Phase-controlled synthesis of cobalt sulfides for lithium ion batteries

Review of Transition Metal Chalcogenides and Halides as Electrode Materials for Thermal Batteries and Secondary Energy Storage Systems

Transition metal chalcogenides and halides (TMCs and TMHs) have been extensively used and reported as electrode materials in diverse primary and secondary batteries. This review summarizes the suitability of TMCs and TMHs as electrode materials focusing on thermal batteries (utilized for defense applications) and energy storage systems like mono- and multivalent rechargeable batteries. The report also identifies the specific physicochemical properties that need to be achieved for the same materials to be employed as cathode materials in thermal batteries and anode materials in monovalent rechargeable systems. For example, thermal stability of the materials plays a crucial role in delivering the performance of the thermal battery system, whereas the electrical conductivity and layered structure of similar materials play a vital role in enhancing the electrochemical performance of the mono- and multivalent rechargeable batteries. It can be summarized that nonlayered CoS2, FeS2, NiS2, and WS2 were found to be ideal as cathode materials for thermal batteries primarily due to their better thermal stability, whereas the layered structures of these materials with a coating of carbon allotrope (CNT, graphene, rGO) were found to be suitable as anode materials for monovalent alkali metal ion rechargeable batteries. On the other hand, vanadium, titanium, molybdenum, tin, and antimony based chalcogenides were found to be suitable as cathode materials for multivalent rechargeable batteries due to the high oxidation state of cathode materials which resists the stronger field produced during the interaction of di- and trivalent ions with the cathode material facilitating higher energy density with minimal structural and volume changes at a high rate of discharge.

Induced Bimetallic Sulfide Growth with Reduced Graphene Oxide for High-Performance Sodium Storage

Metal sulfide has been considered an ideal sodium-ion battery (SIB) anode material based on its high theoretical capacity. Nevertheless, the inevitable volume expansion during charge-discharge processes can lead to unsatisfying electrochemical properties, which limits its further large-scale application. In this contribution, laminated reduced graphene oxide (rGO) successfully induced the growth of SnCoS₄ particles and self-assembled into a nanosheet-structured SnCoS₄@rGO composite through a facile solvothermal procedure. The optimized material can provide abundant active sites and facilitate Na⁺ ion diffusion due to the synergistic interaction between bimetallic sulfides and rGO. As the anode of SIBs, this material maintains a high capacity of 696.05 mAh g^-1 at 100 mA g^-1 after 100 cycles and a high-rate capability of 427.98 mAh g^-1 even at a high current density of 10 A g^-1. Our rational design offers valuable inspiration for high-performance SIB anode materials.

Structural Framework-Guided Universal Design of High-Entropy Compounds for Efficient Energy Catalysis

High-entropy compounds with extraordinary properties due to the synergistic effect of multiple components have exhibited great potential and attracted extensive attention in various fields, including physics, mechanical property analysis, and energy storage. Achieving universal stability and synthesis of high-entropy compounds with a wide range of components and structures continues to be difficult due to the high complexity of multicomponent mixing. Here, we propose a design strategy with high generality for realizing the stability and synthesis of high-entropy compounds that one metal site like the framework in the compound structures with bimetallic sites stabilizes another site to accommodate different elements. Several typical metal compounds with bimetallic sites, including perovskite hydroxides, layered double hydroxide, spinel sulfide, perovskite fluoride, and spinel oxides, have been synthesized into high-entropy compounds. High-entropy perovskite hydroxides (HEPHs) as representative compounds have been synthesized with a highly wide range of components even a septenary component and exhibit great oxygen evolution activity. Our work provides a design platform to develop more high-entropy compound systems with promising development potential for electrocatalysts.

