Inert Basal Plane Research Articles

High-throughput screening of transition metal single-atom catalyst anchored on Janus MoSSe basal plane for hydrogen evolution reaction

Considerable efforts have been made to enhance the hydrogen evolution reaction (HER) catalytic performance of Janus MoSSe monolayer, which have been considered to be a promising candidate due to the unique asymmetry structure. However, the activation effect remains non-optimal for the inert Janus MoSSe basal plane at present. Herein, a train of transition metal (TM) atoms were anchored on the S-/Se-/Mo-defective MoSSe basal plane to screen effective TM single-atom catalysts for HER through density functional theory (DFT) computations. Interestingly, the single Co atom anchored on Mo-defective MoSSe and the single Zn or Cd atom anchored on S-defective MoSSe were judged to possess excellent HER performance yielding a near-zero ΔGH (ΔGH = −0.050, −0.095, −0.098 eV, respectively), which is comparable to the optimized Pt-SACs. The enhanced HER activity is attributed to the doping of TM atoms (Co, Zn and Cd) which improves the conductivity of the original MoSSe and offers unoccupied states near the Fermi level decreasing the energy barrier of electrons transfer between H and TMs@MoSSe surface. In addition, the change of unoccupied antibonding states of active atoms leads to appropriate interaction between the active sites and H. The hybridization between H-s orbital and the TMs@MoSSe systems around the Fermi level also suggests the formation of stable bonding-antibonding hydrogen adsorption states. This work reveals an effective way of activating MoSSe basal plane for HER.

Defect induced electrocatalytic hydrogen properties of pentagonal PdX2 (X = S, Se).

Searching for catalysts of hydrogen evolution reaction (HER) that can replace Pt is critical. Here, we investigated the HER electrocatalytic activity of pentagonal PdS2 (penta-PdS2) and PdSe2 (penta-PdSe2) by first-principles calculations. Three types of vacancies (VS/Se, VPd, DVS/Se) were constructed to activate the inert basal planes of PdS2 and PdSe2. The results show that S/Se and Pd vacancies significantly improve HER performance, and the Gibbs free energy (ΔGH) of systems can be further regulated by vacancy concentration. Particularly, PdS2 with 2.78% VS, 50% VPd and PdSe2 with 12.5% VSe display the optimal ΔGH value and the highest exchange current density. Further analysis of charge transfer and band structures were described that the introduce of vacancies efficiently regulates the electronic properties, resulting in the diminution of bandgap, and accelerates the charge transfer, thereby contributing to an enhanced electron environment for HER process. Our results provide a theoretical guidance for the applications of pentagonal transition-metal dichalcogenides as catalysts of hydrogen evolution reaction.

Understanding the efficient electrocatalytic activities of MoSe2–Cu2S nanoheterostructures

The epitaxial growth of Cu2S NCs over the inert basal planes of MoSe2 NSs increases the number of active sites for OER. The built-in electric field at interfaces greatly favors the OER and HER activities via decreasing the energy barriers.

Photocatalytic activity of co-doped Janus monolayer MoSSe for solar water splitting: A computational investigation

Janus transition-metal dichalcogenide is considered as a promising photocatalyst for solar water splitting because of its inherent internal electric field, tunable electronic and optical properties. However, the limited photocatalytic activity in the inert basal plane hinders its practical application. Here, we propose a heteroatom doping strategy to improve the catalytic activity of the monolayer MoSSe (ML-MoSSe) via charge compensated (N+F) and double-hole mediated (N+P) co-doping. We investigate the possibility of applying co-doped ML-MoSSe as the photocatalyst for water splitting by the first-principles calculations. The calculated results show that the N+F co-doped ML-MoSSe have the relatively higher thermodynamic stability and the reduced direct band gaps in the range of 1.28~1.57 eV with their band edge position satisfying the requirement of the redox potential of water at pH = 0 under the intrinsic polarized electric field. In particular, the doped N sites exhibit highly photocatalytic activity for hydrogen reduction reaction (HER). This work demonstrates that N+F co-doped ML-MoSSe might be a promising photocatalyst that possesses high catalytic activity for HER and simultaneously maintains the intrinsic polarized electric field to facilitate the separation of photogenerated carrier, which will shed light on screening the MoSSe-based photocatalyst.

Controllable fabrication and photocatalytic performance of nanoscale single-layer MoSe2 islands with substantial edges on an Ag(111) substrate.

