3D flower-like MOF-derived NiCo-LDH integrated with Ti3C2Tx for high-performance pseudosupercapacitors

Flexible Hybrid Supercapacitor Achieving 2.2 V with NiCo2S4/Polyaniline/MnO2 and N, S-Co-Doped Carbon Nanofibers for Ultra-High Energy Density

Flexible all-solid-state asymmetric supercapacitors (FAASC) represent a highly promising power sources for wearable electronics. However, their energy density is relatively less as compared to the conventional batteries. Herein, a novel ultra-high energy density FAASC is developed using nickel-cobalt sulfide (NiCo2S4)/polyaniline (PANI)/manganese dioxide (MnO2) ternary composite on carbon fiber felt (CF) as positive and N, S-co-doped carbon nanofibers (CNF)/CF as negative electrode, respectively. Initially, porous δ-MnO2 nanoworm-like network is decorated on CF using potentiodynamic method. Subsequently, interconnected PANI nanostructures is grown on the MnO2 via a facile in situ chemical polymerization, followed by the electrodeposition of highly porous NiCo2S4 nanowalls. Benefiting from 3D porous structure of conductive CF and redox active properties of NiCo2S4, PANI and MnO2, FAASC achieved a superior energy storage capacity. Later, high-performance N, S-co-doped CNF/CF negative electrode is synthesized using electropolymerization of PANI nanofibers on CF, followed by the carbonization process. The assembled FAASC exhibits a wide voltage window of 2.2 V and remarkable specific capacitance of 143 F g-1 at a current density of 1 A g-1. The cell further delivers a superb energy density of 71.6 Wh kg-1 at a power density of 492.7 W kg-1, supreme cycle life and remarkable electrochemical stability under mechanical bending.

Multifunctional Wearable Electronic Based on Fabric Modified by PPy/NiCoAl-LDH for Energy Storage, Electromagnetic Interference Shielding, and Photothermal Conversion

With the rapid advancement of electronic technology, traditional textiles are challenged to keep up with the demands of wearable electronics. It is anticipated that multifunctional textile-based electronics incorporating energy storage, electromagnetic interference (EMI) shielding, and photothermal conversion are expected to alleviate this problem. Herein, a multifunctional cotton fabric with hierarchical array structure (PPy/NiCoAl-LDH/Cotton) is fabricated by the introduction of NiCoAl-layered double hydroxide (NiCoAl-LDH) nanosheet arrays on cotton fibers, followed by polymerization and growth of continuous dense polypyrrole (PPy) conductive layers. The multifunctional cotton fabric shows a high specific areal capacitance of 754.72 mF cm-2 at 5 mA cm-2 and maintains a long cycling life (80.95% retention after 1000 cycles). The symmetrical supercapacitor assembled with this fabric achieves an energy density of 20.83 Wh cm-2 and a power density of 0.23 mWcm-2. Moreover, the excellent electromagnetic interference shielding (38.83 dB), photothermal conversion (70.2 °C at 1000 mW cm-2), flexibility and durability are also possess by the multifunctional cotton fabric. Such a multifunctional cotton fabric has great potential for using in new energy, smart electronics, and thermal management applications.

Layered double hydroxide-based electrode materials derived from metal-organic frameworks: synthesis and applications in supercapacitors

Metal-organic frameworks (MOFs) have emerged as promising electrode materials for supercapacitors (SCs) due to their highly porous structures, tunable chemical compositions, and diverse morphologies. However, their applications are hindered by low conductivity and poor cycling performance. A novel approach for resolving this issue involves the growth of layered double hydroxides (LDHs) using MOFs as efficient templates or precursors for electrode material preparation. This method effectively enhances the stability, electrical conductivity, and mass transport ability of MOFs. The MOF-derived LDH exhibits a well-defined porous micro-/nano-structure, facilitating the dispersion of active sites and preventing the aggregation of LDHs. Firstly, this paper introduces synthesis strategies for converting MOFs into LDHs. Subsequently, recent research progress in MOF-derived LDHs encompassing pristine LDH powders, LDH composites, and LDH-based arrays, along with their applications in SCs, is overviewed. Finally, the challenges associated with MOF-derived LDH electrode materials and potential solutions are discussed.

