Construction of ball-flower like NiS2@MoS2 composite for high performance supercapacitors

Strategies for Advanced Supercapacitors Based on 2D Transition Metal Dichalcogenides: From Material Design to Device Setup

Recently, the development of new materials and devices has become the main research focus in the field of energy. Supercapacitors (SCs) have attracted significant attention due to their high power density, fast charge/discharge rate, and excellent cycling stability. With a lamellar structure, 2D transition metal dichalcogenides (2D TMDs) emerge as electrode materials for SCs. Although many 2D TMDs with excellent energy storage capability have been reported, further optimization of electrode materials and devices is still needed for competitive electrochemical performance. Previous reviews have focused on the performance of 2D TMDs as electrode materials in SCs, especially on their modification. Herein, the effects of element doping, morphology, structure and phase, composite, hybrid configuration, and electrolyte are emphatically discussed on the overall performance of 2D TMDs-based SCs from the perspective of device optimization. Finally, the opportunities and challenges of 2D TMDs-based SCs in the field are highlighted, and personal perspectives on methods and ideas for high-performance energy storage devices are provided.

Sodium titanium phosphate nanocube decorated on tablet-like carbon for robust sodium storage performance at low temperature

Sodium-ion batteries, featuring resource abundance and similar working mechanisms to lithium-ion batteries, have gained extensive interest in both scientific exploration and industrial applications. However, the extremely sluggish reaction kinetics of charge carrier (Na+) at subzero temperatures significantly reduces their specific capacities and cycling life. Herein, this study presents a novel hybrid structure with sodium titanium phosphate (NaTi2(PO4)3, NTP) nanocube in-situ decorated on tablet-like carbon (NTP/C), which manifests superior sodium storage performances at low temperatures. At even -25 °C, a stable cycling with a specific capacity of 94.3 mAh/g can still be maintained after 200 cycles at 0.5 A/g, delivering a high capacity retention of 91.5 % compared with that at room temperature, along with an excellent rate capability. Generally, the superionic conductor structure, flat voltage plateaus, as well as the conductive carbonaceous framework can efficiently facilitate the charge transfer, accelerate the diffusion of Na+, and decrease the electrochemical polarization. Moreover, further investigations on diffusion kinetics, solid electrolyte interface layer, and the interaction between NTP and carbonaceous skeleton reveal its high Na+ diffusion coefficient, robust solid electrolyte interface, and strong electronic interaction, thus contributing to the superior capacity retentions at subzero temperatures.

Tremella-like 2D Nickel-Copper Disulfide with Ultrahigh Capacity and Cyclic Retention for Hybrid Supercapacitors

Two-dimensional (2D) disulfides possess unique physical and chemical properties and are widely used in electronic and photoelectric devices. Tuning the composition and optimizing the structure of the disulfides are feasible approaches to designing target sulfides for hybrid supercapacitors. This work synthesizes the tremella-like nanosheet-connected (Cu_xNi_1-x)S₂ via solvothermal and sulfur-vapor vulcanization. The 2D (Cu_xNi_1-x)S₂ electrode performs a high reversible capacity (526.0 mA h g^-1 at 1 A g^-1), decent capacity retention (75.6%) at 10 A g^-1, and prolonged cyclic retention (94.4% over 15,000 cycles), which is higher than that of (Cu_xNi_1-x)O and monometallic sulfides of NiS₂ and CuS. The elevated electrochemical properties of (Cu_xNi_1-x)S₂ are attributed to the optimized composition with increased redox reaction, enlarged lattice distance, abundant active sites, and attractive electronic and ionic conductivity. Also, (Cu_xNi_1-x)S₂ and active carbon (AC) are assembled to form a hybrid supercapacitor (HSC). The (Cu_xNi_1-x)S₂//AC HSC demonstrates a maximum specific capacitance of 231.0 F g^-1 at 1 A g^-1 and a high energy density of 82.4 W h kg^-1 at a power density of 1.82 kW kg^-1. Outstanding cyclic retentions of 94.9 and 84.5% after 8000 and 10,000 cycles are also obtained. In conclusion, this result suggests a facile routine for preparing a novel 2D layer material of (Cu_xNi_1-x)S₂ with outstanding specific capacity and cycling performance for hybrid supercapacitors.

