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"Transition metal compounds"
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A Review on Engineering Transition Metal Compound Catalysts to Accelerate the Redox Kinetics of Sulfur Cathodes for Lithium–Sulfur Batteries
HighlightsThe representatively engineering strategies of cations/anions doping, bimetallic/bi-anionic transition metal compounds and heterostructure composites catalysts for lithium sulfur batteries are comprehensively reviewed.The promoted mechanism of catalytic performance by regulating electronic structure is focused on, including energy band, electron filling, d/p-band center, valence state.The superiority of the modified transition metal compounds is comprehensively summarized.Engineering transition metal compounds (TMCs) catalysts with excellent adsorption-catalytic ability has been one of the most effective strategies to accelerate the redox kinetics of sulfur cathodes. Herein, this review focuses on engineering TMCs catalysts by cation doping/anion doping/dual doping, bimetallic/bi-anionic TMCs, and TMCs-based heterostructure composites. It is obvious that introducing cations/anions to TMCs or constructing heterostructure can boost adsorption-catalytic capacity by regulating the electronic structure including energy band, d/p-band center, electron filling, and valence state. Moreover, the electronic structure of doped/dual-ionic TMCs are adjusted by inducing ions with different electronegativity, electron filling, and ion radius, resulting in electron redistribution, bonds reconstruction, induced vacancies due to the electronic interaction and changed crystal structure such as lattice spacing and lattice distortion. Different from the aforementioned two strategies, heterostructures are constructed by two types of TMCs with different Fermi energy levels, which causes built-in electric field and electrons transfer through the interface, and induces electron redistribution and arranged local atoms to regulate the electronic structure. Additionally, the lacking studies of the three strategies to comprehensively regulate electronic structure for improving catalytic performance are pointed out. It is believed that this review can guide the design of advanced TMCs catalysts for boosting redox of lithium sulfur batteries.
Journal Article
Judicious Selection of Precursors with Suitable Chemical Valence State for Controlled Growth of Transition Metal Chalcogenides
Transition metal chalcogenides (TMCs) have attracted wide attentions as a class of promising material for both fundamental investigations and electronic applications due to their atomic thin thickness, dangling bond‐free surface, and excellent electronic properties. Specifically, TMCs show outstanding properties such as good thermal conductivity, robust mechanical properties, and extraordinary electronical characteristics, bestowing them utility in both fundamental research and applications. Recently, the development of post‐Moore electronics based on TMCs calls for their large‐size and single‐crystal growth. However, researchers about synthesis usually focus on controlling several growth parameters (such as growth temperature, flow rate, and time). Herein, it is reported that the chemical valence states of transition metal precursors play an important role in controlling the lateral size and crystal quality for TMCs. The study discusses the valence states‐dependent growth mechanism for WS2 and MoS2 from four factors: evaporation temperature, skipping of reaction steps, atomic binding energy of the precursors, and formation energy. In addition, the as‐grown WS2 and MoS2 nanoflakes exhibit good photoelectric response properties. For EuS, the growth results are obviously different by using EuBr3 and EuBr2 as precursors. The studies provide a unique perspective and also new knowledge to controllably grow large‐size and good crystal quality TMCs.
The study reports the chemical valence state of transition metal precursors dependent growth for WS2, MoS2, and EuS. The mechanism can be discussed on four factors: evaporation temperature, skipping of reaction steps, atomic binding energy of the precursors, and formation energy. The lateral size and quality of the as‐grown flakes are all improved. The photoelectric properties of WS2 and MoS2 are comparable with or better than previous reports.
Journal Article
Linker-Dependent Variation in the Photophysical Properties of Dinuclear 2-Phenylpyridinato Complexes Featuring NDI Units
Through-space charge transfer (TSCT) between spatially adjacent donor and acceptor units has garnered considerable attention as a promising design principle for optoelectronic materials. While TSCT systems incorporating rigid spacers have been extensively studied to enhance through-space interactions, transition metal complexes connected by flexible linkers remain underexplored, despite increasing interest in their potential TSCT behavior. Herein, we report the design and synthesis of a donor–acceptor–donor (D-A-D)-type complex (1), in which a central naphthalenediimide (NDI) electron acceptor is linked to 2-phenylpyridinato(salicylaldiminato)platinum(II) complexes via flexible alkyl linkers. By systematically varying the linker length (n = 3, 4, 5, 6; 1a–d), we achieved precise control over the spatial arrangement between the NDI core and the platinum moieties in solution. Notably, compound 1a (n = 3) adopts an S-shaped conformation in solution, giving rise to a distinct TSCT absorption band. The structural and photophysical properties were thoroughly investigated using single-crystal X-ray diffraction, [sup.1]H NMR, NOESY analysis, and DFT calculations, which collectively support the existence of the folded conformation and associated TSCT behavior. These findings highlight that TSCT can be effectively induced in flexible molecular systems by exploiting intramolecular spatial proximity and non-covalent interactions, thereby offering new avenues for the design of responsive optoelectronic materials.
