Single Crystal Materials Research Articles

Advances in Single-Crystal Framework Materials: Design, Synthesis, and Applications

Porous materials are integral to numerous aspects of daily life, from metabolic processes in the human body to various industrial applications. Significant efforts have been directed toward the synthesis of single-crystalline reticular materials with well-defined architectures and enhanced performance by reticulating organic units into extended frameworks. However, the development of these materials for diverse applications is substantially impeded by the limitations of current preparation strategies and the unclear mechanisms underlying single-crystal formation. This review provides a comprehensive summary of recent advancements in the design and synthetic methodologies of single-crystal framework materials, emphasizing solvothermal-induced direct synthesis, template-assisted synthesis, and modulator-assisted preparation. Detailed insights into the challenges of modulating crystal growth are presented. Furthermore, the review discusses the potential large-scale applications of single-crystal frameworks, including catalysis, adsorption/separation, sensing, polarized optics, and life sciences, thereby broadening the scope of their utility across various fields.

Restraining Planar Gliding in Single-Crystalline LiNi0.9Co0.05Mn0.05O2 Cathodes by Combining Bulk and Surface Modification Strategies.

The delamination cracking from planar gliding along the (003) facets and anisotropic lattice strain perpendicular to the (003) facets inevitable lead to degradation of Ni-rich single-crystal cathode materials, adversely affecting their cyclability. Herein, we rationally design a single-crystal LiNi0.9Co0.05Mn0.05O2 (SC90) cathode with robust chemo-mechanical properties, in which coherently grown MgO6 octahedra and BO4 tetrahedra are incorporated into the lattice, and a stabilizing Mg3(BO3)2 layer is concurrently formed on the particle surface. Multiscale in/ex situ characterizations and theoretical calculations indicate that introducing the MgO6 and BO4 units leads to a "pinning effect" within the layered structure. This in turn strongly mitigates mechanical degradation by reducing planar gliding and delamination cracking over extended cycling. Moreover, the Mg3(BO3)2 coating maintains fast lithium diffusion by suppressing parasitic reactions at the cathode|electrolyte interface. The tailored SC90 cathode exhibits a capacity retention of ~88% after 300 cycles at 5C rate, significantly outperforming the pristine counterpart (~60%). Additionally, a pouch-type full cell with a graphite anode sustains a specific discharge capacity of 177 mAh g-1 after 500 cycles, with 90% capacity retention. This work highlights the "pining effect" in preventing unfavorable slab sliding and structural deterioration, offering new insights for designing advanced ultrahigh Ni single-crystal cathodes.

Eliminating chemo-mechanical degradation of lithium solid-state battery cathodes during >4.5 V cycling using amorphous Nb2O5 coatings.

Lithium solid-state batteries offer improved safety and energy density. However, the limited stability of solid electrolytes (SEs), as well as irreversible structural and chemical changes in the cathode active material, can result in inferior electrochemical performance, particularly during high-voltage cycling (>4.3 V vs Li/Li+). Therefore, new materials and strategies are needed to stabilize the cathode/SE interface and preserve the cathode material structure during high-voltage cycling. Here, we introduce a thin (~5 nm) conformal coating of amorphous Nb2O5 on single-crystal LiNi0.5Mn0.3Co0.2O2 cathode particles using rotary-bed atomic layer deposition (ALD). Full cells with Li4Ti5O12 anodes and Nb2O5-coated cathodes demonstrate a higher initial Coulombic efficiency of 91.6% ± 0.5% compared to 82.2% ± 0.3% for the uncoated samples, along with improved rate capability (10x higher accessible capacity at 2C rate) and remarkable capacity retention during extended cycling (99.4% after 500 cycles at 4.7 V vs Li/Li+). These improvements are associated with reduced cell polarization and interfacial impedance for the coated samples. Post-cycling electron microscopy analysis reveals that the Nb2O5 coating remains intact and prevents the formation of spinel and rock-salt phases, which eliminates intra-particle cracking of the single-crystal cathode material. These findings demonstrate a potential pathway towards stable and high-performance solid-state batteries during high-voltage operation.