Immobilized Nanomaterials for Environmental Applications

Nanomaterials (NMs) have been extensively used in several environmental applications; however, their widespread dissemination at full scale is hindered by difficulties keeping them active in engineered systems. Thus, several strategies to immobilize NMs for their environmental utilization have been established and are described in the present review, emphasizing their role in the production of renewable energies, the removal of priority pollutants, as well as greenhouse gases, from industrial streams, by both biological and physicochemical processes. The challenges to optimize the application of immobilized NMs and the relevant research topics to consider in future research are also presented to encourage the scientific community to respond to current needs.

Sulfur-Bridged Bonds Boost the Conversion Reaction of the Flexible Self-Supporting MnS@MXene@CNF Anode for High-Rate and Long-Life Lithium-Ion Batteries

Manganese sulfide (MnS) has been found to be a suitable electrode material for lithium-ion batteries (LIBs) owing to its considerable theoretical capacity, high electrochemical activity, and low discharge voltage platform, while its poor electrical conductivity and severe pulverization caused by volume expansion of the material limit its practical application. To improve the rate performance and cycle stability of MnS in LIBs, the structure-control strategy has been used to design and fabricate new anode materials. Herein, the MnS@MXene@CNF (MMC, CNFs means carbon nanofibers) electrode has been prepared by electrospinning and a subsequent high-temperature annealing process. The MMC electrode exhibits excellent cyclic stability with a capacity retention rate close to 100% after 1000 cycles at 1000 mA/g and an improved rate performance with a specific capacity up to 500 mAh/g at a high current density of 5000 mA/g, much higher than the 308 mAh/g of the MnS@CNF (MC) electrode. The elevated electrochemical performance of the MMC electrode not only benefits from the unique structure of MnS nanoparticles evenly dispersed in the well-designed flexible self-supporting three-dimensional (3D) CNF network but, more importantly, also benefits from the formation of sulfur-bridged Mn-S-C bonds at the MnS/MXene interface. The newly formed bonds between MnS and MXene nanosheets can stabilize the structure of MnS near the interfaces and provide a channel for fast charge transfer, which notably increase both the reversibility and the rate of the conversion reaction during the charge/discharge process. This work may pave a new path for designing stable and self-supporting anodes for high-performance LIBs.

Trends in rare earth thiophosphate syntheses: Rb3Ln(PS4)2 (Ln = La, Ce, Pr), Rb3−xNaxLn(PS4)2 (Ln = Ce, Pr; x = 0.50, 0.55), and RbEuPS4 obtained by molten flux crystal growth

Crystal structures of new rubidium rare earth thiophosphates with the formulas Rb₃Ln(PS₄)₂ (Ln = La, Ce, Pr), Rb_3−xNa_xLn(PS₄)₂ (Ln = Ce, Pr; x = 0.50, 0.55), and RbEuPS₄ crystallized out of a molten RbCl flux.

"Soft" Alkali Bromide and Iodide Fluxes for Crystal Growth

In this review we discuss general trends in the use of alkali bromide and iodide (ABI) fluxes for exploratory crystal growth. The ABI fluxes are ionic solution fluxes at moderate to high temperatures, 207 to ~1,300°C, which offer a good degree of flexibility in the selection of the temperature profile and solubility. Although their main use is to dissolve and recrystallize "soft" species such as chalcogenides, many compositions with "hard" anions, including oxides and nitrides, have been obtained from the ABI fluxes, highlighting their unique versatility. ABI fluxes can serve to provide a reaction and crystallization medium for different types of starting materials, mostly the elemental and binary compounds. As the use of alkali halide fluxes creates an excess of the alkali cations, these fluxes are often reactive, incorporating one of its components to the final compositions, although some examples of non-reactive ABI fluxes are known.