Journal Article
Structural Investigation and Energy Transfer of Eusup.3+/Mnsup.4+ Co-Doped Mgsub.3Gasub.2SnOsub.8 Phosphors for Multifunctional Applications
In recent years, rare earth ion and transition metal ion co-doped fluorescent materials have attracted a lot of attention in the fields of WLEDs and optical temperature sensing. In this study, I successfully prepared the dual-emission Mg[sub.3]Ga[sub.2]SnO[sub.8]:Eu[sup.3+],Mn[sup.4+] red phosphors and the XRD patterns and refinement results show that the prepared phosphors belong to the Fd-3m space group. The energy transfer process between Eu[sup.3+] and Mn[sup.4+] was systematically investigated by emission spectra and decay curves of Mg[sub.3]Ga[sub.2]SnO[sub.8]:0.12Eu[sup.3+],yMn[sup.4+] (0.002 ≤ y ≤ 0.012) phosphors and the maximum value of transfer efficiency can reach 71.2%. Due to the weak thermal quenching effect of Eu[sup.3+], its emission provides a stable reference for the rapid thermal quenching of the Mn[sup.4+] emission peak, thereby achieving good temperature measurement performance. The relative thermometric sensitivities of the fluorescence intensity ratio and fluorescence lifetime methods reached a maximum value of 2.53% K[sup.−1] at 448 K and a maximum value of 3.38% K[sup.−1] at 473 K. In addition, the prepared WLEDs utilizing Mg[sub.3]Ga[sub.2]SnO[sub.8]:0.12Eu[sup.3+] phosphor have a high color rendering index of 82.5 and correlated color temperature of 6170 K. The electroluminescence spectrum of the synthesized red LED device by Mg[sub.3]Ga[sub.2]SnO[sub.8]:0.009Mn[sup.4+] phosphor highly overlaps with the absorption range of the phytochrome P[sub.FR] and thus can effectively promote plant growth. Therefore, the Mg[sub.3]Ga[sub.2]SnO[sub.8]:Eu[sup.3+],Mn[sup.4+] phosphors have good application prospects in WLEDs, temperature sensing, and plant growth illumination.
Journal Article
Advances in Group-10 Transition Metal Dichalcogenide PdSesub.2-Based Photodetectors: Outlook and Perspectives
The recent advancements in low-dimensional material-based photodetectors have provided valuable insights into the fundamental properties of these materials, the design of their device architectures, and the strategic engineering approaches that have facilitated their remarkable progress. This review work consolidates and provides a comprehensive review of the recent progress in group-10 two-dimensional (2D) palladium diselenide (PdSe[sub.2])-based photodetectors. This work first offers a general overview of the various types of PdSe[sub.2] photodetectors, including their operating mechanisms and key performance metrics. A detailed examination is then conducted on the physical properties of 2D PdSe[sub.2] material and how these metrics, such as structural characteristics, optical anisotropy, carrier mobility, and bandgap, influence photodetector device performance and potential avenues for enhancement. Furthermore, the study delves into the current methods for synthesizing PdSe[sub.2] material and constructing the corresponding photodetector devices. The documented device performances and application prospects are thoroughly discussed. Finally, this review speculates on the existing trends and future research opportunities in the field of 2D PdSe[sub.2] photodetectors. Potential directions for continued advancement of these optoelectronic devices are proposed and forecasted.
Journal Article
Triel Bonds between BHsub.3/Csub.5Hsub.4BX and M and Group 10 Transition Metal Electron Donors
A systematic theoretical study was conducted on the triel bonds (TrB) within the BH[sub.3]∙∙∙M(MDA)[sub.2] and C[sub.5]H[sub.4]BX∙∙∙M(MDA)[sub.2] (M = Ni, Pd, Pt, X = H, CN, F, CH[sub.3], NH[sub.2], MDA = enolated malondialdehyde) complexes, with BH[sub.3] and C[sub.5]H[sub.4]BX acting as the electron acceptors and the square-coordinated M(MDA)[sub.2] acting as the electron donor. The interaction energies of these systems range between −4.71 and −33.18 kcal/mol. The larger the transition metal center M, the greater the enhancement of the TrB, with σ–hole TrBs found to be stronger than π–hole TrBs. In the σ–hole TrB complex, an electron-withdrawing substituent on the C opposite to the B atom enhances the TrB, while an electron-donating substituent has little effect on the strength of TrB in the Pd and Pt complexes but enhances the TrB in the Ni-containing complexes. The van der Waals interaction plays an important role in stabilizing these binary systems, and its contribution diminishes with increasing M size. The orbital effect within these systems is largely due to charge transfer from the d[sub.z] [sup.2] orbital of M into the empty p[sub.z] orbital of B.