Two-dimensional (2D) transition metal dichalcogenides (TMDs) are emerging as new electrocatalysts and photocatalysts. The edge sites of 2D TMDs show high catalytic activity and are thus favored at the catalyst surface over TMD inert basal planes. However, 2D TMDs that predominantly expose edges are thermodynamically unfavorable, limiting the number of edge sites at the surface. Herein, we demonstrate a controllable synthesis strategy of single-layer 2D MoSe2 islands with a lateral size of approximately 5-12 nm on an Ag(111) substrate by pre-deposition of excess Se atoms. The surplus Se atoms react with the Ag(111) substrate and form silver selenide compounds to separate MoSe2 islands and further prevent MoSe2 islands from growing up. The nanoscale MoSe2 islands greatly increase the ratio of exposed edge sites relative to the basal plane sites, which leads to excellent photocatalytic activity for the degradation of a methylene blue (MB) organic pollutant. This work paves the way to limit the size of 2D TMDs at the nanoscale and enables new opportunities for enhancing the catalytic activity of 2D TMD materials.

The activation of porous atomic layered MoS2 basal-plane to induce adjacent Mo atom pairs promoting high efficiency electrochemical N2 fixation

MoS2 has been proven to be an efficient NRR electrocatalyst, the activation of inert basal plane and rational utilization of basal plane have become the key to further increasing the activity. The defects of basal plane help to expose active sites, however, they cannot activate basal plane to promote NRR. Herein, based on the calculation results, we designed porous atomic layered 2H-MoS2(PAL-MoS2) by one-step calcination treatment. The porosity of the basal plane effectively utilizes basal plane atoms while the presence of adjacent Mo atom pairs improves the NRR performance. A high Faradic efficiency of 44.36 % and a sizeable NH3 yield of 3405.55 μg h−1 mgcat−1 (1.98 μg h−1 cm−2) at ‒0.1 V vs. reversible hydrogen electrode are obtained in 0.1 M HCl under ambient conditions, as far as we know, outperforming most of Mo-based NRR electrocatalysts reported before. Furthermore, this catalyst also exhibits high selectivity, electrochemical stability and good performance characterization.

Separable magnetic MoS2@Fe3O4 nanocomposites with multi-exposed active edge facets toward enhanced adsorption and catalytic activities

We synthesized fluffy MoS2 material stacked by ultrathin nanosheets through adjusting different mass ratios of starting materials via a facile hydrothermal method. Surprisingly, XRD characterization results demonstrated that the intensity ratio of (100) to (002) of ultrathin MoS2 nanosheets was 0.90 with a 4:5 (CH3CSNH2: Na2MoO4·2H2O) mass ratio (M4-5). To the best of our knowledge, this value should be high, implying that the obtained MoS2 nanosheets exposed considerable (100) facets. Because the noncentrosymmetric Mo-2S on edges terminated by dangling bonds exhibits rich defects, high active MoS2 edge planes (100) prevail over inert MoS2 basal planes (002). To overcome its easy suspension and difficult recovery, the magnetic Fe3O4 was selected for in situ doping with ultrathin M4-5, and a unique structure of stable MoS2@Fe3O4 (M@F) nanocomposites-like randomly stacked rose petals-wrapped spherical chocolate beans was obtained for the first time. The introduction of Fe3O4 has to sacrifice some edge active sites, but after balancing the magnetic and active sites, (100)/(002) of MoS2 in M@F can also reach 0.56, showing that edges of MoS2 nanosheets are still multi-exposed. Abundant exposed edges of M@F provide numerous active centers, so M@F nanocomposites exhibited excellent performance for both the 4-nitrophenol (4-NP) reduction and dye adsorption. Therefore, it has great application prospects in wastewater treatment and reduction reaction and is also worth exploring in other applications.

Low-Power and Ultra-Thin MoS2 Photodetectors on Glass.

Integration of low-power consumer electronics on glass can revolutionize the automotive and transport sectors, packaging industry, smart building and interior design, healthcare, life science engineering, display technologies, and many other applications. However, direct growth of high-performance, scalable, and reliable electronic materials on glass is difficult owing to low thermal budget. Similarly, development of energy-efficient electronic and optoelectronic devices on glass requires manufacturing innovations. Here, we accomplish both by relatively low-temperature (<600 °C) metal-organic chemical vapor deposition growth of atomically thin MoS2 on multicomponent glass and fabrication of low-power phototransistors using atomic layer deposition (ALD)-grown, high-k, and ultra-thin (∼20 nm) Al2O3 as the top-gate dielectric, circumventing the challenges associated with the ALD nucleation of oxides on inert basal planes of van der Waals materials. The MoS2 photodetectors demonstrate the ability to detect low-intensity visible light at high speed and low energy expenditure of ∼100 pico Joules. Furthermore, low device-to-device performance variation across the entire 1 cm2 substrate and aggressive channel length scalability confirm the technology readiness level of ultra-thin MoS2 photodetectors on glass.