A Comprehensive Review of Li-Ion Battery Materials and Their Recycling Techniques

In the context of constant growth in the utilization of the Li-ion batteries, there was a great surge in the quest for electrode materials and predominant usage that lead to the retiring of Li-ion batteries. This review focuses on the recent advances in the anode and cathode materials for the next-generation Li-ion batteries. To achieve higher power and energy demands of Li-ion batteries in future energy storage applications, the selection of the electrode materials plays a crucial role. The electrode materials, such as carbon-based, semiconductor/metal, metal oxides/nitrides/phosphides/sulfides, determine appreciable properties of Li-ion batteries such as greater specific surface area, a minimal distance of diffusion, and higher conductivity. Various classifications of the anode materials such as the intercalation/de- intercalation, alloy/de-alloy, and various conversion materials are illustrated lucidly. Further, the cathode materials, such as nickel-rich LiNixCoyMnzO2 (NCM), were discussed. NCM members such as NCM 333, NCM 523 that enabled to advance for NCM622 and NCM81are reported. The nanostructured materials bridged the gap in the realization of next-generation Li-ion batteries. Li-ion batteries’ electrode nanostructure synthesis, performance, and reaction mechanisms were considered with great concern. The serious effects of Li-ion batteries disposal need to be cut significantly to reduce the detrimental effect on the environment. Hence, the recycling of spent Li-ion batteries has gained much attention in recent years. Various recycling techniques and their effect on the electroactive materials are illustrated. The key areas covered in this review are anode and cathode materials and recent advances along with their recycling techniques. In light of crucial points covered in this review, it constitutes a suitable reference for engineers, researchers, and designers in energy storage applications.

The Progress of Cobalt-Based Anode Materials for Lithium Ion Batteries and Sodium Ion Batteries

Limited by the development of energy storage technology, the utilization ratio of renewable energy is still at a low level. Lithium/sodium ion batteries (LIBs/SIBs) with high-performance electrochemical performances, such as large-scale energy storage, low costs and high security, are expected to improve the above situation. Currently, developing anode materials with better electrochemical performances is the main obstacle to the development of LIBs/SIBs. Recently, a variety of studies have focused on cobalt-based anode materials applied for LIBs/SIBs, owing to their high theoretical specific capacity. This review systematically summarizes the recent status of cobalt-based anode materials in LIBs/SIBs, including Li+/Na+ storage mechanisms, preparation methods, applications and strategies to improve the electrochemical performance of cobalt-based anode materials. Furthermore, the current challenges and prospects are also discussed in this review. Benefitting from these results, cobalt-based materials can be the next-generation anode for LIBs/SIBs.

Co9S8 nanoparticles embedded into amorphous carbon as anode materials for lithium-ion batteries

In this paper, Co9S8 nanoparticles embedded into amorphous carbon have been synthesized by a simple electrospinning method followed by a high-temperature annealing process. The unique structure endows the Co9S8/C composites with excellent electrochemical properties. Co9S8 particles embedded into the carbon matrix show a high Li storage capacity around 1100 and 358 mAhg-1 at a current density of 0.1 and 5.0 Ag-1, respectively. After 200 cycles, an impressive discharge capacity of around 1063.4 mAhg-1 can be obtained at a current density of 0.3 Ag-1.

Preparation of cobalt sulfide@reduced graphene oxide nanocomposites with outstanding electrochemical behavior for lithium-ion batteries

Cobalt sulfide@reduced graphene oxide nanocomposites obtained through a dipping and hydrothermal process, exhibit ascendant lithium-ion storage properties.

A cellulose substance derived nanofibrous CoS–nanoparticle/carbon composite as a high-performance anodic material for lithium-ion batteries

Nanofibrous CoS–nanoparticle/carbon composite derived from a cellulose substance was fabricated, showing enhanced electrochemical performances as an anodic material for lithium-ion batteries.

