Electron-Spin Regulation Driving Heterointerface Electron Distribution and Phase Transition toward Ultrafast and Durable Sodium Storage.

Phase engineering is an effective strategy for modulating the electronic structure and electron transfer mobility of cobalt selenide (CoSe2) with remarkable sodium storage. Nevertheless, it remains challenging to improve fast-charging and cycling performance. Herein, a heterointerface coupling induces phase transformation from cubic CoSe2 to orthorhombic CoSe2 accompanied by the formation of MoSe2 to construct a CoSe2/MoSe2 heterostructure decorated with N-doped carbon layer on a 3D graphene foam (CoSe2/MoSe2@NC/GF). The incorporated Mo cations in the bridged o-CoSe2/MoSe2 not only act an electron donor to regulate charge-spin configurations with more active electronic states but also trigger the upshift of d/p band centers and a decreased ∆d-p band center gap, which greatly enhances ion adsorption capability and lowers the ion diffusion barrier. As expected, the CoSe2/MoSe2@NC/GF anode demonstrates a high-rate capability of 447 mAh g-1 at 2 A g-1 and an excellent cyclability of 298 mAh g-1 at 1 A g-1 over 1000 cycles. The work deepens the understanding of the elaborate construction of heterostructured electrodes for high-performance SIBs.

Spherical Templating of CoSe2 Nanoparticle-Decorated MXenes for Lithium-Sulfur Batteries.

Two-dimensional MXenes produce competitive performances when incorporated into lithium-sulfur batteries (LSBs), solving key problems such as the poor electronic conductivity of sulfur and dissolution of its polysulfide intermediates. However, MXene nanosheets are known to easily aggregate and restack during electrode fabrication, filtration, or water removal, limiting their practical applicability. Furthermore, in complex electrocatalytic reactions like the multistep sulfur reduction process in LSBs, MXene alone is insufficient to ensure an optimal reaction pathway. In this work, we demonstrate for the first time a loose templating of sulfur spheres using Ti3C2Tx MXene nanosheets decorated with polymorphic CoSe2 nanoparticles. This work shows that the templating of sulfur spheres using nanoparticle-decorated MXene nanosheets can prevent nanosheet aggregation and exert a strong electrocatalytic effect, thereby enabling improved reaction kinetics and battery performance. The S@MXene-CoSe2 cathode demonstrated a long cycle life of 1000 cycles and a low capacity decay rate of 0.06% per cycle in LSBs.

Carbon-Encapsulated Ni3 Se4 /CoSe2 Heterostructured Nanospheres: Sodium/Potassium-Ion Storage Anode with Prominent Electrochemical Properties.

Heterogeneous structures are used as energy storage devices because of their ability to accelerate charge transfer, which greatly contributes to the rate capability of devices. However, the construction of heterostructures with conspicuous electrochemical properties remains a huge challenge. In this study, a design of heterostructured Ni3 Se4 /CoSe2 nanospheres encapsulated by a carbon shell (Ni3 Se4 /CoSe2 @C) synthesized through facile hydrothermal and annealing methods is presented. The Ni3 Se4 /CoSe2 @C exhibits excellent cyclic performance with a capacity of 420 mA h g-1 at 0.5 A g-1 after 100 cycles for Na-storage and 330.1 mA h g-1 at 0.1 A g-1 after 200 cycles for K-storage. The excellent cyclic performance can be attributed to the carbon coating that maintains the structural stability and enhances electrical conductivity, and significantly, the heterostructures that promote ion/electron transport. The sodium storage mechanism of the Ni3 Se4 /CoSe2 @C is revealed by ex situ X-ray powder diffraction, ex situ high-resolution transmission electron microscopy, and in situ electrochemical impedance spectra analyses. The first principles density functional theory calculation is performed to prove that the heterostructure on the Ni3 Se4 /CoSe2 interface can induce an electric field and thus improve the electrochemical reaction kinetics. This study provides an effective approach for constructing heterostructured composites for high-performance alkaline batteries.

Catalytically Active CoSe2 Supported on Nitrogen-Doped Three Dimensional Porous Carbon as a Cathode for Highly Stable Lithium-Sulfur Battery.

