CoS2 Nanowires Research Articles

Hierarchical CoS2@NiFe-LDH as an efficient electrocatalyst for alkaline seawater oxidation.

Developing earth-abundant non-noble electrocatalysts with high performance is significant but challenging for the oxygen evolution reaction (OER) in seawater. Herein, a hierarchical electrocatalyst, NiFe-layered double hydroxide (LDH) nanosheet anchored CoS2 nanowires supported on carbon cloth, is developed for efficient OER electrocatalysis in alkaline seawater, demanding a low overpotential of 256 mV to drive a current density of 100 mA cm-2, along with favorable catalytic durability for at least 48 h with negligible decay.

Sulfuration Temperature-Dependent Hydrogen Evolution Performance of CoS2 Nanowires

Densely aligned CoS2 nanowires (NWs) on chemically durable stainless steel fibers felt (SSF) substates were synthesized by thermal sulfuring Co3O4 NWs, which were oxidized from hydrothermal synthesized Co(OH)y(CO3)(1−0.5y)·nH2O NWs precursors. The effect of sulfuration temperature on the composition, morphology, and HER performance of the products was studied in detail. The results show that the high purity together with the enlarged density of active sites given by the twisted morphology of the CoS2 NWs sulfured at 500 °C guarantee its superior hydrogen evolution reaction (HER) performance compared with other samples sulfured at lower temperatures.

Highly efficient methanol oxidation reaction on durable Co9S8 @N, S-doped CNT catalyst for methanol fuel cell applications

The implementation of direct methanol fuel cells is seen as a reliable factor in the future energy mix. Efficient energy conversion from methanol requires an active and durable catalyst to drive the anodic methanol oxidation reaction (MOR) in direct methanol fuel cells. As an alternative to high cost noble metals, cobalt-based electrocatalysts are considered potential replacements that meet the high activity and long-term stability for MOR. Herein, we report the preparation of hierarchical Co9S8 nanowires trapped in N-doped carbon nanotubes (N,S–Co@CNT) derived from melamine showing high activity for MOR in alkaline medium. In order to identify the main active sites, we synthesized cobalt particles embedded in carbon structures in absence of a sulphur source (Co@CNT) and evaluated its performance for MOR. The material characterization shows that adding sulphur during pyrolysis enhances the surface area, pore size and lattice defect. In addition, the morphology changes from hemi-spherical particles to nanowires, that significantly improves the electrochemical properties. The current density of N,S–Co@CNT is exceptionally higher (5.5 times) and the onset potential of MOR is shifted to lower potential when compared to Co@CNT. The enhanced activity, durability and stability of N,S–Co@CNT is ascribed to the unique hierarchical structure and surface properties.

CoS2 nanowires supported graphdiyne for highly efficient hydrogen evolution reaction

Planar unsaturated sulfurs in (211) facet of the CoS 2 nanowires have been successfully activated through constructing Graphdiyne-CoS 2 heterojunction nanocomposites as efficient electrocatalyst toward HER. • The electron transfer between two-dimensional planes greatly enhances the catalytic activity of sulfur active sites. • DFT simulation confirms the reaction process mechanism. • Outstanding HER catalytic performance with good stability has been achieved. • Provide new insights and paves the way for the further efficient transition metal disulfides catalyst manufactures. Transition metal sulfides are an important category for hydrogen evolution reaction (HER). However, only few edge unsaturated sulfurs functionalize as catalytic sites, which has dramatically limited the catalytic activity and stability. In this work, planar unsaturated sulfurs in (211) plane of the CoS 2 nanowires have been successfully activated through constructing Graphdiyne-CoS 2 heterojunction nanocomposites. The corresponding electrons transfer energy barriers for these planar unsaturated sulfurs have been significantly diminished, which are induced by the synergetic effects of the sp 1 hybridized carbons and unsaturated planar sulfurs. In addition, DFT simulations reveal the synergetic effects of the sp 1 hybridized carbons and unsaturated planar sulfurs can promote electron transfer kinetics of the key step, Volmer-Heyrovsky step, of the reaction. As expected, the Graphdiyne-CoS 2 heterojunction nanocomposites exhibit superior HER catalytic performance with low overpotential of 97 mV at 10 mA cm −2 , and the Tafel slope of 56 mV dec −1 . Furthermore, the heterojunction shows outstanding stability as well due to the protection of the Graphdiyne (GDY). The approach thus paves the way for the further efficient transition metal disulfides catalyst manufactures.

Construction of self-supporting, hierarchically structured caterpillar-like NiCo2S4 arrays as an efficient trifunctional electrocatalyst for water and urea electrolysis.

