Green hydrogen produced by water electrolysis is one of the most promising technologies to realize the efficient utilization of intermittent renewable energy and the decarbonizing future. Among various electrolysis technologies, the emerging anion-exchange membrane water electrolysis (AEMWE) shows the most potential for producing green hydrogen at a competitive price. In this review, we demonstrate a comprehensive introduction to AEMWE including the advanced electrode design, the lab-scaled testing system establishment, and the electrochemical performance evaluation. Specifically, recent progress in developing high activity transition metal-based powder electrocatalysts and self-supporting electrodes for AEMWE is summarized. To improve the synergistic transfer behaviors between electron, charge, water, and gas inside the gas diffusion electrode (GDE), two optimizing strategies are concluded by regulating the pore structure and interfacial chemistry. Moreover, we provide a detailed guideline for establishing the AEMWE testing system and selecting the electrolyzer components. The influences of the membrane electrode assembly (MEA) technologies and operation conditions on cell performance are also discussed. Besides, diverse electrochemical methods to evaluate the activity and stability, implement the failure analyses, and realize the in-situ characterizations are elaborated. In end, some perspectives about the optimization of interfacial environment and cost assessments have been proposed for the development of advanced and durable AEMWE.

Carbon-based materials are widely studied for their unique advantages in electrocatalysis. Despite significant progress, the precise interface construction and mechanism exploration of carbon-based materials in the field of electrocatalysis is still in the early stages. Recently, our group and other peers demonstrated that by introducing heterogeneous components into carbon-based materials, and the forming of specific interfaces will serve as active sites or major reaction sites for electrochemical reactions (OER, HER, ORR, CO2RR, NRR, etc.). Modulating the catalyst interface environment and chemical adsorption behavior through interface engineering is an effective strategy to improve the catalytic activity. This review summarizes the latest progress in the field of carbon-based electrocatalyst in a timely and comprehensive manner, including the classification of carbon-based materials and the interface problems involved, as well as the preparation methods of carbon-based materials in recent years. The interface engineering strategies of carbon-based materials, the structure-activity relationship between interface structure and performance, as well as the potential applications of carbon-based materials in heterogeneous catalytic reactions and energy conversion are discussed in detail. Finally, we outline the current challenges and identify the opportunities facing this emerging sector.

The ever-growing market for electric vehicles and grid-scale energy storage is boosting the development of high energy density lithium metal batteries (LMBs). Solid-state electrolytes (SSEs) are not only nonflammable to overcome the intrinsic drawbacks of liquid electrolytes, but also mechanically strong enough to suppress the growth of lithium dendrites, whose development could greatly promote the safety and performance of LMBs. Crystalline porous materials (CPMs) with high surface area, adjustable pores, ordered channels, and versatile functionality have not only provided a promising structural platform for designing fast ionic conducting materials, but also offered great opportunities for manipulating their physicochemical and electrochemical properties, which have shown great potential to fabricate high-performance SSEs and have become an emerging research direction in recent years. In this review, the latest progress of CPMs-based SSEs for LMBs, including pristine CPMs and CPMs-based composites, is systematically summarized. By discussing the pioneer work, both merits and issues arising from CPMs are emphasized as well as an outlook for the development of CPMs-based SSEs with high-performance and reliable safety are presented.

Benefiting from high thermal storage density, wide temperature regulation range, operational simplicity, and economic feasibility, latent heat-based thermal energy storage (TES) is comparatively accepted as a cutting-edge TES concept, especially solid-liquid phase change materials (PCMs). However, liquid phase leakage, low thermal/electrical conductivities, weak photoabsorption capacity, and intrinsic rigidity of pristine PCMs are long-standing bottlenecks in both industrial and domestic application scenarios. Towards these goals, emerging two-dimensional (2D) materials containing regions of empty nanospace are ideal alternatives to efficiently encapsulate PCMs molecules and rationalize physical phase transformation, especially graphene, MXene and BN. Herein, we provide a timely and comprehensive review highlighting versatile roles of 2D materials in composite PCMs and relationships between their architectures and thermophysical properties. In addition, we provide an in-depth understanding of the energy conversion mechanisms and rationalize routes to high-efficiency energy conversion PCMs. Finally, we also introduced critical considerations on the challenges and opportunities in the development of advanced high-performance and multifunctional 2D material-based composite PCMs, hoping to provide constructive references and facilitate their significant breakthroughs in both fundamental researches and commercial applications.

