Facet engineering of ultrathin two-dimensional materials

Origin and enhancement of magnetoresistance in antiferromagnetic tunnel junctions: spin channel selection rules

Antiferromagnetic materials offer superior stability and ultra-fast spin reversal, making them ideal for next-generation magnetoresistive memory. However, magnetoresistance in antiferromagnetic tunnel junctions (AFMTJs) is small because the two spin channels are typically identical. Here, we demonstrate that non-zero or even huge tunneling magnetoresistance (TMR) can be achieved in AFMTJs through a spin-channel selection model, specifically by manipulating the interface tilt angle (ITA) to control the different tunneling distances of the two spin channels. Using 2D antiferromagnetic FeTe-based AFMTJs as an example, we find that varying ITAs can result in giant TMR up to 109%, verifying the spin-channel selection rule in AFMTJs. These findings pave a novel avenue for efficient data manipulation in antiferromagnetic materials through structural engineering.

Cu-Facet Selective Sulfur Chemistry for Ultrastable Sodium-Sulfur Batteries

Sodium-sulfur batteries face significant challenges due to the high solubility of sodium polysulfides and the resulting shuttle effect, which compromise cycling stability and efficiency. This study introduces the Cu(111) facet-selective reactivity of sulfur redox, which promotes the formation of a stable intermediate, NaCu5S3, enabling efficient sulfur conversion, rapid ionic transport, and a fully solid-solid reaction pathway. The system achieves exceptional performance, retaining a specific capacity of 602 mAh g-1 over 800 cycles at 0.5 A g-1 and delivering 463 mAh g-1 at a high current density of 5 A g-1 in ether-based electrolytes, representing the highest rate capability reported for cathodes with sulfur content ≥ 60 wt %. Comparative studies with Cu(100), Cu(110), and aluminum substrates highlight the unique reactivity of Cu(111). Density functional theory calculations further reveal the structural and electronic interactions between copper and sodium polysulfides, clarifying the facet-dependent mechanisms. This work establishes facet engineering as a promising approach to modulating sulfur redox pathways and improving the electrochemical reversibility in metal-sulfur batteries.

Enriching Oxidation Sites-Based Facets in Lead Chromate to Boost Photoelectrochemical Sensing Response

A key issue in photoelectrochemical applications is the modification of the behavior of photogenerated charge barriers. An effective strategy to improve the photoelectrochemical performance of semiconductor materials is to use the facet effect to promote spatial charge separation. In this work, three different morphologies of lead chromate (PbCrO4) crystals are prepared by a simple hydrothermal method that used ammonium fluoride as the structure-directing agents. Spatial separation of photogenerated electrons and holes is clearly demonstrated in the (012), (020), and (200) facets of PbCrO4 crystals. In situ photo-deposition experiments reveal that the oxidation and reduction sites are distributed on the anisotropic (012) and (020)/(200) facets of all the PbCrO4 crystals. PbCrO4 synthesized with a high Pb2+/F- ratio with maximum exposure of (012) facet has remarkably better performance in photoelectrochemical detection of ascorbic acid compared with PbCrO4 synthesized either without ammonium fluoride or with a low Pb2+/F- ratio. The photoelectrochemical detection performance correlates well with the surface photovoltage difference between the anisotropic facets. The study provides fundamental understanding of the facet-dependent activity of PbCrO4 crystals, which will be beneficial for advancing understanding of spatial charge separation in semiconductor-based photoelectrochemical applications.

Synthesis of in-plane Mo2C/MoO3 heterostructures by a novel spatial-confined partial oxidation approach for enhanced TEA sensing

In-plane heterostructures exhibit extraordinary chemical and electron transfer properties, which have received remarkable research attention. However, the synthesis of an in-plane Mo2C/MoO3 heterostructure has been rarely reported, and the deep investigation of the effect of its fine structure on reactivity is of great significance. Notably, the in-plane heterostructures endow the material with abundant grain boundaries, which facilitate the formation of surface acid sites and active oxygen species, thus contributing to the sensing performance. Our work provides a promising platform to design in-plane heterostructures for various advanced applications.