Metal-organic Framework-driven Porous Cobalt Disulfide Nanoparticles Fabricated by Gaseous Sulfurization as Bifunctional Electrocatalysts for Overall Water Splitting

Both high activity and mass production potential are important for bifunctional electrocatalysts for overall water splitting. Catalytic activity enhancement was demonstrated through the formation of CoS2 nanoparticles with mono-phase and extremely porous structures. To fabricate porous structures at the nanometer scale, Co-based metal-organic frameworks (MOFs), namely a cobalt Prussian blue analogue (Co-PBA, Co3[Co(CN)6]2), was used as a porous template for the CoS2. Then, controlled sulfurization annealing converted the Co-PBA to mono-phase CoS2 nanoparticles with ~ 4 nm pores, resulting in a large surface area of 915.6 m2 g-1. The electrocatalysts had high activity for overall water splitting, and the overpotentials of the oxygen evolution reaction and hydrogen evolution reaction under the operating conditions were 298 mV and -196 mV, respectively, at 10 mA cm-2.

MoS2 coated CoS2 nanocomposites as counter electrodes in Pt-free dye-sensitized solar cells

Expensive Pt counter electrodes remain an obstacle for the commercialization of dye-sensitized solar cells (DSSCs). Therefore, research focusing on low-cost alternative counter electrode materials has been considered important for their commercialization. Here, the fabrication of dye-sensitized solar cells has been performed utilizing CoS₂ and MoS₂ coated CoS₂ nanocomposite materials as the counter electrode, which are synthesized via a hydrothermal route involving low-cost precursor materials. The experimental results obtained from XRD, XPS, EDX, SEM, TEM, and Raman etc. have confirmed the successful formation of CoS₂ and MoS₂ coated CoS₂ nanocomposites. The electrochemical characterization of these materials is performed, which suggests that the electrocatalytic activity towards the liquid iodine electrolyte of these materials is as good as that of the conventional Pt counter electrodes. So, dye-sensitized solar cell devices are fabricated by interpolating a (cis-bis(isothiocyanato)bis(2,2'-bipyridyl-4,4'-dicarboxylato)ruthenium(ii)) dye-loaded TiO₂ photoanode and CoS₂, MoS₂ coated CoS₂ and Pt counter electrodes using iodine/iodide as a liquid electrolyte. The devices fabricated with CoS₂ counter electrodes have shown an open circuit voltage of 790 mV, a short circuit current of 11.9 mA cm^-2, a fill factor of 0.54, and a power conversion efficiency of 6%. On the other hand, the device based on a Pt counter electrode has shown an open circuit voltage of 773 mV, a short circuit current of 13.4 mA cm^-2, a fill factor of 0.54, and a power conversion efficiency of 6.6%. In addition, MoS₂ coated with a CoS₂ counter electrode has shown the best performance with an open circuit voltage of 763 mV, a short circuit current of 20.1 mA cm^-2, a fill factor of 0.42, and a power conversion efficiency of 7.6%.

Viromimetic STING Agonist-Loaded Hollow Polymeric Nanoparticles for Safe and Effective Vaccination against Middle East Respiratory Syndrome Coronavirus

The continued threat of emerging, highly lethal infectious pathogens such as Middle East respiratory syndrome coronavirus (MERS-CoV) calls for the development of novel vaccine technology that offers safe and effective prophylactic measures. Here, a novel nanoparticle vaccine is developed to deliver subunit viral antigens and STING agonists in a virus-like fashion. STING agonists are first encapsulated into capsid-like hollow polymeric nanoparticles, which show multiple favorable attributes, including a pH-responsive release profile, prominent local immune activation, and reduced systemic reactogenicity. Upon subsequent antigen conjugation, the nanoparticles carry morphological semblance to native virions and facilitate codelivery of antigens and STING agonists to draining lymph nodes and immune cells for immune potentiation. Nanoparticle vaccine effectiveness is supported by the elicitation of potent neutralization antibody and antigen-specific T cell responses in mice immunized with a MERS-CoV nanoparticle vaccine candidate. Using a MERS-CoV-permissive transgenic mouse model, it is shown that mice immunized with this nanoparticle-based MERS-CoV vaccine are protected against a lethal challenge of MERS-CoV without triggering undesirable eosinophilic immunopathology. Together, the biocompatible hollow nanoparticle described herein provides an excellent strategy for delivering both subunit vaccine candidates and novel adjuvants, enabling accelerated development of effective and safe vaccines against emerging viral pathogens.

