Green Energy and Resources最新文献

The degradation of the catalyst layer significantly affects the gas transport and electrochemical processes in the porous electrodes, thus affecting the performance of proton exchange membrane fuel cells. To reveal the catalyst layer degradation impact, the microscopic porous structure of the cathode catalyst layer was reconstructed by a random algorithm in this work. Consequently, Lattice Boltzmann method was used to study the oxygen transport and electrochemical reaction processes at the limiting current density condition with considering the degradation of platinum, carbon particles, and ionomers under uniform and exponential degradation rates, respectively. The results reveal that the degradation of platinum reduces the reaction sites in the catalyst layer, thus deteriorating the electrochemical kinetics and lowering the total reaction rate. On the contrary, the degradation of carbon and ionomer shows two diametrically opposed effects. On the one hand, the oxygen transport is improved due to carbon and ionomer degradation, especially for ionomer degradation, thereby accelerating the total reaction rate. On the other hand, the degradation of carbon and ionomer triggers the detachment of platinum particles, leading to a decrease in reaction rate. In the early stages of the multi-component simultaneous degradation process, the total reaction rate is prohibited by oxygen transport limitation inside the catalyst layer; as the degradation degree increases, the oxygen transport through the ionomer films is enhanced and the electrochemical kinetics becomes the rate determining factor, especially for exponential degradation rate. This study provides a comprehensive assessment of the oxygen transport and electrochemical reaction within the catalyst layers with respect to different degrees of catalyst layer degradation, which can guide the design of high-performance anti-degradation catalyst layers for the next generation of fuel cells.

The application of ionic liquids (ILs) in the field of thermal energy storage is attracting increasing attention owing to their thermophysical properties, such as an adjustable phase change temperature, low flammability/volatility, and good thermal and chemical stability. A recent utilization was provided by the National Aeronautics and Space Administration (NASA), which employed eutectic phase change materials (PCMs) composed of functional ILs to manage the extreme space environment (solar radiation and extreme cold/hot) of crewed spacecraft for future deep exploration. While the concept of storing latent heat during the ILs' phase transition is not new, large-scale applications employing this concept have not yet realized their full potential. In addition, although a considerable amount of review has been published for traditional PCMs, the information on ILs and their application remain unsystematic; thus, benefits such as structural alterations to cations and anions for tunable chemical and phase properties are long-term neglected in the field of thermal energy storage. This review aims to provide the necessary information on the choice of well-studied ILs and promote further research in this field. This review first discusses the defects of traditional PCMs, followed by reviewing and summarizing the commonly used ILs in terms of their chemical structure, phase transition mechanisms, and thermophysical properties. Finally, the applications of ILs-based PCMs are introduced in detail, and existing problems, solutions, and future research directions are proposed.

Granulated blast furnace slag (GBFS) is widely used in cement and concrete industries due to its excellent hydration properties. However, there is a huge capacity gap between the steel industry and the cement industry, and hence, the supply of GBFS can hardly meet the demand. At present, few studies have focused on the preparation of cementitious materials with GBFS-like properties, and a detailed summary of the mechanisms is lacking. This review summarizes the physical and chemical properties of GBFS and comprehensively discusses the hydration process in cement. In addition, the synergistic effects between GBFS and solid wastes (red mud, steel slag, gypsum and fly ash) were analyzed in detail. Based on the analysis of this work, there are four synergistic mechanisms among them. Moreover, a method for using solid wastes as raw materials to produce composite GBFS is proposed. It is beneficial to valorize various industrial solid wastes, promote cross-industry cooperation and alleviate the demand of the cement industry for high-quality GBFS. Although it is a theoretically possible method, there are still some problems that need to be solved, such as the lack of uniform quality and environmental standards. This work can provide useful advice for the preparation of composite GBFS.

Solar-driven interfacial evaporation for wastewater purification and seawater desalination is perceived an encouraging strategy to simultaneously address water scarcity and the energy crisis. Hydrogel materials can undertake the crucial tasks of water transport and evaporation based on their well-known hydrophilicity and water retention. In the past few years, on account of its merits of low cost, simple preparation method and low energy consumption, hydrogel-based solar energy water purification technology has gradually turned into a research hotspot. This article systematically introduces the latest progress in the field of solar evaporation using hydrogel materials. Three aspects are discussed, including various photothermal materials, different evaporation systems and practical applications. Finally, the challenges in the current development process of solar evaporation technology are analyzed, and the countermeasures are put forward.

