Electrolytes have been identified as some of the most influential components in the performance of electrochemical supercapacitors (ESs), which include: electrical double-layer capacitors, pseudocapacitors and hybrid supercapacitors. This paper reviews recent progress in the research and development of ES electrolytes. The electrolytes are classified into several categories, including: aqueous, organic, ionic liquids, solid-state or quasi-solid-state, as well as redox-active electrolytes. Effects of electrolyte properties on ES performance are discussed in detail. The principles and methods of designing and optimizing electrolytes for ES performance and application are highlighted through a comprehensive analysis of the literature. Interaction among the electrolytes, electro-active materials and inactive components (current collectors, binders, and separators) is discussed. The challenges in producing high-performing electrolytes are analyzed. Several possible research directions to overcome these challenges are proposed for future efforts, with the main aim of improving ESs' energy density without sacrificing existing advantages (e.g., a high power density and a long cycle-life) (507 references).

materials, [2] and their coupled composites. [3] Among them, TM singleatom catalysts (SACs) have recently emerged as a new type of frontier materials with high activity, stability, and selectivity, rendering the great potential for diverse catalytic systems. [4] The unique electronic structure, maximized atomutilization efficiency, and unsaturated coordination bonds of the active centers in SACs contribute to the enhanced performance. [5] Moreover, recent investigations have demonstrated that the introduction of secondary metal atoms can further enhance the activity of SACs, indicating the promising development of dual-metal SACs. [6] Nevertheless, on the one hand, there is a serious lack of effective strategies to achieve the atomic control of targeted reactive sites comprising binary metal atoms; on the other hand, the identification of the diatomic structure in dual-metal SACs and the deeper functional mechanism of bimetallic atoms for synergistic catalysis are still in their infancy.Owing to the increasing concerns from energy and environmental issues, growing attention has been paid on developing sustainable energy conversion and storage technologies, such as water-splitting electrolyzers, fuel cells, metal-air batteries, etc. [7] However, the sluggish kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) on the electrodes has been proven to With the inspiration of developing bifunctional electrode materials for reversible oxygen electrocatalysis, one strategy of heteroatom doping is proposed to fabricate dual metal single-atom catalysts. However, the identification and mechanism functions of polynary single-atom structures remain elusive. Atomically dispersed binary Co-Ni sites embedded in N-doped hollow carbon nanocubes (denoted as CoNi-SAs/NC) are synthesized via proposed pyrolysis of dopamine-coated metalorganic frameworks. The atomically isolated bimetallic configuration in CoNi-SAs/NC is identified by combining microscopic and spectroscopic techniques. When employing as oxygen electrocatalysts in alkaline medium, the resultant CoNi-SAs/NC hybrid manifests outstanding catalytic performance for bifunctional oxygen reduction/evolution reactions, boosting the realistic rechargeable zinc-air batteries with high efficiency, low overpotential, and robust reversibility, superior to other counterparts and state-of-the-art precious-metal catalysts. Theoretical computations based on density functional theory demonstrate that the homogenously dispersed single atoms and the synergistic effect of neighboring Co-Ni dual metal center can optimize the adsorption/desorption features and decrease the overall reaction barriers, eventually promoting the reversible oxygen electrocatalysis. This work not only sheds light on the controlled synthesis of atomically isolated advanced materials, but also provides deeper understanding on the structure-performance relationships of nanocatalysts with multiple active sites for various catalytic applications.To date, large numbers of low cost and efficie...

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The size effect of transition‐metal nanoparticles on electrocatalytic performance remains ambiguous especially when decreasing the size to the atomic level. Herein, we report the spatial isolation of cobalt species on the atomic scale, which was achieved by tuning the zinc dopant content in predesigned bimetallic Zn/Co zeolitic imidazole frameworks (ZnCo‐ZIFs), and led to the synthesis of nanoparticles, atomic clusters, and single atoms of Co catalysts on N‐doped porous carbon. This synthetic strategy allowed an investigation of the size effect on electrochemical behavior from nanometer to Ångström dimensions. Single‐atom Co catalysts showed superior bifunctional ORR/OER activity, durability, and reversibility in Zn–air batteries compared with the other derivatives and noble‐metal Pt/C+RuO2, which was attributed to the high reactivity and stability of isolated single Co atoms. Our findings open up a new avenue to regulate the metal particle size and catalytic performance of MOF derivatives.

A facile and binder-free method is developed for the in-situ and horizontal growth of ultrathin mesoporous Co 3 O 4 layers on the surface of carbon fibers in the carbon cloth (ultrathin Co 3 O 4 /CC) as high-performance air electrode for the flexible Zn-air battery. In particular, the ultrathin Co 3 O 4 layers have a maximum contact area on the conductive support, facilitating the rapid electron transport and preventing the aggregation of ultrathin layers. The ultrathin feature of Co 3 O 4 layers is characterized by the transmission electron microscopy, Raman spectra and X-ray absorption fine structure spectroscopy. Benefiting from the high utilization degree of active materials and rapid charge transport, the mass activity for oxygen reduction and evolution reactions of the ultrathin Co 3 O 4 /CC electrode is more than 10 times higher than that of the carbon cloth loaded with commercial Co 3 O 4 nanoparticles. Compared to the commercial Co 3 O 4 /CC electrode, the flexible Znair battery using ultrathin Co 3 O 4 /CC electrode exhibits excellent rechargeable performance and high mechanical stability. Furthermore, the flexible Zn-air battery was integrated with a flexible display This article is protected by copyright. All rights reserved.3unit. The whole integrated device can operate without obvious performance degradation under serious deformation and even during the cutting process, which makes it highly promising for wearable and roll-up optoelectronics.