Freestanding Binder-Free Electrodes with Nanodisk-Needle-like MnCuCo-LTH and Mn₁Fe₂S₂ Porous Microthorns for High-Performance Quasi-Solid-State Supercapacitors

Abstract

Transition-metal-based layered triple hydroxides (LTHs) are evolving as potential positrode candidates for high-performance supercapacitors; however, their phase stabilization is still critical. Alongside, the availability of limited negatrodes pushes research toward exploring novel alternatives in order to minimize performance limitation issues in the fabricated supercapacitors. Herein, a facile strategy for stabilizing freestanding MnCuCo-LTH-based positrode possessing intermingled nanodisk-needle-like morphology is reported. Alongside, novel high-surface-area negatrodes based on Mn1Fe2S2 exhibiting porous microthorn-like morphology are also optimized. MnCuCo_LTH and Mn1Fe2S2 exhibit remarkably high specific capacities of ∼494 mAh g–1 (∼2540 F g–1) and ∼429 mAh g–1 (∼1546 F g–1), respectively, at 1 A g–1. The fabricated quasi-solid-state supercapacitor equipped with a poly­(vinyl alcohol) (PVA)–KOH gel electrolyte displays a high specific capacity of ∼144 mAh g–1 and a specific capacitance of ∼325 F g–1 at 1 A g–1. The ultrahigh energy cum power traits of ∼105 Wh kg–1 (1 A g–1) and ∼8370 W kg–1 (at 10 A g–1) establish an asymmetric supercapacitor as a high-performance energy storage device. This device shows an appreciably high cycling life with a capacitance retention of ∼93% after 10 000 consecutive cycles, at 10 A g–1. This approach provides a neoteric foresight for developing high-performance advanced energy storage devices equipped with cheaper and eco-friendly components.

NiMn-Layered Double Hydroxide Porous Nanoarchitectures as a Bifunctional Material for Accelerated p-Nitrophenol Reduction and Freestanding Supercapacitor Electrodes

“…The fitting of the observed peaks confirmed the coexistence of Ni 2+ and Ni 3+ oxidation states in the phase with Ni 2+ in major proportion ∼70%. Further, from Figure C, the Mn 2p core-level spectrum shows the existence of two separate peaks corresponding to Mn 2p 3/2 at ∼646 eV and Mn 2p 1/2 at ∼655 eV, respectively, with corresponding satellite peaks distinguished by deconvoluting the profile . The peaks confirmed the presence of manganese in the Mn 3+ oxidation state in the synthesized material.…”

“…The metal-ion layer’s net positive charge is balanced by the anion–water interlayer net negative charge. Thus, it is classified as a hydrotalcite-type hydroxide equipped with two-dimensional brucite-like layers possessing interlayer anions for structure’s charge neutralization . The polycrystalline nature of phases provides flexibility to the structure, which leads to favorable communication with the electrolytic ions for enhancement in the charge storage characteristics.…”

“…Figure shows a schematic representation of the morphology evolution in NiMn LDH_ x H. The sequential time-dependent study provides an insight into the stepwise morphology evolution mechanism. The precipitating agent, that is, urea, served as a constant source of carbonate and hydroxide ions, which maintains the alkaline nature of the solution in order to favor the precipitation process of metal ions, thus stabilizing the metal hydroxides . NH 4 F, working as a complexing agent, supported urea in the process of precipitation by forming a framework necessary for the growth of precipitated metal hydroxides in the desired direction .…”

“…A wide variety of three-dimensional (3D)/ two-dimensional (2D) materials with different morphologies such as solid/hollow spheres, core–shells, rods, discs, and so forth have been proposed, composed of metal oxides and sulfides. − Among 2D and 3D materials, the latter is considered to be more optimum for ion/charge accumulation due to the presence of connected channels in between the layers, which provide directed pathways for an efficient electron relay system. − A novel class of 2D materials include layered double hydroxides (LDHs) based on transition metals, which possess a wide spectrum of properties such as high theoretical capacity, redox reactions-assisted stable potential plateaus, abundance in earth crust, versatile chemical compositions, and synergistic catalytic property enhancement with multiple redox active metals. − They are also known as brucite-like anionic clays, composed of divalent/trivalent cations and an interlayer anion sandwiched between them. , These di- and trivalent cations are orderly distributed within the octahedral voids of edge-sharing hydroxyl layers. , They have become popular because of their biocompatibility, facile synthesis, and eco-friendly nature. , …”

“…Therefore, a stepwise in situ study of the synthesis mechanism needs to be explored to suffice the cause. Various transition metal LDHs have been explored in the literature, for example, NiCo, 51 NiV, 37 ZnCo, 52 and MnCuCo, 15 where morphology optimization is done significantly, but reaction time requirement for phase stabilization is not optimized.…”