Untangling the Role of Capping Agents in Manipulating Electrochemical Behaviors Toward Practical Aqueous Zinc-Ion Batteries

Long-standing challenges including notorious side reactions at the Zn anode, low Zn anode utilization, and rapid cathode degradation at low current densities hinder the advancement of aqueous zinc-ion batteries (AZIBs). Inspired by the critical role of capping agents in nanomaterials synthesis and bulk crystal growth, a series of capping agents are employed to demonstrate their applicability in AZIBs. Here, it is shown that the preferential adsorption of capping agents on different Zn crystal planes, coordination between capping agents and Zn2+ ions, and interactions with metal oxide cathodes enable preferred Zn (002) deposition, water-deficient Zn2+ ion solvation structure, and a dynamic cathode-electrolyte interface. Benefiting from the multi-functional role of capping agents, dendrite-free Zn plating and stripping with an improved Coulombic efficiency of 99.2% and enhanced long-term cycling stability are realized. Remarkable capacity retention of 91% is achieved for cathodes after more than 500 cycles under a low current density of 200 mA g-1, marking one of the best cycling stabilities to date. This work provides a proof-of-concept of capping agents in manipulating electrochemical behaviors, which should inspire and pave a new avenue of research to address the challenges in practical energy storage beyond AZIBs.

Alkali Ion-Accelerated Gelation of MXene-Based Conductive Hydrogel for Flexible Sensing and Machine Learning-Assisted Recognition

Conductive hydrogels are promising active materials for wearable flexible electronics, yet it is still challenging to fabricate conductive hydrogels with good environmental stability and electrical properties. In this work, a conductive MXene/LiCl/poly(sulfobetaine methacrylate) hydrogel system was successfully prepared with an impressive conductivity of 12.2 S/m. Interestingly, the synergistic effect of MXene and a lithium bond can significantly accelerate the polymerization process, forming the conductive hydrogel within 1 min. In addition, adding LiCl to the hydrogel not only significantly increases its water retention ability, but also enhances its conductivity, both of which are important for practical applications. The flexible strain sensors based on the as-prepared hydrogel have demonstrated excellent monitoring ability for human joint motion, pulse, and electromyographic signals. More importantly, based on machine learning image recognition technology, the handwritten letter recognition system displayed a high accuracy rate of 93.5%. This work demonstrates the excellent comprehensive performance of MXene-based hydrogels in health monitoring and image recognition and shows potential applications in human-machine interfaces and artificial intelligence.

Metal-organic frameworks for organic transformations by photocatalysis and photothermal catalysis

Organic transformation by light-driven catalysis, especially, photocatalysis and photothermal catalysis, denoted as photo(thermal) catalysis, is an efficient, green, and economical route to produce value-added compounds. In recent years, owing to their diverse structure types, tunable pore sizes, and abundant active sites, metal-organic framework (MOF)-based photo(thermal) catalysis has attracted broad interest in organic transformations. In this review, we provide a comprehensive and systematic overview of MOF-based photo(thermal) catalysis for organic transformations. First, the general mechanisms, unique advantages, and strategies to improve the performance of MOFs in photo(thermal) catalysis are discussed. Then, outstanding examples of organic transformations over MOF-based photo(thermal) catalysis are introduced according to the reaction type. In addition, several representative advanced characterization techniques used for revealing the charge reaction kinetics and reaction intermediates of MOF-based organic transformations by photo(thermal) catalysis are presented. Finally, the prospects and challenges in this field are proposed. This review aims to inspire the rational design and development of MOF-based materials with improved performance in organic transformations by photocatalysis and photothermal catalysis.