A comprehensive exploration of the structural, vibrational, optical, and thermal properties of 2, 4, 6-triamino-1, 3, 5-triazinium perchlorate monohydrate layered hybrid ionic material

New single-crystal hybrid material: 2,4,6-triamino-1,3,5-triazinium perchlorate monohydrate was synthesized and comprehensively characterized. Its structure was affined by single-crystal XRD, revealing P1− triclinic system, cell parameters a = 5.6698(4), b = 7.5566(6), c = 11.9230(9)Å, β = 94.527(3) and filling rate Z = 2. The supramolecular 3D-network was investigated, attributing a layered structure like along z-direction, formed by bi-organic by bi-inorganic supramolecular layers. The Hirshfeld surface analysis was employed to examine the intermolecular interactions, identifying O∙∙∙H/H∙∙∙O and N∙∙∙H/H∙∙∙N contacts as the most prominent, each contributing 66.1 % to the overall interaction profile. The material exhibits transparency in the near-UV and visible regions. The FT-IR spectroscopy was used to analyze vibrational modes, while the TGA/DTG analysis indicates a multi-stage decomposition process, with thermal stability up to 315 °C.

3D Crystal Construction by Single-Crystal 2D Material Supercell Multiplying.

2D stacking presents a promising avenue for creating periodic superstructures that unveil novel physical phenomena. While extensive research has focused on lateral 2D material superstructures formed through composition modulation and twisted moiré structures, the exploration of vertical periodicity in 2D material superstructures remains limited. Although weak van der Waals interfaces enable layer-by-layer vertical stacking, traditional methods struggle to control in-plane crystal orientation over large areas, and the vertical dimension is constrained by unscalable, low-throughput processes, preventing the achievement of global order structures. In this study, a supercell multiplying approach is introduced that enables high-throughput construction of 3D superstructures on a macroscopic scale, utilizing artificially stacked single-crystalline 2D multilayers as foundational repeating units. By employing wafer-scale single-crystalline 2D materials and referencing the crystal orientation of substrates, the method ensures precise alignment of crystal orientation within and across each supercell, thereby achieving controllable periodicity along all three axes. A centimeter-scale 3R-MoS₂ crystal is successfully constructed, comprising over 200 monolayers of single-crystalline MoS₂, through a bottom-up stacking process. Additionally, the approach accommodates the integration of amorphous oxide, enabling the assembly of 3D non-linear optical crystals with quasi-phase matching. This method paves the way for the bottom-up construction of macroscopic artificial 3D crystals with atomic plane precision, enabling tailored optical, electrical, and thermal properties and advancing the development of novel artificial materials and high-performance applications.

Facile synthesis of polyhedral oligomeric silsesquioxanes with excellent thermosetting, fibrous and crystalline properties

The development of multifunctional polyhedral oligomeric silsesquioxanes (POSS) that are more serialized than traditional POSS is essential to reduce the economic investment and expand the category of high-performance POSS. This work employed a simple one-step method to synthesize a series of different physical states of methacryloxypropyl-phenyl POSS (AcPhPOSS). The FTIR, NMR and MS results showed that the products were mainly composed of regular T8, T10 and T12 cage-like structures, and the outer periphery of the AcPhPOSS cage carried different proportions of flexible methacryloxypropyl (R1) and rigid phenyl (R2) groups. In addition, the curable, fibrous, and crystalline properties of liquid, semi-solid, and powder AcPhPOSS were studied through thermal curing, electrospinning, and crystallization methods, respectively. The results showed that AcPhPOSS in three different states, especially AcPhPOSS@1:0 (liquid), AcPhPOSS@1:3 (semi-solid) and AcPhPOSS@0:1 (powder), exhibited good thermal curing properties, fiber and crystallization, respectively. Hence, this work proposes a facile strategy for producing multifunctional materials with good curing properties, fiber-forming properties, and crystallinity, which have broad application potential in thermosetting resins, fiber materials, and single crystal materials.