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.

Transmission electron microscopy (TEM) is widely used in the materials science community because of its high spatial, temporal and energy resolution. However, for electron beam-sensitive halide perovskites (HPs), the achievements offered by TEM are still in their infancy due to the nonnegligible structural damage caused by the incident electron beams to the fragile structure. Despite these challenges, the potential for TEM to provide unique insights into the microstructure and phase evolution of HPs at the atomic scale, to track the dynamic ion migration behaviors, and to explore the effects of lattice defects on physicochemical properties is still fascinating. In this review, we summarize recent achievements in HPs through advanced analytical methods embedded in the TEM, including high-resolution/scanning TEM (HRTEM/STEM) imaging, electron diffraction (ED) analysis, X-ray energy dispersive spectroscopy (EDS), and electron energy-loss spectroscopy (EELS) measurement, and in-situ TEM observation, with the aim of providing a multi-dimensional and multi-scale understanding of the intrinsic properties of HPs that have not yet been discovered. In addition, we delve into the inherent beam-damage mechanisms affecting the delicate HPs crystal, thereby emphasizing the significant hurdles associated with employing TEM in HPs research. Finally, we present a number of effective strategies that may be beneficial in reducing the damage caused by beams. In particular, the introduction of a direct-detection electron-counting (DDEC) camera has contributed significantly to the advancement of low-dose imaging and the suppression of beam damage to the intrinsic structure of HPs. With the improvement of low-dose imaging technology, TEM characterization is expected to promote a comprehensive understanding of the intrinsic properties of HPs in terms of structure-property-performance and to expand the wide range of applications of HPs in optoelectronic devices.

Considering the wide abundance and low cost of sodium resources and their similar electrochemistry to the well-established lithium-ion batteries (LIBs), sodium-ion batteries (SIBs) have been regarded as potential alternatives to LIBs. Iron-based materials have attracted considerable attention as promising electrode materials for SIBs due to their high theoretical capacitance, natural abundance, and low cost. However, their sluggish reaction kinetics, accompanied with severe volume change during cycling sodiation/desodiation process and their unsatisfied electric conductivity, always leads to inferior long-term cycling stability and rate performance. To resolve these issues, significant and effective efforts have been made to improve their electrochemical performance, and great processes have been achieved. In this review, some recent progress on the development and design of nanostructured iron-based anodes, including oxides, chalcogenides, phosphides, nitrides, alloys, etc., are summarized, mainly focusing on the relationship between their structural features and sodium storage performance to understand the mechanisms behind the improvement of their sodium storage performance. In addition, the current challenges and future directions upon improving iron-based anodes for SIBs are briefly reviewed. These iron-based electrode materials are expected to be competitive and attractive electrodes for next-generation energy storage devices.

Semiconductor photocatalysis is considered as a cutting-edge research topic for the production of value-added fuels and chemicals to confront the global energy crisis. In order to improve the solar-to-chemical conversion efficiency of pristine semiconductors, combining them with cocatalysts to form heterostructures has been extensively investigated. Among studied formulations, bimetallic nanoparticles (NPs), featuring enhanced light harvesting, efficient capture of photogenerated electrons and abundant surface active sites are ideal cocatalysts to improve the photocatalytic performance of semiconductor-based photocatalysts. In this review, we begin with a concise overview of representative synthesis and characterization methods of bimetallic NPs. Then, we predominantly summarize the typical applications of semiconductor/bimetallic NPs-based composites in photoredox catalysis, including hydrogen evolution, carbon dioxide reduction, selective organic synthesis and environmental remediation. In particular, we highlight the regulatory effects of parameters of bimetallic NPs (composition, structure, morphology, size, atomic arrangement, loading position, etc.) on the photocatalytic activity and selectivity. Finally, the remaining challenges and future perspectives for the utilization of bimetallic NPs in photoredox catalysis are discussed and anticipated to stimulate the sparkling ideas in the construction of high-efficiency semiconductor/bimetallic NPs-based photocatalytic systems.

