Sulfidation of CoAl-layered double hydroxide on Ni foam for high-performance supercapacitors

Controlled Hierarchical Construction of Ultrahomogeneous Co9S8@CoAl-LDH/NF Layered Core-Shell Heterostructures for High-Performance Asymmetric Supercapacitors

The rational collocation and construction of multiphase composite electrode materials with ingenious structures is a key strategic to enhance the electrochemical performance of supercapacitors (SCs). Within this project, a unique Co9S8@CoAl-LDH/NF core-shell heterostructure consisting of CoAl-LDH/NF ultrathin nanosheets sturdily attached to Co9S8/NF needle-like nanorods is grown in situ on self-supported conductive substrate nickel foam (NF) by an effortless and productive multistep hydrothermal method. The construction of the core-shell structure can effectively enhance the capacitive properties as well as the mechanical strength of the material. Compared with the single-component materials Co9S8/NF (1769.6 mF cm-2 and 91.6%) and CoAl-LDH/NF (858 mF cm-2 and 85.2%), the Co9S8@CoAl-LDH/NF composites have excellent capacitance properties (5052.4 mF cm-2) along with exceptional capacitance retention (5000 cycles) 98.5% even after undergoing charging and discharging. Furthermore, the asymmetric SCs fabricated with Co9S8@CoAl-LDH/NF and AC/NF exhibit an energy density of 0.17 mWh cm-2 at 3.20 mW cm-2. Therefore, the innovative core-shell heterostructure of Co9S8@CoAl-LDH/NF presented in this study holds immense practical potential as a groundbreaking electrode material in the realm of SCs.

In Situ Transformation of Metal Molybdates into Polymetallic Sulfides with Enriched Edge Sites for High-Performance Supercapacitors

An effective approach to synthesize polycrystalline Ni-Co-Mo sulfide (NiCoMoS) is developed through doping engineering coupled with chemical transformation. The polycrystalline NiCoMoS with enriched active edge sites is designed and fabricated on a Ni foam (NF) via a facile hydrothermal calcination and post-sulfidation approach, where the polycrystalline NiCoMoO₄ precursor is elaborately prepared by doping Co ions into the NiMoO₄ lattice and subsequently in-situ-converted into NiCoMoS with 3D architectures of ordered nanoneedle arrays. Benefiting from the unique 3D structure and synergistic effects of each component, the optimized needle-like NiCoMoS_(2.0) arraying on a NF as a self-standing electrode exhibits superior electrochemical performances with a high specific charge (920.0 C g^-1 at 1.0 A g^-1), excellent rate capability, and good long-term stability. Furthermore, the assembled NiCoMoS//activated carbon hybrid device presents a satisfactory supercapacitor performance, affording an energy density of 35.2 W h kg^-1 at a power density of 800.0 W kg^-1 and competitive long-term stability (83.8% retention at 15 A g^-1 after 10,000 cycles). Such a novel strategy may pave a new route for exploring other polymetallic sulfides with enriched, exposed active edge sites for energy-related applications.

Ni-Co-Mn hydrotalcite-derived hierarchically porous sulfide for hybrid supercapacitors

Ternary transition metal sulfides have attracted much attention due to their superior electrochemical properties. Nevertheless, it is difficult to commercialize sulfides due to their intrinsic properties such as dull reaction kinetics and an insufficient number of active sites. Herein, a self-supporting porous NiCoMnS sulfide (NiCoMnS/NF) arrayed on nickel foam (NF) with 3D honeycomb-like structure was designed and prepared via a hydrothermal and post-sulfidation process. It was found that the 3D hierarchically network architecture, constructed by nanosheets with abundant cavities, endowed NiCoMnS/NF with a high specific area and rich ion/electron-transport channels, which facilitated ion/electron transfer and Faradaic reaction kinetic. The optimal NiCoMnS/NF exhibited a markedly improved electrochemical performance due to the merits of complementary multi-composition and unique 3D network structure with multi-level "superhighways". Furthermore, the NiCoMnS//AC device fabricated with NiCoMnS/NF cathode and activated carbon (AC) anode delivered an excellent specific charge and exceptional energy density. This work offers a reference for designing the structure of electrode materials.