Tuning Molten-Salt-Mediated Calcination in Promoting Single-Crystal Synthesis of Ni-Rich LiNixMnyCozO2 Cathode Materials

High Ni-content LiNixMnyCozO2 (NMC) cathodes (with x ≥ 0.8, x + y + z = 1) have gained attention recently for their high energy density in electric vehicle (EV) Li-ion batteries. However, Ni-rich cathodes pose challenges in capacity retention due to inherent structural and surface redox instabilities. One promising strategy is to make the Ni-rich NMC material in the form of single-crystal micron-sized particles, as they resist intergranular and surface degradation during cycling. Among various methods to synthesize single-crystal NMC (SC-NMC) particles, molten-salt-assisted calcination offers distinct processing advantages but at present, is not yet optimized or mechanistically clarified to yield the desired control over crystal growth and morphology. In this project, molten-salt-mediated transformation of Ni0.85Mn0.05Co0.15(OH)2 precursor (P-NMC) particles to LiNi0.85Mn0.05Co0.15O2 particles is investigated in terms of the crystal growth mechanism and its electrochemical response. Unlike previous studies that involved large volumes of molten salt, using a smaller volume of molten KCl is found to result in larger primary particles with improved cycling performance achieved via partial reactive dissolution and heterogeneous nucleation growth, suggesting that the ratio of molten salt volume to NMC mass is an important parameter in the synthesis of single-crystal Ni-rich NMC materials.

Exploring the potential and impact of single-crystal active materials on dry-processed electrodes for high-performance lithium-ion batteries

Roll-to-roll powder-to-film dry processing (DP) and single-crystal (SC) active materials (AMs) with many advantages are two hot topics of lithium-ion batteries (LIBs). However, DP of SC AMs for LIBs is rarely reported. Consequently, the impact of SC AMs on dry-processed LIBs is not well understood. Herein, for the first time, via a set of experimental and theoretical studies of the conventional polycrystalline-AM- and SC-AM-based DPed electrodes (DPEs), this work not only reports a high-performance dry SC-AM cathode for LIB manufacturing, but also establishes some fundamental understanding of SC-based dry-processed electrodes, including their morphology, structure, mechanical strength, electronic conductivity and LIB electrochemical behavior. The results suggest that DP of SC AMs is promising, which can dramatically improve the electrochemical kinetics at electrode level and particle level. Specifically, for the rate capability and long-term cyclability in full cells, SC DPEs exhibit a discharge specific capacity of 152.1 mAh g−1 at 1C and a capacity retention rate of 79.9 % at C/3 over 500 cycles, which are superior to those of PC DPEs (135.6 mAh g−1 and 68.3 %) at the same conditions and are further confirmed by the simulation data from the theoretical modelling study. Therefore, this comprehensive work marks a significant milestone for DP strategy and SC AMs, enlightening future research and development of LIB manufacturing.

Emerging New-Generation Semiconductor Single Crystals of Metal Halide Perovskites for Radiation Detection

Radiation detection uses semiconductor materials to convert high-energy photons into charge (direct detection) or low-energy photons (indirect detection), and it has a wide range of applications in nuclear physics, medical imaging, astronomical detection, homeland security, and other fields. Metal halide perovskites have the advantages of high frequency number, high carrier mobility, high defect tolerance, low defect density, adjustable band gap, and fast light response, and they have wide application prospects in the field of radiation detection. However, the research is still in its infancy stage, and it is far from meeting the requirements of industrial application. This paper focuses on the advantages of metal halide perovskite single-crystal materials in both semiconductors-based direct conversion detection and scintillator-based indirect detection as well as the latest progress in this promising field. This paper not only introduces the latest application of lead halide perovskite monocrystalline materials in high-energy electromagnetic radiation detection (X-ray and γ-rays), but it also introduces the latest development of α-particle/β-particle/neutron detection. Finally, this paper points out the challenges and future prospects of metal halide perovskite single-crystal materials in radiation detection.