In this study, we have developed intriguing self-supporting caterpillar-like spinel NiCo2S4 arrays with a hierarchical structure of nanowires on a nanosheet skeleton, which can be used as a self-supporting trifunctional electrocatalyst for the oxygen evolution reaction (OER), hydrogen evolution reaction (HER) and urea oxidation reaction (UOR). The caterpillar-like NiCo precursor arrays are first in situ grown on carbon cloth (NiCo2O4/CC) by a facile hydrothermal reaction, which is followed by an anion exchange process (or sulfuration treatment) with Na2S to form self-supporting spinel NiCo2S4 arrays (NiCo2S4/CC) with a roughened nanostructure. Taking advantage of the bimetallic synergistic effect, the unique hierarchical nanostructure, and the self-supporting nature, the resultant NiCo2S4/CC electrode exhibits high activities toward the OER, HER and UOR, which are highly superior to the monometallic counterparts of NiS nanosheets and Co9S8 nanowires on a carbon cloth substrate. The comparison of the three electrodes also indicates that the hierarchically structured bimetallic electrode combines the morphological and structural characteristics of monometallic Ni-based nanosheets and Co-based nanowires. When assembling a two-electrode electrolytic cell with NiCo2S4/CC as both the anode and cathode, an applied cell voltage of only 1.66 V is required to deliver a current density of 10 mA cm-2 in water electrolysis. By using the same two-electrode setup, the applied voltage for urea electrolysis is further reduced to 1.45 V that produces hydrogen at the cathode with the same current density. This study paves the way for exploring the feasibility of future less energy-intensive and large-scale hydrogen production.

Accelerating water dissociation kinetic in Co9S8 electrocatalyst by mn/N Co-doping toward efficient alkaline hydrogen evolution

Electrocatalytic hydrogen evolution under alkaline media holds great promising in hydrogen energy production. Transition-metal sulfides (TMSs) are attractive for electrocatalytic alkaline hydrogen evolution, yet their catalytic performance is unsatisfactory owing to the sluggish water dissociation kinetics. Herein, a Mn/N co-doping strategy is proposed to regulate the water dissociation kinetics of Co9S8 nanowires array grown on nickel foam thus improve the activity of hydrogen evolution reaction (HER). The optimal Mn/N co-doping Co9S8 (Mn–N–Co9S8) catalyst achieves low overpotentials of 102 and 238 mV at 10 and 100 mA cm−2 in the 1 M KOH solution, respectively, remarkably higher than the single-doping Mn–Co9S8 and N–Co9S8 as well as superior to many reported Co9S8-based HER electrocatalysts. Density functional theory (DFT) calculation results confirm that the water dissociation barrier of the Mn–N–Co9S8 is reduced significantly owing to the synergistic co-doping of Mn and N, which accounts for the enhanced alkaline HER performance. This study offers an effective strategy to enhance the alkaline HER activity of TMSs by accelerating water dissociation kinetic via the cation and anion co-doping strategy.

Multi-dimensional hierarchical CoS2@MXene as trifunctional electrocatalysts for zinc-air batteries and overall water splitting

The demanding all-in-one electrocatalyst system for oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in zinc-air batteries or water splitting requires elaborate material manufacturing, which is usually complicated and time-consuming. Efficient interface engineering between MXene and highly active electrocatalytic species (CoS2) is, herein, achieved by an in situ hydrothermal growth and facile sulfurization process. The CoS2@MXene electrocatalyst is composed by one-dimensional CoS2 nanowires and two-dimensional MXene nanosheets, which lead to a hierarchical structure (large specific surface area and abundant active sites), a spatial electron redistribution (high intrinsic activity), and high anchoring strength (superior performance stability). Therefore, the electrocatalyst achieves enhanced catalytic activity and long-time stability for ORR (a half-wave potential of 0.80 V), OER (an overpotential of 270 mV at 10 mA cm−2, i.e., η10 = 270 mV) and HER (η10 = 175 mV). Furthermore, the asymmetry water splitting system based on the CoS2@MXene composites delivers a low overall voltage of 1.63 V at 10 mA cm−2. The solid-state zinc-air batteries using CoS2@MXene as the air cathode display a small charge-discharge voltage gap (0.53 V at 1 mA cm−2) and superior stability (60 circles and 20-h continuous test). The energy interconversion between the chemical energy and electricity can be achieved by a self-powered system via integrating the water splitting system and quasi-solid-state zinc-air batteries. Supported by in situ Raman analyses, the formation of cobalt oxyhydroxide species provides the active sites for water oxidation. This study paves a promising avenue for the design and application of multifunctional nanocatalysts.

