Single Transition Metal Atom Bound to the Unconventional Phase of the MoS2 Monolayer for Catalytic Oxygen Reduction Reaction: A First-Principles Study

Influence of Inorganic Anions on the Chemical Stability of Molybdenum Disulfide Nanosheets in the Aqueous Environment

Chemical stability is closely associated with the transformations and bioavailabilities of engineered nanomaterials and is a key factor that governs broader and long-term application. With the growing utilization of molybdenum disulfide (MoS2) nanosheets in water treatment and purification processes, it is crucial to evaluate the stability of MoS2 nanosheets in aquatic environments. Nonetheless, the effects of anionic species on MoS2 remain largely unexplored. Herein, the stability of chemically exfoliated MoS2 nanosheets (ceMoS2) was assessed in the presence of inorganic anions. The results showed that the chemical stability of ceMoS2 was regulated by the nucleophilicities and the resultant charging effects of the anions in aquatic systems. The anions promote the dissolution of ceMoS2 by triggering a shift in the chemical potential of the ceMoS2 surface as a function of the anion nucleophilicity (i.e., charging effect). Fast charging with HCO3- and HPO42-/H2PO4- was validated by a phase transition from 1T to 2H and the emergence of MoV, and it promoted oxidative dissolution of the ceMoS2. Additionally, under sunlight, ceMoS2 dissolution was accelerated by NO3-. These findings provide insight into the ion-induced fate of ceMoS2 and the durability and risks of MoS2 nanosheets in environmental applications.

Theoretical study of highly efficient VS2-based single-atom catalysts for lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries have become a research hotspot due to their high energy density. However, they also have certain disadvantages and limitations. To enhance the performance of Li-S batteries, this study focuses on the utilization of transition metal (TM)-embedded vanadium disulfide (VS2) materials as cathode catalysts. Using density functional theory (DFT), comprehensive calculations and atomic-level screening of ten TM atoms were conducted to understand the underlying mechanisms and explore the potential of TM@VS2 catalysts for enhancing battery performance. The computational results indicate that five selected catalysts possess sufficient bonding strength towards high-order lithium polysulfide intermediates by the formation of a significant covalent bond between S atoms in Li2Sn and TM atoms, thereby effectively suppressing the shuttle effect. The Ni@VS2 catalyst can effectively decrease the decomposition energy barrier of Li2S in the charge reaction and can have an optimal Gibbs free energy at the rate-determining step among TM@VS2 catalysts for the discharge reaction. This study elucidates the mechanism of VS2-based transition-metal single-atom catalysts and provides an effective reference for the anchoring of TM atoms on other materials.

Rational design of MoS2-supported Cu single-atom catalysts by machine learning potential for enhanced peroxidase-like activity

Two-dimensional molybdenum disulfide (2D-MoS₂)-supported single atom nanomaterials with enhanced enzyme-like activities are potential substitutes for natural enzymes due to their huge specific surface areas, ease of decoration, high catalytic activity and high catalytic stability. However, their catalytic mechanism remains unclear, making the rational design of nanozymes difficult to achieve. Herein, the mechanisms have been explored to enhance the peroxidase-like activity of MoS₂ for H₂O₂ decomposition. Global neutral network (G-NN) potentials were constructed to accurately and quickly illustrate the mechanisms of MoS₂ catalysts and their surface modifications. The high peroxidase-like activity of the MoS₂-supported Cu single atom catalyst with sulfur vacancy (Cu@MoS₂-Vs) in acidic conditions was systematically evaluated using the trained G-NN potential and density functional theory (DFT), as well as experimental validation. Further analysis of the geometric and electronic properties of pivotal stationary structures revealed the enhanced electron transfer process for high catalytic performance with the modulation of the Cu single atom loading, sulfur vacancy engineering and the surrounding acidic and alkaline environment regulation on the MoS₂ basal plane. The results also showed that Cu@MoS₂-Vs in an acidic environment exhibited the highest peroxidase-like activity. This work is expected to provide broad implications for the rational design of substrate-supported single-atom catalysts with superior performance and lower cost by surface modification and acidic and alkaline environment regulation.

