Graphitic Carbon Nitride-Induced Multifold Enhancement in Electrochemical Charge Storage of CoS-NiCo2S4 for All-Solid-State Hybrid Supercapacitors

Hierarchical NiCo2O4@CuS composite electrode with enhanced surface area for high-performance hybrid supercapacitors

Hierarchical binder-free NiCo2O4@CuS composite electrodes have been successfully fabricated on a nickel foam surface using a facile hydrothermal method and directly used as a battery-type electrode material for supercapacitor applications. The surface morphological studies reveal that the composite electrode exhibited porous NiCo2O4 nanograss-like structures with CuS nanostructures. The surface area of the composite is significantly enhanced (91.38 m2 g-1) compared to NiCo2O4 (52.16 m2 g-1), with a predominant pore size of 3-6 nm. This synergistic combination enhanced the electrode's electrochemical properties. The NiCo2O4@CuS electrode delivered an impressive specific capacitance of 141.13 mA h g-1 at 1 A g-1, surpassing the performance of the bare NiCo2O4 electrode. The composite electrode also exhibited excellent rate capability and cycling stability, retaining 87.49% of its initial capacity at high current densities and 88.62% after 3000 cycles. A hybrid supercapacitor (HSC) device assembled using NiCo2O4@CuS and G-ink electrodes attained a peak energy density of 28.85 W h kg-1 at a power density of 238.2 W kg-1, outperforming many reported HSCs. Additionally, the HSC device demonstrated exceptional cycling stability, retaining 87.59% of its initial capacitance after 4000 cycles. The superior performance of the NiCo2O4@CuS composite electrode is attributed to the synergistic combination of NiCo2O4 and CuS, which promotes interfacial electron separation and facilitates rapid electron transfer.

Hierarchical Mn3O4/NiSe2-MnSe2: A Versatile Electrode Material for High-Performance All-Solid-State Hybrid Pseudocapacitors with Supreme Working Durability

As highly efficient electrochemical energy storage devices are in indispensable demand for numerous modern-day technologies, herein sluggish precipitation followed by an anion exchange procedure has been developed to synthesize an oxide-selenide mixed phase (Mn3O4/NiSe2-MnSe2) novel electrode material with high surface area and porosity for high-performance all-solid-state hybrid pseudocapacitors (ASSHPC). Mn3O4/NiSe2-MnSe2 shows a rich Tyndall effect (in H2O) and possesses randomly arranged low-dimensional crystallites of nearly similar size and uniform shape. The electrochemical analyses of Mn3O4/NiSe2-MnSe2 corroborate good electrochemical reversibility during charge transfer, superior pseudocapacitive charge-storage efficiency, and very low charge transfer and series resistance, ion-diffusion resistance, and relaxation time, which endorse the quick pseudocapacitive response of the material. The Mn3O4/NiSe2-MnSe2||N-rGO ASSHPC device demonstrates excellent charge-storage physiognomies suggestive of rich electrochemical and electromicrostructural compatibility between the electrode materials in the fabricated assembly. The Mn3O4/NiSe2-MnSe2||N-rGO ASSHPC device delivers high mass and area specific capacitance/capacity, very low charge-transfer resistance (∼0.74 Ω), total series resistance (∼0.76 Ω), diffusion resistance, and a relaxation time constant, which endorse the quick pseudocapacitive response of the device. The device delivers higher energy and power density (∼34 W h kg-1 at ∼2994 W kg-1), rate efficiency (∼17 W h kg-1 at ∼11,995 W kg-1), and cyclic performance (∼97.2% specific capacity/capacitance retention after 9500 continuous GCD cycles). The superior Ragone and cyclic efficiencies of the ASSHPC device are ascribed to the multiple redox-active Ni and Mn ions which lead to the supplemented number of redox reactions; "electroactive-ion buffering pool"-like physiognomics of Mn3O4/NiSe2-MnSe2, which facilitate the electrolyte ion dissemination to the electroactive sites even at high rate redox condition; and ideal electro-microstructural compatibility between the electrode materials, which leads to assisted charge transfer and absolute ion dissemination during the charge-storage process.