Bonding mechanism on TGDDM/CF and the influences of functional groups and interfacial water: An MD and DFT investigation

Bonding mechanism between tetraglycidyl diamino diphenyl methane (TGDDM) epoxy resin and carbon fiber (CF) is investigated by employing MD and DFT methods. Edge sites of CF surface (CF(100) and (110)) are focused due to they are chemically active than the inert basal planes. Two kinds functional groups (OH and COOH) are anchored on these sites, and the impacts of interfacial water are examined. The most negative adsorption energy (Ead) goes to the model of TGDDM absorbed onto COOH-functionalized CF(110) (noted as CF(110)COOH). Mulliken population analysis implies that O-H hydrogen bonds have formed across the interface. More bonds tend to form with CF(110) surface and COOH groups. The energy per each hydrogen bond is around 25.95–31.07 kJ/mol, and bond length ranges around 1.81–2.49 Å, which are consistent with previous reports. For the interfacial bonds associated with OH-functionalizaion, TGDDM and OH groups are hydrogen acceptors and donors, respectively. While for the cases with COOH groups, both the TGDDM and COOH groups can act as either acceptors, or donors. Caused by interfacial water, the interfacial hydrogen bonds will be detached, and the interaction energy (Eint) between TGDDM-CF(110) decreases 84.04%. Meanwhile, new hydrogen bonds will form between H2O-TGDDM (and H2O-CF).

Oxygen-facilitated dynamic active-site generation on strained MoS2 during photo-catalytic hydrogen evolution

Molybdenum disulfide (MoS2) is considered as one of the most effective materials which can supersede the high cost and scarcity of metal platinum (Pt) for the hydrogen evolution reaction (HER). One road block lying in access to high catalytic performance of MoS2 emanates from the inert basal plane. To enable inert basal plane of flexible MoS2, we demonstrate an effective synthesis strategy via the progressive transformation of MoS2 to MoS2-xOx with O atomically dispersed under actual photo-catalytic hydrogen evolution condition. The rate of hydrogen production of new reconstructed MoS2-xOx nanosheets is improved to be much higher than that of the initial MoS2. Our theoretical calculation results indicate that the appropriate O substitution and strain could modulate the surface electronic state and optimize the Gibbs free energy (ΔGH) of MoS2, thus dramatically accelerating the catalytic efficiency. This work showcases a promising route to achieve tunable photochemical reconstruction by optimizing the electronic structure for low-cost and robust MoS2-based HER catalysts.

Defects Enhance the Electrocatalytic Hydrogen Evolution Properties of MoS2 -based Materials.

MoS2 have recently emerged as alternatives to noble metals as electrocatalysts for the hydrogen evolution reaction (HER) owing to their abundance and low cost. Considering the shortcomings of MoS2 , including insufficient active sites, inert basal plane, and poor conductivity, the electrocatalytic hydrogen evolution properties of MoS2 can be improved in three ways: activating the inert basal plane to improve intrinsic activity, increasing active edge sites, and improving the conductivity. Defects can adjust the surface electronic structure of the crystal to bring the hydrogen adsorption free energy closer to zero. Therefore, current research has mainly used S-vacancies to activate the inert basal surface of MoS2 ; used edge defects to increase the number of active sites; and used defective conductive carbon supports to improve the conductivity of MoS2 -based catalysts. This review introduces researches on improving the performance of MoS2 for HER by considering the purpose, characterization, and preparation of defects.

Photo-Degradation Performance for RhB under Visible Light Irradiation

MoS2 is a promising photo-catalyst for the degradation of organic pollution due to its large surface area, low cost, easy preparation, and earth abundance. However, their limited quantity of active sites, high recombination of photo-generated charge, and poor conductivity has hampered the efficiency of photo-degradation. In this work, P heteroatoms were doped into the plane of ultrathin MoS2 nanosheets via a facile hydrothermal method, which introduce the new active sites in the inert basal plane of MoS2, improve the separation efficiency of photo-generated charges and help improve the intrinsic electronic conductivity, leading to a significantly improved activity for photo-degradation of RhB.

