Two‐dimensional (2D) transition‐metal dichalcogenide (TMD) nanosheets have emerged as a fascinating new class of materials for catalysis. These nanosheets are active for several important catalysis ...reactions including hydrogen evolution from water. The rich chemistry of TMDs combined with numerous strategies that allow tuning of their electronic properties make these materials very attractive for understanding the fundamental principles of electro‐ and photocatalysis, as well as for developing highly efficient, renewable, and affordable catalysts for large‐scale production of hydrogen. Recent developments are highlighted and important challenges in using TMDs as catalysts are also discussed.
Transition metal dichalcogenide (TMD) nanosheets are promising catalysts for evolution of hydrogen. TMDs possess a wide range of electronic and catalytic properties so that important fundamental parameters related to catalysis can be investigated. Recent progress on the study of 2D TMD nanosheets for enhancing their electro‐ and photocatalytic activity is discussed.
As the dimensions of the semiconducting channels in field-effect transistors decrease, the contact resistance of the metal-semiconductor interface at the source and drain electrodes increases, ...dominating the performance of devices
. Two-dimensional (2D) transition-metal dichalcogenides such as molybdenum disulfide (MoS
) have been demonstrated to be excellent semiconductors for ultrathin field-effect transistors
. However, unusually high contact resistance has been observed across the interface between the metal and the 2D transition-metal dichalcogenide
. Recent studies have shown that van der Waals contacts formed by transferred graphene
and metals
on few-layered transition-metal dichalcogenides produce good contact properties. However, van der Waals contacts between a three-dimensional metal and a monolayer 2D transition-metal dichalcogenide have yet to be demonstrated. Here we report the realization of ultraclean van der Waals contacts between 10-nanometre-thick indium metal capped with 100-nanometre-thick gold electrodes and monolayer MoS
. Using scanning transmission electron microscopy imaging, we show that the indium and gold layers form a solid solution after annealing at 200 degrees Celsius and that the interface between the gold-capped indium and the MoS
is atomically sharp with no detectable chemical interaction between the metal and the 2D transition-metal dichalcogenide, suggesting van-der-Waals-type bonding between the gold-capped indium and monolayer MoS
. The contact resistance of the indium/gold electrodes is 3,000 ± 300 ohm micrometres for monolayer MoS
and 800 ± 200 ohm micrometres for few-layered MoS
. These values are among the lowest observed for three-dimensional metal electrodes evaporated onto MoS
, enabling high-performance field-effect transistors with a mobility of 167 ± 20 square centimetres per volt per second. We also demonstrate a low contact resistance of 220 ± 50 ohm micrometres on ultrathin niobium disulfide (NbS
) and near-ideal band offsets, indicative of defect-free interfaces, in tungsten disulfide (WS
) and tungsten diselenide (WSe
) contacted with indium alloy. Our work provides a simple method of making ultraclean van der Waals contacts using standard laboratory technology on monolayer 2D semiconductors.
Low-dimensional materials have been examined as electrocatalysts for the hydrogen evolution reaction (HER). Among them, two-dimensional transition metal dichalcogenides (2D-TMDs) such as MoS2 have ...been identified as potential candidates. However, the performance of TMDs toward HER in both acidic and basic media remains inferior to that of noble metals such as Pt and its alloys. This calls for investigating the influence of controlled defect engineering of 2D TMDs on their performance toward hydrogen production. Here, we explored the HER activity from defective multilayered MoS2 over a large range of surface S vacancy concentrations up to 90%. Amorphous MoS2 and 2H MoS2 with ultrarich S vacancies demonstrated the highest HER performance in acid and basic electrolytes, respectively. We also report that the HER performance from multilayered MoS2 can be divided into two domains corresponding to “point defects” at low concentrations of surface S vacancies (Stage 1) and large regions of undercoordinated Mo atoms for high concentrations of surface S vacancies (Stage 2). The highest performance is obtained for Stage 2 in the presence of undercoordinated Mo atoms with a TOF of ∼2 s–1 at an overpotential of 160 mV in 0.1 M KOH which compares favorably to the best results in the literature. Overall, our work provides deeper insight on the HER mechanism from defected MoS2 and provides guidance for the development of defect-engineered TMD-based electrocatalysts.
Abstract Supporting materials for electrocatalysts must exhibit relative chemical inertness to facilitate unimpeded movement of gas, and demonstrate electrical conductivity to promote efficient ...electron transfer to the catalyst. Conventional catalyst electrodes, such as glassy carbon, carbon cloths, or Ni foam, are commonly employed. However, the challenge lies in the limited stability observed during testing due to the relatively weak adhesion between the catalyst and the electrode. Addressing this limitation is crucial for advancing the stability and performance of catalyst-electrode systems in various applications. Here, we suggest a novel fabrication method for a freestanding conducting film, accomplished through gelation, incorporating 1T-MoS 2 and graphene oxide. 1T-MoS 2 nanosheets play a crucial role in promoting the reduction of graphene oxide (GO) on the Zn foil. This contribution leads to accelerated film formation and enhanced electrical conductivity in the film. The synergistic effect also enhances the film’s stability as catalyst supports. This study provides insights into the effective utilization of MoS 2 and graphene oxide in the creating of advanced catalyst support systems with potential applications in diverse catalytic reaction.
