Insight into the decay mechanism of cycling capacitance for layered double hydroxides at subnanometer scale

Tip effect of NiCo-LDH with low crystallinity for enhanced energy storage performance of yarn-shaped supercapacitors

Layered double hydroxides (LDHs) are considered promising materials for supercapacitor applications. However, the development of yarn-shaped supercapacitors (YSCs) with high electrochemical performance utilizing LDHs remains challenging. In this study, the NiCo-LDHs with various morphologies (nano-needles, nano-sheets, needle-sheet composites, and nano-flowers) were grown on carbon nanotubes (CNTs)-functionalized cotton yarn via a co-precipitation technique for YSC applications. Among these, the yarn incorporating nano-needle NiCo-LDHs exhibited reduced crystallinity yet demonstrated a superior areal capacitance compared to other morphologies, following a diffusion-controlled process. Finite element simulations were subsequently conducted to investigate this phenomenon, revealing that the lower-crystallinity nano-needle NiCo-LDHs accumulated a greater charge at their tips, thereby enhancing redox reactions and achieving higher energy storage capacitance. Subsequently, the yarns with nano-needle NiCo-LDHs were assembled into flexible quasi-solid-state symmetric YSCs, achieving a peak areal capacitance of 124.27 mF cm-2 and an exceptionally high energy density of 39.4 μWh cm-2 at a current density of 0.2 mA cm-2. Furthermore, our YSCs can be scaled up through serial or parallel connections and integrated into fabrics, making them suitable for wearable energy storage applications. This work provides an efficient method for fabricating high-performance YSCs and demonstrates significant potential for wearable energy storage devices.

Out-of-plane coordination of iridium single atoms with organic molecules and cobalt-iron hydroxides to boost oxygen evolution reaction

Advancements in single-atom-based catalysts are crucial for enhancing oxygen evolution reaction (OER) performance while reducing precious metal usage. A comprehensive understanding of underlying mechanisms will expedite this progress further. Here we report Ir single atoms coordinated out-of-plane with dimethylimidazole (MI) on CoFe hydroxide (Ir1/(Co,Fe)-OH/MI). This Ir1/(Co,Fe)-OH/MI catalyst, which was prepared using a simple immersion method, delivers ultralow overpotentials of 179 mV at a current density of 10 mA cm-2 and 257 mV at 600 mA cm-2 as well as an ultra-small Tafel slope of 24 mV dec-1. Furthermore, Ir1/(Co,Fe)-OH/MI has a total mass activity exceeding that of commercial IrO2 by a factor of 58.4. Ab initio simulations indicate that the coordination of MI leads to electron redistribution around the Ir sites. This causes a positive shift in the d-band centre at adjacent Ir and Co sites, facilitating an optimal energy pathway for OER.

Synthesis and Fabrication of Metal Cation Intercalation in Multilayered Ti3C2Tx Composite CNF Electrode for Asymmetric Coin Cell Supercapacitors

Ti3C2Tx has attracted considerable attention from researchers in energy storage due to its unique structure and beneficial surface functional group characteristics. Recent studies have focused extensively on developing Ti3C2Tx composites to create potential electrode materials for energy storage applications. Carbon nanofiber is often combined with Ti3C2Tx to produce high-performance functional nanocomposites, effectively harnessing the unique properties of Ti3C2Tx nanosheets while ensuring exceptional electrochemical behavior. This work employs an ultrasonication method to prepare a Na-Ti3C2Tx/CNF electrode. Establishing a stable interlayer structure between Ti3C2Tx nanosheets and cationic metal intercalation materials is crucial for expanding the interlayer spacing of Ti3C2Tx and creating multidirectional stable ion transport channels. Consequently, this process exposes more active sites that are accessible to ions. At a current density of 1 A g-1, the resulting Na-Ti3C2Tx/CNF demonstrates an impressive specific capacitance of 680.2 F g-1. Notably, the asymmetric supercapacitor assembled with Na-Ti3C2Tx/CNF as the positive electrode and activated carbon as the negative electrode exhibits remarkable cyclic retention of 83.1% and the Coulombic efficiency of 90.5% after 10,000 cycles at 10 A g-1, a wide voltage window of 1.5 V, a high energy density of 102.5 W h kg-1, and a power density of 2963.7 W kg-1. The fabricated coin cell ASC devices, which include glowing red light-emitting diodes, were demonstrated in practical applications. The optimization strategy for developing Na-Ti3C2Tx/CNF provides essential technical support for integrating Na-Ti3C2Tx/CNF into the next generation of portable and adaptable wearable electrochemical energy storage devices.

Advanced High-Energy All-Solid-State Hybrid Supercapacitor with Nickel-Cobalt-Layered Double Hydroxide Nanoflowers Supported on Jute Stick-Derived Activated Carbon Nanosheets

Developing efficient, lightweight, and durable all-solid-state supercapacitors is crucial for future energy storage systems. The study focuses on optimizing electrode materials to achieve high capacitance and stability. This study introduces a novel two-step pyrolysis process to synthesize activated carbon nanosheets from jute sticks (JAC), resulting in an optimized JAC-2 material with a high yield (≈24%) and specific surface area (≈2600 m2 g-1). Furthermore, an innovative in situ synthesis approach is employed to synthesize hybrid nanocomposites (NiCoLDH-1@JAC-2) by integrating JAC nanosheets with nickel-cobalt-layered double hydroxide nanoflowers (NiCoLDH). These nanocomposites serve as positive electrode materials and JAC-2 as the negative electrode material in all-solid-state asymmetric hybrid supercapacitors (HSCs), exhibiting remarkable performance metrics. The HSCs achieve a specific capacitance of 750 F g-1, a specific capacity of 209 mAh g-1 (at 0.5 A g-1), and an energy density of 100 Wh kg-1 (at 250 W kg-1) using PVA/KOH solid electrolyte, while maintaining outstanding cyclic stability. Importantly, a density functional theory framework is utilized to validate the experimental findings, underscoring the potential of this novel approach for enhancing HSC performance and enabling the large-scale production of transition metal-based layered double hydroxides.