Enhanced electrochemical performance of the cobalt chloride carbonate hydroxide hydrate via micromorphology and phase transformation

Micromorphology and conductivity are two vital factors for the practical capacitance of the electrode materials for supercapacitors. In this work, a novel two-step electrochemical activation method involving a cyclic voltammetry (CV) treatment within 0-0.7 V followed by a CV treatment within -1.2-0 V is explored to induce the micromorphology and phase transformation of the cobalt chloride carbonate hydroxide hydrate (CCCH) nanoneedle arrays. The first-step activation transforms the CCCH to Co(OH)₂ and then the reversible transformation between Co(OH)₂ and CoOOH generates plenty of pores in the sample, thereby increasing the specific capacitance from 0.54 to 1.74 F cm^-2 at the current density of 10 mA cm^-2. The second-step activation inducing the reversible transformation between Co(OH)₂ and Co not only endows the final sample with a nanosheets-assembled fasciculate structure but also decreases the internal resistance via generating Co⁰ in the final sample (CCCH-P75N50). Consequently, the CCCH-P75N50 shows a high specific capacitance of 3.83 F cm^-2 at the current density of 10 mA cm^-2. Besides, the aqueous asymmetric supercapacitor assembled with CCCH-P75N50 and commercial conductive carbon cloth (CC) delivers a high energy density of 2.75 mWh cm^-3 at a power density of 37.5 mW cm^-3. This work provides a novel, facile and promising method to optimize the micromorphology and conductivity of Co-based electrodes.

Construction of NiCoZnS materials with controllable morphology for high-performance supercapacitors

A facile two-step hydrothermal approach with post-sulfurization treatment was put forward to construct the mixed transition metal sulfide (NiCoZnS) with a high electrochemical performance. The different morphologies of NiCoZnS materials were successfully fabricated by adjusted the Ni/Co molar ratio of the NiCoZn(OH)F precursor. Moreover, thein situphase transformation from the NiCoZn(OH)F phase to Zn_0.76Co_0.24S and NiCo₂S₄phases and lattice defects via the S^2-ion-exchange were determined by x-ray diffractometer, transmission electron microscopy and x-ray photoelectron spectroscopy techniques, which improved electric conductivity and interfacial active sites of the NiCoZnS, and so promoted the reaction kinetics. Significantly, the urchin-like NiCoZnS_1/1prepared at the Ni/Co molar ratio of 1.0 exhibited promising electrochemical performances with high capacitance and excellent cycling stability. Furthermore, the asymmetric device (NiCoZnS//AC) using NiCoZnS_1/1as the positive electrode had excellent supercapacitor performances with an energy density of 57.8 Wh·kg^-1at a power density of 750 W·kg^-1as well as a long cycle life (79.2% capacity retention after 10 000 cycles), indicating the potential application in high-performance supercapacitors.

Nickel hydroxide/sulfide hybrids: halide ion controlled synthesis, structural characteristics, and electrochemical performance

Focusing on the synthesis of nickel-based materials (such as nickel sulfides, nickel hydroxides, and nickel oxides) is an urgent need in the fields of batteries, supercapacitors, and catalysis. However, their controlled synthesis still remains a great challenge because of the inadequate understanding of the control factor of their synthesis. A two-step solvo-/hydrothermal process with halide ion embedding/releasing was proposed to understand the effect of the halide ions on the synthesis and sulfidation of nickel hydroxy-halides. We find that the halide ions determine the formation, growth, and evolution of nickel hydroxy halides and promote them to form unique architectures and morphologies, leading to obvious differences in structural characteristics, including conductivity and electrochemical activity. Because of the presence of halide ions, a series of hybrids with multiple interfaces, which consist of hydroxides and sulfides and have various morphologies, such as flower-like balls, solid balls, porous balls, schistose, and thorny balls, with capacities ranging from 100.7 to 261.2 mA h g^-1, can be easily obtained. It is fully demonstrated that the halide anion plays a core role in the synthesis process of nickel-based materials, and this finding will provide more chances for controllably synthesizing high-activity electrode materials.

Fabrication of Nanoflower-like MCoP (M = Fe and Ni) Composites for High-Performance Supercapacitors

Elaborating the development of functional materials with excellent performance for supercapacitors is important in energy storage devices. In the present study, nanoflower-like MCoP (M = Ni and Fe) composites were successfully fabricated on Ni foam (denoted as NF@MCoP) by a cost-effective hydrothermal and low-temperature phosphating method. Simultaneously, the unique three-dimensional structure, nanoflower morphology, and the conductive substrate provide a favorable large electroactive area, shorter electron transfer distance, and rapid electron conductivity. The as-synthesized nanoflower-like MCoP composites exhibit outstanding energy density, power density, and long-term cycling stability. These results show that the developed electrode materials with excellent performance have great application prospects in the field of supercapacitor applications.

