Graphene is composed of single-layered sp² graphite and has been widely used in electrochemical energy conversion and storage due to its appealing physical and chemical properties. In recent years, a new kind of the self-supported graphene nanosheet-based composite (GNBC) has attracted significant attention. Compared with conventional powdered materials, a binder-free electrode architecture has several strengths, including a large surface area, enhanced reaction kinetics, and great structural stability, and these strengths allow users to realize the full potential of graphene. Based on these findings, this review presents preparation strategies and properties of self-supported GNBCs. Additionally, it highlights recent significant developments with integrated binder-free electrodes for several practical applications, such as lithium-ion batteries, lithium-metal batteries, supercapacitors, water splitting and metal-air batteries. In addition, the remaining challenges and future perspectives in this emerging field are also discussed.

Recently, heterogeneous single-atom catalysts (SACs) have attracted enormous attention in electrochemical applications owing to their advantages of high metal utilization, well-defined active sites, tunable selectivity, and excellent activity. To avoid the aggregation of atomically dispersed metal sites, an appropriate support has to be adopted to reduce the surface free energy of catalysts. Graphene with a high surface area, outstanding conductivity, and unique electronic properties has generally been utilized as the substrate for SACs. Moreover, the correlations between metal–support interactions and the electrocatalytic performance at the atomic scale can be studied on graphene-supported single-atom catalyst (G-SAC) nanoplatforms. In this review, we start from an overview of the synthetic methods for G-SACs. Subsequently, several advanced and effective characterization techniques are discussed. Then, we present a comprehensive summary of recent progress in G-SACs for a variety of electrochemical applications. Finally, we present challenges for and an outlook on the development of G-SACs with outstanding catalytic activity, stability, and selectivity.

The emerging direction toward the ever-growing market of wearable electronics has contributed to the progress made in energy storage systems that are flexible while maintaining their electrochemical performance. Endowing lithium-ion batteries with high flexibility is currently considered to be one of the most essential choices in future. Here, we first propose the basic deformation mode according to the manifestation of flexibility and constructively reevaluate the concept of flexible lithium-ion batteries. Furthermore, the failure mechanism of flexible lithium-ion batteries is investigated with regard to their mechanical failure and electrochemical failure, and the related strategies of battery design and manufacturing are analyzed. More importantly, an in-depth analysis is conducted on the approaches to overcome mechanical failure through stress dispersion, stress absorption, prestress concentration, stress transfer, and other flexible reinforcement methods. Additionally, the advantages of suppressing electrochemical failure are discussed by enhancing the surface roughness, pore formation, surface coating, chemical bonding, in situ encapsulation, etc. Regarding self-healing technology, the general approaches taken for self-healing batteries to achieve flexibility are explained through the classification of macroscopic self-healing (to avert mechanical failure) and microscopic self-healing (to respond to electrochemical failure). Finally, after considering the current state of flexible lithium-ion batteries, future challenges are presented.

The flexible lithium-ion batteries were re-evaluated from the insights of mechanics and electrochemistry.

Transition metal phosphides (TMPs) have attracted attention in electrocatalytic hydrogen production because of their multiple active sites, adjustable structures, complex and variable composition, and distinctive electronic structures. However, the catalytic performance of pure TMPs in the hydrogen evolution reaction (HER) is not ideal. Fortunately, this situation can be changed by atom doping engineering because atom doping can efficaciously adjust the electronic structure, Gibbs free energy (ΔG _H*) and d-band center to enhance the kinetics of catalytic reactions. Thus, atom doping engineering has aroused widespread interest. This review examines, analyzes and summarizes our previous work and that of others on atom doping engineering, including the activity origin of doped TMPs, doping with nonmetals (B, S, N, O, F, etc.), doping with metals (Ni, Co, Fe, Mn, Mo, Al, etc.) and codoping with nonmetals and metal atoms, as well as direct doping and synergetic doping, doping methods and the resulting HER properties. Finally, the key problems and future directions for development of atom doping in TMPs are discussed. This review will aid the design and construction of high-performance nonnoble metal catalysts for the HER and other electrocatalytic processes.

Atoms doping can effectively change the electronic structure to improve catalytic performance of catalysts. Accordingly, this review summarizes the doping engineering,including the electrochemical activity sources of TMPs, the doping modes and doping methods, the HER properties, and the existing key problems and future development directions of doped TMPs.