Microporous Battery Electrodes from Molecular Cluster Precursors

Developing novel energy storage materials is critical to many renewable energy technologies. In this work, we report on the synthesis and electrochemical properties of materials composed of porous cobalt selenide microspheres prepared from molecular cluster precursors. The cobalt selenide microspheres excel as Na⁺ ion battery electrode materials, with a specific capacity of ∼550 mA h/g and excellent cycling stability of 85% over 100 cycles, and perform equally well as Li⁺ ion battery electrodes with a specific capacity of ∼600 mA h/g and cycling stability of 80% over 100 cycles. Materials which reversibly store large amounts of Na⁺ ions are uncommon, and these performances represent significant advances in the field. More broadly, this work establishes metal chalcogenide molecular clusters as valuable precursors for creating new, tunable energy storage materials.

Co9 S8 -Catalyzed Growth of Thin-Walled Graphite Microtubes for Robust, Efficient Overall Water Splitting

Co₉ S₈ crystals can catalyze the growth of thin-walled graphite microtubes (GMTs) through a catalytic chemical vapor deposition (CCVD) process using thiourea as the precursor. The growth of GMTs follows a tip-growth mechanism with tube diameters up to a few micrometer. The hollow interiors of the GMTs are filled with carbon nanotubes and wrinkled graphene layers, which form a unique nanotube/graphene-in-microtube structure. As-formed GMTs are N,S-codoped with lots of Co₉ S₈ nanoparticles encapsulated in their inner walls. These GMTs are room-temperature ferromagnets and can be loaded on Ni foams to work as binder-free electrocatalysts with low overpotential (310 mV at 50 mA cm^-2 for the oxygen evolution reaction (OER) and 284 mV at 50 mA cm^-2 for the hydrogen evolution reaction (HER)) and long-term durability (continuous work for 120 h without loss in performance). Our research proves that metal sulfides can catalyze the growth of graphite microtubes and as-formed GMTs may potentially be used as functional building blocks to construct new kinds of electrochemical devices for various energy-related applications.

CoSe2 Nanoparticles Encapsulated by N-Doped Carbon Framework Intertwined with Carbon Nanotubes: High-Performance Dual-Role Anode Materials for Both Li- and Na-Ion Batteries

It is of fundamental and technological significance to develop dual-role anode materials for both lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) with high performance. Here, a composite material based on CoSe2 nanoparticles encapsulated in N-doped carbon framework intertwined with carbon nanotubes (CoSe2@N-CF/CNTs) is prepared successfully from cobalt-based zeolitic imidazolate framework (ZIF-67). As anode materials for LIBs, CoSe2@N-CF/CNTs composites deliver a reversible capacity of 428 mAh g-1 even after 500 cycles at a current density of 1 A g-1 with almost 100% Coulombic efficiency. The charge and discharge mechanisms of CoSe2 are characterized using ex situ X-ray diffraction and Raman analysis, from which the lithiation products of CoSe2 are found to be Li x CoSe2 and Li2Se, which are further converted to CoSe2 upon delithiation. The CoSe2@N-CF/CNTs composites also demonstrate excellent electrochemical performance as anode materials for SIBs with a carbonate-based electrolyte, with specific capacities of 606 and 501 mAh g-1 at 0.1 and 1 A g-1 in the 100th cycle. The electrochemical performance of the anode materials is further studied by pseudocapacitance and galvanostatic intermittent titration technique (GITT) measurements. This work may be exploited for the rational design and development of dual-role anode materials for both Li- and Na-ion batteries.

Designed formation of Co3O4@NiCo2O4 sheets-in-cage nanostructure as high-performance anode material for lithium-ion batteries

Structural and compositional control of functional nanoparticles is considered to be an efficient way to obtain enhanced chemical and physical properties. A unique Co3O4@NiCo2O4 sheets-in-cage nanostructure is fabricated via a facile conversion reaction, involving subsequent hydrolysis and annealing treatment. Such hollow nanoparticles provide an excellent property for Li storage.

