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MXenes, a family of 2D transition metal carbides, are considered promising high‐rate pseudocapacitive materials because of their metallic‐like conductivity and transition metal oxide‐like surfaces. Currently, nearly 50 stoichiometric MXenes have been synthesized. However, only a few MXenes, such as Ti3C2, have shown stable pseudocapacitive charge storage so far. Further improving the inherent pseudocapacitance of MXenes without losing their cyclability remains a challenge. Herein, a mild method is reported to produce highly stable bimetallic solid‐solution MXene Ti2VC2 using a solution of potassium fluoride and hydrochloric acid. The electrochemical properties of resulting multilayered clay‐like and delaminated Ti2VC2 films are investigated, exceeding the performance of typical Ti3C2 in acidic electrolytes. These electrodes deliver up to 2000 F cm−3 and retain more than 90% of their initial capacitance after 20 000 cycles, surpassing most state‐of‐the‐art supercapacitor materials known. The pseudocapacitive charge storage of Ti2VC2 is deeply investigated through in situ and ex situ experimental studies, confirmed the pseudocapacitive mechanism is a combination of hydrated H+ intercalation and surface redox. This work provides a practical route toward future rational design on the atomic scale for high‐performance pseudocapacitive materials. [ABSTRACT FROM AUTHOR]

Li et al. [[3]] fabricated a CoFe SB 2 sb O SB 4 sb /g-C SB 3 sb N SB 4 sb composite catalyst with CoFe SB 2 sb O SB 4 sb particles supported on the flaky g-C SB 3 sb N SB 4 sb using a scalable facile method. However, currently, Li-S batteries suffer from low volumetric energy density and poor cycling stability due to the intrinsic low conductivity of sulfur and its discharge product, lithium polysulfide shuttle effect, and so on. Developing efficient and low-cost energy conversion and storage devices and technologies is all-important issue in order to achieve a low-carbon society, whose performance essentially depends on the properties of materials. Zhao et al. [[8]] designed a single-atom catalyst Au/WSSe by filling the single Au atom at the S vacancy site in the Janus WSSe monolayer. [Extracted from the article]

Herein, interconnected hierarchical NiCo2O4 microspheres (IH-NiCo2O4) were prepared via a solvothermal method followed by an annealing treatment. IH-NiCo2O4 possesses large tunnels and abundant mesopores, which are in favor of their applications in energy storage field. When employed as an electrode material for supercapacitors, IH-NiCo2O4 exhibits a high specific capacitance of 1822.3 F g−1 at a current density of 2 A g−1, an excellent rate property of 68.6% capacity retention at 20 A g−1, and an 87.6% specific capacitance retention of its initial value after 7000 cycles at a high current density of 10 A g−1, superior to those of IH-Co3O4. Furthermore, an optimal asymmetric supercapacitor (ASC) was also constructed with IH-NiCo2O4 as the positive electrode and graphene as the negative electrode. The ASC delivers a high energy density of 39.4 Wh kg−1 at a power density of 800 W kg−1. Even at a high power density of 8000 W kg−1, the energy density still reaches 27.2 Wh kg−1. Moreover, the ASC shows a good cycling stability with 80.1% specific capacitance retention after 5000 cycles at 6 A g−1. The excellent electrochemical performance of IH-NiCo2O4 makes it a promising electrode material in energy storage field. [ABSTRACT FROM AUTHOR]

Integrated nanodevices with the capability of storing energy are widely applicable and have thus been studied extensively. To meet the demand for flexible integrated devices, all-solid-state asymmetric supercapacitors that simultaneously realize energy storage and optoelectronic detection were fabricated by growing Co3O4 nanowires on nickel fibers, thus giving the positive electrode, and employing graphene as both the negative electrode and light-sensitive material. The as-assembled integrated systems were characterized by an improved energy storage, enhanced power density (at least by 1860 % enhanced) by improving the potential window from 0-0.6 V to 0-1.5 V, excellent photoresponse to white light, and superior flexibility of both the fiber-based asymmetric supercapacitor and the photodetector. Such flexible integrated devices might be used in smart and self-powered sensory, wearable, and portable electronics. [ABSTRACT FROM AUTHOR]

Biomass-waste activated carbon/molybdenum oxide/molybdenum carbide ternary composites are prepared using a facile in-situ pyrolysis process in argon ambient with varying mass ratios of ammonium molybdate tetrahydrate to porous peanut shell activated carbon (PAC). The formation of MoO2 and Mo2C nanostructures embedded in the porous carbon framework is confirmed by extensive structural characterization and elemental mapping analysis. The best composite when used as electrodes in a symmetric supercapacitor (PAC/MoO2/Mo2C-1//PAC/MoO2/Mo2C-1) exhibited a good cell capacitance of 115 F g−1 with an associated high specific energy of 51.8 W h kg−1, as well as a specific power of 0.9 kW kg−1 at a cell voltage of 1.8 V at 1 A g−1. Increasing the specific current to 20 A g−1 still showcased a device capable of delivering up to 30 W h kg−1 specific energy and 18 kW kg−1 of specific power. Additionally, with a great cycling stability, a 99.8% coulombic efficiency and capacitance retention of ~83% were recorded for over 25,000 galvanostatic charge-discharge cycles at 10 A g−1. The voltage holding test after a 160 h floating time resulted in increase of the specific capacitance from 74.7 to 90 F g−1 at 10 A g−1 for this storage device. The remarkable electrochemical performance is based on the synergistic effect of metal oxide/metal carbide (MoO2/Mo2C) with the interconnected porous carbon. The PAC/MoO2/Mo2C ternary composites highlight promising Mo-based electrode materials suitable for high-performance energy storage. Explicitly, this work also demonstrates a simple and sustainable approach to enhance the electrochemical performance of porous carbon materials. [ABSTRACT FROM AUTHOR]

