Co-doped MoS2 Research Articles

Nuclear irradiation resistance of MoS2-based nanocomposite films: Insights from in situ macroscopic tribometry

In situ performance enhancement of solid lubricating materials are pivotal for the advancement of nuclear facilities. Here, we conducted in situ tribotests against 5.4 MeV Xe20+ ion irradiation for Ti-doped (MoST) and C/Ti co-doped (MoSCT) MoS2 films. The pristine MoST film outperformed MoSCT film but suffered severe degradation owing to irradiation-induced hardening of the amorphized MoS2 phase. Carbon co-doping effectively mitigated the hardening issue through irradiation-induced graphitization of the carbon phase, thereby enhancing the irradiation resistance of MoS2-based films. Both in situ and ex situ irradiation did not adversely affect the shearing-induced re-ordering of MoS2 basal planes, but they inhibit the graphitization and selective release of non-lubricative carbon phase, resulting in an increase in the film wear rate to 7.34 × 10−7 mm3/N·m.

Activation of inert surface of monolayer MoS2 by transition metal and nitrogen co-doping to promote hydrogen evolution reaction

In this work, we systematically investigate the possible H adsorption sites, charge density difference, partial density of states, p-band center and Bader charge of transition metal (TM) and nitrogen (N) co-doped monolayer MoS2. The results show that the equilibrium of H adsorption and desorption can be achieved in TM-N co-doped monolayer MoS2. The ΔGH at the S site of Co-N co-doped system is −0.05 eV, which is better than that of traditional Pt site (ΔGH=-0.09 eV) and Mo site at the MoS2 edge (ΔGH=0.08 eV). This work has important implications for designing more efficient electrocatalysts.

Chitosan-derived N-doped carbon supported Cu/Fe co-doped MoS2 nanoparticles as peroxymonosulfate activator for efficient dyes degradation

Peroxymonosulfate (PMS), which is dominated by free radical (SO4•-) pathway, has a good removal effect on organic pollutants in complex water matrices. In this article, a new catalyst (CFM@NC) was synthesized by hydrothermal carbonization method with chitosan (CS) as N and C precursors, and used to activate PMS to degrade dye wastewater. CFM@NC/PMS system can degrade 50 mg·L−1 rhodamine B by 99.59 % within 30 min, and the degradation rate remains as high as 97.32 % after 5 cycles. It has good complex background matrices, acid-base anti-interference ability (pH 2.6–10.1), universality and reusability. It can degrade methyl orange and methylene blue by >98 % within 30 min. The high efficiency of the composite is due to the fact that CS-modified MoS2 as a carrier exposes a large number of active sites, which not only disperses CuFe2O4 nanoparticles and improves the stability of the catalyst, but also provides abundant electron rich groups, which promotes the activation of PMS and the production of reactive oxygen species (ROS). PMS is effectively activated by catalytic sites (Cu+/Cu2+, Fe2+/Fe3+, Mo4+/Mo6+, pyridine N, pyrrole N, edge sulfur and hydroxyl group) to produce a large number of radicals to attack RhB molecules, causing chromophore cleavage, ring opening, and mineralization. Among them, free radical SO4•- is the main ROS for RhB degradation. This work is expected to provide a new idea for the design and synthesis of environmentally friendly and efficient heterogeneous catalysts.

Polyacrylonitrile-based 3D N-rich activated porous carbon synergized with Co-doped MoS2 for promoted electrocatalytic hydrogen evolution

MoS2 is a promising electrocatalyst for the hydrogen evolution reaction (HER), but it is limited by its own agglomeration, low conductivity, and surface inertness. In this study, we report a well-organized 3D hybrid structure of N-rich active porous carbon (CN) synergized with Co-doped molybdenum disulfide (Co-MoS2@CN) for promoted electrocatalytic hydrogen evolution. MoS2 nanosheets were grown vertically on CN and the pore structure was improved, which exposed abundant edge active sites. The N-rich graphite structure and abundant pore structure of CN enhanced the electron transfer ability and stability of the 3D hybrid structure. Meanwhile, doping of Co atoms optimized the catalytic activity of the in-plane sulfur sites and induced a partial transition from 2H-MoS2 to 1 T-MoS2. The resulting Co-MoS2@CN 3D hybrid structure exhibited excellent HER electrocatalytic performance, had a current density of 10 mA cm−2 in a 0.5 M H2SO4 aqueous solution by an overpotential of 137 mV, and showed excellent stability in a 24 h HER test. DFT calculations confirmed that the heterogeneous interface constructed by CN and Co-MoS2 effectively optimized Gibbs free energy (ΔGH*) of the MoS2 hydrogen adsorption site and enhanced the interfacial electron transfer capacity, which ensured rapid HER kinetics during the electrocatalytic process.