N-Doped CrS2 Monolayer as a Highly-Efficient Catalyst for Oxygen Reduction Reaction: A Computational Study

Searching for low-cost and highly-efficient oxygen reduction reaction (ORR) catalysts is crucial to the large-scale application of fuel cells. Herein, by means of density functional theory (DFT) computations, we proposed a new class of ORR catalysts by doping the CrS₂ monolayer with non-metal atoms (X@CrS₂, X = B, C, N, O, Si, P, Cl, As, Se, and Br). Our results revealed that most of the X@CrS₂ candidates exhibit negative formation energy and large binding energy, thus ensuring their high stability and offering great promise for experimental synthesis. Moreover, based on the computed free energy profiles, we predicted that N@CrS₂ exhibits the best ORR catalytic activity among all considered candidates due to its lowest overpotential (0.41 V), which is even lower than that of the state-of-the-art Pt catalyst (0.45 V). Remarkably, the excellent catalytic performance of N@CrS₂ for ORR can be ascribed to its optimal binding strength with the oxygenated intermediates, according to the computed linear scaling relationships and volcano plot, which can be well verified by the analysis of the p-band center as well as the charge transfer between oxygenated species and catalysts. Therefore, by carefully modulating the incorporated non-metal dopants, the CrS₂ monolayer can be utilized as a promising ORR catalyst, which may offer a new strategy to further develop eligible electrocatalysts in fuel cells.

Computational screening of single-atom catalysts supported by VS2 monolayers for electrocatalytic oxygen reduction/evolution reactions

The development of highly efficient bifunctional electrocatalysts to boost oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is highly desirable for energy conversion and storage devices. Herein, by means of comprehensive first-principles computations, we systematically explored the catalytic activities of a series of single transition metal atoms anchored on two-dimensional VS₂ monolayers (TM@VS₂) for ORR/OER. Our results revealed that Ni@VS₂ exhibits low overpotentials for both ORR (0.45 V) and OER (0.31 V), suggesting its great potential as a bifunctional catalyst, which is mainly induced by its moderate interaction with oxygenated intermediates according to the established scaling relationship and volcano plot. Interestingly, the substituted doping of nitrogen heteroatoms into the VS₂ substrate can further effectively improve the ORR/OER activity of the active metal atom to achieve more eligible ORR/OER bifunctional catalysts. Our results not only propose a new class of potential bifunctional oxygen catalysts but also offer a feasible strategy for further tuning their catalytic activity.

Deciphering the Role of Substitution in Transition-Metal Phosphorous Trisulfide (100) Surface: A Highly Efficient and Durable Pt-free ORR Electrocatalyst

Rational design and development of earth-abundant, cost-effective, environmentally benign and highly robust oxygen reduction reaction (ORR) electrocatalyst can circumvent the obstacles associated with large scale commercialization of fuel cell. Here using first-principles based density functional theory (DFT), we have computationally screened the potential and feasibility of transition-metal phosphorous trisulfides TMPS3(100) surfaces as efficient ORR electrocatalyst in acidic fuel cell application. MnPS3(100) surface emerges to be the best among TMPS3 surfaces with optimal O2 activation resulting very low overpotential. The study reveals that ORR occurs on MnPS3 surface via 4e reduction associative pathway where kinetically rate determining step (RDS) is O* + H2O formation with an activation barrier of 0.66 eV. Substitution in half of the Mn sites of MnPS 3 (100) surface with Co enhances the ORR activity considerably. Mn0.5Co0.5PS3(100) surface exhibit an ultralow overpotential of 0.39 V vs RHE switching ORR pathway from associative to dissociative. Spontaneous dissociation of H2O2 on Mn0.5Co0.5PS3 proves 4e reduction pathway excluding 2e one. Electronic structure analysis reveals that pristine MnPS3(100) surface is a narrow band gap semiconductor which upon Co substitution transforms into a conducting metallic surface enhancing ORR activity.

Modulating the Local Coordination Environment of Single-Atom Catalysts for Enhanced Catalytic Performance in Hydrogen/Oxygen Evolution Reaction

Single-atom catalysts (SACs) hold the promise of utilizing 100% of the participating atoms in a reaction as active catalytic sites, achieving a remarkable boost in catalytic efficiency. Thus, they present great potential for noble metal-based electrochemical application systems, such as water electrolyzers and fuel cells. However, their practical applications are severely hindered by intrinsic complications, namely atom agglomeration and relocation, originating from the uncontrollably high surface energy of isolated single-atoms (SAs) during postsynthetic treatment processes or catalytic reactions. Extensive efforts have been made to develop new methodologies for strengthening the interactions between SAs and supports, which could ensure the desired stability of the active catalytic sites and their full utilization by SACs. This review covers the recent progress in SACs development while emphasizing the association between the regulation of coordination environments (e.g., coordination atoms, numbers, sites, structures) and the electrocatalytic performance of the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The crucial role of coordination chemistry in modifying the intrinsic properties of SACs and manipulating their metal-loading, stability, and catalytic properties is elucidated. Finally, the future challenges of SACS development and the industrial outlook of this field are discussed.