Encapsulation of CoS x Nanocrystals into N/S Co-Doped Honeycomb-Like 3D Porous Carbon for High-Performance Lithium Storage

A honeycomb-like 3D N/S co-doped porous carbon-coated cobalt sulfide (CoS, Co9S8, and Co1-x S) composite (CS@PC) is successfully prepared using polyacrylonitrile (PAN) as the nitrogen-containing carbon source through a facile solvothermal method and subsequent in situ conversion. As an anode for lithium-ion batteries (LIBs), the CS@PC composite exhibits excellent electrochemical performance, including high reversible capacity, good rate capability, and cyclic stability. The composite electrode delivers specific capacities of 781.2 and 466.0 mAh g-1 at 0.1 and 5 A g-1, respectively. When cycled at a current density of 1 A g-1, it displays a high reversible capacity of 717.0 mAh g-1 after 500 cycles. The ability to provide this level of performance is attributed to the unique 3D multi-level porous architecture with large electrode-electrolyte contact area, bicontinuous electron/ion transport pathways, and attractive structure stability. Such micro-/nanoscale design and engineering strategies may also be used to explore other nanocomposites to boost their energy storage performance.

Rapid Amorphization in Metastable CoSeO3·H2O Nanosheets for Ultrafast Lithiation Kinetics

The realization of high-performance anode materials with high capacity at fast lithiation kinetics and excellent cycle stability remains a significant but critical challenge for high-power applications such as electric vehicles. Two-dimensional nanostructures have attracted considerable research interest in electrochemical energy storage devices owing to their intriguing surface effect and significantly decreased ion-diffusion pathway. Here we describe rationally designed metastable CoSeO₃·H₂O nanosheets synthesized by a facile hydrothermal method for use as a Li ion battery anode. This crystalline nanosheet can be steadily converted into amorphous phase at the beginning of the first Li⁺ discharge cycling, leading to ultrahigh reversible capacities of 1100 and 515 mAh g^-1 after 1000 cycles at a high rate of 3 and 10 A g^-1, respectively. The as-obtained amorphous structure experiences an isotropic stress, which can significantly reduce the risk of fracture during electrochemical cycling. Our study offers a precious opportunity to reveal the ultrafast lithiation kinetics associated with the rapid amorphization mechanism in layered cobalt selenide nanosheets.

Improved Electrochemical Performance Based on Nanostructured SnS2@CoS2-rGO Composite Anode for Sodium-Ion Batteries

A promising anode material composed of SnS₂@CoS₂ flower-like spheres assembled from SnS₂ nanosheets and CoS₂ nanoparticles accompanied by reduced graphene oxide (rGO) was fabricated by a facile hydrothermal pathway. The presence of rGO and the combined merits of SnS₂ and CoS₂ endow the SnS₂@CoS₂-rGO composite with high conductivity pathways and channels for electrons and with excellent properties as an anode material for sodium-ion batteries (SIBs). A high capacity of 514.0 mAh g^-1 at a current density of 200 mA g^-1 after 100 cycles and a good rate capability can be delivered. The defined structure and good sodium-storage performance of the SnS₂@CoS₂-rGO composite demonstrate its promising application in high-performance SIBs.