Highly Selective Electroreduction of Nitrobenzene to Aniline by Co-Doped 1T-MoS2.

The selective electrocatalytic reduction of nitrobenzene (NB) to aniline demands a desirable cathodic catalyst to overcome the challenges of the competing hydrogen evolution reaction (HER), a higher overpotential, and a lower selectivity. Here, we deposit Co-doped 1T MoS2 on Ti mesh by the solvothermal method with different doping percentages of Co as x % Co-MoS2 (where x = 3, 5, 8, 10, and 12%). Because of the lowest overpotential, lower charge-transfer resistance, strong suppression of the competing HER, and higher electrochemical surface area, 8% Co-MoS2 achieves 94% selectivity of aniline with 54% faradaic efficiency. The reduction process follows first-order dynamics with a reaction coefficient of 0.5 h-1. Besides, 8% Co-MoS2 is highly stable and retains 81% selectivity even after 8 cycles. Mechanistic studies showed that the selective and exothermic adsorption of the nitro group at x % Co-MoS2 leads to a higher rate of NB reduction and higher selectivity of aniline. The aniline product is successfully removed from the solution by polymerization at FTO. This study signifies the impact of doping metal atoms in tuning the electronic arrangement of 1T-MoS2 for the facilitation of organic transformations.

Influence of Eu and Nd dopants on the photovoltaic properties of monolayer MoS2: A first-principles study

In this paper, the effects of Eu, Nd doping, and Eu–Nd co-doping on the stability, magnetic and optical properties of monolayer MoS2 are investigated by the density functional theory based on the first principle's calculations. It was found that the Eu–Nd co-doped monolayer MoS2 is more stable than other considered doping structures. After the introduction of Eu and Nd atoms, the band gap are decreased to different degrees, indicating that the doping is favorable to the electronic jump, which might enhances the conductivity of the system. All doped systems exhibit magnetic properties. In addition, the absorption spectra of all doped systems show significant red-shift compared with those of pure monolayer MoS2, indicating that the doping improves the absorption capacity in visible light. These results might provide theoretical guidance for the design of novel monolayer MoS2 semiconductor materials.

Hierarchical Spatial Confinement Unlocking the Storage Limit of MoS2 for Flexible High-Energy Supercapacitors.

Molybdenum sulfide (MoS2) is a promising electrode material for supercapacitors; however, its limited Mo/S edge sites and intrinsic inert basal plane give rise to sluggish active electronic states, thus constraining its electrochemical performance. Here we propose a hierarchical confinement strategy to develop ethylene molecule (EG)-intercalated Co-doped sulfur-deficient MoS2 (Co-EG/SV-MoS2) for efficient and durable K-ion storage. Theoretical analyses suggest that the intercalation-confined EG and lattice-confined Co can enhance the interfacial K-ion storage capacity while reducing the K-ion diffusion barrier. Experimentally, the intercalated EG molecules with mildly reducing properties induced the creation of sulfur vacancies, expanded the interlayer spacing, regulated the 2H-1T phase transition, and strengthened the structural grafting between layers, thereby facilitating ion diffusion and ensuring structural durability. Moreover, the Co dopants occupying the initial Mo sites initiated charge transfer, thus activating the basal plane. Consequently, the optimized Co-EG/SV-MoS2 electrode exhibited a substantially improved electrochemical performance. Flexible supercapacitors assembled with Co-EG/SV-MoS2 delivered a notable areal energy density of 0.51 mW h cm-2 at 0.84 mW cm-2 with good flexibility. Furthermore, supercapacitor devices were integrated with a strain sensor to create a self-powered system capable of real-time detection of human joint motion.

On the origin of the improved hydrogen evolution reaction in Mn- and Co-doped MoS2.

In the field of hydrogen production, MoS2 demonstrates good catalytic properties for the hydrogen evolution reaction (HER) which improve when doped with metal cations. However, while the role of sulfur atoms as active sites in the HER is largely reported, the role of metal atoms (i.e. molybdenum or the dopant cations) has yet to be studied in depth. To understand the role of the metal dopant, we study MoS2 thin films doped with Co and Mn ions. We identify the contribution of the electronic bands of the Mn and Co dopants to the integral valence band of the material using in situ resonant photoemission measurements. We demonstrate that Mn and Co dopants act differently: Mn doping favors the shift of the S-Mo hybridized band towards the Fermi level, while in the case of Co doping it is the less hybridized Co band that shifts closer to the Fermi level. Doping with Mn increases the effectiveness of S as the active site, thus improving the HER, while doping with Co introduces the metallic site of Co as the active site, which is less effective in improving HER properties. We therefore clarify the role of the dopant cation in the electronic structure determining the active site for hydrogen adsorption/desorption. Our results pave the way for the design of efficient materials for hydrogen production via the doping route, which can be extended to different catalytic reactions in the field of energy applications.