Asymmetric surfaces endow Janus bismuth oxyhalides with enhanced electronic and catalytic properties for the hydrogen evolution reaction

The electronic and catalytic properties of Janus bismuth oxyhalide (Bi₂O₂XY, where X/Y = Cl, Br, or I, and X ≠ Y) for the hydrogen evolution reaction (HER) are evaluated through first-principles calculations. Janus Bi₂O₂XY shows an enhanced separation efficiency of electron-hole pairs and an augmented utilization of solar energy due to Janus asymmetry. The asymmetric halogen surfaces on both sides of Janus Bi₂O₂XY induce an electrostatic potential difference, which leads to a staggered band alignment. The solar-to-hydrogen (STH) efficiencies of Janus Bi₂O₂BrI and Bi₂O₂ClI have greatly improved compared to those of pristine BiOBr and BiOCl. Additionally, Janus Bi₂O₂XY achieves stronger internal electric fields (IEFs) and a more suitable Gibbs free energy of hydrogen adsorption (ΔG_H) than pristine BiOX. Moreover, the halogen layer with a smaller electronegativity in Janus Bi₂O₂XY forms a stronger IEF with the oxygen layer; consequently, the ΔG_H of terminations value is closer to the ideal value for the HER. The localized edge states in the p-orbital density of states (DOS) projected onto O atoms are responsible for the HER activity of terminations. This work provides a comprehensive understanding of Janus Bi₂O₂XY for the HER and provides a strategy for improving photocatalysis.

Optimized Pt Single Atom Harvesting on TiO2 Nanotubes-Towards a Most Efficient Photocatalyst

In the present work the authors show that anodic TiO₂ nanotubes (NT) show excellent harvesting properties for Pt single atoms (Pt SAs) from highly dilute Pt solutions. The tube walls of anodic nanotubes, after adequate annealing to anatase, provide ample of suitable trapping sites-that is, surface Ti³⁺ -O_v (O_v : oxygen vacancy) defects that are highly effective to extract and accumulate Pt in the form of SAs. A saturated (maximized) SA density can be achieved by an overnight immersion of a TiO₂ NT layer to a H₂ PtCl₆ solution with a concentration that is as low as 0.01 mm Pt. Such TiO₂ NTs with surface trapped Pt SAs provide a maximized high activity for photocatalytic H₂ generation (reaching a turnover frequency (TOF) of 1.24 × 10⁶ h^-1 at a density of 1.4 × 10⁵ Pt atoms µm^-2 )-a higher loading with Pt nanoparticles does not further increase the photocatalytic activity. Overall, these findings show that anodic TiO₂ nanotubes provide a remarkable substrate for Pt extraction and recovery from very dilute solutions that directly results in a highly efficient photocatalyst, fabricated by a simple immersion technique.

Metal-based electrocatalysts for room-temperature Na-S batteries

Room-temperature sodium-sulfur (RT Na-S) batteries have recently captured intensive research attention from the community and are regarded as one of promising next-generation energy storage devices since they not only integrate the advantages in high abundance and low commercial cost of elemental Na/S but also exhibit exceptionally high theoretical capacity and energy density. Whereas, the notorious shuttle effect of soluble intermediates and sluggish kinetics remain two main obstacles for RT Na-S batteries to step into new developmental stage. Recently, impressive advancements of metal-based electrocatalysts have offered a viable solution to stabilize S cathodes and unlocked new opportunities for RT Na-S batteries. Here, we underline the recent progress on metal-based electrocatalysts for RT Na-S batteries for the first time by shedding light on this emerging but promising field. The involved metal-based electrocatalysts include metals, metal oxides, metal sulfides, metal carbides, and other metal-based catalytic species. Our emphasis is focused on the discussion of design, fabrication, and properties of these electrocatalysts as well as interactions between electrocatalysts and sodium polysulfides. Otherwise, some potential electrocatalysts for RT Na-S batteries are pointed out as well. At last, perspectives for the future development of RT Na-S batteries with S cathode electrocatalysts are offered.