Journal Article
Interfacial Interaction in NiFe LDH/NiSsub.2/VSsub.2 for Enhanced Electrocatalytic Water Splitting
A bifunctional electrocatalyst with high efficiency and low costs for overall water splitting is critical to achieving a green hydrogen economy and coping with the energy crisis. However, developing robust electrocatalysts still faces huge challenges, owing to unsatisfactory electron transfer and inherent activity. Herein, NiFe LDH/NiS[sub.2]/VS[sub.2] heterojunctions have been designed as freestanding bifunctional electrocatalysts to split water, exhibiting enhanced electron transfer and abundant catalytic sites. The optimum NiFe LDH/NiS[sub.2]/VS[sub.2] electrocatalyst exhibits a small overpotential of 380 mV at 10 mA cm[sup.−2] for overall water splitting and superior electrocatalytic performance in both hydrogen and oxygen evolution reactions (HER/OER). Specifically, the electrocatalyst requires overpotentials of 76 and 286 mV at 10 mA cm[sup.−2] for HER and OER, respectively, in alkaline electrolytes, which originate from the synergistic interaction among the facilitated electron transfer and increasingly exposed active sites due to the modulation of interfaces and construction of heterojunctions.
Journal Article
Roles of Impurity Levels in 3d Transition Metal-Doped Two-Dimensional Gasub.2Osub.3
Doping engineering is crucial for both fundamental science and emerging applications. While transition metal (TM) dopants exhibit considerable advantages in the tuning of magnetism and conductivity in bulk Ga[sub.2]O[sub.3], investigations on TM-doped two-dimensional (2D) Ga[sub.2]O[sub.3] are scarce, both theoretically and experimentally. In this study, the detailed variations in impurity levels within 3d TM-doped 2D Ga[sub.2]O[sub.3] systems have been explored via first-principles calculations using the generalized gradient approximation (GGA) +U method. Our results show that the Co impurity tends to incorporate on the tetrahedral GaII site, while the other dopants favor square pyramidal GaI sites in 2D Ga[sub.2]O[sub.3]. Moreover, Sc[sup.3+], Ti[sup.4+], V[sup.4+], Cr[sup.3+], Mn[sup.3+], Fe[sup.3+], Co[sup.3+], Ni[sup.3+], Cu[sup.2+] , and Zn[sup.2+] are the energetically favorable charge states. Importantly, a transition from n-type to p-type conductivity occurs at the threshold Cu element as determined by the defect formation energies and partial density of states (PDOS), which can be ascribed to the shift from electron doping to hole doping with respect to the increase in the atomic number in the 3d TM group. Moreover, the spin configurations in the presence of the square pyramidal and tetrahedral coordinated crystal field effects are investigated in detail, and a transition from high-spin to low-spin arrangement is observed. As the atomic number of the 3d TM dopant increases, the percentage contribution of O ions to the total magnetic moment significantly increases due to the electronegativity effect. Additionally, the formed 3d bands for most TM dopants are located near the Fermi level, which can be of significant benefit to the transformation of the absorbing region from ultraviolet to visible/infrared light. Our results provide theoretical guidance for designing 2D Ga[sub.2]O[sub.3] towards optoelectronic and spintronic applications.
Journal Article
Evolution of the Fermi Surface of 1T-VSesub.2 across a Structural Phase Transition
Periodic lattice distortion, known as the charge density wave, is generally attributed to electron–phonon coupling. This correlation is expected to induce a pseudogap at the Fermi level in order to gain the required energy for stable lattice distortion. The transition metal dichalcogenide 1T-VSe[sub.2] also undergoes such a transition at 110 K. Here, we present detailed angle-resolved photoemission spectroscopy experiments to investigate the electronic structure in 1T-VSe[sub.2] across the structural transition. Previously reported warping of the electronic structure and the energy shift of a secondary peak near the Fermi level as the origin of the charge density wave phase are shown to be temperature independent and hence cannot be attributed to the structural transition. Our work reveals new states that were not resolved in previous studies. Earlier results can be explained by the different dispersion natures of these states and temperature-induced broadening. Only the overall size of the Fermi surface is found to change across the structural transition. These observations, quite different from the charge density wave scenario commonly considered for 1T-VSe[sub.2] and other transition metal dichalcogenides, bring fresh perspectives toward correctly describing structural transitions. Therefore, these new results can be applied to material families in which the origin of the structural transition has not been resolved.
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