Transition metal (Mn, Fe, Co, Ni) and nitrogen co-doping for improving the photocatalytic activity of monolayer MoS2

Exploring efficient photocatalyst is important for environmental protection. In this work, we systematically investigate the doping configuration, formation energy, band structures, density of state, recombination rate, catalytic active site, work function, redox potential, and optical absorption properties of transition metal and nitrogen co-doped monolayer MoS2. In transition doped MoS2, transition metal atoms replace Mo. Transition metal and nitrogen atoms substitute Mo and S atoms in transition metal and nitrogen co-doped MoS2, respectively. Compared with undoped MoS2, transition metal and nitrogen co-doped MoS2 have low photogenerated carrier recombination rate, abundant catalytic active sites, small work function, suitable redox potentials, and strong light absorption, especially Mn-N and Ni-N co-doped MoS2.

Multiscale Synergetic Bandgap/Structure Engineering in Semiconductor Nanofibrous Aerogels for Enhanced Solar Evaporation.

Solar-driven interface evaporation has been identified as a sustainable seawater desalination and water purification technology. Nonetheless, the evaporation performance is still restricted by salt deposition and heat loss owing to weak solar spectrum absorption, tortuous channels, and limited plane area of conventional photothermal material. Herein, the semiconductor nanofibrous aerogels with a narrow bandgap, vertically aligned channels, and a conical architecture are constructed by the multiscale synergetic engineering strategy, encompassing bandgap engineering at the atomic scale and structure engineering at the nano-micro scale. As a proof-of-concept demonstration, a Co-doped MoS2 nanofibrous aerogel is synthesized, which exhibits the entire solar absorption, superhydrophilic, and excellent thermal insulation, achieving a net evaporation rate of 1.62 kg m-2 h-1 under 1 sun irradiation, as well as a synergistically efficient dye ion adsorption function. This work opens up new possibilities for the development of solar evaporators for practical applications in clean water production.

Tuning magnetic and optical properties in As–Ge (Si) co-doped MoS2 monolayer by defect-defect interaction

Modulating magnetic properties in monolayer MoS2 is important for the applications in spintronics and magnetism devices. In this work, we have studied the electronic, magnetic and optical properties of co-doped monolayer MoS2 with As–Ge (Si) doping on S surfaces through the first-principle calculations. Our results show that the magnetic properties of monolayer MoS2 can be tuned effectively by the distance of co-doped atoms. The projected density of state and the charge transfer demonstrate the interaction and superexchange coupling between As and Ge (Si) atoms are the key factor in the magnetic properties of co-doped structures. Furthermore, it is found that co-doping can also induce spin-polarized optical properties in low-energy region, which makes the co-doped MoS2 attractive candidates for spin-polarized photoelectric device applications.

Impurity tuning for enhanced electrocatalytic reduction of N2 to NH3 over Fe/Co Co-doped MoS2 nanosheets

The electrochemical N2 reduction reaction (NRR) has attracted much attention for its use in the production of fertilizers and other chemicals. Herein, we demonstrate that the NRR can be enhanced when using Fe/Co co-doped MoS2 (FeCo–MoS2) nanosheets as the electrocatalyst. At the optimal doping concentration, the FeCo–MoS2 nanosheets provided a NH3 yield rate of 3.27 μg/h/cm2 at −0.55 V [vs reversible hydrogen electrode (RHE)], a value superior to those of undoped MoS2, Fe-doped MoS2, and Co-doped MoS2 samples by 191, 176, and 116%, respectively. Moreover, the Faradaic efficiency of 6.28% at −0.35 V (vs RHE) exceeded those of the undoped MoS2, Fe-doped MoS2, and Co-doped MoS2 samples by 217, 186, and 132%, respectively. Density functional theory calculations revealed that the preferred reaction mediated by the FeCo–MoS2 electrocatalyst followed a distal pathway, with its potential-determining step having an energy barrier (0.54 eV) lower than that of undoped MoS2 (1.13 eV), suggesting that the FeCo–MoS2 nanosheets possessed superior electrocatalytic activity. We conclude that Fe and Co are efficient dopants for boosting the NRR activity of MoS2 catalysts.