Synthesis, Modulation, and Application of Two-Dimensional TMD Heterostructures

Two-dimensional (2D) transition metal dichalcogenide (TMD) heterostructures have attracted a lot of attention due to their rich material diversity and stack geometry, precise controllability of structure and properties, and potential practical applications. These heterostructures not only overcome the inherent limitations of individual materials but also enable the realization of new properties through appropriate combinations, establishing a platform to explore new physical and chemical properties at micro-nano-pico scales. In this review, we systematically summarize the latest research progress in the synthesis, modulation, and application of 2D TMD heterostructures. We first introduce the latest techniques for fabricating 2D TMD heterostructures, examining the rationale, mechanisms, advantages, and disadvantages of each strategy. Furthermore, we emphasize the importance of characteristic modulation in 2D TMD heterostructures and discuss some approaches to achieve novel functionalities. Then, we summarize the representative applications of 2D TMD heterostructures. Finally, we highlight the challenges and future perspectives in the synthesis and device fabrication of 2D TMD heterostructures and provide some feasible solutions.

2D Exfoliation Chemistry Towards Covalent Pseudo-Layered Phosphate Framework Derived by Radical/Strain-Synergistical Process

2D compounds exfoliated from weakly bonded bulk materials with van der Waals (vdW) interaction are easily accessible. However, the strong internal ionic/covalent bonding of most inorganic crystal frameworks greatly hinders 2D material exfoliation. Herein, we first proposed a radical/strain-synergistic strategy to exfoliate non-vdW interacting pseudo-layered phosphate framework. Specifically, hydroxyl radicals (⋅OH) distort the covalent bond irreversibly, meanwhile, H2O molecules as solvents, further accelerating interlayered ionic bond breakage but mechanical expansion. The innovative 2D laminar NASICON-type Na3V2(PO4)2O2F crystal, exfoliated by ⋅OH/H2O synergistic strategy, exhibits enhanced sodium-ion storage capacity, high-rate performance (85.7 mAh g-1 at 20 C), cyclic life (2300 cycles), and ion migration rates, compared with the bulk framework. Importantly, this chemical/physical dual driving technique realized the effective exfoliation for strongly coupled pseudo-layered frameworks, which accelerates 2D functional material development.

Atomic engineering of two-dimensional materials via liquid metals

Two-dimensional (2D) materials, known for their distinctive electronic, mechanical, and thermal properties, have attracted considerable attention. The precise atomic-scale synthesis of 2D materials opens up new frontiers in nanotechnology, presenting novel opportunities for material design and property control but remains challenging due to the high expense of single-crystal solid metal catalysts. Liquid metals, with their fluidity, ductility, dynamic surface, and isotropy, have significantly enhanced the catalytic processes crucial for synthesizing 2D materials, including decomposition, diffusion, and nucleation, thus presenting an unprecedented precise control over material structures and properties. Besides, the emergence of liquid alloy makes the creation of diverse heterostructures possible, offering a new dimension for atomic engineering. Significant achievements have been made in this field encompassing defect-free preparation, large-area self-aligned array, phase engineering, heterostructures, etc. This review systematically summarizes these contributions from the aspects of fundamental synthesis methods, liquid catalyst selection, resulting 2D materials, and atomic engineering. Moreover, the review sheds light on the outlook and challenges in this evolving field, providing a valuable resource for deeply understanding this field. The emergence of liquid metals has undoubtedly revolutionized the traditional nanotechnology for preparing 2D materials on solid metal catalysts, offering flexible possibilities for the advancement of next-generation electronics.

Activating Inert Crystal Face via Facet-Dependent Quench-Engineering for Electrocatalytic Water Oxidation

Developing a facile strategy to activate the inert crystal face of an electrocatalyst is critical to full-facet utilization, yet still challenging. Herein, the electrocatalytic activity of the inert crystal face is activated by quenching Co3O4 cubes and hexagonal plates with different crystal faces in Fe(NO3)3 solution, and the regulation mechanism of facet-dependent quench-engineering is further revealed. Compared to the Co3O4 cube with exposed {100} facet, the Co3O4 hexagonal plate with exposed {111} facet is more responsive to quenching, accompanied by a rougher surface, richer defect, and more Fe doping. Theoretical calculations indicate that the {111} facet has a more open structure with lower defect formation energy and Fe doping energy, ensuring its electronic and coordination structure is easier to optimize. Therefore, quench-engineering largely increases the catalytic activity of {111) facet for oxygen evolution reaction by 13.2% (the overpotential at 10 mA cm-2 decreases from 380 to 330 mV), while {100} facet only increases by 7.6% (from 393 to 363 mV). The quenched Co3O4 hexagonal plate exhibits excellent electrocatalytic activity and stability in both zinc-air battery and water-splitting. The work reveals the influence mechanism of crystal face on quench-engineering and inspires the activation of the inert crystal face.

