Doping of MoS2 by "Cu" and "V": An Efficient Strategy for the Enhancement of Hydrogen Evolution Activity

Electric-Field-Assisted Synthesis of Cu/MoS2 Nanostructures for Efficient Hydrogen Evolution Reaction

Molybdenum sulfide-oxide (MoS2, MS) emerges as the prime electrocatalyst candidate demonstrating hydrogen evolution reaction (HER) activity comparable to platinum (Pt). This study presents a facile electrochemical approach for fabricating a hybrid copper (Cu)/MoS2 (CMS) nanostructure thin-film electrocatalyst directly onto nickel foam (NF) without a binder or template. The synthesized CMS nanostructures were characterized utilizing energy-dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), X-ray diffraction (XRD), and electrochemical methods. The XRD result revealed that the Cu metal coating on MS results in the creation of an extremely crystalline CMS nanostructure with a well-defined interface. The hybrid nanostructures demonstrated higher hydrogen production, attributed to the synergistic interplay of morphology and electron distribution at the interface. The nanostructures displayed a significantly low overpotential of -149 mV at 10 mA cm-2 and a Tafel slope of 117 mV dec-1, indicating enhanced catalytic activity compared to pristine MoS2.This research underscores the significant enhancement of the HER performance and conductivity achieved by CMS, showcasing its potential applications in renewable energy.

Elucidating Local Structure and Positional Effect of Dopants in Colloidal Transition Metal Dichalcogenide Nanosheets for Catalytic Hydrogenolysis

Tailoring nanoscale catalysts to targeted applications is a vital component in reducing the carbon footprint of industrial processes; however, understanding and controlling the nanostructure influence on catalysts is challenging. Molybdenum disulfide (MoS2), a transition metal dichalcogenide (TMD) material, is a popular example of a nonplatinum-group-metal catalyst with tunable nanoscale properties. Doping with transition metal atoms, such as cobalt, is one method of enhancing its catalytic properties. However, the location and influence of dopant atoms on catalyst behavior are poorly understood. To investigate this knowledge gap, we studied the influence of Co dopants in MoS2 nanosheets on catalytic hydrodesulfurization (HDS) through a well-controlled, ligand-directed, tunable colloidal doping approach. X-ray absorption spectroscopy and density functional theory calculations revealed the nonmonotonous relationship between dopant concentration, location, and activity in HDS. Catalyst activity peaked at 21% Co:Mo as Co saturates the edge sites and begins basal plane doping. While Co prefers to dope the edges over basal sites, basal Co atoms are demonstrably more catalytically active than edge Co. These findings provide insight into the hydrogenolysis behavior of doped TMDs and can be extended to other TMD materials.

Enhancing photocatalytic overall water-splitting performance on dual-active-sites of the Co-P@MoS2 catalysts: a DFT study

The rational construction of photocatalysts possesses tremendous potential to solve the energy crisis and environmental pollution; however, designing a catalyst for solar-driven overall water-splitting remains a great challenge. Herein, we propose a new MoS2-based photocatalyst (Co-P@MoS2), which skillfully uses the cobalt (Co) atom to stimulate in-plane S atoms and employs the phosphorus (P) atom to stabilize the basal plane by forming the Co-P bands. Using density functional theory (DFT), it was found that oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) can occur at the P site and S2 site of the Co-P@MoS2, respectively, and the dual-active sites successfully makes a delicate balance between the adsorption and dissociation of hydrogen. Furthermore, the improved overall water-splitting performance of Co-P@MoS2 was verified by analyzing the results of the electron structure and the dynamics of photogenerated carries. It was found that the imbalance of electron transfer caused by the introduction of the Co atom was the main contributor to the catalytic activity of Co-P@MoS2. Our study broadens the idea of developing photocatalysts for the overall water-splitting.

