Phase Transitions and Water Splitting Applications of 2D Transition Metal Dichalcogenides and Metal Phosphorous Trichalcogenides

The Latest Advances in Ink-Based Nanogenerators: From Materials to Applications

Nanogenerators possess the capability to harvest faint energy from the environment. Among them, thermoelectric (TE), triboelectric, piezoelectric (PE), and moisture-enabled nanogenerators represent promising approaches to micro-nano energy collection. These nanogenerators have seen considerable progress in material optimization and structural design. Printing technology has facilitated the large-scale manufacturing of nanogenerators. Although inks can be compatible with most traditional functional materials, this inevitably leads to a decrease in the electrical performance of the materials, necessitating control over the rheological properties of the inks. Furthermore, printing technology offers increased structural design flexibility. This review provides a comprehensive framework for ink-based nanogenerators, encompassing ink material optimization and device structural design, including improvements in ink performance, control of rheological properties, and efficient energy harvesting structures. Additionally, it highlights ink-based nanogenerators that incorporate textile technology and hybrid energy technologies, reviewing their latest advancements in energy collection and self-powered sensing. The discussion also addresses the main challenges faced and future directions for development.

Understanding Advanced Transition Metal-Based Two Electron Oxygen Reduction Electrocatalysts from the Perspective of Phase Engineering

Non-noble transition metal (TM)-based compounds have recently become a focal point of extensive research interest as electrocatalysts for the two electron oxygen reduction (2e- ORR) process. To efficiently drive this reaction, these TM-based electrocatalysts must bear unique physiochemical properties, which are strongly dependent on their phase structures. Consequently, adopting engineering strategies toward the phase structure has emerged as a cutting-edge scientific pursuit, crucial for achieving high activity, selectivity, and stability in the electrocatalytic process. This comprehensive review addresses the intricate field of phase engineering applied to non-noble TM-based compounds for 2e- ORR. First, the connotation of phase engineering and fundamental concepts related to oxygen reduction kinetics and thermodynamics are succinctly elucidated. Subsequently, the focus shifts to a detailed discussion of various phase engineering approaches, including elemental doping, defect creation, heterostructure construction, coordination tuning, crystalline design, and polymorphic transformation to boost or revive the 2e- ORR performance (selectivity, activity, and stability) of TM-based catalysts, accompanied by an insightful exploration of the phase-performance correlation. Finally, the review proposes fresh perspectives on the current challenges and opportunities in this burgeoning field, together with several critical research directions for the future development of non-noble TM-based electrocatalysts.

Transition metal-based electrocatalysts for alkaline overall water splitting: advancements, challenges, and perspectives

Water electrolysis is a promising method for efficiently producing hydrogen and oxygen, crucial for renewable energy conversion and fuel cell technologies. The hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are two key electrocatalytic reactions occurring during water splitting, necessitating the development of active, stable, and low-cost electrocatalysts. Transition metal (TM)-based electrocatalysts, spanning noble metals and TM oxides, phosphides, nitrides, carbides, borides, chalcogenides, and dichalcogenides, have garnered significant attention due to their outstanding characteristics, including high electronic conductivity, tunable valence electron configuration, high stability, and cost-effectiveness. This timely review discusses developments in TM-based electrocatalysts for the HER and OER in alkaline media in the last 10 years, revealing that the exposure of more accessible surface-active sites, specific electronic effects, and string effects are essential for the development of efficient electrocatalysts towards electrochemical water splitting application. This comprehensive review serves as a guide for designing and constructing state-of-the-art, high-performance bifunctional electrocatalysts based on TMs, particularly for applications in water splitting.

Questing for High-Performance Electrocatalysts for Oxygen Evolution Reaction: Importance of Chemical Complexity, Active Phase, and Surface-Adsorbed Species

Rational design of advanced electrocatalysts for oxygen evolution reaction (OER) is of vital importance for the development of sustainable energy. Entropy engineering is emerging as a promising approach for the design of efficient OER electrocatalysts. However, other multi-anion/cation electrocatalysts with compositional complexity, particularly the medium-entropy and other non-equimolar cation/anion complex electrocatalysts, have not received noteworthy attention. In this perspective, we review and highlight the importance of compositionally complex catalysts and propose a concept of chemical complexity to correlate the OER catalytic activity with the contributions from the pairwise cation-anion interactions. Then, we offer a new view on the active catalytic sites being the hydroxylated reacting interface in an alkaline solution. Further, we argue that the common discrepancies between computationally predicted OER activities and experimental results stem from lack of considerations of surface-adsorbed species in modeling the active catalytic phases or sites. This perspective would facilitate achieving a renewed and profound understanding of the OER mechanism and promote efficient design of OER electrocatalysts for renewable energy conversion and storage.