Synthesis of Monodisperse and Discrete Ultra-High Nickel LiNi0.97Co0.02Mn0.01O2 Octahedral Single Crystals via Single Crystal Intermediates for Li-Ion Batteries.

Micrometer-sized single crystal cathodes have garnered significant interest as promising cathode materials for lithium-ion batteries due to their ability to reduce surface area exposure to electrolytes and suppress side reactions, thereby enhancing electrochemical performance. One of the challenging issues with single crystal cathode materials is synthesizing monodisperse and discrete single crystals rather than agglomerated quasi-single crystals. However, conventional solid-state synthesis of most single crystals results in severe agglomeration and cation mixing, as it requires high temperatures to promote particle growth to several micrometers. In this study, a novel morphology-conserving reaction strategy that employs octahedron single crystal intermediates is introduced to synthesize discrete, monodisperse LiNi0.97Co0.02Mn0.01O2 octahedron single crystals. This scalable and cost-effective approach involves using rock-salt Ni0.97Co0.02Mn0.01O1+x octahedrons as single crystal intermediates, which are transformed in unreactive unary lithium salt melts (LiCl and Li2SO4) from spherical Ni0.97Co0.02Mn0.01(OH)2 obtained via coprecipitation. These intermediates are then subjected to a stoichiometric amount of Li precursor in a conventional solid-state synthesis to produce layered LiNi0.97Co0.02Mn0.01O2. This process is a morphology-conserving lithiation reaction, leading to the formation of discrete and monodisperse LiNi0.97Co0.02Mn0.01O2 octahedron single crystals. The resultant LiNi0.97Co0.02Mn0.01O2 single crystals demonstrate superior electrochemical performance, including stable capacity retention over 150 cycles, which surpasses that of typical quasi-single crystals produced through conventional methods. This is attributed to negligible crack formation during cycling, in contrast to significant cracking observed in conventional quasi-single crystals. This implies that single-crystal forms are preferred over agglomerated quasi-single crystal forms for enhancing cycle performance. These findings provide valuable insights into the industrial synthesis of discrete and monodisperse ultrahigh-nickel oxide cathode materials.

A Preisach Model Defining Correlation between Monotonic and Cyclic Response of Structural Mild Steel

This article delivers a new Preisach model representing the correlation between the elastoplastic behavior of structural mild steel under axial monotonic and cyclic loading with damage. The newly formed model is based on the experimentally defined correlation between axial monotonic and cyclic behavior of structural mild steel. To examine the monotonic and cyclic behavior of structural mild steel and find fitting material properties for the model, monotonic and cyclic axial tensile tests are performed. Tests are executed on coupons of the commonly used European structural steel S275. The model represents a mathematical description of modified single-crystal material behavior under monotonic loading. Two different approaches were used to describe damage in the multilinear mechanical model. The excellent agreement with experimental results is achieved by infinitely linking many single-crystal elements in parallel, forming the polycrystalline model. This model provides a good solution for everyday engineering practice due to its geometric representation in the form of the Preisach triangle and the lower costs of monotonic tests used to define material properties compared to cyclic tests.

Constructing electrochemically stable single crystal Ni-rich cathode material via modification with high valence metal oxides

Single crystal Ni-rich cathode materials (SCNCM) are a good supplement in the market of nickel-based materials due to their safety and excellent electrochemical performance. However, the challenges of cation mixing, phase change during charge/discharge, and low thermal stability remain unresolved in single crystal particles. To address these issues, SCNCM are rationally modified by incorporating transition metal (TM) oxides, and the influence of metal ions with different valence states on the electrochemical properties of SCNCM is methodically explored through experimental results and theoretical calculations. Enhanced structural stability is demonstrated in SCNCM after the modifications, and the degree of improvement in the matrix materials varies depending on the valence state of doped TM ions. The highest structural stability is found in WO3-modified SCNCM, due to the smaller effective ion radii, higher electro-negativity, stronger W–O bond, and efficient suppression of oxygen vacancy generation. As a result, WO3-modified SCNCM have outstanding cycle performance, with a capacity retention rate of 90.2% after 200 cycles. This study provides an insight into the design of advanced SCNCM with enhanced reversibility and cyclability.