Abstract Anode materials are demonstrated to essentially affect the electrochemical performance of sodium-ion batteries (SIBs), which are considered as a promising large-scale energy storage device. In this work, alloying ZnS x Se 1-x (x = 0.24) and N doped carbon composite (ZnS x Se 1-x /N-C (x = 0.24)) hierarchical nanospheres are prepared by selenizing the ZnS precursor. The corresponding X-ray diffraction and high-resolution transmission electron microscopy results prove the formation of an alloyed phase, resulting in a wider lattice compared with ZnS. Benefitting from the coexistence of S2− and Se2− in the ZnS x Se 1-x lattice, the weaker Zn-Se bonds and wider lattice spacing facilitate ultrafast pseudocapacitive sodium storage capability and enhanced cycling stability, when ZnS x Se 1-x /N-C is used as anode material for SIBs. At current of 1.0 A g−1, it delivers a capacity of 378 mAh g−1 after 130 cycles with capacity retention of 87.9%, which is much higher than 34.3% for the ZnS/N-C electrode. In addition, for the rate performance, it can maintain an impressive capacity of 233 mAh g−1 at 10.0 A g−1 with a capacity retention of 55.9% in comparison with the capacity at 0.2 A g−1. This work provides us common thoughts to enhance the electrochemical performance of transition metal chalcogenide anode through anion substitution. Highlights • Binary anion-based chalcogenide ZnS x Se 1-x /N-C nanospheres were prepared. • The coexistence of S2− and Se2− in the lattice facilitate the sodium storage. • ZnS x Se 1-x /N-C exhibited enhanced cycling stability. • Capacitive contribution promotes the rate performance for sodium storage. [ABSTRACT FROM AUTHOR]

[Display omitted] • New 3D bulk MOF and 2D ultrathin MOF nanosheets are synthesized. • The planar micro-supercapacitors with the interdigital microelectrodes are achieved based on MOF bulk and MOF nanosheets. • The MOF-nanosheets for micro-supercapacitors displays enhanced performance than MOF bulk. Due to the advantages of ultrahigh power density, long lifespan and easy integration with wearable and microscale electronics, micro-supercapacitors (MSCs) have attracted great interest in recent years. However, new high-performance electrode materials for such micro-electrochemical energy storage devices require deep excavation. Herein, we precisely synthesized a new 3D bulk MOF and new 2D ultrathin MOF nanosheets with a thickness of less than 10 nm, and utilized them as high-capacitance microelectrode materials for sophisticated all-solid-state MSC devices respectively. Notably, the MSCs based on MOF nanosheets displayed a high areal capacitance of 28.3 mF·cm−2, and a volumetric capacitance of 15.7 F·cm−3 at 0.2 mA·cm−2. Especially, our MSCs exhibited remarkable energy density of 8.7 mWh·cm−3 at a power density of 110.3 mW·cm−3, and excellent cycling lifespans with retention of 96.0% after 10,000 cycles, and all performances are better than the MSCs based on MOF bulks. This work provides a new way to further explore the inherent advantages of MOFs and stimulates the synthesis of advanced MOFs materials for application in microscale energy storage. [ABSTRACT FROM AUTHOR]

Molybdenum disulfide (MoS 2), as a classic two-dimensional material, is limited in applications with its relatively poor conductivity and chemical instability due to its single morphology/phase structure in electrocatalytic activity and specific capacitance. Moreover, up to date, it is still an open area in establishing cost-effective approaches to fabricate exotic MoS 2 nanostructures with desired morphology and phase component for exhibiting excellent performance in energy conversion and storage. Herein, only using extremely ordinary sources of molybdenum and sulfur and a simple one-pot hydrothermal method, we efficiently and economically synthesized two types of stable MoS 2 nanostructures with a certain percentage of the metastable metallic (1T) phase, i.e., spherical nanoflowers (SNF) and random nanosheets (RNS). Both SNF–MoS 2 and RNS-MoS 2 exhibited excellent electrocatalytic activity for hydrogen evolution reaction with ultra-high stability and high specific capacitance. These remarkable properties are due to the dramatically increased number of active sites in these unique nanostructures and their enhanced electric conductivities due to the metallic 1T phase. Furthermore, when these two types of nanostructures are physical decorated with carbon black, their electrocatalysis is further enhanced. Our findings offer an economical approach to fabricate stable MoS 2 -based nanomaterials for practical applications with highly efficient energy conversion and energy storage. Image 1 • Spherical nanoflower and random nanosheet MoS 2 are mixed with 1T phase. • The preparation method is extremely simple and cost effective. • SNF- and RNS-MoS 2 possess significant HER and supercapacitors performance. • HER performance is enhanced upon the physical mixing of carbon black. • Excellent stability is surveyed for HER. [ABSTRACT FROM AUTHOR]