases with increasing SiO2 nanofluid concentration and optical path. The higher nanofluid concentration leads to a lower electrical conversion efficiency, a higher thermal conversion efficiency, and an overall system efficiency. Considering the overall efficiency and economic cost, the optimal SiO2 nanofluid concentration is 0.10 wt.% (wt.%, mass fraction). Increasing the optical path (from 0 to 30 mm) results in a 60.43% reduction in electrical conversion efficiency and a 50.84% increase in overall system efficiency. However, the overall system efficiency rises sharply as the optical path increases in the 0–10 mm range, and then slowly at the optical path of 10–30 mm. Additionally, the overall system efficiency increases first and then drops upon increasing the focusing ratio. The maximum efficiency is 51.93% at the focusing ratio of 3.
To improve the adaptability of solar refrigeration systems to different heat sources, a single-double-effect LiBr−H2O absorption refrigeration system (ARS) driven by solar energy was designed and analyzed. The system was optimized using a multi-objective optimization method based on Sobol sensitivity analysis to enhance solar energy efficiency and reduce costs. The model of the solar single-double-effect LiBr−H2O ARS was developed, and the continuous operation characteristics of the system in different configurations were simulated and compared. The results show that the average cooling time of the system without auxiliary heat source is approximately 8.5 h per day, and the double-effect mode (DEM) generates about 11 kW of cooling capacity during continuous operation for one week under the designated conditions, and the system with adding auxiliary heat source meet the requirements of daily cooling time, the solar fraction (SF) of the system reaches 59.29%. The collector area has a greater effect on SF, while the flowrate of the hot water circulating pump and the volume of storage tank have little effect on SF. The optimized SF increases by 3.22% and the levelized cost decreases by 10.18%. Moreover, compared with the solar single-effect LiBr−H2O ARS, the SF of the system is increased by 15.51% and 17.42% respectively after optimization.
The use of two-dimensional (2D) layered metal-organic frameworks (MOFs) as self-sacrificial templates has been proven to be a successful method to create high-efficiency Selenium (Se)-containing electrocatalysts for overall water splitting. Herein, two strategies are then utilized to introduce Se element into the Co–Fe MOF, one being the etching of as-prepared MOF by SeO2 solution, and the other, the replacing of SCN− with SeCN− as the construction unit. The electrochemical activity of the pristine 2D MOF and their calcinated derivatives for catalyzing the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is evaluated and further discussed. It is found that the effect of introducing Se on improving electrochemical catalytic activity is significant for the HER process. Specifically, the calcinated derivative in the replacing method exhibits an overpotential of 235 mV for HER and 270 mV for OER at a current density of 10 mA/cm2. For comparing the two methods of introducing Se element into MOF, similar electrocatalytic activity can be achieved on the their calcinated derivatives. The high electrochemical performance of 2D CoFe-MOF derivatives may be resulted from the unique 2D hierarchical porous structure and strong synergistic effect between different components in the material.
The electrochemistry of cathode materials for sodium-ion batteries differs significantly from lithium-ion batteries and offers distinct advantages. Overall, the progress of commercializing sodium-ion batteries is currently impeded by the inherent inefficiencies exhibited by these cathode materials, which include insufficient conductivity, slow kinetics, and substantial volume changes throughout the process of intercalation and deintercalation cycles. Consequently, numerous methodologies have been utilized to tackle these challenges, encompassing structural modulation, surface modification, and elemental doping. This paper aims to highlight fundamental principles and strategies for the development of sodium transition metal oxide cathodes. Specifically, it emphasizes the role of various elemental doping techniques in initiating anionic redox reactions, improving cathode stability, and enhancing the operational voltage of these cathodes, aiming to provide readers with novel perspectives on the design of sodium metal oxide cathodes through the doping approach, as well as address the current obstacles that can be overcome/alleviated through these dopant strategies.
Proton exchange membrane fuel cells (PEMFCs) are playing irreplaceable roles in the construction of the future sustainable energy system. However, the insufficient performance of platinum (Pt)-based electrocatalysts for oxygen reduction reaction (ORR) hinders the overall efficiency of PEMFCs. Engineering the surface strain of catalysts is considered an effective way to tune their electronic structures and therefore optimize catalytic behavior. In this paper, insights into strain engineering for improving Pt-based catalysts toward ORR are elaborated in detail. First, recent advances in understanding the strain effects on ORR catalysts are comprehensively discussed. Then, strain engineering methodologies for adjusting Pt-based catalysts are comprehensively discussed. Finally, further information on the various challenges and potential prospects for strain modulation of Pt-based catalysts is provided.
Exploring advanced platinum (Pt)-based electrocatalysts is vital for the widespread implementation of proton exchange membrane fuel cells (PEMFCs). Morphology control represents an effective strategy to optimize the behavior of Pt catalysts. In this work, an attempt is made to comprehensively review the effect of morphology control on the catalytic behavior of catalysts in the oxygen reduction reaction (ORR). First, the fundamental physicochemical changes behind morphology control, including exposing more active sites, generating appropriate lattice strains, and forming different crystalline surfaces, are highlighted. Then, recently developed strategies for tuning the morphologies of electrocatalysts, including core-shell structures, hollow structures, nanocages, nanowires, and nanosheets, are comprehensively summarized. Finally, an outlook on the future development of morphology control of Pt catalysts is presented, including rational design strategies, advanced in situ characterization techniques, novel artificial intelligence, and mechanical learning. This work is intended to provide valuable insights into designing the morphology and technological innovation of efficient redox electrocatalysts in fuel cells.
Great progress has been made in the electrochromic (EC) technology with potential applications in various fields. As one of the most promising EC materials, Prussian blue (PB) has attracted great attention due to its excellent EC performance, such as low cost, easy synthesis, rich color states, chemical stability, suitable redox potential, and fast color-switching kinetics. This review summarizes the recent progress in PB electrodes and devices, including several typical preparation techniques of PB electrodes, as well as the recent key strategies for enhancing EC performance of PB electrodes. Specifically, PB-based electrochromic devices (ECDs) have been widely used in various fields, such as smart windows, electrochromic energy storage devices (EESDs), wearable electronics, smart displays, military camouflage, and other fields. Several opportunities and obstacles are suggested for advancing the development of PB-based ECDs. This comprehensive review is expected to offer valuable insights for the design and fabrication of sophisticated PB-based ECDs, enabling their practical integration into real-world applications.