Application of precursor with ultra-small particle size and uniform particle distribution for ultra-high nickel single-crystal cathode materials by coprecipitation method

Ultra-high nickel single-crystal cathode materials have become the most promising for lithium-ion batteries. However, the preparation of ultra-high nickel single-crystal precursors by a continuous coprecipitation method has the disadvantages of large particle size, wide distribution, poor morphology. The extent of the inhomogeneous reactions can be more severe in single-crystal cathodes with larger particle size. Herein, the coprecipitation method with a solid concentrator was adopted, and citrate sodium was used as a complexing agent to improve the physical properties of precursors and electrochemical performance of single-crystal cathode materials. By analyzing the morphology and agglomeration mechanism of the precursor nucleuses under different pH values, it was found that hexagonal nanosheets grew along the 101 direction, and the primary particles showed thicker at pH of 11.4. The hexagonal nanosheets grew along the 001 direction, and the primary particles showed finer at pH of 12.2. The morphology and particle size uniformity of the secondary particles formed by agglomeration at these two pH values showed poor. However, hexagonal nanosheets grew synergistically along the 001 and 101 directions at pH of 11.8, so the primary particles with uniform particle size gradually agglomerated, and then the secondary particles with ultra-small particle size and uniform distribution obtained. Compared to materials prepared by the traditional continuous coprecipitation method, the precursor displays a smaller particle size(D50 = 1.8 µm), higher sphericity, uniformity and denser internal structure. In order to evaluate the performance of Ni0.94Co0.04Mn0.02(OH)2 with ultra-small particle size, the sintering conditions of LiNi0.94Co0.04Mn0.02O2 need to be explored. It was found that the LiNi0.94Co0.04Mn0.02O2 cathode material prepared at 790 °C exhibited higher discharge capacity, cycle and rate performance, compared to materials prepared at 760 °C and 820 °C. We further utilized TEM, EPMA, and XPS to test the internal structure and valence state of LiNi0.94Co0.04Mn0.02O2 cathode material. The results show that the LiNi0.94Co0.04Mn0.02O2 calcined at 790 °C has a good single crystal structure. The LiNi0.94Co0.04Mn0.02O2 cathode materials inherited the structure and particle size of Ni0.94Co0.04Mn0.02(OH)2 precursors, and displayed discharge capacity of 194.7 mAh/g and capacity retention rate of 89.8 % after 100 cycles at 1 C. The microstructure and phase transition of the as-prepared cathode material are well-maintained after long-term cycling, without obvious inter-crystalline micro-crack. The results indicate that its electrochemical performance is better than that of cathode materials with precursors prepared by a continuous coprecipitation method. This work provides new insights for the preparation of small-particle-size precursor and single-crystal cathode materials.

Experimental Research on Pollution-Free Alcohol Cutting Fluid in Scratching of Single-Crystal Copper Material

Cutting fluid can improve the heat dissipation and lubrication in the cutting process and thus increase the machining quality. In this work, a pollution-free alcohol solution was proposed as the cutting fluid in an ultra-precision cutting process to explore green cutting fluids. The scratching experiments were conducted with the alcohol cutting fluid to study its effect on the cutting process. It is found that the use of an alcohol cutting fluid, on average, reduces the tangential and normal force about 27–53%, but exhibits few effects on the friction coefficient in the cutting process. Compared to dry cutting, the alcohol cutting fluid reduces the exposed shear slip steps on the outside surface of the chip, which implies the decreased chip deformation degree of workpiece material in the cutting process. The alcohol cutting fluid can reduce microburrs and decrease the machined surface roughness Ra from 21 nm to 9.9 nm in the ultra-precision turning application on single-crystal copper material.