Making Stretchable Hybrid Supercapacitors by Knitting Non‐Stretchable Metal Fibers

AbstractTo obtain supercapacitors for wearable electronic devices, highly conductive stretchable electrode substrates with excellent tensile recovery are required. However, the simultaneous realization of the above mentioned characteristics is difficult. In this study, tough stainless‐steel fibers (SSFs) are employed as the substrates for knitting into stainless‐steel meshes (SSMs), for the fabrication of textile electrodes with typical 2D‐interconnected networks. The obtained knitted networks can transform the angular elasticity of SSFs into the stretchability of the textile electrodes. The electrodes based on the SSM substrates can be obtained via the in situ growth of NiCo2S4 nanosheets covered by CoS2 nanowires, which exhibit a high specific capacity, high rate capability, and excellent cycling stability. Moreover, the first stretchable solid‐state hybrid supercapacitors based on SSM display excellent performances with respect to a high energy density (60.2 Wh kg−1 at 800 W kg−1), remarkable tensile recovery (≤40% elongation), and high stability (≈76.4% capacity retention at 30% strain for 1000 stretching cycles). The highly stretchable supercapacitor is sewn on the elbow of a garment to drive a light‐emitting diode, and it maintains a high performance with respect to the repetitive process of bending and straightening, thus demonstrating the high applicability of the designed SSMs to wearable electronics.

Surface-Induced 2D/1D Heterostructured Growth of ReS2/CoS2 for High-Performance Electrocatalysts.

Two-dimensional/one-dimensional (2D/1D) heterostructures have received much attention from researchers for their abundant catalytically active sites and low contact resistance due to formation of chemical bonds at the interface. The investigation of such heterostructures, however, is confined to lattice-matched materials, which severely limits the material candidates. Herein, we demonstrate a lattice-mismatched 2D/1D heterostructured electrocatalyst consisting of 2D ReS2 nanosheets and 1D CoS2 nanowires. We propose that the higher surface energy of the CoS2 nanowire and the lattice mismatch between 1D and 2D units are crucial for the growth process of ReS2 nanosheets. More importantly, the terminal S2- exposed on the surface of CoS2 nanowires serves not only as the nucleus of ReS2 nanosheets but also as a bridge to enhance electron transport efficiency. Thus, the ReS2/CoS2 heterostructures show outstanding hydrogen evolution reaction performance. This work is of general interest for the design of complex multidimensional nano-heterostructures with outstanding functionalities.

Tuning the electron status of urchin-like CoS2 nanowires by selenium doping toward highly efficient hydrogen evolution reaction

Abstract Cobalt disulfide (CoS2) for hydrogen evolution reaction (HER) suffers from unfavorable hydrogen adsorption properties due to the strong interaction between the adsorbed H and the intensely electropositive cobalt atom. Herein, we successfully demonstrate a general strategy to improve the hydrogen evolution activity of CoS2 by modulating the surface electron density. The selenium doped CoS2 (Se-CoS2) nanowires arrays exhibit a durable activity for electrochemical hydrogen evolution in 0.5 M H2SO4 solution to deliver 10 mA cm−2 at the overpotential of only 139 mV. Our density functional theory studies consistently confirm that the surface electron density of CoS2 has been effectively manipulated by Se doping. The adsorbed hydrogen binding energy to Se-CoS2 can be optimized to provide an optimal condition for electron and proton transferring to the adsorbed H2, thereby promoting HER activity of CoS2.

Coupling Co2P and CoP nanoparticles with copper ions incorporated Co9S8 nanowire arrays for synergistically boosting hydrogen evolution reaction electrocatalysis

Rational design of high-performance and low-cost electrocatalyst for the hydrogen evolution reaction (HER) is highly desirable but remains a long-standing challenge. Herein, an integration of interfacial engineering and ions incorporation was achieved to develop high-performance hybrid electrocatalyst through a facile phosphidation treatment of Cu2+-doped Co9S8 nanowires arrays (Co9S8-Cu NAs) growth on nickel foam. Through this treatment, cobalt phosphide (CoxP, i.e., Co2P and CoP) nanoparticles are decorated on the surface of Co9S8-Cu NAs, forming a novel ternary CoxP/Co9S8-Cu NAs electrocatalyst. The incorporation of Cu2+ enables the modulation of electronic structures of Co9S8 and contributes to the optimization of reaction immediate energetics. The formed abundant interfaces between CoxP and Co9S8-Cu facilitate the charge transfer and create more exposed active sites, further boosting the HER performance. As a result, the CoPx/Co9S8-Cu NAs exhibited high HER activity and stability with a low overpotential of 118 mV to reach a current density of 10 mA cm−2 in alkaline solution, which can surpass many previously reported Co-based HER catalysts. This work highlights the synergy of the interfacial engineering and ions incorporation in the construction of high-performance and stable electrocatalysts for the water splitting application.