Ultralight porous carbon loaded Co-doped MoS2 as an efficient electrocatalyst for hydrogen evolution reaction in acidic and alkaline media

Molybdenum disulfide (MoS2) has a Gibbs free energy comparable to platinum (Pt), suggesting it can replace Pt as a hydrogen evolution reaction (HER) catalyst. However, the shortcomings of the restricted number of MoS2 active sites and poor intrinsic electrical conductivity have resulted in impeding its widespread application. In this work, Co/MoS2@NPC electrocatalyst was prepared by using nitrogen-doped porous carbon (NPC) as a substrate material, and then hydrothermally anchoring cobalt-doped molybdenum disulfide (Co-doped MoS2) on the substrate. Co/MoS2@NPC was subsequently applied to hydrogen evolution reaction in acidic and alkaline media. It was found that the overpotential of 0.2Co/MoS2@NPC was only 139 mV for HER at 10 mA cm−2 with a Tafel slope of 69 mV dec−1 in acidic medium; while in alkaline medium, its overpotential was 163 mV with a Tafel slope of 106 mV dec−1, and it operated stably over 10 h. The superior HER performance may be related to the point that NPC as a substrate can uniformly disperse MoS2, exposing more active sites and ensuring high electronic conductivity of MoS2. In addition, the introduction of Co into MoS2 changed the intrinsic activity of MoS2 and interacted with CoSx and pyridine nitrogen in NPC, constituting a ternary catalytic interaction. Therefore, this study provides a novel strategy for optimizing the HER activity of MoS2.

Multiband Monochromatic Upconversion Emissions of Lanthanide Codoped Monolayer MoS2 Nanosheets for Lighting Applications

Upconversion materials have attracted much attention because of their broad application prospects in biomedicine and energy. Although various methods have been tried in nanoparticles and nanocrystals, it is still a challenge to realize monochromatic upconversion luminescence (UCL) in traditional lanthanide-doped materials. Two-dimensional transition metal chalcogenides (2D-TMDs) are a class of excellent luminescent semiconductors, offering a promising platform due to their chemical accessibility and physical sensitivity. However, multi-lanthanide doping, typically boosting the upconversion efficiency, has not been accomplished in monolayer TMD nanosheets. In this work, an optimized liquid precursor-assisted technique is designed to synthesize monolayer MoS2 nanosheets embedded with Er/Yb and Er/Ho by surmounting the precipitation of Ln3+-doped precursors, which is confirmed by structural characterization. The monolayer MoS2 can split the 4f configuration remarkably to produce diverse energy levels due to its strong Coulomb binding and spin–orbit coupling, as well as the unique asymmetric crystal field along the [001] direction. Hence, multiband monochromatic UCL from violet to near-infrared ranges was obtained on these codoped MoS2 nanosheets. This work provides an effective way to tune the luminescence performance and wavelength of 2D-TMD nanosheets as well as a strategy for the design of UCL nanomaterials for light applications as nanophotonic devices.

A one-step soft-template hydrothermal preparation and piezoelectric catalytic activity of flowers-like Co-doped MoS2 microspheres

A one-step soft-template hydrothermal preparation and piezoelectric catalytic activity of flowers-like Co-doped MoS2 microspheres

Engineering the interfacial doping of 2D heterostructures with good bidirectional reaction kinetics for durably reversible sodium-ion batteries

Interfacial doping engineering has been considered a promising strategy to improve the reaction kinetics of 2D heterostructures in sodium-ion batteries (SIBs). Much attention has been paid to the enhancement mechanism of reaction kinetics of pristine heterostructures during discharge, whereas less attention has been given to the optimization of reaction kinetics of discharged products during charge. Therefore, there is an urgent need for systematic understanding and design guide for interfacial doping engineering of 2D heterostructures to achieve good bidirectional reaction kinetics. In this paper, interfacial doping engineering is designed by the guidance of theoretical calculation, a new interface composed of Co-doped MoS2 (Co-MoS2) and N-doped graphene (NG) has excellent electrical conductivity and Na+ adsorption ability during discharge. Moreover, the revealed Na2S-Mo(Co)/NG interface is greatly beneficial to the dispersion, adsorption, and decomposition of Na2S and the overall electrical conductivity during charge. The good bidirectional reaction kinetics of Co-MoS2/NG interfaces in cobalt-doped MoS2 anchored on three-dimensional nitrogen-doped carbon (Co-MoS2/3DNC) composites have been systematically demonstrated by electrochemical characterization technologies. Therefore, an efficient reversible conversion reaction is enabled by the Co-MoS2/NG interfaces. The Co-MoS2/3DNC shows good rate performance and excellent long-term cycling stability of 1500 cycles at the current density of 1 A g−1. This work provides new insight into designing interfacial doping engineering for highly reversible and durable conversion-type composite anodes.