Use of transition metal dichalcogenides (TMDs) in analytical sample preparation applications

Since the discovery of graphene, nano-sized two-dimensional (2D) transition metal dichalcogenides (TMDs) such as MoS2, MoSe2, MoTe2, NbS2, NbSe2, WS2, WSe2, TaS2 and TaSe2, which have been classified as next-generation nanomaterials resembling graphene (G) have complementary basic properties with those of graphene in terms of their practical applications. TMDs are attracting great attention due to their attractive physical, chemical and electronic properties. Despite being overshadowed by graphene in terms of frequency of use, TMDs have been used frequently in many areas in recent years instead of carbon-based materials such as graphene (G), graphene oxide (GO), carbon nanotubes (CNTs) and nanodiamonds (NDs). It is seen that the first and frequent uses of TMDs, which are classified as new generation materials, are in the fields of catalysis, electronic applications, hydrogen production processes and energy storage, but it has been used as an adsorbent in sample preparation techniques in recent years. Similar to graphene, layers of TMDs are held together by weak van der Waals interactions. The sandwiched layers of TMDs provide sufficient and effective interlayer spaces so that foreign molecules, ions and atoms can easily enter these spaces between the layers. Intermolecular interactions increase with the entry of different materials into these spaces, and thus, high activity, adsorption capacity and efficiency are obtained in adsorption-based analytical sample preparation methods. Although there are about 35 research articles using TMDs, which are classified as promising materials in analytical sample preparation techniques, no review studies have been found. This review, which was designed with this awareness, contains important informations on the properties of metal dichalcogenides, their production methods and their use in analytical sample preparation techniques.

Synergistic effects of mixing and strain in high entropy spinel oxides for oxygen evolution reaction

Developing stable and efficient electrocatalysts is vital for boosting oxygen evolution reaction (OER) rates in sustainable hydrogen production. High-entropy oxides (HEOs) consist of five or more metal cations, providing opportunities to tune their catalytic properties toward high OER efficiency. This work combines theoretical and experimental studies to scrutinize the OER activity and stability for spinel-type HEOs. Density functional theory confirms that randomly mixed metal sites show thermodynamic stability, with intermediate adsorption energies displaying wider distributions due to mixing-induced equatorial strain in active metal-oxygen bonds. The rapid sol-flame method is employed to synthesize HEO, comprising five 3d-transition metal cations, which exhibits superior OER activity and durability under alkaline conditions, outperforming lower-entropy oxides, even with partial surface oxidations. The study highlights that the enhanced activity of HEO is primarily attributed to the mixing of multiple elements, leading to strain effects near the active site, as well as surface composition and coverage.

Electron-Extraction Engineering Induced 1T''-1T' Phase Transition of Re0.75 V0.25 Se2 for Ultrafast Sodium Ion Storage

Inducing new phases of transition metal dichalcogenides by controlling the d-electron-count has attracted much interest due to their novel structures and physicochemical properties. 1T'' ReSe₂ is a promising candidate for sodium storage, but the low electronic conductivity and limited active sites hinder its electrochemical capacity. Herein, new-phase 1T' Re_0.75 V_0.25 Se₂ crystals (P2/m) with zig-zag chains are successfully synthesized. The 1T''-1T' phase transition results from the electronic reorganization of 5d orbitals via electron extraction after V-atom doping. The electrical conductivity of 1T' Re_0.75 V_0.25 Se₂ is 2.7 × 10⁵ times higher than that of 1T'' ReSe₂ . Moreover, density functional theory (DFT) calculations reveal that 1T' Re_0.75 V_0.25 Se₂ has a larger interlayer spacing, lower bonding energy, and migration energy barrier for Na⁺ ions than 1T'' ReSe₂ . As a result, 1T' Re_0.75 V_0.25 Se₂ electrode shows an excellent rate capability of 203 mAh g^-1 at 50 C with no capacity fading over 5000 cycles for sodium storage, which is superior to most reported sodium-ion anode materials. This 1T' Re_0.75 V_0.25 Se₂ provides a new platform for various applications such as electronics, catalysis, and energy storage.

Bimetal Modulation Stabilizing a Metallic Heterostructure for Efficient Overall Water Splitting at Large Current Density

Large current-driven alkaline water splitting for large-scale hydrogen production generally suffers from the sluggish charge transfer kinetics. Commercial noble-metal catalysts are unstable in large-current operation, while most non-noble metal catalysts can only achieve high activity at low current densities <200 mA cm^-2 , far lower than industrially-required current densities (>500 mA cm^-2 ). Herein, a sulfide-based metallic heterostructure is designed to meet the industrial demand by regulating the electronic structure of phase transition coupling with interfacial defects from Mo and Ni incorporation. The modulation of metallic Mo₂ S₃ and in situ epitaxial growth of bifunctional Ni-based catalyst to construct metallic heterostructure can facilitate the charge transfer for fast Volmer H and Heyrovsky H₂ generation. The Mo₂ S₃ @NiMo₃ S₄ electrolyzer requires an ultralow voltage of 1.672 V at a large current density of 1000 mA cm^-2 , with ≈100% retention over 100 h, outperforming the commercial RuO₂ ||Pt/C, owing to the synergistic effect of the phase and interface electronic modulation. This work sheds light on the design of metallic heterostructure with an optimized interfacial electronic structure and abundant active sites for industrial water splitting.