Multidefect N-Nb2 O5- x @CNTs Incorporated into Capillary Transport Framework for Li+ /Na+ Storage

As an ion-embedded material with small strain and low transport energy barrier, the limited ion transport rate and conductivity of niobium pentaoxide (Nb₂ O₅ ) are the main factors limiting its application in lithium/sodium storage systems. In this work, the microsphere composites (N-Nb₂ O_{5- x} @CNTs) are prepared by combining Nb₂ O₅ , rich in nitrogen doping and vacancy defects, with carbon nanotubes (CNTs) penetrating the bulk phase. With the capillary effect, CNTs can enable the rapid electrolyte infiltration into the microspheres, thus shorting the Li⁺ /Na⁺ transport path. In addition, CNTs also hinder the direct contact between the electrolyte and Nb₂ O₅ , and inhibit the irreversible reaction. Meanwhile, nitrogen doping and oxygen vacancy defects reduce the energy barrier of Li⁺ /Na⁺ transport, and improve their transport rate, proved by density functional theory. Highly conductive CNTs and unpaired electrons from defects also ameliorate the insulation property of Nb₂ O₅ . Therefore, N-Nb₂ O_{5- x} @CNTs display good electrochemical performance in both Li/Na half-cell and Li/Na hybrid capacitors. Interestingly, kilogram-scale microsphere composites can be produced in laboratory conditions by using industrial grade raw materials, implying its potential for practical application.

Ultrafast and stable ion/electron transport of MnNb2O6 in LIC/SC via interface protection and lattice defects

Interface protection and kinetics optimization could effectively relieve the shortcomings of bimetallic oxides, such as low conductivity, strong hydrophobicity, insufficient ion diffusion rate and metal interatomic instability. In this work, ultrathin amorphous carbon shells and lattice defects (heteroatoms and vacancies) are introduced into the MnNb₂O₆ nanofiber surface to improve the electron/ion kinetic stability, conductivity and electrochemical activity. The ultrathin carbon interface protects unstable lattice with defects, thus restraining the adverse reaction between bimetallic oxides and electrolyte. Especially, ultrathin amorphous carbon layer enhances the stability and uniformity of ion transport as the substitute of solid-liquid ion exchange membrane. Lattice defects (N doping and oxygen vacancy) also enhance the ionic kinetics of the material. MnNb₂O₆ nanofiber, being optimized by interface protection and lattice defects, shows excellent electrochemical performances in Lithium-ion battery and supercapacitor.

Carbon-doped tin disulfide nanoflowers: a heteroatomic doping strategy for improving the electrocatalytic performance of nitrogen reduction to ammonia

In this work, hydrophobic carbon-doped tin disulfide (C-SnS2) was fabricated for the first time and adopted as an advanced catalyst for the eNRR.

Boosting the lithium storage performance by synergistically coupling ultrafine heazlewoodite nanoparticle with N, S co-doped carbon

Transition metal sulfides, as an important class of inorganics, have been shown to be potential high-performance electrode candidates for lithium-ion batteries (LIBs) in account of their high activity towards lithium storage, rich types and diverse structures. Despite these advantages, structure degradation related with volume variations upon electrochemical cycling restricts their further development. In this present study, a unique hybrid structure with ultrafine heazlewoodite nanoparticles (less than 10 nm) in-situ confined in nitrogen and sulfur dual-doped carbon (Ni₃S₂@NSC) was constructed though a facile pyrolysis process, using a novel Ni-based metal chelates as the precursor. Specifically, enhanced structure stability, shortened Li⁺ migration distance and improved reaction dynamics can be obtained simultaneously in the designed structure, thereby allowing to realize high lithium storage performance. Consequently, a remarkable reversible capacity of 955.9 mAh g^-1 (0.1 A g^-1 after 100 cycles) and a superior long-term cycling stability up to 1200 cycles (863.7 mAh g^-1 at 1.0 A g^-1) are obtained. Importantly, the fundamental understanding on the improved lithium storage of Ni₃S₂@NSC based on the synergistic coupling reveals that the combination between Ni₃S₂ and NSC at the hetero-interface through the doped sulfur atoms contributes to the integrity of electrode and improved kinetics.

Strongly coupled Fe-doped NiS2/MoS2 composite for high-efficiency water splitting

We developed a simple method to fabricate a strongly coupled Fe-doped NiS₂/MoS₂ composite by introducing dual confinement effects during the vapor vulcanization of precursors, which involves the controlled release of metal species and the in situ formation of an N-doped carbon layer. The Fe-doped NiS₂/MoS₂ composite exhibited a much-enhanced hydrogen/oxygen evolution reaction performance.