Lithium-sulfur batteries are promising secondary energy storage devices that are mainly limited by its unsatisfactory cyclability owing to inefficient reversible conversion of sulfur and lithium sulfide on the cathode during the discharge/charging process. In this study, nitrogen-doped three-dimensional porous carbon material loaded with CoSe2 nanoparticles (CoSe2 -PNC) is developed as a cathode for lithium-sulfur battery. A combination of CoSe2 and nitrogen-doped porous carbon can efficiently improve the cathode activity and its conductivity, resulting in enhanced redox kinetics of the charge/discharge process. The obtained electrode exhibits a high discharge specific capacity of 1139.6 mAh g-1 at a current density of 0.2 C. After 100 cycles, its capacity remained at 865.7 mAh g-1 thus corresponding to a capacity retention of 75.97 %. In a long-term cycling test, discharge specific capacity of 546.7 mAh g-1 was observed after 300 cycles performed at a current density of 1 C.

Three-dimensional graphene encapsulated hollow CoSe2-SnSe2nanoboxes for high performance asymmetric supercapacitors.

Construction of metal selenides with a large specific surface area and a hollow structure is one of the effective methods to improve the electrochemical performance of supercapacitors. However, the nano-material easily agglomerates due to the lack of support, resulting in the loss of electrochemical performance. Herein, we successfully design a three-dimensional graphene (3DG) encapsulation-protected hollow nanoboxes (CoSe2-SnSe2) composite aerogel (3DG/CoSe2-SnSe2) via a co-precipitation method coupled with self-assembly route, followed by a high temperature selenidation strategy. The obtained aerogel possesses porous 3DG conductive network, large specific surface area and plenty of reactive active sites. It could be used as a flexible and binder-free electrode after a facile mechanical compression process, which provided a high specific capacitance of 460 F g-1at 0.5 A g-1, good rate capability of 212.7 F g-1at 10 A g-1The capacitance retention rate is 80% at 2 A g-1after 5000 cycles due to the fast electron/ion transfer and electrolyte diffusion. With the as-prepared 3DG/CoSe2-SnSe2as positive electrodes and the AC (activated carbon) as negative electrodes, an asymmetric supercapacitor (3DG/CoSe2-SnSe2//AC) was fabricated, which delivered a high specific capacity of 38 F g-1at 1 A g-1and an energy density of 11.89 Wh kg-1at 749.9 W kg-1, as well as excellent cycle stability. This work provides a new method for preparing electrode material.

Salt-Templated Nanoarchitectonics of CoSe2-NC Nanosheets as an Efficient Bifunctional Oxygen Electrocatalyst for Water Splitting.

Recently, the extensive research of efficient bifunctional electrocatalysts (oxygen evolution reaction (OER) and hydrogen evolution reaction (HER)) on water splitting has drawn increasing attention. Herein, a salt-template strategy is prepared to synthesize nitrogen-doped carbon nanosheets encapsulated with dispersed CoSe2 nanoparticles (CoSe2-NC NSs), while the thickness of CoSe2-NC NSs is only about 3.6 nm. Profiting from the ultrathin morphology, large surface area, and promising electrical conductivity, the CoSe2-NC NSs exhibited excellent electrocatalytic of 10 mA·cm-2 current density at small overpotentials of 247 mV for OER and 75 mV for HER. Not only does the nitrogen-doped carbon matrix effectively avoid self-aggregation of CoSe2 nanoparticles, but it also prevents the corrosion of CoSe2 from electrolytes and shows favorable durability after long-term stability tests. Furthermore, an overall water-splitting system delivers a current density of 10 mA·cm-2 at a voltage of 1.54 V with resultants being both the cathode and anode catalyst in alkaline solutions. This work provides a new way to synthesize efficient and nonprecious bifunctional electrocatalysts for water splitting.

Cobalt Selenide Hollow Polyhedron Encapsulated in Graphene for High-Performance Lithium/Sodium Storage.