Ultra-Durable Polysilicon Based Tribovoltaic Nanogenerators for Bearing In Situ Rotational Speed Sensing.

Tribovoltaic nanogenerator (TVNG) is an emerging energy device with the advantages of direct current and high power density. At present, many TVNGs are based on single-crystal materials, which are expensive and fragile during structural processing. Here, a polysilicon-based TVNG for bearing in situ rotational speed sensing is developed, which has the same level of performance and lower cost compared to monocrystalline silicon. The defects in polysilicon can provide additional carriers, but the grain boundaries can suppress the transport process of carriers, resulting in almost the same electrical output as single crystals. The oiled sliding mode TVNG has an impressive durability of up to 1 million cycles. The friction coefficient of rolling mode TVNG is as low as 0.14. Based on rolling mode polysilicon TVNG, the tapered roller bearing, thrust ball bearing, and deep groove ball bearing are manufactured by cutting and engraving processes. Moreover, their short-circuit current and open-circuit voltage are linear with speed, and the fitting coefficient is as high as 0.99, providing favorable conditions for in situ rotational speed sensing. This work presents a structure-function integrated bearing design methodology, demonstrating the considerable potential of in situ sensing for intelligent components in the industrial Internet of Things.

A level-set method for simulating solid-state dewetting in systems with strong crystalline anisotropy

Accurately modeling solid-state dewetting in materials with strong crystalline anisotropy is an open problem in materials science with importance for both the manufacturing and reliability of nano-scale devices. In this work, we propose and demonstrate a level-set method framework for simulating solid-state dewetting which is capable of modeling systems with strongly anisotropic surface energies and diffusivities. Surface energy anisotropy is handled through the use of the Cahn-Hoffman vector construction, and surface self-diffusivity anisotropy is handled through the use of a diffusivity tensor. We benchmark our method against isotropic phenomena with analytical descriptions and go on to demonstrate that our method is capable of reproducing a host of experimentally observed behaviors in strongly anisotropic single-crystal materials.

Effect of crystallographic orientation on mechanical properties of Al0.25CoCrFeNi high entropy alloy under tension

The deformation behavior of single-crystal materials is closely related to the crystallographic orientation. However, there are few simulations and experimental studies on the effect of crystallographic orientation on the tensile properties of single-crystal AlxCoCrFeNi high entropy alloys (HEAs). Molecular dynamics simulations were used to analyze the mechanical properties and structural variations of Al0.25CoCrFeNi HEAs with different crystallographic orientations under tension. Prior to yielding, elastic softening occurred in [111], [110] and [11̅0]-oriented HEAs, except for [100]-oriented HEA. During plastic deformation, [100]-oriented HEA had high strength and flow stress due to the low Schmid factors of leading partial dislocations and multiple activatable slip systems. [111]-oriented HEA also showed high strength and flow stress, which were attributed to the low Schmid factors of the activatable slip systems and the existence of incomplete stacking fault tetrahedrons. Both [110]- and [11̅0]-oriented HEAs showed low strength, but the presence of the secondary increased stress suggested they had good plasticity. The difference between them was that [110]-oriented HEA was easier to form hexagonal close-packed lamellae and experienced secondary yielding at larger strain. This suggested that different crystallographic orientations in the non-tensile direction also affected the mechanical properties.