Engineering van der Waals Materials for Advanced Metaphotonics

The outstanding chemical and physical properties of 2D materials, together with their atomically thin nature, make them ideal candidates for metaphotonic device integration and construction, which requires deep subwavelength light-matter interaction to achieve optical functionalities beyond conventional optical phenomena observed in naturally available materials. In addition to their intrinsic properties, the possibility to further manipulate the properties of 2D materials via chemical or physical engineering dramatically enhances their capability, evoking new science on light-matter interaction, leading to leaped performance of existing functional devices and giving birth to new metaphotonic devices that were unattainable previously. Comprehensive understanding of the intrinsic properties of 2D materials, approaches and capabilities for chemical and physical engineering methods, the resulting property modifications and novel functionalities, and applications of metaphotonic devices are provided in this review. Through reviewing the detailed progress in each aspect and the state-of-the-art achievement, insightful analyses of the outstanding challenges and future directions are elucidated in this cross-disciplinary comprehensive review with the aim to provide an overall development picture in the field of 2D material metaphotonics and promote rapid progress in this fast emerging and prosperous field.

Transport properties of MoS2/V7(Bz)8 and graphene/V7(Bz)8 vdW junctions tuned by bias and gate voltages

The MoS2/V7(Bz)8 and graphene/V7(Bz)8 vdW junctions are designed and the transport properties of their four-terminal devices are comparatively investigated based on density functional theory (DFT) and the nonequilibrium Green's function (NEGF) technique. The MoS2 and graphene nanoribbons act as the source-to-drain channel and the spin-polarized one-dimensional (1D) benzene-V multidecker complex nanowire (V7(Bz)8) serves as the gate channel. Gate voltages applied on V7(Bz)8 exert different influences of electron transport on MoS2/V7(Bz)8 and graphene/V7(Bz)8. In MoS2/V7(Bz)8, the interplay of source and gate bias potentials could induce promising properties such as negative differential resistance (NDR) behavior, output/input current switching, and spin-polarized currents. In contrast, the gate bias plays an insignificant effect on the transport along graphene in graphene/V7(Bz)8. This dissimilarity is attributed to the fact that the conductivity follows the sequence of MoS2 < V7(Bz)8 < graphene. These transport characteristics are examined by analyzing the conductivity, the currents, the local density of states (LDOS), and the transmission spectra. These results are valuable in designing multi-terminal nanoelectronic devices.

Transition Metal Dichalcogenides [MX2] in Photocatalytic Water Splitting

The quest for a clean, renewable and sustainable energy future has been highly sought for by the scientific community over the last four decades. Photocatalytic water splitting is a very promising technology to proffer a solution to present day environmental pollution and energy crises by generating hydrogen fuel through a “green route” without environmental pollution. Transition metal dichalcogenides (TMDCs) have outstanding properties which make them show great potential as effective co-catalysts with photocatalytic materials such as TiO2, ZnO and CdS for photocatalytic water splitting. Integration of TMDCs with a photocatalyst such as TiO2 provides novel nanohybrid composite materials with outstanding characteristics. In this review, we present the current state of research in the application of TMDCs in photocatalytic water splitting. Three main aspects which consider their properties, advances in the synthesis routes of layered TMDCs and their composites as well as their photocatalytic performances in the water splitting reaction are discussed. Finally, we raise some challenges and perspectives in their future application as materials for water-splitting photocatalysts.

Understanding the thermodynamic, dynamic, bonding, and electrocatalytic properties of low dimensional MgPSe3

The study of novel two-dimensional structures for potential applications in photocatalysis or in optoelectronics is a challenging task. In this work, first-principles calculations have been carried out to explore the...

In Situ Construction of Co-MoS2/Pd Nanosheets on Polypyrrole-Derived Nitrogen-Doped Carbon Microtubes as Multifunctional Catalysts with Enhanced Catalytic Performance

The structural design of multiple functional components could integrate synergistic effects to enhance the catalytic performance of MoS₂-based composites for catalytic applications. Herein, one-dimensional (1D) Co-MoS₂/Pd@NCMTs composites were designed to prepare Co-doped MoS₂/Pd nanosheets (NSs) on N-doped carbon microtubes (NCMTs) from tubular polypyrrole (PPy) as multifunctional catalysts. The Co-MoS₂/Pd@NCMTs composites integrated the synergistic effects of Co-doping, a 1D tubular structure, and noble-metal Pd decoration. Thus, a higher catalytic activity was observed in 4-nitrophenol (4-NP) reduction and peroxidase-like catalysis than other components, such as MoS₂, MoS₂@NCMTs, and Co-MoS₂@NCMTs. Remarkably, the results indicated that the dissolution, diffusion, and redistribution led to the dissolution of MoO₃@ZIF-67 cores and generation of Co-doped MoS₂ NSs. Benefiting from the synergistic effect from these components, Co-MoS₂/Pd@NCMTs were considered as a facile colorimetric sensing platform for detecting tannic acid. Moreover, outstanding performance was realized in the reduction of 4-NP with the composites. Thus, we provide a simple synthetic strategy for simultaneously integrating electronic engineering and structural advantages to develop an efficient MoS₂-based multifunctional catalyst.