environmental friendliness, and long cycling life, which are highly expected as a promising candidate to meet the demands to supply power for electric vehicles and portable electronics. [4][5][6][7] However, largescale applications of supercapacitors remain a challenge, with unmet energy demands. [8,9] Electrode materials, such as carbonaceous materials, [10][11][12] conducting polymers, [13,14] and transition metal oxides, [15][16][17][18] played a vital role to obtain superior performance and have attracted much research interests in past years. To date, carbonaceous materials have been frequently used as electrodes in commercial supercapacitors due to their excellent cyclic stability and high power density, but they suffer from a poor energy density that cannot meet the demands of modern electronics. [19,20] Conducting polymers are also promising electrode materials for supercapacitors due to their exceptional electrochemical properties. Unfortunately, conducting polymers suffer from poor cycling performance during long-term charge/discharge, which leads to a poor cycling life for supercapacitors. [21,22] On the other hand, low electrical conductivity and unsatisfactory rate capability of the transition metal oxides limit them from wideranging commercialization. [23] Thus, progress for large-scale, highly electrically conductive, highly stable, and environmental friendly electrode materials for high-energy supercapacitors remains an interesting task for the scientific community.Recently, transition metal sulfides are extensively investigated for electrochemical energy storage as well as for energy conversion devices due to their rational fabrication strategy that favors an enhanced electrical conductivity, low electronegativity, and high electrochemical activity when compared to the corresponding oxides. [24][25][26] Specifically, research has focused on developing ternary transition metal sulfides with attractive nanostructures that possess richer Faradaic reactions and higher capacities due to an improvement in electrochemical properties compared to binary metal sulfides or ternary metal oxides. [27][28][29][30] Among ternary metal oxides, Zn-Co-O is pro mising for future use in supercapacitors and Li-ion batteries. [31][32][33] Zn-Co-O electrode materials show better battery-type Faradaic performance and higher catalytic activity but suffer from a poor cycling life. [34] In this regard, replacing oxygen with sulfur might also result in greater flexibility and stability for electrode materials due to the lower electronegativity of sulfur compared to that of oxygen. [35] To the best of our knowledge, little attention has A facile two-step strategy is developed to design the large-scale synthesis of hierarchical, unique porous architecture of ternary metal hydroxide nanowires grown on porous 3D Ni foam and subsequent effective sulfurization. The hierarchical Zn-Co-S nanowires (NWs) arrays are directly employed as an electrode for supercapacitors application. The as-synthesized Zn-Co-S NWs deliver an ultrahigh ...

Because of the demand for sustainable energy storage devices, investigating high energy density and cost-effective electrodes for flexible supercapacitors (SCs) is essential; however, the emergence of such high-performance electrodes to fulfill the requirements of industrial sectors remains a highly challenging task. Herein, we successfully demonstrated the preparation of ternary metal selenides of nickel–vanadium selenide (Ni x V3–x Se4) and nickel–iron selenide (Ni x Fe3–x Se4) series by a simple and low-cost hydrothermal method, followed by selenization for flexible asymmetric SC (ASC). The impacts of Ni2+ are studied and shown to lead to a significant enhancement in electrochemical properties, which varied with the stoichiometric ratio of Ni–V/Fe in Ni x V3–x Se4 and Ni x Fe3–x Se4 nanosheet arrays. The optimized NiV2Se4 and NiFe2Se4 electrodes displayed high specific capacities (∼329 and 261 mA h g–1, respectively, at 1 mA cm–2), excellent rate performances (capacity retentions of about 79.33 and 77.78%, respectively, even at 50 mA cm–2), and outstanding cycling stabilities (98.6 and 97.9% capacity retentions after 10 000 cycles, respectively). Most notably, the NiV2Se4//NiFe2Se4 ASC provides an excellent energy density of 73.5 W h kg–1 at a power density of 0.733 kW kg–1 and superior cycling performance (96.6% capacity retention after 10 000 cycles). The high-performance nanostructured flexible ASCs show promise in portable electronics and zero-emission transportation.

Highly flexible supercapacitors (SCs) have great potential in modern electronics such as wearable and portable devices. However, ultralow specific capacity and low operating potential window limit their practical applications. Herein, a new strategy for the fabrication of free-standing NiMoS and NiFeS nanosheets (NSs) for high-performance flexible asymmetric SC (ASC) through hydrothermal and subsequent sulfurization technique is reported. The effect of Ni 2+ is optimized to attain hierarchical NiMoS and NiFeS NS architectures with high electrical conductivity, large surface area, and exclusive porous networks. Electrochemical properties of NiMoS and NiFeS NS electrodes exhibit that both have ultrahigh specific capacities (≈312 and 246 mAh g −1 at 1 mA cm −2 ), exceptional rate capabilities (78.85% and 78.46% capacity retention even at 50 mA cm −2 , respectively), and superior cycling stabilities. Most importantly, a flexible NiMoS NS//NiFeS NS ASC delivers a high volumetric capacity of ≈1.9 mAh cm −3 , excellent energy density of ≈82.13 Wh kg −1 at 0.561 kW kg −1 , exceptional power density (≈13.103 kW kg −1 at 61.51 Wh kg −1 ) and an outstanding cycling stability, retaining ≈95.86% of initial capacity after 10 000 cycles. This study emphasizes the potential importance of compositional tunability of the NS architecture as a novel strategy for enhancing the charge storage properties of active electrodes.

A novel Co2CuS4/NG composite based asymmetric supercapacitor delivers superb energy density (~53.3 W h kg−1), high power density (~10936 W kg−1 at 38.4 W h kg−1) and outstanding cycling stability (~4000 cycles).

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