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).

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date, there have been commercial efforts to manufacture lithium thin film batteries (<1 mm in thickness) being flexible and suitable for use in card-type and wearable devices. [3] However, these thin and flexible lithium-ion batteries have typically exhibited far less volumetric energy densities (<200 Wh L −1 ) than those of conventional lithium-ion batteries (<650 Wh L −1 ). [4] This performance roll-off is largely due to the fact that high barrier encapsulation of air and moisture sensitive lithium battery materials can severely impact the effective volumetric efficiency as the batteries are miniaturized. Therefore, high volumetric energy density lithium batteries with thickness <1 mm will be critical to enabling flexible electronics. [5] To this end, notable advancements have been made in the design of flexible lithium-sulfur and lithium-air batteries-those cathode chemistries enable high theoretical energy densities of 2800 and 6940 Wh L −1 , respectively-yet there remains substantial room for improvement. [6][7][8] The potential to yield high volumetric capacities by using less environmentally sensitive materials in the batteries sees zinc as an attractive anode alternative to lithium. In addition to the stability, zinc is likely to experience less cost pressure on raw material availability compared to lithium. In all cases, zinc secondary batteries represent a highly promising area of technology for Flexible Zn-based batteries are regarded as promising alternatives to flexible lithium-ion batteries for wearable electronics owing to the natural advantages of zinc, such as environmental friendliness and low cost. In the past few years, flexible Zn-based batteries have been studied intensively and exciting achievements have been obtained in this field. However, the development of flexible Zn-based batteries is still at an early stage. The challenges of developing flexible lithium-ion batteries are presented here. Then, a brief overview of recent progress in flexible zinc secondary batteries from the perspective of advanced materials and some issues that remain to be addressed are discussed.

Carbon dioxide electroreduction provides a useful source of carbon monoxide, but comparatively few catalysts could be sustained at current densities of industry level. Herein, we construct a high-yield, flexible and self-supported single-atom nickel-decorated porous carbon membrane catalyst. This membrane possesses interconnected nanofibers and hierarchical pores, affording abundant effective nickel single atoms that participate in carbon dioxide reduction. Moreover, the excellent mechanical strength and well-distributed nickel atoms of this membrane combines gas-diffusion and catalyst layers into one architecture. This integrated membrane could be directly used as a gas diffusion electrode to establish an extremely stable three-phase interface for high-performance carbon dioxide electroreduction, producing carbon monoxide with a 308.4 mA cm−2 partial current density and 88% Faradaic efficiency for up to 120 h. We hope this work will provide guidance for the design and application of carbon dioxide electro-catalysts at the potential industrial scale.

Rapid consumption of fossil fuels (coal, oil, and natural gas) has caused a series of environmental hazards, thus exploring renewable and clean energies (e.g., H 2) is of great importance for the future development of sustainable society. [1] Owing to

This is the first review on potassium–sulfur (K–S) batteries (KSBs), which are emerging metal battery (MB) systems. Since KSBs are quite new, there are fundamental questions regarding the electrochemistry of S‐based cathode and of K metal anode, as well as the holistic aspects of full‐cell performance. The manuscript begins with a critical discussion regarding the potassium–sulfur electrochemistry and on how it differs from the much better‐known lithium–sulfur. Cathodes are discussed next, focusing on the role of sulfur structure, carbon host chemistry and porosity, and electrolytes in establishing the reversible potassium sulfide K2Sn phase sequence, the parasitic polysulfide shuttle, pulverization‐driven capacity fade, etc. Following is a discussion of solid‐state electrolytes (SSEs), including of hybrid solid–liquid systems that show much promise. Potassium metal anodes are then critically reviewed, emphasizing electrolyte reactions to form stable versus unstable solid electrolyte interphase (SEI), covering the current understanding of potassium dendrites, and highlighting the deep‐eutectic K–Na alloying approaches for room temperature liquid anodes. The manuscript concludes with K–S batteries, focusing on cell architectures and providing quantitative performance comparisons as master plots. Unanswered scientific/technological questions are identified, emerging research opportunities are discussed, and potential experimental and simulation‐based studies that can unravel these unknowns are proposed.

Constructing heterostructures with abundant interfaces is essential for integrating the multiple functionalities in single entities. Herein, the synthesis of NiSe2/CoSe2 heterostructures with different interfacial densities via an innovative strategy of successive ion injection is reported. The resulting hybrid electrocatalyst with dense heterointerfaces exhibits superior electrocatalytic properties in an alkaline electrolyte, superior to other benchmarks and precious metal catalysts. Advanced synchrotron techniques, post structural characterizations, and density functional theory (DFT) simulations reveal that the introduction of atomic‐level interfaces can lower the oxidation overpotential of bimetallic Ni and Co active sites (whereas Ni2+ can be more easily activated than Co2+) and induce the electronic interaction between the core selenides and surface in situ generated oxides/hydroxides, which play a critical role in synergistically reducing energetic barriers and accelerating reaction kinetics for catalyzing the oxygen evolution. Hence, the heterointerface structure facilitates the catalytic performance enhancement via increasing the intrinsic reactivity of metallic atoms and enhancing the synergistic effect between the inner selenides and surface oxidation species. This work not only complements the understanding on the origins of the activity of electrocatalysts based on metal selenides, but also sheds light on further surface and interfacial engineering of advanced hybrid materials.