Fast diffusion and stable topotactic reaction in single crystal conversion anode

Conversion electrodes typically have high theoretical specific capacity, but mostly suffer large structural changes during charge/discharge and result in poor cycling stability. The optimization of the polycrystalline materials is the mostly used strategy, however, these polycrystalline materials are intrinsically vulnerable to grain-boundary (intergranular) fracture caused by the anisotropic volume change during sodiation/desodiation, resulting in rapid impedance growth and capacity decay. Herein, we propose an alternative pathway to design single-crystal materials as potential conversion anodes. As an example, SnO2 with different crystallinities is successfully synthesized via solvothermal methods and compared to determine the implications of different crystallinity for the electrochemical properties of conversion anodes. It is demonstrated that the single-crystal SnO2 not only has faster Na+ diffusion dynamics but also maintains structural stability via topotactic reaction. Further optimization of the electron conduction and structural robustness is realized by uniformly covering a graphitic carbon shell on the surface of single-crystal SnO2 nanosheets. The modified single-crystal SnO2 exhibits a high reversible capacity of 436.2 mA h g–1 and maintains a high capacity of 257.1 mA h g-1 and remarkable capacity retention of about 98.9% after 9000 cycles at 5000 mA g-1. The deep understandings of the topotactic reaction in single crystal conversion anode in this work provide a theoretical foundation and new direction for further developing electrode materials with excellent electrochemical performance, especially high rate capabilities, and long cyclability.

Quasi-equilibrium growth of inch-scale single-crystal monolayer α-In2Se3 on fluor-phlogopite

Epitaxial growth of two-dimensional (2D) materials with uniform orientation has been previously realized by introducing a small binding energy difference between the two locally most stable orientations. However, this small energy difference can be easily disturbed by uncontrollable dynamics during the growth process, limiting its practical applications. Herein, we propose a quasi-equilibrium growth (QEG) strategy to synthesize inch-scale monolayer α-In2Se3 single crystals, a semiconductor with ferroelectric properties, on fluor-phlogopite substrates. The QEG facilitates the discrimination of small differences in binding energy between the two locally most stable orientations, realizing robust single-orientation epitaxy within a broad growth window. Thus, single-crystal α-In2Se3 film can be epitaxially grown on fluor-phlogopite, the cleavage surface atomic layer of which has the same 3-fold rotational symmetry with α-In2Se3. The resulting crystalline quality enables high electron mobility up to 117.2 cm2 V−1 s−1 in α-In2Se3 ferroelectric field-effect transistors, exhibiting reliable nonvolatile memory performance with long retention time and robust cycling endurance. In brief, the developed QEG method provides a route for preparing larger-area single-crystal 2D materials and a promising opportunity for applications of 2D ferroelectric devices and nanoelectronics.

One-Dimensional Single-Crystal Mesoporous TiO2 Supported CuW6O24 Clusters as Photocatalytic Cascade Nanoreactor for Boosting Reduction of CO2 to CH4.

Constructing nanoreactors with multiple active sites in well-defined crystalline mesoporous frameworks is an effective strategy for tailoring photocatalysts to address the challenging of CO2 reduction. Herein, one-dimensional (1-D) mesoporous single-crystal TiO2 nanorod (MS-TiO2-NRs, ≈110nm in length, high surface area of 117 m2 g-1, and uniform mesopores of ≈7.0nm) based nanoreactors are prepared via a droplet interface directed-assembly strategy under mild condition. By regulating the interfacial energy, the 1-D mesoporous single-crystal TiO2 can be further tuned to polycrystalline fan- and flower-like morphologies with different oxygen vacancies (Ov). The integration of single-crystal nature and mesopores with exposed oxygen vacancies make the rod-like TiO2 nanoreactors exhibit a high-photocatalytic CO2 reduction selectivity to CO (95.1%). Furthermore, photocatalytic cascade nanoreactors by in situ incorporation of CuW6O24 (W-Cu) clusters onto MS-TiO2-NRs via Ov are designed and synthesized, which improved the CO2 adsorption capacity and achieved two-step CO2-CO-CH4 photoreduction. The second step CO-to-CH4 reaction induced by W-Cu sites ensures a high generation rate of CH4 (420.4µmol g-1 h-1), along with an enhanced CH4 selectivity (≈94.3% electron selectivity). This research provides a platform for the design of mesoporous single-crystal materials, which potentially extends to a range of functional ceramics and semiconductors for various applications.