High-sensitive sensor for the simultaneous determination of phenolics based on multi-walled carbon nanotube/NiCoAl hydrotalcite electrode material

The ternary NiCoAl hydrotalcite (NiCoAl-LDH) was combined with carboxylic multi-walled carbon nanotube (MWCNT) to fabricate a novel electrochemical sensor for simultaneously determining the co-existing trace phenolic substances. The morphology, structure, and electrochemical behavior of the as-prepared materials were characterized by various techniques. Benefitting from the great conductivity of MWCNT and high electrocatalytic activity of NiCoAl-LDH for phenolic substances, the advanced MWCNT/NiCoAl-LDH sensor presented a fast response, high sensitivity, excellent stability, and satisfactory replicability. The sensor offered good linear responses in the ranges1.50~600 μM to hydroquinone (HQ), 5.00~1.03 × 10³ μM to catechol (CC), and 6.00 × 10^-2~250 μM to bisphenol A (BPA). The detection limits of HQ, CC, and BPA were 0.4, 0.8, and 6. × 10^-3 μM (S/N = 3), respectively. In environmental water, the sensor achieved satisfactory recoveries for the simultaneous detection of HQ (98.6~101%), CC (98.0~101%), and BPA (97.5~101%), with relative standard deviations less than 4.4%.

Controllable architecture of the NiCoZnS@NiCoFe layered double hydroxide coral-like structure for high-performance supercapacitors

The rational design of the morphological structure of electrode materials is considered as an important strategy to obtain high-performance supercapacitors. So, NiCoZnS materials with different Ni/Co/Zn molar ratios on Ni foam (NF) were synthesized, in which the Ni/Co/Zn molar ratio plays a key role in the morphological structure and electrochemical performances. Furthermore, the pre-prepared NiCoZnS materials act as substrates to guide the self-assembling of NiCoFe layered double hydroxide (LDH) nanosheets on the substrate surface to form core-shell electrode materials (NiCoZnS@NiCoFe-LDH) with a 3D mesoporous hierarchical network structure for further improving electrochemical performances. The unique interconnected coral-like NiCoZnS₁@NiCoFe-LDH with a large specific surface area (93.1 m² g^-1) and high specific capacitance is achieved at the Ni/Co/Zn molar ratio of 1 : 1 : 1. Benefiting from the unique structural feature and respective merits of the NiCoZnS and NiCoFe-LDH, the NiCoZnS₁@NiCoFe-LDH demonstrates an ultrahigh specific capacitance of 1524.0 C g^-1 (3386.7 F g^-1) at 1.0 A g^-1 and excellent 95.0% capacitance retention at 10 A g^-1 after 5000 cycles. As for practical application, the assembled NiCoZnS₁@NiCoFe-LDH//AC delivers a favorable energy density of 66.25 W h kg^-1 at 1500 W kg^-1 and a long-term cycling lifetime (86.04% retention at 5.0 A g^-1 after 10 000 cycles), which suggests promising potential in energy storage and conversion.

Sulfur and phosphorus co-doped nickel-cobalt layered double hydroxides for enhancing electrochemical reactivity and supercapacitor performance

Layered double hydroxides (LDHs) have drawn significant interest as emerging active materials for advanced energy storage devices; however, their low electric and ionic conductivity limit their applications. In this study, we report sulfur (S) and phosphorus (P) co-doped NiCo LDH nanoarrays prepared via a facile phosphor-sulfurization process to impart diverse co-doping effects. Combining the benefits of their unique hierarchical structure and reduced charge transfer resistance, the S and P co-doped NiCo LDH (NiCo LDH-SP) nanoarrays realize faster and more efficient redox reactions and achieve enhanced surface reactivity, thereby resulting in a performance superior to that of pristine NiCo LDH. Therefore, a NiCo LDH-SP shows an ultra-high specific capacitance of 3844.8 F g-1 at a current density of 3 A g-1 and maintains a specific capacitance of 2538.8 F g-1 at a high current density of 20 A g-1. Additionally, an asymmetric supercapacitor, assembled with the NiCo LDH-SP as the cathode and activated carbon (AC) as the anode (NiCo LDH-SP//AC), shows a high energy density of 74.5 W h kg-1 at a power density of 0.8 kW kg-1 and outstanding cycling stability, thereby retaining ∼81.3% of its initial specific capacitance after 5000 cycles. This study presents a facile and promising strategy for developing LDH-based electrode materials with excellent electrochemical performance for advanced energy storage applications.