Metallic transition metal dichalcogenides (TMDs)
are good catalysts for the hydrogen evolution reaction (HER). The overpotential and Tafel slope values of metallic phases and edges
of two-dimensional ...(2D) TMDs approach those of Pt. However, the overall current density of 2D TMD catalysts remains orders of magnitude lower (~10-100 mA cm
) than industrial Pt and Ir electrolysers (>1,000 mA cm
)
. Here, we report the synthesis of the metallic 2H phase of niobium disulfide with additional niobium (2H Nb
S
, where x is ~0.35)
as a HER catalyst with current densities of >5,000 mA cm
at ~420 mV versus a reversible hydrogen electrode. We find the exchange current density at 0 V for 2H Nb
S
to be ~0.8 mA cm
, corresponding to a turnover frequency of ~0.2 s
. We demonstrate an electrolyser based on a 2H Nb
S
cathode that can generate current densities of 1,000 mA cm
. Our theoretical results reveal that 2H Nb
S
with Nb-terminated surface has free energy for hydrogen adsorption that is close to thermoneutral, facilitating HER. Therefore, 2H Nb
S
could be a viable catalyst for practical electrolysers.
The excellent catalytic activity of metallic MoS2 edges for the hydrogen evolution reaction (HER) has led to substantial efforts towards increasing the edge concentration. The 2H basal plane is less ...active for the HER because it is less conducting and therefore possesses less efficient charge transfer kinetics. Here we show that the activity of the 2H basal planes of monolayer MoS2 nanosheets can be made comparable to state-of-the-art catalytic properties of metallic edges and the 1T phase by improving the electrical coupling between the substrate and the catalyst so that electron injection from the electrode and transport to the catalyst active site is facilitated. Phase-engineered low-resistance contacts on monolayer 2H-phase MoS2 basal plane lead to higher efficiency of charge injection in the nanosheets so that its intrinsic activity towards the HER can be measured. We demonstrate that onset potentials and Tafel slopes of ∼-0.1 V and ∼50 mV per decade can be achieved from 2H-phase catalysts where only the basal plane is exposed. We show that efficient charge injection and the presence of naturally occurring sulfur vacancies are responsible for the observed increase in catalytic activity of the 2H basal plane. Our results provide new insights into the role of contact resistance and charge transport on the performance of two-dimensional MoS2 nanosheet catalysts for the HER.
With the exploding interest in transition metal chalcogenides, sulfide minerals containing the dianion S2 2–, such as pyrite (FeS2), cattierite (CoS2), and vaesite (NiS2), have recently attracted ...much attention for potential applications in energy conversion and storage devices. However, the synthesis of the patronite structure (VS4, V4+(S2 2–)2) and its applications have not yet been clearly demonstrated because of experimental difficulties and the existence of nonstoichiometric phases. Herein, we report the synthesis of VS4 using a simple, facile hydrothermal method with a graphene oxide (GO) template and the characterization of the resulting material. Tests of various templates such as CNT, pyrene, perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA), and graphite led us to the conclusion that the graphitic layer plays a role in the nucleation during growth of VS4. Furthermore, the VS4/rGO hybrid was proved to be a promising functional material in energy storage devices.
Two dimensional (2D) materials-based plasmon-free surface-enhanced Raman scattering (SERS) is an emerging field in nondestructive analysis. However, impeded by the low density of state (DOS), an ...inferior detection sensitivity is frequently encountered due to the low enhancement factor of most 2D materials. Metallic transition-metal dichalcogenides (TMDs) could be ideal plasmon-free SERS substrates because of their abundant DOS near the Fermi level. However, the absence of controllable synthesis of metallic 2D TMDs has hindered their study as SERS substrates. Here, we realize controllable synthesis of ultrathin metallic 2D niobium disulfide (NbS2) (<2.5 nm) with large domain size (>160 μm). We have explored the SERS performance of as-obtained NbS2, which shows a detection limit down to 10–14 mol·L–1. The enhancement mechanism was studied in depth by density functional theory, which suggested a strong correlation between the SERS performance and DOS near the Fermi level. NbS2 features the most abundant DOS and strongest binding energy with probe molecules as compared with other 2D materials such as graphene, 1T-phase MoS2, and 2H-phase MoS2. The large DOS increases the intermolecular charge transfer probability and thus induces prominent Raman enhancement. To extend the results to practical applications, the resulting NbS2-based plasmon-free SERS substrates were applied for distinguishing different types of red wines.
The purpose of this work is to check if additive manufacturing technologies are suitable for reproducing porous samples designed for sound absorption. The work is an inter-laboratory test, in which ...the production of samples and their acoustic measurements are carried out independently by different laboratories, sharing only the same geometry codes describing agreed periodic cellular designs. Different additive manufacturing technologies and equipment are used to make samples. Although most of the results obtained from measurements performed on samples with the same cellular design are very close, it is shown that some discrepancies are due to shape and surface imperfections, or microporosity, induced by the manufacturing process. The proposed periodic cellular designs can be easily reproduced and are suitable for further benchmarking of additive manufacturing techniques for rapid prototyping of acoustic materials and metamaterials.
We report edge-selective functionalization of graphite (EFG) for the production of large-area uniform graphene films by simply solution-casting EFG dispersions in dichloromethane on silicon oxide ...substrates, followed by annealing. The resultant graphene films show ambipolar transport properties with sheet resistances of 0.52–3.11 kΩ/sq at 63–90% optical transmittance. EFG allows solution processing methods for the scalable production of electrically conductive, optically transparent, and mechanically robust flexible graphene films for use in practice.
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