Preparation of Large-Scale CoS<sub>2 </sub>Nanowires and their Raman Study

Structurally sound self-growing large-scale CoS2 nanowires were synthesized via a template-free and catalyst thermal sulfurization process on Co films. After annealing cobalt thin films in pure sulfur (S) vapor produced large area of CoS2 nanowires, we observe symmetrical and vertically alligned nanowires on the thin film surface. After running the thermal treatment in static S atmosphere, the cobalt thin film is converted into polycrystalline CoS2 nanowires and CoS2 film. We recorded the form of the CoS2 nanowires after the cobalt thin film was annealed. We also investigated the influence of the film annealing time and temperature. Aligned and long nanowires can be effectively formed at a temperature of around 400 °C for 5-10 h. The diameter of the CoS2 nanowires is around 10 nm with a length of ~ 2 µm. In addition, the Raman spectra of isolated CoS2 nanowired were lso studied.

Co9S8 nanowires@NiCo LDH nanosheets arrays on nickel foams towards efficient overall water splitting

Water electrolysis is considered to be an effective way to fabricate hydrogen, and it is desirable to find the highly efficient, inexpensive and good durability bifunctional electrocatalysts for overall water splitting. In this paper, we synthesis a unique structured catalyst that was composed by Co9S8 nanowires and nickel cobalt layered double hydroxide (NiCo-LDH) nanosheets. The ultrathin nanosheets decorated on the Co9S8 nanoarrays offer large specific surface area, numerous active edge sites and excellent electrical conductivity for fast electron transfer. Benefiting from this heterogeneous structure, the catalyst presents excellent catalytic performance in alkaline media. It requires 168 mV to reach current density of 10 mA/cm2 for HER and 278 mV to reach current density of 30 mA/cm2 for OER. When used as electrode in a homemade two-electrode system, it only needs t a voltage of 1.63 V to achieve current densities of 10 mA/cm2, which proves Co9S8@NiCo LDH/NF as a superior bifunctional catalyst for water splitting.

Theoretical Expectation and Experimental Implementation of In Situ Al-Doped CoS2 Nanowires on Dealloying-Derived Nanoporous Intermetallic Substrate as an Efficient Electrocatalyst for Boosting Hydrogen Production

Foreign atom doping is known to not only modify the electronic structure but also improve the intrinsic activity of catalysts. Herein, we fabricate three-dimensional (3D) self-supporting nanoporous cobalt–aluminum intermetallic (np-Co(Al)) through dealloying of Al90Co10 master alloy to in situ introduce Al element into the precursor. The intrinsic Al dopant is determined to be insensitive to S vapor but beneficial to generate numerous Al-doped CoS2 nanowires (Al-CoS2 NWs) when they were subjected to solid–vapor sulfurization treatment. The density functional theory (DFT) calculations evidence that spontaneous Al-doping in CoS2 crystal could enhance the hybridization between Co d-orbital and S p-orbital near the Fermi level. On the one hand, the Co-sites are more active than that of the S-sites, and the intermediate hydrogen (H*) adsorption free energy (ΔGH*) of Al-CoS2 is only −0.16 eV when adsorbed on the bridge site of Co. On the other hand, the embedded Al can not only facilitate the activity improveme...

Fabrication of hierarchical NiCo2S4@CoS2 nanostructures on highly conductive flexible carbon cloth substrate as a hybrid electrode material for supercapacitors with enhanced electrochemical performance

In this study, we fabricated the hierarchical NiCo2S4@CoS2 nanostructures on highly conductive flexible carbon cloth (CC) via two-steps hydrothermal method for high-performance supercapacitor hybrid electrode material. The surface morphology of the fabricated hybrid electrode material NiCo2S4@CoS2@CC exposed the formation of hierarchical NiCo2S4 ultrathin nanosheets on CoS2 nanowires over the carbon cloth substrate and thus forming a three-dimensional interconnected porous network. During the electrochemical analysis, the hybrid NiCo2S4@CoS2 nanostructures on CC exhibited an enhanced specific capacitance of ∼1565 F g−1 at a current density of 1 A g−1. A capacitance retention of ∼91% was achieved after 8000 galvanostatic charge/discharge cycles at a current density of 1 A g−1 and a maximum energy density of ∼17 Wh Kg−1 at a power density of 242.8 W Kg−1. Thus, the electrode had a significantly improved supercapacitor performance in terms of a high specific capacitance, excellent cycle stability, and good rate capability.