Heterostructure of 3D sea-grape-like MoS2/graphene on carbon cloth for enhanced water splitting

MoS2 has been widely used as a hydrogen evolution reaction (HER) electrocatalyst because of its unique characteristics, such as a tunable band gap, near-zero Gibbs free energy, and earth abundance. However, its low electrical conductivity and the electrochemically inert basal plane of MoS2 decrease the HER performance. Herein, we used graphene and carbon cloth (CC) to boost the electrocatalytic activity of MoS2. Using nickel electrodeposition and chemical vapor deposition (CVD) at high temperature, graphene was grown on carbon cloth (Gr/CC) and a sea-grape-like morphology was formed simultaneously. Finally, Gr/CC was covered up with MoS2 using two-zone CVD (MoS2/Gr/CC), resulting in a three-dimensional (3D) sea-grape-like heterostructure. The MoS2/Gr/CC exhibits outstanding HER performance, with a suitable onset potential (50 mV), low ŋ10 (91 mV, overpotential at 10 mA cm−2), high electrical double layer capacitance (Cdl; 239 mF cm−2), low Tafel slope value (48 mV dec−1), and high stability in 0.5 M H2SO4 for two days at various overpotentials. The 3D sea-grape-like morphology and the synergistic effect of MoS2 and graphene led to the enhanced electrocatalytic activity of MoS2/Gr/CC, indicating much better HER performance than most electrocatalysts based on graphene and MoS2.

Revisiting the Active Sites at the MoS2/H2O Interface via Grand-Canonical DFT: The Role of Water Dissociation.

MoS2 is a promising low-cost catalyst for the hydrogen evolution reaction (HER). However, the nature of the active sites remains a subject of debate. By taking the electrochemcal potential explicitly into account using grand-canonical density functional theory (DFT) in combination with the linearized Poisson-Boltzmann equation, we herein revisit the active sites of 2H-MoS2. In addition to the well-known catalytically active edge sites, also specific point defects on the otherwise inert basal plane provide highly active sites for HER. Given that HER takes place in water, we also assess the reactivity of these active sites with respect to H2O. The thermodynamics of proton reduction as a function of the electrochemical potential reveals that four edge sites and three basal plane defects feature thermodynamic overpotentials below 0.2 V. In contrast to current proposals, many of these active sites involve adsorbed OH. The results demonstrate that even though H2O and OH block "active" sites, HER can also occur on these "blocked" sites, reducing protons on surface OH/H2O entities. As a consequence, our results revise the active sites, highlighting the so far overlooked need to take the liquid component (H2O) of the functional interface into account when considering the stability and activity of the various active sites.

Designing Champion Nanostructures of Tungsten Dichalcogenides for Electrocatalytic Hydrogen Evolution.

Fine-tuning strain and vacancies in 2H-phase transition-metal dichalcogenides, although extremely challenging, is crucial for activating the inert basal plane for boosting the hydrogen evolution reaction (HER). Here, atomically curved 2H-WS2 nanosheets with precisely tunable strain and sulfur vacancies (S-vacancies) along with rich edge sites are synthesized via a one-step approach by harnessing geometric constraints. The approach is based on the confined epitaxy growth of WS2 in ordered mesoporous graphene derived from nanocrystal superlattices. The spherical curvature imposed by the graphitic mesopores enables the generation of uniform strain and S-vacancies in the as-grown WS2 nanosheets, and simultaneous manipulation of these two key parameters can be realized by simply adjusting the pore size. In addition, the formation of unique mesoporous WS2 @graphene van der Waals heterostructures ensures the ready access of active sites. Fine-tuning the WS2 layer number, strain, and S-vacancies enables arguably the best-performing HER 2H-WS2 electrocatalysts ever reported. Density functional theory calculations indicate that compared with strain, S-vacancies play a more critical role in enhancing the HER activity.

Solvothermal synthesis of oxygen-incorporated MoS2-x nanosheets with abundant undercoordinated Mo for efficient hydrogen evolution

Activating the inert basal planes of layered molybdenum disulfide (MoS2) is critical to deliver its high hydrogen evolution reaction (HER) efficiency. Herein, oxygen-incorparated MoSx with abundant undercoordinated Mo atoms is fabricated by a facile solvothermal procedure, which realizes synergistically structural and electronic regulations of MoS2 inert basal planes. Experiment results reveal that oxygen incoparation can effectively modulate the electronic structure and further optimize the intrinsic conductivity, while the defect-rich structure with abundant undercoordinated Mo atoms increases the number of active sites. Moreover, the influence of solvothermal temperature on activity of MoS2-x is also investigated. The achieved MoSx electrocatalyst prepared at 220 °C exhibits a superior activity for HER with a low overpotential of 191 mV at 10 mA cm−2, a small Tafel slope of 67 mV dec−1, and an excellent stability due to the largest surface area and superior conductivity.