NiAlP@Cobalt substituted nickel carbonate hydroxide heterostructure engineered for enhanced supercapacitor performance

Transitional metal phosphides with high electrical conductivity and superb physicochemical features have been recognized as ideal battery-type electrode materials for outstanding performance supercapacitors. However, their specific capacities and structural stability are needed to be enhanced for large-scale practical applications. To overcome these shortcomings, we fabricated heterostructured NiAlP@cobalt substituted nickel carbonate hydroxide (Co-NiCH) nanosheet arrays by sequential a hydrothermal reaction, a phosphorization treatment, and a second hydrothermal reaction. Profiting from its core-shell porous nanostructure and synergistic effect of NiAlP with high electrical conductivity and Co-NiCH with high redox reactivity, the resultant NiAlP@Co-NiCH electrode delivers a large specific capacity of 825.7C g^-1 at 1 A g^-1, excellent rate capability with 78.9% capacity retention and long lifespan, superior to those of pure NiAlP and Co-NiCH electrodes. Additionally, an aqueous asymmetric supercapacitor device is constructed by NiAlP@Co-NiCH and lotus pollen-derived hierarchical porous carbon, which demonstrates a large energy density of 82.3 Wh kg^-1 at a power density of 739.8 W kg^-1, and wonderful cycle stability with 88.2% capacity retention after 10,000 cycles. This work proposes a feasible strategy on construction of transitional metal phosphide-based heterojunctions for advanced asymmetric supercapacitor devices.

Flexible nickel disulfide nanoparticles-anchored carbon nanofiber hybrid mat as a flexible binder-free cathode for solid-state asymmetric supercapacitors

Nickel disulfide nanoparticles (NiS₂NPs)-anchored carbon nanofibers (NiS₂NPs@CNF) hybrid mats were fabricated via the sequential process of stabilization and carbonization of electrospun polyacrylonitrile-based fibers followed by hydrothermal growth of NiS₂NPs on the porous surface of CNFs. The vertical growth of NiS₂NPs on entire surfaces of porous CNFs appeared in the SEM images of hybrid mat. The hierarchical NiS₂NPs@CNF core-shell hybrid nanofibers with 3D interconnected network architecture can endow continuous channels for easy and rapid ionic diffusion to access the electroactive NiS₂NPs. The conductive and interconnected CNF core could facilitate electron transfer to the NiS₂shell. Moreover, the porous CNF as a buffering matrix can resist volumetric deformation during the long-term charge-discharge process. The NiS₂NPs@CNF electrode can yield high specific capacitance (916.3 F g^-1at 0.5 A g^-1) and reveal excellent cycling performances. The solid-state asymmetric supercapacitor (ASC) was fabricated with NiS₂NPs@CNF mat as a binder-free positive electrode and activated carbon cloth as a negative electrode. As-assembled ASC not only produce high specific capacitance (364.8 F g^-1at 0.5 A g^-1) but also exhibit excellent cycling stability (∼92.8% after 5000 cycles). The ASC delivered a remarkably high energy density of 129.7 Wh kg^-1at a power density of 610 W kg^-1. These encouraging results could make this NiS₂NPs@CNF hybrid mat a good choice of cathode material for the fabrication of flexible solid-state ASC for various flexible/wearable electronics.

Coordination agent-dominated phase control of nickel sulfide for high-performance hybrid supercapacitor

The property of an active material is not only influenced by its morphology and size, but also by its crystal phase. The present phase regulation of nickel sulfide is mainly achieved by controlling the participation of sulfur source in reaction. Thus, new perspectives direct at phase control need to be explored and supplemented. Herein, we proposed a novel coordination agent-dominated phase modulation strategy assisted by a hydrothermal process. It is found that increasing the amount of coordination agent can drove the phase transformation from the initial composite of β-NiS/α-NiS/Ni₃S₄ to β-NiS/α-NiS, and then to pure β-NiS. The mechanism of phase regulation has been proposed, and the general application of this method has been demonstrated. By employing coordination agent, the size of resulted products is reduced, and the morphology is optimized. As a result, all of the pure β-NiS electrodes indicate significantly enhanced specific capacity than the pristine β-NiS/α-NiS/Ni₃S₄ composite. Notably, the sample synthesized with 3 mmol of urea (S11) shows uniform morphology and smallest size, and it gives a highest specific capacity of 223.8 mAh g^-1 at 1 A g^-1, almost 1.5 times of the original sample. The fabricated S11//rGO device delivers a high energy density of 56.6 Wh·kg^-1 at a power density of 407.5 W·kg^-1, and keeps an impressive capacity retention of 84% after 20,000 cycles. This work put forwards a new prospect for controlling the phase and composition of nickel sulfide based on coordination chemistry.