Fuel cell reactors can be tailored to simultaneously cogenerate value-added chemicals and electrical energy while releasing negligible CO₂ emissions or other pollution; moreover, some of these reactors can even “breathe in” poisonous gas as feedstock. Such clean cogeneration favorably offsets the fast depletion of fossil fuel resources and eases growing environmental concerns. These unique reactors inherit advantages from fuel cells: a high energy conversion efficiency and high selectivity. Compared with similar energy conversion devices with sandwich structures, fuel cell reactors have successfully “hit three birds with one stone” by generating power, producing chemicals, and maintaining eco-friendliness. In this review, we provide a systematic summary on the state of the art regarding fuel cell reactors and key components, as well as the typical cogeneration reactions accomplished in these reactors. Most strategies fall short in reaching a win–win situation that meets production demand while concurrently addressing environmental issues. The use of fuel cells (FCs) as reactors to simultaneously produce value-added chemicals and electrical power without environmental pollution has emerged as a promising direction. The FC reactor has been well recognized due to its “one stone hitting three birds” merit, namely, efficient chemical production, electrical power generation, and environmental friendliness. Fuel cell reactors for cogeneration provide multidisciplinary perspectives on clean chemical production, effective energy utilization, and even pollutant treatment, with far-reaching implications for the wider scientific community and society. The scope of this review focuses on unique reactors that can convert low-value reactants and/or industrial wastes to value-added chemicals while simultaneously cogenerating electrical power in an environmentally friendly manner.

A schematic diagram for the concept of fuel cell reactors for cogeneration of electrical energy and value-added chemicals

Lithium-rich materials (LRMs) are among the most promising cathode materials toward next-generation Li-ion batteries due to their extraordinary specific capacity of over 250 mAh g⁻¹ and high energy density of over 1 000 Wh kg⁻¹. The superior capacity of LRMs originates from the activation process of the key active component Li₂MnO₃. This process can trigger reversible oxygen redox, providing extra charge for more Li-ion extraction. However, such an activation process is kinetically slow with complex phase transformations. To address these issues, tremendous effort has been made to explore the mechanism and origin of activation, yet there are still many controversies. Despite considerable strategies that have been proposed to improve the performance of LRMs, in-depth understanding of the relationship between the LRMs’ preparation and their activation process is limited. To inspire further research on LRMs, this article firstly systematically reviews the progress in mechanism studies and performance improving attempts. Then, guidelines for activation controlling strategies, including composition adjustment, elemental substitution and chemical treatment, are provided for the future design of Li-rich cathode materials. Based on these investigations, recommendations on Li-rich materials with precisely controlled Mn/Ni/Co composition, multi-elemental substitution and oxygen vacancy engineering are proposed for designing high-performance Li-rich cathode materials with fast and stable activation processes.

The “Troika” of composition adjustment, elemental substitution, and chemical treatment can drive the Li-rich cathode towards stabilized and accelerated activation.

Renewable-electricity-powered electrochemical CO₂ reduction reactions (CO₂RR) to highly value-added multi-carbon (C₂₊) fuels or chemicals have been widely recognized as a promising approach for achieving carbon recycling and thus bringing about sustainable environmental and economic benefits. Cu-based catalysts have been demonstrated as the only candidate metal CO₂RR electrocatalysts that catalyze the C–C coupling. Unfortunately, huge challenges still exist in the highly selective CO₂RR to C₂₊ products due to the higher activation barrier of C–C coupling and complex multi-electron reaction. Key fundamental issues regarding both active species and product formation pathways have not been elucidated by now, but recent developments of advanced strategies and characterization tools allow one to comprehensively understand the Cu-based CO₂RR mechanism. Herein, we review recent advance and perspective of Cu-based CO₂RR catalysts, especially in terms of active phases and product formation pathways. Then, strategies in catalysts design for CO₂RR toward C₂₊ products are also presented. Importantly, we systematically summarized the advanced tools for investigating the CO₂RR mechanism, including in situ/operando spectroscopy techniques, isotope labeling, and theoretical calculations, aiming at unifying the knowledge of active species and product formation pathways. Finally, future challenges and constructive perspectives are discussed, facilitating the accelerated advancement of CO₂RR mechanism research.