Morphology-controlled synthesis of MoS2 using citric acid as a complexing agent and self-assembly inducer for high electrochemical performance

Two-dimensional MoS₂ with a controllable morphology was prepared via a simple one-step hydrothermal method. Citric acid was used as a complexing agent and self-assembly inducer. The morphology of MoS₂ changed from clusters to nanosheets, and, eventually, to stacked nanorods. A formation mechanism is proposed for the observed evolution of the morphology. The nanosheet structure presents a relatively large specific surface area, more exposed active sites and greater 1T phase content compared to the other morphologies. The electrochemical performance tests show that the MoS₂ nanosheets exhibit excellent electrochemical behavior. Their specific capacitance is 320.5 F g^-1, and their capacitance retention is up to 95% after 5000 cycles at 5 mA cm^-2. This work provides a feasible approach for changing the morphology of MoS₂ for high efficiency electrode materials for supercapacitors.

Recent advances in solution assisted synthesis of transition metal chalcogenides for photo-electrocatalytic hydrogen evolution

Hydrogen evolution from water splitting is considered to be an important renewable clean energy source and alternative to fossil fuels for future energy sustainability. Photocatalytic and electrocatalytic water splitting is considered to be an effective method for the sustainable production of clean energy, H₂. This perspective especially emphasizes research advances in the solution-assisted synthesis of transition metal chalcogenides for both photo and electrocatalytic hydrogen evolution applications. Transition metal chalcogenides (CdS, MoS₂, WS₂, TiS₂, TaS₂, ReS₂, MoSe₂, and WSe₂) have received intensified research interest over the past two decades on account of their unique properties and great potential across a wide range of applications. The photocatalytic activity of transition metal chalcogenides can further be improved by elemental doping, heterojunction formation with noble metals (Au, Pt, etc.), non-chalcogenides (MoS₂, In₂S₃, NiS_1-X), morphological tuning, through various solution-assisted synthesis processes, including liquid-phase exfoliation, heat-up, hot-injection methods, hydrothermal/solvothermal routes and template-mediated synthesis processes. In this review we will discuss recent developments in transition metal chalcogenides (TMCs), the role of TMCs for hydrogen production and various strategies for surface functionalization to increase their activity, different synthesis methods, and prospects of TMCs for hydrogen evolution. We have included a brief discussion on the effect of surface hydrogen binding energy and Gibbs free energy change for HER in electrocatalytic hydrogen evolution.

Integrating Amorphous Molybdenum Sulfide Nanosheets with a Co9S8@Ni3S2 Array as an Efficient Electrocatalyst for Overall Water Splitting

It is highly challenging to design low-cost, efficient electrocatalysts for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Herein, a hierarchical heterostructure was constructed on three-dimensional (3D) Ni foam, which contains Ni₃S₂ nanorods decorated with both Co₉S₈ and amorphous MoS_x nanosheets and Ni₃S₂ nanowires decorated with amorphous MoS_x nanosheets, namely, MoS_x@Co₉S₈@Ni₃S₂/NF. The synergistic effects from the strong interactions of the heterointerface and unique hierarchical heterostructure endow the MoS_x@Co₉S₈@Ni₃S₂/NF with abundant active sites and effective mass and electron transport pathways, resulting in excellent activity toward both HER and OER in 1 M KOH. It only gives a low overpotential of 76.5 mV to achieve 10 mA cm^-2 for HER and a low overpotential of 310 mV to achieve 100 mA cm^-2 for OER. Based on the superior catalytic activity of MoS_x@Co₉S₈@Ni₃S₂/NF for OER and HER, we demonstrated the activity of overall water splitting using MoS_x@Co₉S₈@Ni₃S₂/NF as both the anode and cathode. It shows a higher catalytic activity for overall water splitting with a low cell voltage of 1.52 V at 10 mA cm^-2 than commercial Pt/C/NF||IrO₂/NF (1.61 V) and superior stability. This work provides a platform for the design and preparation of efficient electrocatalysts with various hierarchical heterostructures.

Exposing Cu(100) Surface via Ion-Implantation-Induced Oxidization and Etching for Promoting Hydrogen Evolution Reaction

Metallic materials with unique surface structure have attracted much attention due to their unique physical and chemical properties. However, it is hard to prepare bulk metallic materials with special crystal faces, especially at the nanoscale. Herein, we report an efficient method to adjust the surface structure of a Cu plate which combines ion implantation technology with the oxidation-etching process. The large number of vacancies generated by ion implantation induced the electrochemical oxidation of several atomic layers in depth; after chemical etching, the Cu(100) planes were exposed on the surface of the Cu plate. As a catalyst for acid hydrogen evolution reaction, the Cu plate with (100) planes merely needs 273 mV to deliver a current density of 10 mA/cm² because the high-energy (100) surface has moderate hydrogen adsorption and desorption capability. This work provides an appealing strategy to engineer the surface structure of bulk metallic materials and improve their catalytic properties.