Template-free synthesis of β-NiS ball-in-ball microspheres for a high-performance asymmetrical supercapacitor

While significant advances have been made in the synthesis of core-/multi-shell materials, the synthetic process usually involves a soft/hard template and complicated procedures. In particular, it is extremely difficult to fabricate single-component core-shell structures for nickel sulfides (NSs) with a controlled phase. In this work, we demonstrate a novel facile method to synthesize a single-component β-NiS ball-in-ball microsphere. The ball-in-ball structure is easily obtained by uniquely employing 2-mercaptopropionic acid (2-MPA) as the sulfur source and ethanol as the solvent based on the Ostwald ripening process. In particular, our work demonstrates that the chemical structure of sulfur sources and solvents plays a key role in the formation of the pure β-NiS ball-in-ball structure. When used as an electrode active material, the β-NiS ball-in-ball microspheres exhibit two times stronger specific capacity and three times higher rate performance than NSs produced by a hydrothermal method. The fabricated NS-2//rGO asymmetrical supercapacitor (ASC) displays an energy density of 46.4 W h kg^-1 at a power density of 799.0 W kg^-1 and good cycling performance. Thus, this study provides a new method for controlling the phase and morphology of NSs.

Facile in-situ synthesis of heazlewoodite on nitrogen-doped reduced graphene oxide for enhanced sodium storage

Nickel sulfide based anode materials, featuring rich types, high specific capacities and favorable conversion kinetics, have been proved to be promisingly applied in high-performance sodium-ion batteries (SIBs). Unfortunately, the poor electronic/ionic conductivity, together with the structure change induced degraded capacity upon cycling, restricts their further development. In this work, heazlewoodite nanoparticles decorated on nitrogen doped reduced graphene oxide (Ni₃S₂/NrGO) were fabricated via a facile combined approach with freeze-drying and subsequent in-situ sulfidation. In the obtained hybrid structure, the synergistic effect between Ni₃S₂ and NrGO endows the composite with highly conductive pathways, thus accelerating the charge transfer. Benefitting from the buffering matrix offered by NrGO as well as the tight combination between Ni₃S₂ and NrGO, this novel Ni₃S₂/NrGO demonstrates satisfying sodium storage performance, with a stable reversible capacity of 299.2 mAh g^-1 up to 100 cycles (0.1 A g^-1) and a high initial Coulombic efficiency of 76.8%. Importantly, the rational structure design and synthesis method, as well as the insights on the improved electrochemical performance reported in this work, should be helpful for the development of new-type host materials with high performance for SIBs.

Transition metal dichalcogenide (TMDs) electrodes for supercapacitors: a comprehensive review

As globally, the main focus of the researchers is to develop novel electrode materials that exhibit high energy and power density for efficient performance energy storage devices. This review covers the up-to-date progress achieved in transition metal dichalcogenides (TMDs) (e.g. MoS₂, WS₂, MoSe_2,and WSe₂) as electrode material for supercapacitors (SCs). The TMDs have remarkable properties like large surface area, high electrical conductivity with variable oxidation states. These properties enable the TMDs as the most promising candidates to store electrical energy via hybrid charge storage mechanisms. Consequently, this review article provides a detailed study of TMDs structure, properties, and evolution. The characteristics technique and electrochemical performances of all the efficient TMDs are highlighted meticulously. In brief, the present review article shines a light on the structural and electrochemical properties of TMD electrodes. Furthermore, the latest fabricated TMDs based symmetric/asymmetric SCs have also been reported.

Vanadium-Doped NiS2 Porous Nanosphere with High Selectivity and Stability for Electroreduction of Nitrogen to Ammonia

In comparison with the traditional Harber-Bosch process, the electrocatalytic nitrogen reduction reaction (NRR) with high purity and sustainability became a popular process to satisfy the demand of ammonia. However, the...