Facet-dependent transformation and toxicity of nanoscale zinc oxide in the synthetic saliva

The nanoscale zinc oxide (n-ZnO) was used in food packages due to its superior antibacterial activity, resulting in potential intake of n-ZnO through the digestive system, wherein n-ZnO interacted with saliva. In recent, facet engineering, a technique for controlling the exposed facets, was applied to n-ZnO, whereas risk of n-ZnO with specific exposed facets in saliva was ignored. ZnO nanoflakes (ZnO-0001) and nanoneedles (ZnO-1010) with the primary exposed facets of {0001} and {1010} respectively were prepared in this study, investigating stability and toxicity of ZnO-0001 and ZnO-1010 in synthetic saliva. Both ZnO-0001 and ZnO-1010 partially transformed into amorphous Zn3(PO4)2 within 1 hr in the saliva even containing orgnaic components, forming a ZnO-Zn3(PO4)2 core-shell structure. Nevertheless, ZnO-1010 relative to ZnO-0001 would likely transform into Zn3(PO4)2, being attributed to superior dissolution of {1010} facet due to its lower vacancy formation energy (1.15 eV) than {0001} facet (3.90 eV). The toxicity of n-ZnO to Caco-2 cells was also dependent on the primary exposed facet; ZnO-0001 caused cell toxicity through oxidative stress, whereas ZnO-1010 resulted in lower cells viability than ZnO-0001 through oxidative stress and membrane damage. Density functional theory calculations illustrated that ·O2- was formed and released on {1010} facet, yet O22- instead of ·O2- was generated on {0001} facet, leading to low oxidative stress from ZnO-0001. All findings demonstrated that stability and toxicity of n-ZnO were dependent on the primary exposed facet, improving our understanding of health risk of nanomaterials.

Regulating Crystal Orientation in VO2 for Aqueous Zinc Batteries with Enhanced Pseudocapacitance

Although aqueous zinc batteries have attracted extensive interest, they are limited by relatively low rate capabilities and poor cyclic stability of cathodes. The crystal orientation of the cathode is one important factor influencing electrochemical properties. However, it has rarely been investigated. Herein, VO2 cathodes with different crystal orientations are developed via tuning the number of hydroxyl groups in polyol, such as using glycerol, erythritol, xylitol, or mannitol. The polyols serve as a reductant as well as a structure-directing agent through a hydrothermal reaction. Xylitol-derived VO2 shows a (110)-orientated crystalline structure and ultrathin nanosheet morphology. Such features greatly enhance the pseudocapacitance to 76.1% at a scan rate of 1.0 mV s-1, which is significantly larger than that (61.6%) of the (001)-oriented VO2 derived from glycerol. The corresponding aqueous zinc batteries exhibit a high energy storage performance with a reversible specific capacity of 317 mAh g-1 at 0.5 A g-1, rate ability of 220 mAh g-1 at 10 A g-1, and capacity retention of 81.0% at 10 A g-1 over 2000 cycles. This work demonstrates a facile method for tailoring VO2 crystal orientations, offers an understanding of the Zn2+ storage mechanism upon different VO2 facets, and provides a novel method to develop cathode materials toward advanced aqueous zinc batteries.

2D quasi-layered material with domino structure

Interlayer coupling strength dichotomizes two-dimensional (2D) materials into layered and non-layered types. Traditionally, they can be regarded as atomic layers intrinsically linked via van der Waals (vdW) forces or covalent bonds, oriented orthogonally to their growth plane. In our work, we report a material system that differentiates from layered and non-layered materials, termed quasi-layered domino-structured (QLDS) materials, effectively bridging the gap between these two typical categories. Considering the skewed structure, the force orthogonal to the 2D QLDS-GaTe growth plane constitutes a synergistic blend of vdW forces and covalent bonds, with neither of them being perpendicular to the 2D growth plane. This unique amalgamation results in a force that surpasses that in layered materials, yet is weaker than that in non-layered materials. Therefore, the lattice constant contraction along this unique orientation can be as much as 7.7%, tantalizingly close to the theoretical prediction of 10.8%. Meanwhile, this feature endows remarkable anisotropy, second harmonic generation enhancement with a staggering susceptibility of 394.3 pm V-1. These findings endow further applications arranged in nonlinear optics, sensors, and catalysis.