Synergistic dual atomic sites with localized electronic modulation enable high-performance lithium–oxygen batteries

Lithium-oxygen batteries (LOBs) are recognized as promising candidates for next-generation energy storage system technologies due to their high theoretical energy density. Unfortunately, some fundamental issues still constrain the practical implementation of LOBs, including large overpotential, cathode clogging, and poor long-term stability, mainly due to the slow cathodic reaction kinetics. Therefore, the successful construction of rational catalysts becomes an urgent demand for the development of LOBs. Herein, Ni and Mn co-doped MoS2 (Ni/Mn-MoS2) is fabricated via a facile one-pot hydrothermal method and employed as an efficient cathode catalyst for LOBs. The electrochemical results show that the as-prepared Ni/Mn-MoS2 cathode catalyst exhibits low overpotential with a potential gap of 0.78 V, large discharge capacity of 28,195 mAh g−1 at a current density of 100 mA g−1, and enhanced rate capability. The theoretical calculations further reveal that the synergistic effect of Ni and Mn dual atomic sites modulates the electronic structure of catalyst surface, and then enhances the adsorption energy of intermediate product LiO2 and significantly reduces the overpotential for the formation/decomposition of the amorphous discharge product, thereby accelerating the reaction kinetics. This work may provide inspiration for the rational design of MoS2-based materials as highly efficient electrocatalysts for LOBs.

Monolayer MoS2 Fabricated by In Situ Construction of Interlayer Electrostatic Repulsion Enables Ultrafast Ion Transport in Lithium-Ion Batteries

HighlightsIn-situ construction of electrostatic repulsion between MoS2 interlayers is first proposed to successfully prepare Co-doped monolayer MoS2 under high vapor pressure.The doped Co atoms radically decrease bandgap and lithium ion diffusion energy barrier of monolayer MoS2 and can be transformed into ultrasmall Co nanoparticles (~2 nm) to induce strong surface-capacitance effect during conversion reaction.The Co doped monolayer MoS2 shows ultrafast ion transport capability along with ultrahigh capacity and outstanding cycling stability as lithium-ion-battery anodes.High theoretical capacity and unique layered structures make MoS2 a promising lithium-ion battery anode material. However, the anisotropic ion transport in layered structures and the poor intrinsic conductivity of MoS2 lead to unacceptable ion transport capability. Here, we propose in-situ construction of interlayer electrostatic repulsion caused by Co2+ substituting Mo4+ between MoS2 layers, which can break the limitation of interlayer van der Waals forces to fabricate monolayer MoS2, thus establishing isotropic ion transport paths. Simultaneously, the doped Co atoms change the electronic structure of monolayer MoS2, thus improving its intrinsic conductivity. Importantly, the doped Co atoms can be converted into Co nanoparticles to create a space charge region to accelerate ion transport. Hence, the Co-doped monolayer MoS2 shows ultrafast lithium ion transport capability in half/full cells. This work presents a novel route for the preparation of monolayer MoS2 and demonstrates its potential for application in fast-charging lithium-ion batteries.

Coupled Co-Doped MoS2 and CoS2 as the Dual-Active Site Catalyst for Chemoselective Hydrogenation

Catalytic hydrogenation plays an important role in the industrial production of fine chemicals. Herein, we report a Co-doped MoS2 and CoS2 composite with a coupling interface and successfully apply it for the chemoselective hydrogenation of p-chloronitrobenzene to p-chloroaniline. The target catalyst 0.5CoMoS has ∼100% conversion and ∼100% selectivity. Experiments and theoretical calculations reveal that CoS2 is more favorable for adsorbing and activating H2 and provides active hydrogen (Ha) to Co-doped MoS2 by the coupling interface. By matching the production and consumption rates of Ha, the maximization of the reaction yield was achieved. This work may promote the study of MoS2-based catalysts for chemoselective hydrogenation.

Synthesis of Ni, Co-doped MoS2 as Electrocatalyst for Oxygen Evolution Reaction

Synthesis of Ni, Co-doped MoS2 as Electrocatalyst for Oxygen Evolution Reaction