Suppressing self-discharge of Li–B/CoS2 thermal batteries by using a carbon-coated CoS2 cathode

Thermal batteries with molten salt electrolytes are used for many military applications, primarily as power sources for guided missiles. The Li–B/CoS₂ couple is designed for high-power, high-voltage thermal batteries. However, their capacity and safe properties are influenced by acute self-discharge that results from the dissolved lithium anode in molten salt electrolytes. To solve those problems, in this paper, carbon coated CoS₂ was prepared by pyrolysis reaction of sucrose at 400 °C. The carbon coating as a physical barrier can protect CoS₂ particles from damage by dissolved lithium and reduce the self-discharge reaction. Therefore, both the discharge efficiency and safety of Li–B/CoS₂ thermal batteries are increased remarkably. Discharge results show that the specific capacity of the first discharge plateau of carbon-coated CoS₂ is 243 mA h g⁻¹ which is 50 mA h g⁻¹ higher than that of pristine CoS₂ at a current density of 100 mA cm⁻². The specific capacity of the first discharge plateau at 500 mA cm⁻² for carbon-coated CoS₂ and pristine CoS₂ are 283 mA h g⁻¹ and 258 mA h g⁻¹ respectively. The characterizations by XRD and DSC indicate that the carbonization process has no noticeable influence on the intrinsic crystal structure and thermal stability of pristine CoS₂.

Suppressing self-discharge of Li–B/CoS₂ thermal batteries through modifying the CoS₂ cathode with a protective carbon coating layer.

TiO₂ Nanobelt@Co₉S₈ Composites as Promising Anode Materials for Lithium and Sodium Ion Batteries

TiO₂ anodes have attracted great attention due to their good cycling stability for lithium ion batteries and sodium ion batteries (LIBs and SIBs). Unfortunately, the low specific capacity and poor conductivity limit their practical application. The mixed phase TiO₂ nanobelt (anatase and TiO₂-B) based Co₉S₈ composites have been synthesized via the solvothermal reaction and subsequent calcination. During the formation process of hierarchical composites, glucose between TiO₂ nanobelts and Co₉S₈ serves as a linker to increase the nucleation and growth of sulfides on the surface of TiO₂ nanobelts. As anode materials for LIBs and SIBs, the composites combine the advantages of TiO₂ nanobelts with those of Co₉S₈ nanomaterials. The reversible specific capacity of TiO₂ nanobelt@Co₉S₈ composites is up to 889 and 387 mAh·g⁻¹ at 0.1 A·g⁻¹ after 100 cycles, respectively. The cooperation of excellent cycling stability of TiO₂ nanobelts and high capacities of Co₉S₈ nanoparticles leads to the good electrochemical performances of TiO₂ nanobelt@Co₉S₈ composites.

Electrodeposited Nickel-Cobalt-Sulfide Catalyst for the Hydrogen Evolution Reaction

A novel Ni-Co-S-based material prepared by the potentiodynamic deposition from an aqueous solution containing Ni²⁺, Co²⁺, and thiourea is studied as an electrocatalyst for the hydrogen evolution reaction (HER) in a neutral phosphate solution. The composition of the catalyst and the HER activity are tuned by varying the ratio of the concentrations of Ni²⁺ and Co²⁺ ions in the electrolytes. Under optimized deposition conditions, the bimetallic Ni-Co-S exhibits higher electrocatalytic activity than its monometallic counterparts. The Ni-Co-S catalyst requires an overpotential of 150 mV for the HER onset, and 10 mA cm^-2 current density is obtained at 280 mV overpotential. The catalyst exhibits two different Tafel slopes (93 and 70 mV dec^-1) indicating two dissimilar mechanisms. It is proposed that the catalyst comprises two types of catalytic active sites, and they contribute selectively toward HER in different potential regions.

Formation of graphene-encapsulated CoS2 hybrid composites with hierarchical structures for high-performance lithium-ion batteries

Hierarchical structure CoS₂ nanospheres with graphene (CoS₂/G) composite is fabricated by a simple hydrothermal method. This composite exhibits excellent electrochemical performance, especially long cycle life.

Hydrazine-assisted electrolytic hydrogen production: CoS2nanoarray as a superior bifunctional electrocatalyst

A CoS₂nanoarray on Ti mesh acts as an efficient and durable catalyst for the hydrazine oxidation reaction and it only needs 0.81 V to attain 100 mA cm⁻²in 1.0 M KOH with 100 mM hydrazine for its two-electrode electrolyser.