Regional energy systems are designed to contribute to a green and “carbon neutral” economy of localities. In this system, the engine combustion is significant for power generation. Therefore, this study mainly investigated the effect of throttle openings on the combustion characteristics of hydrogen (H₂) and methane (CH₄) mixtures to achieve high efficiency. Throttle opening has a strong relationship with combustion performance, particularly for power output and efficiency. Therefore, 10%, 20%, 40%, and 100% throttle openings were tested to obtain higher efficiency for power generation. Combustion characteristics of CH₄ and CH₄+H₂ were also compared. With H₂ addition, the volume percentage of H₂ varied between 10%, 30%, and 50%. The ratio of air to gas fuel was controlled to determine λ varying from 1.0 to 1.4. Subsequently, the effect of throttle openings under different λ with H₂ addition was examined. Finally, brake thermal efficiency (BTE), power output, brake mean effective pressure (BMEP) and brake specific fuel consumption (BSFC) were compared. Moreover, the maximum value of the cylinder pressure in cycles (P_max) and the coefficient of variation (COV) in P_max were discussed. The results showed that the torque and power output decreased slightly from full throttle opening to 40% throttle opening. The 30% H₂ addition in Case # 5 (full opening under lean-burn conditions) is the best working condition to satisfy both the power generation and energy-saving requirements in this study. Furthermore, P_max decreased with smaller throttle opening, and H₂ addition increased P_max. In addition, H₂ addition decreased COV, but throttle opening had less effect on COV.

The consumption of energy by buildings accounts for 30% of the total amount of social primary energy used, and approximately 30%∼50% of this is lost through windows. To promote energy conservation, the green development of buildings, and revolutionarily upgrade energy production and consumption, developing energy-efficient windows while preserving architectural aesthetics is necessary. Electrochromic smart windows (ESWs) can control the amount of solar energy transmitted into buildings based on personal preference or weather conditions, thereby reducing the amount of energy consumed by buildings for lighting and cooling. The optical transmittance of ESWs is changed by applying different voltages, and they maintain their state without the input of energy. Metal oxides are considered among the most promising electrochromic films for use in ESWs because of their relatively good physical and chemical stabilities. After nearly half a century of development, the practical application of metal oxide-based ESWs is nearly realized. This review presents an evaluation of the performance of ESWs and summarizes five strategies that can be used to enhance the electrochromic properties of metal oxides. These include controlling the oxygen vacancy concentration, doping aliovalent ions, controlling the morphology, selecting the optimal electrolyte, and controlling crystallinity. This review also investigates the development of metal-oxide-based ESWs.

Tower receivers in next-generation concentrated solar power towers (SPTs) face an increasing challenge to suppress the massive radiation heat loss associated with an elevated operating temperature. Negative thermal-flux regions (NTRs) exist in tower receivers owing to the high but uneven temperature and solar concentration ratio on their surfaces. Spectrally selective coatings on NTRs are proposed in this study to reduce the radiation heat loss and thus improve the solar-thermal conversion efficiency of tower receivers. Four coatings, namely, black Cr, Ag film, and ideal coatings with cutoff wavelengths of 2.5 and 1.5 μm, are investigated to evaluate the compatibility and effectiveness of coatings with diverse spectral selectivities to improve NTR solar-thermal conversion performance. The Dunhuang 10 MWe SPT plant using a binary salt as the heat transfer fluid was selected for the study. A novel spectral heat transfer model of the tower receiver and an economic assessment model of the Dunhuang SPT plant were established and verified by the experimental results. These results showed that the spectral coatings locally coupled on NTRs were effective in regulating NTR radiation properties and reducing radiation heat loss, thus improving the thermal performance of the tower receiver. The tower receiver efficiencies with Ag and ideal coating (cutoff wavelength of 1.5 μm) were significantly improved by 6.92% and 12.03%, respectively, compared to that of a prototype receiver. The novel receiver based Dunhuang SPT plant harvested an annual power output improvement of 5.8% and levelized cost of energy reduction of 5.6%.

The goal of this study was to investigate a new aspect of polymeric film modification used in triboelectric nanogenerators (TENGs). TENGs were fabricated using fluorinated ethylene propylene (FEP) and chemically etched nylon films. The FTIR spectra confirmed the retained polymeric nature of the modified nylon films, and the AFM results showed an improvement in the roughness of the film surfaces after chemical treatment. The as-fabricated floatable TENGs delivered an open-circuit voltage of 12 V when subjected to an external force, and could glow a few light-emitting diodes (LEDs) with water waves. The findings of this study will open new prospects for the future development and optimization of polymer-based TENGs for blue energy harvesting.

Non-thermal plasma as a tool in chemical reaction engineering has been studied for many years. The temperature of electrons in non-thermal plasma far exceeds other particles, which leads to its high efficiency. Besides the well-studied destruction of volatile organic compounds (VOCs), the reaction environment generated by non-thermal plasma is also suitable for the activation of many significant gas-phase chemical reactions, e.g., as methane coupling, reduction of carbon dioxide, ammonia synthesis, nitrogen fixation, as well as some liquid phase chemical reactions such as the treatment of contaminated water. Material synthesis is another target field of non-thermal plasma. Plasma in micro scale with several enhanced properties makes it an even more promising tool for plasma-chemical processing. This work summarizes different types of non-thermal plasmas and their performance in commonly studied chemical reactions. The advantages gained by generating non-thermal plasma in micro scale with constricted spaces, reduced timescales, and micro-/nano-structured electrodes are also discussed.