Owing to the high specific capacities, high electrochemical activity, and various electronic properties, transition metal selenides are considered as promising anodes for lithium- and sodium-ion storage. However, poor electronic conductivity and huge volume expansion during cycling are still responsible for their restricted electrochemical performance. Herein, CoSe hollow polyhedron anchoring onto graphene (CoSe/G) is synthesized by self-assembly and subsequent selenization. In CoSe/G composites, the CoSe nanoparticles, obtained by in situ selenization of metal-organic frameworks (MOFs) in high temperature, are distributed among graphene sheets, realizing N element doping, developing robust heterostructures with a chemical bond. The unique architecture ensures the cohesion of the structure and endorses the reaction kinetics for metal ions, identified by in situ and ex situ testing techniques, and kinetics analysis. Thus, the CoSe/G anodes achieve excellent cycling performance (1259 mAh g-1 at 0.1 A g-1 after 300 cycles for lithium storage; 214 mAh g-1 at 2 A g-1 after 600 cycles for sodium storage) and rate capability (732 mAh g-1 at 5 A g-1 for lithium storage; 290 mAh g-1 at 5 A g-1 for sodium storage). The improved electrochemical performance for alkali-ion storage provides new insights for the construction of MOFs derivatives toward high-performance storage devices.

Nitrogen-Doped Cobalt Diselenide with Cubic Phase Maintained for Enhanced Alkaline Hydrogen Evolution.

The introduction of heteroatoms is one of the most important ways to modulate the intrinsic electronic structure of electrocatalysts to improve their catalytic activity. However, for transition metal chalcogenides with highly symmetric crystal structure (HS-TMC), the introduction of heteroatoms, especially those with large atomic radius, often induces large lattice distortion and vacancy defects, which may lead to structural phase transition of doped materials or structural phase reconstruction during the catalytic reaction. Such unpredictable situations will make it difficult to explore the connection between the intrinsic electronic structure of doped catalysts and catalytic activity. Herein, taking thermodynamically stable cubic CoSe2 phase as an example, we demonstrate that nitrogen incorporation can effectively regulate the intrinsic electronic structure of HS-TMC with structural phase stability and thus promote its electrocatalytic activity for the hydrogen evolution activity (HER). In contrast, the introduction of phosphorus can lead to structural phase transition from cubic CoSe2 to orthorhombic phase, and the structural phase of phosphorus-doped CoSe2 is unstable for HER.

Coupled Vacancy Pairs in Ni-Doped CoSe for Improved Electrocatalytic Hydrogen Production Through Topochemical Deintercalation.

Vacancy engineering plays vital role in the design of high-performance electrocatalysts. Here, we introduced coupled cation-vacancy pairs in Ni-doped CoSe to achieve boosted hydrogen evolution reaction (HER) activity through a facile topochemical intercalation approach. Adjacent Co vacancy pairs and heteroatom Ni doping contribute together for the upshift of the Se 4pz orbital, which induces larger overlap between the Se 4p and H 1s orbitals. As a result, the free energy of H adsorption can be lowered significantly. With an advanced HER activity of 185.7 mV at 10 mA cm-2 , this work provides new direction and guidance for the design of novel electrocatalysts.

Rational Construction of Hollow Core-Branch CoSe2 Nanoarrays for High-Performance Asymmetric Supercapacitor and Efficient Oxygen Evolution.

Metal selenides have great potential for electrochemical energy storage, but are relatively scarce investigated. Herein, a novel hollow core-branch CoSe2 nanoarray on carbon cloth is designed by a facile selenization reaction of predesigned CoO nanocones. And the electrochemical reaction mechanism of CoSe2 in supercapacitor is studied in detail for the first time. Compared with CoO, the hollow core-branch CoSe2 has both larger specific surface area and higher electrical conductivity. When tested as a supercapacitor positive electrode, the CoSe2 delivers a high specific capacitance of 759.5 F g-1 at 1 mA cm-2 , which is much larger than that of CoO nanocones (319.5 F g-1 ). In addition, the CoSe2 electrode exhibits excellent cycling stability in that a capacitance retention of 94.5% can be maintained after 5000 charge-discharge cycles at 5 mA cm-2 . An asymmetric supercapacitor using the CoSe2 as cathode and an N-doped carbon nanowall as anode is further assembled, which show a high energy density of 32.2 Wh kg-1 at a power density of 1914.7 W kg-1 , and maintains 24.9 Wh kg-1 when power density increased to 7354.8 W kg-1 . Moreover, the CoSe2 electrode also exhibits better oxygen evolution reaction activity than that of CoO.

Plasma-Triggered Synergy of Exfoliation, Phase Transformation, and Surface Engineering in Cobalt Diselenide for Enhanced Water Oxidation.