Construction of porous flower-like Ru-doped CoNiFe layered double hydroxide for supercapacitors and oxygen evolution reaction catalysts

In recent years, ternary layered double hydroxide (LDH) has become a research hotspot for electrode materials and oxygen evolution reaction (OER) catalyst due to the enhanced synergistic effect between individual elements. However, the application of LDH is greatly limited by its low electrical conductivity and the disadvantage that nanosheets tend to accumulate and mask the active sites. Herein, a novel Ru-doped CoNiFe - LDH was prepared via a facile hydrothermal method. According to the density functional theory (DFT) calculations, the doping of Ru element could improve electron state density and band gaps of LDH and consequently boosted the electrochemical reaction kinetics as well as electrical conductivity. Furthermore, introduction of Ru atom induced the formation of porous flower-like structures in nanosheets. Compared to CoNiFe - LDH (28.9 m2/g), Ru-doped CoNiFe - LDH performed larger specific surface area of 53.1 m2/g, resulting in more electrochemically active sites. In these case, Ru-doped CoNiFe - LDH demonstrated better energy storage performance of 176.0 mAh/g at 1 A/g compared to original CoNiFe - LDH (78.9 mAh/g at 1 A/g). Besides, the assembled Ru-doped CoNiFe - LDH//activated carbon (AC) device delivered a maximum energy density of 36.4 W h kg-1 at the power density of 740.3 W kg-1 and an outstanding cycle life (78.7 % after 10,000 cycles). Meanwhile, Ru-doped CoNiFe - LDH exhibited lower overpotential (339 mV at 50 mA cm-2) and Tafel slope (93.2 mV dec-1). Therefore, this work provided novel and valuable insights into the rational doping of Ru elements for the controlled synthesis of supercapacitor electrode materials and OER catalysts.

Effect of synthesis temperature on the structural morphology of a metal-organic framework and the capacitor performance of derived cobalt-nickel layered double hydroxides

Three-dimensional interconnected nickel-cobalt layered double hydroxides (NiCo-LDHs) were prepared on nickel foam by ion exchange using a cobalt-based metal-organic framework (Co-MOF) as a template at different temperatures. The effects of the Co-MOF preparation temperature on the growth, mass, morphology, and electrochemical properties of the Co-MOF and derived NiCo-LDH samples were studied. The synthesis temperature from 30 to 50 °C gradually increased the mass of the active material and the thickness of the Co-MOF sheets grown on the nickel foam. The higher the temperature is, the larger the proportion of Co3+. β-Cobalt hydroxide (β-Co(OH)2) sheets were generated above 60 °C. The morphology and mass loading pattern of the derived flocculent layer clusters of NiCo-LDH were inherited from metal-organic frameworks (MOFs). The areal capacitance of NiCo-LDH shows an inverted U-shaped curve trend with increasing temperature. The electrode material synthesized at 50 °C had a tremendous specific capacitance of 7631 mF·cm-2 at a current density of 2 mA·cm-2. The asymmetric supercapacitor assembled with the sample and active carbon (AC) achieved an energy density of 55.0 Wh·kg-1 at a power density of 800.0 W·kg-1, demonstrating the great potential of the NiCo-LDH material for energy storage. This work presents a new strategy for designing and fabricating advanced green supercapacitor materials with large power and energy densities.

Construction of rod-like cobalt-pyridinedicarboxylic acid/MXene nanosheets composites for hydrogen evolution reaction and supercapacitor

Metal-organic frameworks (MOFs) have attracted considerable attention in the field of energy storage and conversion due to their large specific surface area, regulatable pore structure and composition. However, the poor electrical conductivity and few active sites of MOFs impede their application. Herein, highly conductive MXene nanosheets are introduced to modulate the electronic conductivity and structure of rod-like Co-pyridinedicarboxylic acid (Co-PDC), and thus enhancing the electrochemical performance of MOFs. The heterostructural Co-PDC/MXene (CPM) was facily synthesized at room temperature. The as-prepared CPM-30 with 30 % MXene only requires the overpotential of 75.1 mV to achieve a current density of 10 mA cm-2 for hydrogen evolution reaction (HER), and the assembled electrolytic cell with CPM-30 and RuO2 as cathode and anode electrodes can achieve a current density of 10 mA cm-2 at a voltage of 1.65 V. In addition, CPM-10 exhibits a high specific capacitance of 583.1 F g-1 at 0.5 A g-1 and an excellent rate performance of 41.6 % at 50 A g-1. Furthermore, the assembled asymmetric supercapacitor CPM-10//AC exhibited an energy density of 15.55 Wh kg-1 at a power density of 750 W kg-1 and excellent stability with a capacitance retention rate of 95 % after 10,000 cycles. The excellent electrochemical properties of Co-PDC/MXene are attributed to the unique structure and synergistic effect of Co-PDC and MXene.

Cobalt coordinated carbon quantum dots boosting the performance of NiCo-LDH for energy storage

Transition metal layered double hydroxides have extremely high specific capacitances but suffer from poor rate performance and cycling stability due to their low conductivity and structural stability. In this study, cobalt-coordinated carbon quantum dots (CoCQDs) were designed and synthesized to enhance the energy storage performance of nickel-cobalt layered double hydroxides (NiCo-LDH). Nickel and cobalt ions were co-electrodeposited with the CoCQDs to form a NiCo-LDH based composite electrode (denoted as CoC@LDH). Since the CoCQDs participated in the formation of the NiCo-LDH, the carbon quantum dots could be strongly bonded to the NiCo-LDH nanosheets through coordination interactions. Thus, the conductivity as well as the structure stability of the NiCo-LDH was effectively improved, which greatly boosted the cycle stability and rate performance of the NiCo-LDH. Several CoCQDs with different Co contents (nCoCQDs, n = 0.5, 1.0, 2.0) were fabricated and their effects on the performance of the resultant electrodes nCoC@LDH were investigated. The 1.0CoC@LDH electrode exhibited an impressive specific capacitance of 1867 F g-1 at 1 A-g-1, along with a significantly enhanced capacitance retention of 84.6 % after 6000 cycles at 5 A g-1 (benchmark 49.5 %). This ingenious design provides a new avenue for fabricating pseudo-capacitive materials with unprecedented high performance.