Metal-organic frameworks (MOFs) show great promise for electrochemical energy storage applications due to their high surface area, tunable porosity, ordered crystal structure, and facile tolerability. However, some MOFs with high electrochemical performance are usually unstable in aqueous solutions, which limits their development in aqueous electrochemical energy storage systems, which are cheaper, safer, and more ionically conductive than those operating in conventional organic electrolytes. Numerous efforts have been made to construct stable MOFs or control MOF derivation processes induced by chemical or thermal forces to optimize their properties and performance. Therefore, a review summarizing the MOFs applied in aqueous electrochemical energy storage devices would be useful. In this review, the chemical stability and thermal stability of MOFs under aqueous conditions are discussed. The evolution processes of MOFs when they exceed their stability are summarized. Furthermore, the recent fast-growing literature on MOF-based aqueous ion batteries and supercapacitors is comprehensively reviewed, and guidelines for designing high-performance aqueous electrochemical devices are provided. The current challenges and opportunities for applying MOFs in aqueous electrochemical energy-storage devices are provided. We hope this review will promote the development of MOFs in aqueous electrochemical devices by exploiting the advantages and remedying the disadvantages of MOFs.

Electrochemical conversion is an eco-friendly and controllable way to achieve sustainable use of energy. An enhanced energy conversion efficiency requires efficient electrocatalysts to reduce the electrochemical energy barrier. The hollow structures, which have the advantage of optimizing mass/charge transfer, provide a platform for full contact between the electrocatalysts and the reactants, which has great potential for advanced electrocatalysts. In addition, rare earth-based materials integrate unique electronic configuration and chemical behavior into electrocatalysts, leading to improved performance and selectivity for various electrocatalysis. Combining hollow structures with rare earths is fascinating and challenging in terms of synthesis and electrocatalysis. This review expounds general synthesis methods of hollow structures with rare earths and then summarizes strategies to prepare highly efficient hollow electrocatalysts with rare earths.

The sufficient supply of energy remains one of the most important challenges for a sustainable development of our society. In this respect, capturing sunlight energy by photocatalytic reduction of the greenhouse gas CO2 is interesting. In a more general way, the smart use of CO2 as C1-feedstock and its conversion to valuable carbon-based materials and energy sources can be the basis to establish a closed-CO2 cycle. This review summarizes recent advances in photocatalytic utilization of CO2 catalyzed by most prominent TiO2 based systems. The influences of different structures (i.e. crystal phase, morphology, vacancies, and defects), co-catalysts, and reaction conditions onto the catalyst performance are specifically highlighted. Furthermore, the reader attention is drawn to the oxidation counter reaction, which has been often neglected in the past.

Electrochemical water splitting, especially in acidic media, is a promising technology for hydrogen production and sustainable energy conversion. However, it remains a challenge to synthesize suitable acidic oxygen evolution reaction (OER) electrocatalysts that provide high activity and long-term stability according to the industrial standards. Up to date, quite few reviews provide a systematic summarization of the strategies and approaches to improving the electrocatalytic performances of the catalysts in acidic electrolytes. Herein, we analyze the electrochemical behavior of the reported state-of-the-art OER catalysts and provide a comprehensive review of the systematic strategies for preparing high-performance electrocatalysts. First, we introduce some fundamentals of OER mechanism to give readers a deeper understanding of this field. Then, we summarize and discuss various design strategies, including electronic state modulation, structural manipulation, etc. Finally, the challenges, opportunities, and future outlook regarding acidic OER electrocatalysts are delivered. This review will serve as a useful guiding resource for researchers seeking in-depth understanding of the OER mechanism in acidic media as well as learning approaches for synthesizing highly efficient and cost-effective OER electrocatalysts.

With the advantages of high safety and environmental friendliness, aqueous batteries have shown beneficial application scenarios in the field of large-scale energy storage. Compared to the conventional metal ions storage processes, non-metal carriers like protons are less concerned about due to the unconventional storage mechanism, which could be regarded as a promising green battery technology with high power density and adequate lifespan. Owing to the unique working mechanism and properties, aqueous proton batteries (APBs) can deliver excellent low-temperature electrochemical performance with cost effectiveness, further allowing full play to the best ability of aqueous storage technique. However, the issue on lack of advanced electrode materials still hinders the research progress on commercial applications of APBs. In this review, we present a comprehensive summary on the development of APBs, from the perspective of electrode materials, electrolytes, and current collectors, including cross-sectional host and corresponding design principles and energy storage mechanism. This review aims to clarify the status quo and emerging challenges for further development of APBs devices.