Various strategies, such as increasing active site numbers and structural and surface engineering, have been used to improve the oxygen evolution reaction (OER) performance of transition-metal dichalcogenides. However, it is challenging to combine these strategies in one system to realize the full catalytic potential. Now, an Ar/O2 plasma method is used to simultaneously induce exfoliation, surface reorganization (formation of an oxidative layer with rich oxygen vacancies), and phase transformation (cubic-to-orthorhombic) on CoSe2 to generate an exceptionally outstanding OER electrocatalysts. The as-made samples require an overpotential of only 251 mV at 10 mA cm-2 , outperforming commercial RuO2 and most reported OER catalysts. The striking catalytic activity originates from the optimized chemical and electronic environment. This work provides valuable insights into the design of promising OER electrocatalysts with high natural abundance via multilevel structural modulation.

Unusual Formation of CoSe@carbon Nanoboxes, which have an Inhomogeneous Shell, for Efficient Lithium Storage.

Hybrid hollow nanostructures with tailored shell architectures are attractive for electrochemical energy storage applications. Starting with metal-organic frameworks (MOFs), we demonstrate a facile formation of hybrid nanoboxes with complex shell architecture where a CoSe-enriched inner shell is intimately confined within a carbon-enriched outer shell (denoted as CoSe@carbon nanoboxes). The synthesis is realized through manipulation of the template-engaged reaction between Co-based zeolitic imidazolate framework (ZIF-67) nanocubes and Se powder at elevated temperatures. By virtue of the structural and compositional features, these unique CoSe@carbon nanoboxes manifest excellent lithium-storage performance in terms of high specific capacity, exceptional rate capability, excellent cycling stability, and high initial Coulombic efficiency.

Size-controlled synthesis of La and chitosan doped cobalt selenide nanostructures for catalytic and antibacterial activity with molecular docking analysis.

Co-precipitation method was adopted to synthesize ternary heterostructure catalysts La/CS-CoSe NSs (lanthanum/chitosan­cobalt selenide nanostructures) without the use of a surfactant. During synthesis, a fixed amount (3 wt%) of CS was doped with 2 and 4 wt% La to control the growth, recombination rate and stability of CoSe NSs. The doped samples served to enhance the surface area, porosity and active sites for catalytic degradation of rhodamine B dye and antibacterial potential against Staphylococcus aureus (S. aureus). Additionally, the synthesized catalysts were examined for morphological, structural and optical characteristics to assess the influence of dopants to CoSe. XRD spectra verified the hexagonal and cubic structure of CoSe, whereas the porosity of the undoped sample (CoSe) increased from 45 to 60 % upon incorporation of dopants (La and Cs). Among the samples analyzed during this study, 4 % La/CS-CoSe exhibited significant bactericidal behavior as well as the highest catalytic reduction of rhodamine B dye in a neutral environment. Molecular docking analysis was employed to elucidate the underlying mechanism behind the bactericidal activity exhibited by CS-CoSe and La/CS-CoSe NSs against DHFRS. aureus and DNA gyraseS. aureus.

Manipulating Orbital Hybridization of CoSe2 by S Doping for the Highly Active Catalytic Effect of Lithium-Sulfur Batteries.

In recent years, various transition metal compounds have been extensively studied to deal with the problems of slow reaction kinetics and the shuttle effect of lithium-sulfur (Li-S) batteries. Nevertheless, their catalytic performance still needs to be further improved by enhancing intrinsic catalytic activity and enriching active sites. Doping is an effective means to boost the catalytic performance through adjusting the electron structure of the catalysts. Herein, the electron structure of CoSe2 is adjusted by doping P, S with different p electron numbers and electronegativity. After S doping (S-CoSe2), the content of Co2+ increases, and charge is redistributed. Furthermore, more electrons are transferred between Li2S4/Li2S and S-CoSe2, and optimal Co-S bonds are formed between them with optimized d-p orbital hybridization, making the bonds of Li2S4/Li2S the longest and easy to break and decompose. Consequently, the Li-S batteries with the S-CoSe2-modified separator achieve improved rate performance and cycling performance, benefiting from the better bidirectional catalytic activity. This work will provide reference for the selection of the anion doping element to enhance the catalytic effect of transition metal compounds.

Exo â ¢-assisted amplification signal strategy synergized with Au@Pt NFs/CoSe2 for sensitive detection of enrofloxacin.