In Situ Growth of Nickel-Cobalt Metal Organic Frameworks Guided by a Nickel-Molybdenum Layered Double Hydroxide with Two-Dimensional Nanosheets Forming Flower-Like Struc-Tures for High-Performance Supercapacitors

Metal organic frameworks (MOFs) are a kind of porous coordination polymer supported by organic ligands with metal ions as connection points. They have a controlled structure and porosity and a significant specific surface area, and can be used as functional linkers or sacrificial templates. However, long diffusion pathways, low conductivity, low cycling stability, and the presence of few exposed active sites limit the direct application of MOFs in energy storage applications. The targeted design of MOFs has the potential to overcome these limitations. This study proposes a facile method to grow and immobilize MOFs on layered double hydroxides through an in situ design. The proposed method imparts not only enhanced conductivity and cycling stability, but also provides additional active sites with excellent specific capacitance properties due to the interconnectivity of MOF nanoparticles and layered double hydroxide (LDH) nanosheets. Due to this favorable heterojunction hook, the NiMo-LDH@NiCo-MOF composite exhibits a large specific capacitance of 1536 F·g^-1 at 1 A·g^-1. In addition, the assembled NiMo-LDH@NiCo-MOF//AC asymmetric supercapacitor can achieve a high-energy density value of 60.2 Wh·kg^-1 at a power density of 797 W·kg^-1, indicating promising applications.

Magneto-Electrodeposition of 3D Cross-Linked NiCo-LDH for Flexible High-Performance Supercapacitors

Layered double hydroxides (LDHs) with outstanding redox activity on flexible current collectors can serve as ideal cathode materials for flexible hybrid supercapacitors in wearable energy storage devices. Electrodeposition is a facile, time-saving, and economical technique to fabricate LDHs. The limited loading mass induced by insufficient mass transport and finite exposure of active sites, however, greatly hinders the improvement of areal capacity. Herein, magneto-electrodeposition (MED) under high magnetic fields up to 9 T is developed to fabricate NiCo-LDH on flexible carbon cloth (CC) as well as Ti₃ C₂ T_x functionalized CC. Owing to the magneto-hydrodynamic effect induced by magnetic-electric field coupling, the loading mass and exposure of active sites are significantly increased. Moreover, a 3D cross-linked nest-like microstructure is constructed. The MED-derived NiCo-LDH delivers an ultrahigh areal capacity of 3.12 C cm^-2 at 1 mA cm^-2 and as-fabricated flexible hybrid supercapacitors show an excellent energy density with an outstanding cycling stability. This work provides a novel route to improve electrochemical performances of layered materials through MED technique.

Unprecedented Duel Role of Polyaniline for Enhanced Pseudocapacitance of Cobalt-iron Layered Double Hydroxide

Creating nanosized pores in layered materials can increase the abundant active surface area and boost potential applications of energy storage devices. Herein, a unique synthetic strategy based on the polyaniline (PANI) doped two-dimensional (2D) cobalt-iron layered double hydroxide (CoFe-LDH/P) nanomaterials are being designed, and the formation of pores at low temperature (80 °C) is developed. It is found that the optimized concentration of PANI creates the nanopores on the CoFe-LDH nanosheets among all other polymers. The well-ordered pores of CoFe-LDH/P allow the high accessibility of the redox-active sites and promote effective ion diffusion. The optimized CoFe-LDH/P2 cathode reveals a specific capacitance 1686 (1096 Cg^-1 ) and 1200 Fg^-1 (720 Cg^-1 ) at 1 and 30 Ag^-1 respectively, a high rate capability (71.2%), and a long cycle life (98% over 10000 cycles) for supercapcitor applications. Charge storage analysis suggested that the CoFe-LDH/P2 electrode displays like a capacitive-type storage mechanism (69% capacitive at 1 mVs^-1 ). Moreover, an asymmetric aqueous supercapacitor (CoFe-LDH/P2//AC) was fabricated, delivering the excellent energy density (75.9 Wh kg^-1 at 1124 W kg^-1 ) with outstanding stability (97.5%) over 10000 cycles. This work opens a new avenue for designing porous 2D materials at low temperature for aqueous energy storage devices. This article is protected by copyright. All rights reserved.