EnergyChem最新文献

Reticular frameworks including metal−organic frameworks (MOFs) and covalent organic frameworks (COFs), and their derived materials have drawn global attention in the capture and conversion of CO₂ as a cheap feedstock into fine chemicals and fuels due to their facile synthesis and programmable highly porous structures. This review comprehensively summarizes the progress in thermo−catalysis of CO₂ conversion by reticular framework−based catalysts to afford chemicals such as cyclic carbonates, cyclic carbamates, formamides, carboxylic acid, carbon monoxide, formate, methanol, methane, and light olefins. Firstly, the characteristics and advantages of MOF−based materials for CO₂ conversion are introduced. Secondly, the characteristics and advantages of COF−based materials for CO₂ conversion are presented. Subsequently, the CO₂ conversion reactions are briefly classified and discussed. Particularly, MOF or COF−based catalysts for each reaction are summarized in terms of catalyst design, catalytic performance and catalytic mechanism. Finally, the perspectives for further development of reticular framework−based catalysts for efficient CO₂ conversion are discussed. We hope this review can provide an inspiration for the rational design of porous crystalline materials for thermal catalytic CO₂ conversion.

Since the late 1990s, much progress has been made in the field of the chemistry of flexible porous coordination polymers (PCPs). Various PCP architectures have been recognized and several promising applications have been identified, e.g., in the areas of selective gas capture and separation, sensors, and drug carriers. The crystalline and flexible frameworks of PCPs can respond to various external stimuli and then adjust themselves to adapt to new environments in a tuneable fashionࣧ behavior that is seldom observed in other porous solids. Over the past decade, following on from developments made in terms of flexible PCP performance, how to accurately build these architectures with the required functions has become a new challenge. In this review, the authors focus on the three aspects of flexible PCPs: 1) classifying the flexible systems with different fashions of pore opening, 2) classifying the flexible PCPs with governing factors of internal structure and external conditions, and 3) introducing, and summarizing, flexibility- and structure-dependent performance. The goal is to present the state-of-art chemistry and application of flexible PCPs and to offer an outlook towards discovering and designing further new materials.

The performance degradation of proton exchange membrane fuel cells (PEMFCs) is one of the most critical challenges in their practical applications. Degradations of electrocatalysts for oxygen reduction reaction (ORR) at cathode and hydrogen oxidation reaction (HOR) at the anode are the major contributors to PEMFC degradation, which are mainly induced by fuel/air impurities, unintentional harmful species during the preparation and use of the catalysts, as well as catalyst decomposition during the operation. This review summarizes the recent research on PEMFC performance degradation and the progress in developing mitigation strategies for avoiding the degradation. Several aspects are emphasized as follows: the understanding of catalyst poisoning phenomena, influencing factors, and general degradation mechanisms. Several technical challenges are analyzed and the corresponding future research directions are proposed to facilitate the further research and development of mitigation strategies for PEMFC catalyst degradation.

Electrochromic devices (ECDs), which generate reversible color changes by the electrochemical reaction, have shown tremendous promise in the field of smart windows, displays, and the future wearable electronics, due to their benefits of simple structure, low power consumption, as well as multi-colors. In the past decade, two-dimensional (2D) materials, such as graphene, metal oxides/carbides/nitrides/dichalcogenides, conductive polymer, metal-organic frameworks, and covalent organic frameworks, that represent good mechanical properties, superior electrochemical activity, fast charge transfer speed, and other unique physical properties, have been widely applied in the ECDs and induced great improvement of the field. As a result, some long-playing issues of ECDs are in prospect to be settled by using 2D materials. This review starts from summarizing the evaluation standard of ECDs, followed by highlighting the most up-to-date exciting results regarding the design and application of 2D materials for the electrochromic layer. Meanwhile, the superior effects of graphene and MXenes for advanced flexible transparent conducting layer are discussed in detail. At last, the remaining challenges and possible research directions for the future of this field are also proposed. Hopefully, the review may shed light on the main trends for developing high-performance ECDs, and provide referencing value for other researchers, to and finally boost the practical applications of ECDs.

The huge market in electric road vehicles and portable electronic devices is boosting the development of high-energy-density solid-state alkali-metal batteries with high safety, including lithium-metal batteries and sodium-metal batteries. However, solid-state electrolytes (SSEs) are still the main barrier that hinders the development of solid-state alkali-metal batteries, because there is no such a single SSE that is compatible with both the highly reductive and chemically active alkali-metal anodes and oxidative high-voltage cathodes. Asymmetric solid-state electrolytes (denoted as ASEs) with more than one layer of SSE are reported to be able to effectively tackle such issues by constructing a multiple layered-like structure. In ASEs, each layer of SSE contains a different composition or morphology. SSEs with such an asymmetric structure exhibit Janus property, which not only satisfies the different stability requirements from the cathode and the anode respectively, but also compensates the disadvantages of the individual SSEs ingenuously. In this way, the advantages of each individual SSE are fully utilized and superior electrochemical performances of solid-state full cells are realized. This review focuses on discussing various original ASEs that have been developed recently, including design principles, synthetic methods of bilayer/tri-layer structured polymer/ceramic ASEs and asymmetric gel electrolytes, and the exhibited electrochemical properties of solid-state lithium/sodium-metal batteries. Finally, we provide perspectives and suggestions towards ASEs for future applications in solid-state batteries.