Accelerated Hydrogen Evolution Reaction in CoS2 by Transition-Metal Doping

Cobalt pyrite (CoS2) is one of the promising candidate catalysts for electrocatalytic hydrogen evolution because of its efficient catalytic activity sites and inherent metallicity. Herein, we report the greatly improved electrocatalytic activity of CoS2 resulting from Mn doping. First, we give the theoretical prediction that Mn is the most excellent dopant to activate the electrocatalytic activity of CoS2 with the smallest Gibbs free energy (|ΔGH*|) while remaining metallic. Second, to provide experimental evidence, Mn-doped CoS2 nanowires are prepared by a hydrothermal and postsulfuration method. The optimized sample shows a low overpotential of 43 mV at 10 mA/cm2, a Tafel slope of only 34 mV/dec, and long-time stability for the hydrogen evolution reaction. This work reveals a new way to stimulate the electrocatalytic activity of other pristine candidate catalysts.

Co9S8@N,S-codoped carbon core–shell structured nanowires: constructing a fluffy surface for high-density active sites

Co9S8 nanowires are coated with a fluffy surface layer constructed of N,S-codoped carbon nanotubes to form high-density active sites.

Quaternary pyrite-structured nickel/cobalt phosphosulfide nanowires on carbon cloth as efficient and robust electrodes for water electrolysis

The strategy of element substitution is an effective way to tune the electronic structures of the active sites in catalysts, thereby leading to improvements in both the catalytic activity and stability. Herein, we design and synthesize pyrite-type nickel/phosphorus co-doped CoS2 nanowires on carbon cloth (NiCoPS/CC) as efficient and durable electrodes for water electrolysis. Introduction of nickel and phosphorus produced stepwise and superb enhancement of the performance of the electrodes in the hydrogen evolution reaction due to regulation of the electronic structures of the active sites of the catalyst and accelerated charge transfer over a wide pH range (0−14). The NiCoPS/CC electrodes also delivered a nearly undecayed catalytic current density of 10 mA·cm−2 at a low overpotential of 230 mV for oxygen evolution due to in situ formation of surficial Ni–Co oxo/hydroxide in 1.0 M KOH. Thus, the NiCoPS/CC electrodes gave rise to a catalytic current density of 10 mA·cm−2 for overall water splitting at potentials as low as 1.54 V during operation over 100 h in 1.0 M KOH with a Faradic efficiency of ~100%.

Single-Step Synthesis of Cobalt Sulfide Nanowires Encapsulated in Carbon Nanotubes

We describe the single-step synthesis of Co9S8 nanowires encapsulated in carbon nanotubes (CNTs) from a dimethyl sulfide precursor, using a simple chemical vapor deposition method. The optimum dimethyl sulfide vapor concentration for the production of Co9S8 nanowires-filled CNTs is around 1.26-1.47%. The carbon nanotubes/Co9S8 nanowires were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction measurements, and energy dispersive X-ray spectroscopy. Transmission electron microscopy shows that the nanowires consist of well crystallized Co9S8 cores which are completely encapsulated by the sheath-like carbon nanotubes. The encapsulated Co9S8 nanowires are single-crystalline, and their lengths are about 10 microm with their [1, -1,0] direction parallel to the axis of the CNTs. Thorough investigation manifests that the filling of the Co9S8 nanowires can be ascribed to the volume increase which was induced by a phase transition from cobalt to cobalt sulfide combined with the in situ extruding action of carbon nanotubes as nanomolds. A detailed filling mechanism is proposed.

Filling Carbon Nanotubes with Co9S8 Nanowires through in Situ Catalyst Transition and Extrusion

We describe the synthesis of novel Co9S8-nanowire-filled carbon nanotubes (CNTs) by a simple method involving the pyrolysis of thiophene on cobalt catalyst in a conventional chemical vapor decomposition system. The encapsulated Co9S8 nanowires are single-crystalline, and their lengths are about 10 μm with their [110] direction parallel to the axis of the CNTs. Detailed investigation suggests that the filling of the Co9S8 nanowires results from the volume increase induced by a phase transition from cobalt to cobalt sulfide together with the in situ extruding action of CNTs as nanomolds. A new filling mechanism is thus found and proposed.