Cobalt Carbonate-Coated Nitrogen-Doped Carbon Nanotubes with a Sea-Cucumber Morphology for Electrocatalytic Water Splitting

Herein, we report CoCO₃-coated nitrogen-doped carbon nanotubes (NCNTs) with a sea cucumber-like morphology for water splitting. The sample with a CoCO₃ content of 26.8 wt % (CoCO₃/NCNT-1) exhibits excellent performance for the hydrogen evolution reaction in 1.0 M KOH electrolyte with an overpotential of 58 mV to reach 10 mA cm^-2, better than the most non-noble metal catalysts reported; meanwhile, it exhibits superior electrocatalytic activity for the oxygen evolution reaction. The excellent performance of the catalyst is attributed to the nanotip effect caused by the sea-cucumber-like morphology. Notably, CoCO₃/NCNT-1 can attain turnover frequencies of 2.7 s^-1 at an overpotential of 50 mV, higher than that of Pt/C (1.5 s^-1). A cell constructed using CoCO₃/NCNT-1 as the catalyst of the electrode pair needs a low cell voltage of 1.54 V at 10 mA cm^-2, superior to most reported cells. In addition, CoCO₃/NCNT-1 can maintain 10 mA cm^-2 for overall water splitting for 100 h without activity loss.

Synergistic Promotion Effect of ZnCoS Solid Solution and Co1-xS on Photocatalytic Hydrogen Production of the CdS Composite

Photocatalytic reactions over effective photocatalysts are attractive to explore clean hydrogen energy from water with the utilization of solar energy. Ternary Co_1-xS@ZnCoS/CdS (ZCS/CdS) composites are constructed as photocatalysts through the hydrothermal formation of Co_1-xS and ZnCoS nanoparticles on CdS nanorods. Superior to the binary Co_1-xS/CdS composite, ZCS/CdS shows the improved photocatalytic activity with a hydrogen production rate of 58.4 mmol·g^-1·h^-1, which is 31.4 and 2.1 times higher than those of CdS and Co_1-xS/CdS, respectively. Different from binary Co_1-xS/CdS, the participation of a small amount of zinc favors the formation of ZnCoS solid solution in ZCS/CdS. A synergistic promotion effect of ZnCoS and Co_1-xS is confirmed due to tight heterojunctions among Co_1-xS, ZnCoS, and CdS in ZCS/CdS. The unique heterostructure of ZCS/CdS benefits its enhanced absorption ability of visible light, accelerating the separation of photoinduced electron-hole pairs and the electron transfer. ZCS/CdS exhibits the strong reduction ability and superior photocatalytic stability due to the role of double Z-scheme electron transfer pathways in the ternary composite. This work provides a suitable way to tune noble metal-free composite photocatalysts for efficient H₂ production.

MoS2-2xSe2x Nanosheets Grown on Hollow Carbon Spheres for Enhanced Electrochemical Activity

Electrochemical catalysts with high conductivity and low reaction potential are respected. In this paper, hollow carbon spheres (HCSs) were homogeneously coated with Se-doped MoS₂ (MoS_2-2xSe_2x) nanosheets by hydrothermal synthesis. The HCSs reduced the agglomeration of MoS_2-2xSe_2x nanosheets and improved their conductivity. Compared with the MoS₂-modified samples, Se doping increased the interlayer spacing which provided more active catalytic sites and improved the charge transfer. Thus, MoS_2-2xSe_2x-decorated samples revealed enhanced electrocatalytic activity. The composition of MoS_2-2xSe_2x nanosheets was adjusted by changing the ratios of sulfur and selenium precursors. In the case of a Se/S molar ratio of 0.1, the composite of HCS decorated with MoS_2-2xSe_2x nanosheets (C@MoS_2-2xSe_2x) revealed the lowest overpotential and the smallest Tafel slope.