Overuse of enrofloxacin (ENR) has posed a potential threat to ecosystems and public health, so it is critical to sensitive and accurate determination of ENR residues. In this work, a novel ultra-sensitive and specific electrochemical aptasensor was fabricated based on the cobalt diselenide loaded gold and platinum nanoflowers (Au@Pt NFs/ CoSe2) and Exonuclease III (Exo III)-assisted cycle amplification strategy for the detection of ENR. Au@Pt NFs/ CoSe2 nanosheets as the substrate material, with large surface area, accelerate electron transfer and attach more DNA probes on the electrode substrate, have effectively enhanced the electrochemical performance of the electrode. With the existence of Enrofloxacin (ENR), the aptamer recognizes and binds to ENR, thus the signal probe cDNA was released and immobilized onto the electrode surface to hybridized with methylene blue (MB) labelled DNA (MB-DNA), thereby triggering the Exo III-assisted cycle for further signal amplification. As expected, the prepared aptasensor demonstrated excellent sensitivity and selectivity, with a wide linear range from 5.0 × 10-6 ng/mL to 1.0 × 10-2 ng/mL for ENR, a low detection limit of 1.59 × 10-6 ng/mL. Consequently, this strategy provided a promising avenue for ultrasensitive and accurate detection of ENR in milk samples.

Interfacial coupling of Ce-CoSe2 nanoneedle arrays with MXene for efficient overall water splitting.

Designing highly effective, low-cost bifunctional electrocatalysts without noble metals for overall water splitting remains a significant challenge. In this work, interfacial coupling of Ce-doped CoSe2 nanoneedle arrays with MXene (Ce-CoSe2/MXene) is developed via the facile hydrothermal and selenization methods. The extensive specific surface area and favorable hydrophilicity of Ti3AlC2, combined with the optimized electronic structure and abundant active sites from Ce-doping and selenization, contribute to the exceptional bifunctional electrocatalytic performance of the Ce-CoSe2/MXene electrode. Specifically, this heterostructure achieves a low hydrogen evolution reaction (HER) overpotential of 34 mV at 10 mA cm-2, an oxygen evolution reaction (OER) overpotential of 279 mV at 100 mA cm-2, and an overall water splitting (OWS) potential as low as 1.45 V at 10 mA cm-2. In-situ Raman spectroscopy reveals that surface reconstruction would improve catalytic activity and stability. Theoretical calculations indicate that the Ce-CoSe2/MXene can improve the adsorption of intermediates and facilitate HER/OER process by lowering the kinetic barrier, thereby enhancing electrocatalytic activity. This research marks a substantial advancement in the development of low-cost, efficient electrocatalysts for overall water splitting.

Solvent-free synthesis of foam board-like CoSe2 alloy to selectively generate singlet oxygen via peroxymonosulfate activation for sulfadiazine degradation.

Singlet oxygen (1O2) is a highly effective reactive species in selectively oxidizing organic pollutants. However, it is still challenging to rationally design robust catalysts for the selective generation of 1O2. Herein, the coordination and engineering architecture of the foam board-like CoSe2 alloy were facilely constructed through a green solvent-free method and displayed almost 100% 1O2 production selectivity. The CoSe2 alloy showed excellent catalytic ability for the efficient and fast removal of organic pollutants via peroxymonosulfate (PMS) activation compared with previously reported cobalt-based catalysts. The CoSe2/PMS system exhibited strong resistance for a broad pH range (3.0-11.0) and various coexisting inorganic ions owing to the advantage of the strong bonding of Co-Se in CoSe2 alloy. Mechanism studies revealed that 1O2 was the only reactive oxygen species in the CoSe2/PMS system. Theoretical calculations demonstrated that Co was the dominant adsorption site for PMS in CoSe2, and the production pathway of 1O2 was PMS* â†’ *OH → *O → 1O2. In addition, it was proved that *OH and *O served as the rate-determining steps for the formation of 1O2 by PMS activation on CoSe2 alloy. These findings provide a rational strategy for preparing a series of low-cost transition metal-based alloy catalysts for PMS activation to achieve high-efficiency 1O2 production in the elimination of organic pollutants.

Modulation of Phase Transition in Cobalt Selenide with Simultaneous Construction of Heterojunctions for Highly-Efficient Oxygen Electrocatalysis in Zinc-Air Battery.

