Incorporation of α-MnO₂ Nanoflowers into Zinc-Terephthalate Metal–Organic Frameworks for High-Performance Asymmetric Supercapacitors

Abstract

Herein, we report the synthesis of α-MnO 2 nanoflower-incorporated zinc-terephthalate MOFs (MnO 2 @Zn-MOFs) via the conventional solution phase synthesis technique as an electrode material for supercapacitor applications. The material was characterized by powder-X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy techniques. The prepared electrode material exhibited a specific capacitance of 880.58 F g −1 at 5 A g −1 , which is higher than the pure Zn-BDC (610.83 F g −1 ) and pure α-MnO 2 (541.69 F g −1 ). Also, it showed a 94% capacitance retention of its initial value after 10,000 cycles at 10 A g −1 . The improved performance is attributed to the increased number of reactive sites and improved redox activity due to MnO 2 inclusion. Moreover, an asymmetric supercapacitor assembled using MnO 2 @Zn-MOF as the anode and carbon black as the cathode delivered a specific capacitance of 160 F g −1 at 3 A g −1 with a high energy density of 40.68 W h kg −1 at a power density of 20.24 kW kg −1 with an operating potential of 0−1.35 V. The ASC also exhibited a good cycle stability of 90% of its initial capacitance.

Rational synthesis of 3D coral-like ZnCo2O4 nanoclusters with abundant oxygen vacancies for high-performance supercapacitors

“…The 3D coral-like ZnCo 2 O 4 -0.5 nanoclusters with rougher surface not only enhance the material's surface area and facilitate electrode-electrolyte contact but also provide additional active sites, thereby accelerating the redox reaction rate and optimizing its electrochemical performance. 37 The microstructure of ZnCo 2 O 4 -0.5 was further evidenced through TEM images. Fig.…”

Superior Cyclic Stability and Capacitive Performance of Cation- and Water Molecule-Preintercalated δ-MnO2/h-WO3 Nanostructures as Supercapacitor Electrodes

“…Because of the presence of K + ions, Mn’s oxidation state is predicted to be about 3.77, which is in line with the estimated value from the XPS analysis. As depicted in Figure e, the deconvoluted asymmetric O 1s spectrum can be fitted using three Gaussian components corresponding to three peaks at 529.74 eV (lattice oxygen, Mn–O–Mn bond), 531.29 eV (oxygen-deficient regions, O V ), and 532.85 eV (adsorbed surface water, O–H bond). , The as-prepared product is thus found to have the chemical formula K 0.46 Mn 2 O 4 .…”

“…The lack of redox peaks in the CV curves suggests the existence of constant-rate reversible electrochemical reactions in the materials . Moreover, ultrafast charge-transfer kinetics, reversible redox processes, and simple access to electrolyte ions at the interface between electrode and electrolyte are all inferred from the almost repeatable and conserved form of CV curves, even at high scan rates . At a low scan rate, the output current is minimal because the ions have more time to disperse in the active material’s microscopic pores, promoting greater charge storage.…”

“…The measurements were carried out with a working potential window of −0.4 to 0.4 V, and the EIS measurements were carried out using a sinusoidal signal over a frequency range from 0.1 to 10 5 Hz. From the GCD results, using the following equations, the specific capacitance ( C sp ), power density ( P ), and energy density ( E ) of the system were calculated: C sp false( normalF 0.25em normalg − 1 false) = I Δ t m Δ V E false( normalW 0.25em normalh 0.25em kg − 1 false) = C sp Δ V 2 2 × 3.6 P 0.25em false( normalW 0.25em kg − 1 false) = E × 3600 Δ t …”

“…Among the available alternatives to electrode materials for SCs, MnO 2 nanomaterials and vanadium-based materials stand out because of their superior theoretical capacity and easy fabrication. , Especially, MnO 2 possesses a lack of toxicity, a wide potential window, low cost due to its abundant availability, variable oxidation states, high surface area, and high theoretical capacitance, which contribute to its wide research in SC devices . The synthesis route and reaction conditions determine the crystalline phases and morphologies of the MnO 2 nanostructures .…”