Design of MoS2/Graphene van der Waals Heterostructure as Highly Efficient and Stable Electrocatalyst for Hydrogen Evolution in Acidic and Alkaline Media

The thermodynamically stable phase of molybdenum disulfide (MoS2) is evaluated as a promising and durable nonprecious-metal electrocatalyst toward the hydrogen evolution reaction (HER); however, its actual catalytic activity is restricted by an inert basal plane, low electronic conductivity, low density, and using efficiency of edged atoms. Moreover, 2D/2D van der Waals (vdws) heterostructures (HSs) with face-to-face contact can construct a highly coupled interface and are demonstrated to have immense potential for catalytic applications. In the present work, a 2D/2D hetero-layered architecture of an electrocatalyst, based on the alternate arrangement of ultrasmall monolayer MoS2 nanosheets (approximately 5-10 nm) and ultrathin graphene (G) sheets, is prepared by a facilely chemical process, which is named as MoS2/G HS. The unique structural characteristic of MoS2/G HS is in favor of accommodating more active sites as the centers of ad/desorption hydrogen and transferring and separating the charges at a coupled interface to improve the electronic conductivity and durability. The density functional theory calculation results further confirm that the alternately arranged G layers and MoS2 monolayers, as well as the expanded interplanar distance of 1.104 nm for MoS2/G HS, can exhibit a superior HER performance in both 0.5 M H2SO4 and 1.0 M KOH.

Prediction of intrinsic electrocatalytic activity for hydrogen evolution reaction in Ti4X3 (X = C, N)

Two-dimensional electrocatalytic materials for hydrogen evolution reaction (HER) have attracted considerable attention recently. However, most of the reported systems exhibit an inert basal plane, and extra engineering are needed to trigger the activity, greatly hindering their practical applications. Herein, using first-principles calculations, we identify a family of promising HER catalytic materials with high intrinsic activity in MXene Ti4X3O2 (X = C, N). We find that Ti4X3 are terminated by a mixture of OH* and O* under standard condition by plotting Pourbaix diagram. The adsorption of atomic hydrogen on Ti4X3O2 exhibits a low Gibbs free energy difference, and the obtained activity barrier of Volmer-Heyrovsky step for Ti4N3O2 is only 30 meV, which indicates the excellent intrinsic HER activity. Furthermore, we explore the HER activity of Ti4X3O2 in aqueous solution through applying biaxial strain, and find that the low Gibbs free energy is well preserved, demonstrating the high stability of the intrinsic HER activity of Ti4X3O2 in solution environment.

MoS2 Nanoplates Embedded in Co–N-Doped Carbon Nanocages as Efficient Catalyst for HER and OER

Molybdenum disulfide (MoS2), although it has shown great potential use in electrocatalysis, owns inert basal planes and the low electrical conductivity that limit its effective application. In this...

Investigation of electronic properties and chemical interactions of graphene-MoSx composites

Nanostructured transition metal dichalcogenide (TMDs) materials exhibit promising potential in next-generation optoelectronic devices and catalysts. TMDs possess chemically inert basal planes and catalytically active edge sites, with the relative population of the latter being a decisive factor for tailoring the structural, chemical and electronic properties of such nanostructures. In virtually all applications, TMD-based assemblies must be interfaced with other materials (such as graphitic domains in an electrode). During the in situ growth of MoS2 nanostructures in the presence of oxygen-doped graphitic materials, the formation of amorphous and/or crystalline Mo-based species could influence the chemical environment and electronic properties of the composites. In this study a detailed investigation of both graphene oxide (GO) and reduced graphene oxide (rGO) with MoSxOy composites were studied for the first time with X-ray and ultra-violet photoelectron spectroscopies (XPS/UPS). The composites were obtained upon gradual heating of GO and rGO with ammonium tetrathiomolubdate (ATTM) hybrid films in Ultra High Vacuum where Mo6+, Moa+ (5 ≤ a < 6), MoS2 and sulphur oxides were formed. An accurate assessment of the chemical environment of the component interfaces along with its electronic properties was performed. These findings have implications for electronic transport and the understanding of behavior of such hybrid assemblies in many applications.