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Flexible supercapacitors based on electrostatic double-layer capacitors as next-generation energy storage systems hold great promise for wearable and flexible electronic devices owing to their high flexibility and electrochemical cyclability. However, the challenge of low charge-storing ability still remains, as electronic devices require a high charge storage capability. As one of the advanced strategies for enhancing charge-storing ability in flexible supercapacitors, the introduction of a redox mediator (RM) into a gel electrolyte has recently attracted great interest. Here, we present a fiber-based flexible energy storage system (f-FESS) integrated with iodine-based chemical species as a novel RM, carbon fiber-based electrodes, and a solid-state polymer-gel electrolyte so as to enhance the charge storage capability of flexible supercapacitors. The as-prepared f-FESS-RM exhibits enhanced charge storage capabilities of up to 461.8 F L −1 and 64.14 mWh L −1 , which are 3.6 times higher than those of f-FESS without RM. The enhanced capacitive properties of f-FESS-RM are attributed to their additional Faradic redox reaction of iodine-based chemical species in the electrolyte as well as electrical double-layer capacitive behavior. Also, the f-FESS-RM shows remarkably superior mechanical robustness under various bending, winding, knotting, and weaving conditions. Furthermore, we have demonstrated that the f-FESS-RM is stably workable under deionized water and base electrolytes. In combination, these outcomes provide a novel advanced strategy to enhance the chargestoring ability with strong mechanical robustness in flexible supercapacitors.

Hydrogen gas (H2) is being intensively proposed as a next-generation clean energy owing to the depletion of fossil fuels. Electrochemical water splitting is one of the most promising processes for hydrogen production. Furthermore, many efforts focusing on electrochemical water splitting have been made to develop low-cost, electrochemically active, and stable catalysts for efficient hydrogen production. MoS2 has emerged as an attractive material for developing catalysts for the hydrogen evolution reaction (HER). Hence, in this study, we design hierarchically ordinated two-dimensional (2D) MoS2 nanosheets on three-dimensional (3D) reduced graphene oxide (rGO) (H-2D/3D-MoS2-rGO) aerogel structures as a new class of electrocatalysts for the HER. We use the one-pot hydrothermal synthesis route for developing high-performance electroactive materials for the HER. The as-prepared H-2D/3D-MoS2-rGO contains a unique 3D hierarchical structure providing large surface areas owing to the 3D porous networks of rGO and more active sites owing to the many edge sites in the MoS2 nanosheets. In addition, the H-2D/3D-MoS2-rGO structure exhibits remarkable electrochemical properties during the HER. It shows a lower overpotential than pure MoS2 and excellent electrochemical stability owing to the large number of active sites (highly exposed edge sites) and high electrical conductivity from the rGO structure.

Here,nonprecious high‐entropy chalcogenide glasses (N‐HECGs) consisting of Co, Fe, Ni, Mo, W, and Te are demonstrated in a first demonstration of acidic oxygen evolution reaction (OER). N‐HECGs electrocatalysts with high activity and stability are synthesized using a hierarchical hybrid approach based on a combination of electrochemical deposition and tellurization process. The as‐prepared CoFeNiMoWTe N‐HECGs electrocatalysts exhibit an amorphous, porous structure of arrayed nanosheets with abundant active sites and the increased valence states of metal cations due to the incorporated non‐metallic Te, enabling the enhancement of glass forming ability and the valence states of metal elements. Thanks to the combination of their unique geometrical and chemical structure, as well as high configuration entropy nature and high corrosion‐resistance ability, the resultant CoFeNiMoWTe N‐HECGs exhibit excellent acidic OER catalytic performance with a superior overpotential of 373 mV and outstanding stability of 100 h at the current density of 10 mA cm−2 in 0.5 m H2SO4. Moreover, the CoFeNiMoWTe‐based proton exchange membrane water electrolyzer is demonstrated to require a cell voltage of 1.81 V at 70 °C to obtain the practically high current density of 1 A cm−2, and exhibits remarkably long‐term stability for 100 h with small potential degradation of only 30 mV.

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