Phase transformation of cobalt selenide (CoSe2 ) can effectively modulate its intrinsic electrocatalytic activity. However, enhancing electroconductivity and catalytic activity/stability of CoSe2 still remains challenging. Heterostructure engineering may be feasible to optimize interfacial properties to promote the kinetics of oxygen electrocatalysis on a CoSe2 -based catalyst. Herein, a heterostructure consisting of CoSe2 and cobalt nitride (CoN) embedded in a hollow carbon cage is designed via a simultaneous phase/interface engineering strategy. Notably, the phase transition of orthorhombic-CoSe2 to cubic-CoSe2 (c-CoSe2 ) accompanied by in situ CoN formation is realized to build the c-CoSe2 /CoN heterointerface, which exhibits excellent/highly stable activities for oxygen reduction/evolution reactions (ORR/OER). Notably, heterostructure can modulate the local coordination environment and increase Co-Se/N bond lengths. Theoretical calculations show that Co-site (c-CoSe2 ) with an electronic state near Fermi energy level is the main active site for ORR/OER.Energetical tailoring of the d-orbital electronic structure of the Co atom of c-CoSe2 in heterostructure by in situ CoN incorporation lowers thermodynamic barriers for ORR/OER. Attractively, a zinc-air battery with a c-CoSe2 -CoN cathode displays excellent cycling stability (250 h) and charge/discharge voltage loss (0.953/0.96 V). It highlights that heterointerface engineering provides an option for modulating the bifunctional activity of metal selenides with controlled phase transformation.

Hollow CoSe2-ZnSe microspheres inserted in reduced graphene oxide serving as advanced anodes for sodium ion batteries.

Transition metal selenides are promising anode candidates for sodium ion batteries (SIBs) because of their higher theoretical capacity and conductivity than metal oxides. However, the disadvantages of severe capacity degradation and poor magnification performance greatly limit their commercial applications. Herein, we have developed a new hollow bimetallic selenides (CoSe2-ZnSe)@reduced graphene oxide (rGO) composite with abundant heterointerfaces. The rGO could not only alleviate the volume variations of hollow CoSe2-ZnSe microspheres during cycling, but also improve the conductivity of composite. The presence of the heterointerfaces could help to accelerate ionic diffusion kinetics and improve electron transfer, resulting in the improved sodium storage performance. As an advanced anode for SIBs, the CoSe2-ZnSe@rGO exhibits an enhanced initial coulombic efficiency of 75.1% (65.2% of CoSe2@rGO), extraordinary rate capability, and outstanding cycling stability (540.3 mAh/g at 0.2 A/g after 150 cycles, and 395.2 mAh/g at 1 A/g after 600 cycles). The electrochemical mechanism was also studied by kinetic analysis, showing that the charging/discharging process of CoSe2-ZnSe@rGO is mostly related to a capacitive-controlled behavior.

Anchoring Active Li Metal in Oriented Channel by In Situ Formed Nucleation Sites Enabling Durable Lithium-Metal Batteries.

Lithium metal is the ultimate anode material for pursuing the increased energy density of rechargeable batteries. However, fatal dendrites growth and huge volume change seriously hinder the practical application of lithium metal batteries (LMBs). In this work, a lithium host that preinstalled CoSe nanoparticles on vertical carbon vascular tissues (VCVT/CoSe) is designed and fabricated to resolve these issues, which provides sufficient Li plating space with a robust framework, enabling dendrite-free Li deposition. Their inherent N sites coupled with the in situ formed lithiophilic Co sites loaded at the interface of VCVT not only anchor the initial Li nucleation seeds but also accelerate the Li+ transport kinetics. Meanwhile, the Li2Se originated from the CoSe conversion contributes to constructing a stable solid-electrolyte interphase with high ionic conductivity. This optimized Li/VCVT/CoSe composite anode exhibits a prominent long-term cycling stability over 3000 h with a high areal capacity of 10 mAh cm-2. When paired with a commercial nickel-rich LiNi0.83Co0.12Mn0.05O2 cathode, the full-cell presents substantially enhanced cycling performance with 81.7% capacity retention after 300 cycles at 0.2 C. Thus, this work reveals the critical role of guiding Li deposition behavior to maintain homogeneous Li morphology and pave the way to stable LMBs.