Defective carbon-based materials (DCMs) have recently been considered as one of the most promising alternatives to precious metal electrocatalysts owing to their irreplaceable advantages, such as environmentally friendly, low cost and high structural tunability. Despite remarkable progress has been achieved, grand challenges of their further development are still remained by the traditional “trial-and-error” approaches, mainly due to the lack of precise synthetic methodologies as well as in-depth understandings of active centers and underlying electrocatalytic mechanisms. Herein, this review will provide a comprehensive overview and perspective on the critical issues and possible solutions regarding the controllable synthesis of DCMs, with special emphasis on the theoretical guidance in designing complex carbon defect structures and operando characterizations in exploring “dynamic” active centers. More importantly, it will also highlight recent advances in the applications of DCMs for the cutting-edge “E-Refinery”, focusing on the electrochemical conversion of electricity into fuels and chemical building blocks (e.g., H₂, O₂, CH₄, C₂H₄, CH₃OH, C₂H₅OH, NH₃ and other organic compounds). Finally, further challenges and opportunities are summarized to shed some light on the unexploited area and future directions in expectation of stimulating the broad interest of interdisciplinary researchers.

The concept of a rechargeable lithium metal battery (LMB) was established and commercially realized before the lithium-ion battery (LIB), although safety concerns related to the lithium metal anode (LMA) prevented LMBs from flourishing. As Li-ion chemistry approaches its limitations in meeting the demands of high-energy-density for modern battery technology, research on the LMA has been revived for the production of next-generation Li batteries. With new concepts and technologies being developed and implemented, unprecedented progress has been achieved towards safer and more efficient LMAs, although there are still gaps in putting laboratory-based achievements into real life. This may be caused by the intrinsic shortcomings of the methods and protocols for evaluating LMA, which provide a one-sided perspective and leave key problems unrecognized. This review presents a comprehensive overview of the fundamental problems involved in using LMAs. A dynamic picture of Li metal functioning as an anode is made based on recent knowledge. Realistic requirements for achieving the high-energy-density advantage of LMAs are emphasized. Based on the understanding of these, strategies for Li stabilization are revisited and some overlooked issues need to be addressed.

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  In this review, we consider the working mechanism of lithium metal anodes (LMAs) with a dynamic picture, including a separate deposition/dissolution process under the influence of spontaneously formed SEI, as well as the repeated cycling along with the evolution of the electrodes.

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  The requirements for a Li metal anode under realistic conditions are discussed in detail.

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  Based on a dynamic and realistic perspective, we carefully assess the testing procedures for LMAs and the meaning of the test results. Coulombic inefficiency, or loss of active lithium, is analyzed qualitatively or quantitatively according to the latest understanding.

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  Finally, we revisit the strategies for LMA protection based on the above discussion and understanding, and highlight some issues that are often overlooked in current research.

To meet the growing energy demands in a low-carbon economy, the development of new materials that improve the efficiency of energy storage and conversion systems is essential. Layered nanoclay offers opportunities in energy storage and conversion applications owing to their great reserves, high surface areas, multi-pore structure and other unique physical and chemical properties. These characteristics provide opportunities and advantages for the application of layered nanoclay in electrochemical energy. In this review, we summarized the structure, classification, modification method and properties of nanoclays, along with discussed their applications as electrodes, electrolytes filler, separators, artificial solid electrolyte interface (SEI) layer in rechargeable batteries and supercapacitors (SCs), and as catalysts in water splitting, CO₂ reduction and oxygen reduction. Finally, we concluded the current problems of layered nanoclay in energy storage and conversion, and pointed out the possible future development trend and strategy, which increases their contribution in electrochemical energy applications.

Rechargeable zinc-air batteries (R-ZABs) are attractive for many essential energy storage applications – from portable electronics, electric vehicles to incorporation of renewable energy due to their high energy storage density, abundant raw materials, and inherent safety. However, alkaline electrolytes cause critical obstacles in realizing a long battery life. Thus, neutral electrolytes are attracting growing interest. However, the current understandings of R-ZABs in neutral/near-neutral electrolytes are far behind those in alkaline electrolytes. This review summarizes the latest research progress of neutral electrolytes used in R-ZABs, including aqueous inorganic and organic salt solutions, water-in-salt electrolytes, and quasi-solid electrolytes based on polymer hydrogels. Research efforts in improving the stability of Zn anodes in neutral electrolytes are also reviewed. Reaction mechanisms of oxygen reduction and evolution reactions in alkaline and neutral electrolytes are compared in the context of R-ZABs, together with a summary of potential oxygen electrocatalysts applicable in neutral conditions. Different device configurations are introduced. We further provide our perspectives on future research directions of R-ZABs with neutral electrolytes.

Hydrocarbon separations are crucial to the chemical industry for the production of valuable feedstocks. However, their structural and chemical similarities have proven daunting challenges to incumbent separation technologies, which are energy- and capital-intensive. Approaches capable of discerning and exploiting minute differences in isomeric hydrocarbons, in particular, may provide solutions to this problem. Metal-organic frameworks (MOFs) integrating the merits of tunable pore size at sub-angstrom scale and pore chemistry in confined spaces have presented promising prospects in adsorptive separation to recognize the minor differences in gas molecules via the judicious design and functionalization. In this Review, we explore the usage of MOFs for the underexplored adsorptive separation of hydrocarbons in the liquid/vapor phase, especially for C6 and C8 isomers. The in-depth insights into the structure-property relationship and the dominant mechanisms, including host-guest interaction modes for the effective adsorption of C6 and C8 hydrocarbons, are systematically discussed. Finally, the effectiveness and scope to translate such design strategies into other systems and the perspective on future development in MOFs for separation are provided.