Electrochemical water splitting in alkaline media provides a promising pathway for sustainable hydrogen production that is enssential for a future hydrogen economy. However, the slow reaction rate of hydrogen reaction in alkaline media, and unfavorable kinetics for oxygen evolution reaction have hindered the progress of water splitting technologies for clean hydrogen production. Considering the high price and scarce storage of noble metals which are known as the most effective catalysts for water splitting, it is urgently required to develop non-noble metals based alternatives with highly intrinsic acivity, low price and high tolerance to increase electrocatalytic efficiency and reduce the reaction overpotential from an economic perspective. In this review, we summarize recent research efforts in exploiting advanced transition metal based electrocatalysts with outstanding performance for water splitting catalysis, mainly including transition-metal-based chalcogenides, phosphides, nitrides and carbides as well as single atom catalysts. First, we give a simple description of water splitting mechanism in alkaline media. Then we discuss the promising structural design of transition metal based electrocatalysts for enhancing water splitting, and disclose the underlying relationship between structure and electrocatalytic performance for water splitting with assistance of theoretical simulation. Finally, we provide our personal perspective to highlight the challenges and propose the opportunities for developing transition metal based electrocatalysts for water splitting in alkaline solution.

The development of clean sustainable energy conversion technologies to deal with energy shortage and environmental pollution has aroused a widespread concern. To improve the rate and selectivity of the pivotal chemical reactions involved in these technologies, high-performance electrocatalysts are crucial. Alloys have sparked research hotspot in electrocatalysis because of their higher catalytic activity, stability, and selectivity than their single-metal counterparts. In this review, the design strategies for alloy electrocatalysts are firstly introduced with a focus on how to achieve optimal performance by composition regulation, size optimization and morphology control. Subsequently, we offer a comprehensive overview of the electrocatalytic applications of binary, ternary, quaternary, and high-entropy alloys to different types of electrochemical energy conversion processes, including the hydrogen evolution, oxygen evolution, oxygen reduction, CO2 reduction, formic acid oxidation, methanol oxidation, and ethanol oxidation reactions. Finally, the challenges and future outlook are presented for the rational design of advanced alloy electrocatalysts.

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.

Lithium-sulfur batteries (LSBs) with high energy density have been drawn the tremendous interests in academia as well as industry. Nevertheless, sluggish redox kinetics of sulfur species has been challenging for high performance LSBs. The design of catalytic materials, being a promising strategy for kinetics modulation by controlling polysulfides conversion, has been mainly focused. To improve battery performance of LSBs, in this review, the effect of functional catalysts with different morphologies, crystal configurations, energy band behaviors, coordination environments on kinetics modulation was summarized. Furthermore, some optimized bidirectional catalysts were mainly addressed to deeply understand appropriate adsorption capacity, prominent mass transfer capability, outstanding catalytic activity/selectivity. In addition, a great quantity of cutting-edge strategies, such as structure engineering, defect, interface engineering and atomic bonding for metal compounds as well as metal-based single atom catalysts, were proposed to uncover the synthesis behaviors of optimum bidirectional catalysts. Eventually, various advanced characterization methods were provided to evaluate catalysis. It is believed that this review will provide a novel insight for the design of bidirectional catalysts with high activity, high catalytic selectivity, long lifespan toward high-performance LSBs.

Aqueous zinc-metal batteries have gained widespread attention because of their high safety, large capacity, cost effectiveness, and environmental friendliness. However, zinc anodes have long encountered with dendrite formation, inferior cycle life and low coulombic efficiency, which severely hinder the practical application. Here, the latest advances of zinc metal anodes for aqueous zinc-metal batteries are reviewed. The merits of zinc metal anodes, the reaction mechanisms in different media, and the issues faced are firstly summarized. Then the prominent progresses of zinc anodes in aqueous media are highlighted, including electrolyte optimization, host construction, interface modification, anode structure design, and working model regulation. Finally, the remaining challenges of zinc anodes are fully discussed, and the future perspectives of pursing stable zinc metal anodes by integrating multi-strategies, conducting in situ study of zinc plating/stripping behavior, exploring advanced cathode materials, and developing smart devices are also provided.