Photothermal-Magnetic Synergistic Effects in an Electrocatalyst for Efficient Water Splitting under Optical-Magnetic Fields

The slow oxygen evolution reaction (OER) limits water splitting, and external fields can help improve it. However, the effect of a single external field on the OER is limited and unsatisfactory. Furthermore, the mechanism by which external fields improve the OER is unclear, particularly in the presence of multiple fields. Herein, a strategy is proposed for enhancing the OER activity of a catalyst using the combined effect of an optical-magnetic field, and the mechanism of catalytic activity enhancement is studied. Under the optical-magnetic field, Co3 O4 reduces the resistance by increasing the catalyst temperature. Meanwhile, CoFe2 O4 further reduces the resistance via the negative magnetoresistance effect, thus decreasing the resistance from 16 to 7.0 Ω. Additionally, CoFe2 O4 acts as a spin polarizer, and electron polarization results in a parallel arrangement of oxygen atoms, which increases the kinetics of the OER under the magnetic field. Benefiting from the optical and magnetic response design, Co3 O4 /CoFe2 O4 @Ni foam requires an overpotential of 172.4 mV to reach a current density of 10 mA cm-2 under an optical-magnetic field, which is significantly higher than those of recently reported state-of-the-art transition-metal-based catalysts.

Synergistic effects of extrinsic photoconduction and photogating in a short-wavelength ZrS3 infrared photodetector

Two-dimensional (2D) material-based photodetectors, especially those working in the infrared band, have shown great application potential in the thermal imaging, optical communication, and medicine fields. Designing 2D material photodetectors with broadened detection band and enhanced responsivity has become an attractive but challenging research direction. To solve this issue, we report a zirconium trisulfide (ZrS₃) infrared photodetector with enhanced and broadened response with the assistance of the synergistic effects of extrinsic photoconduction and photogating effect. The ZrS₃ photodetectors can detect infrared light up to 2 μm by extrinsic photoconduction and exhibit a responsivity of 100 mA W^-1 under 1550 nm illumination. Furthermore, the ZrS₃ infrared photodetectors with an oxide layer show a triple enhanced responsivity due to the photogating effect. Additionally, the infrared imaging capability of the ZrS₃ infrared photodetectors is also demonstrated. This work provides a potential way to extend the response range and improve the responsivity for nanomaterial-based photodetectors at the same time.

A Two-Dimensional Porphyrin Coordination Supramolecular Network Cathode for High-Performance Aqueous Dual-Ion Battery

Iodine has great potential in the energy storage, but high solubility of I₃ ^- has seriously delayed its promotion. Benefited from abundant active sites and the open channel, two-dimensional coordination supramolecular networks (2D CSNs) is considered to be a candidate for the energy storage. Herein, a 2D porphyrin-CSN cathode named Zn-TCPP for aqueous iodine dual-ion battery (DIB) shows an excellent specific capacity of 278 mAh g^-1 , and a high energy density of 340 Wh kg^-1 at 5 A g^-1 , as well as a durable cycle performance of 5000 cycles and a high Coulombic efficiency of 98 %. Molecular orbital theory, UV/VIS, Raman spectroscopy and density functional theory (DFT) calculations reveal charge-transfer interaction between the donor of porphyrin nitrogen and the acceptor of I₃ ^- , and computational fluid dynamics (CFD) simulations demonstrate the contribution of 2D layered network structure of Zn-TCPP to the penetration of I₃ ^- .

2D Mesoporous Zincophilic Sieve for High-Rate Sulfur-Based Aqueous Zinc Batteries

Sulfur-based aqueous zinc batteries (SZBs) attract increasing interest due to their integrated high capacity, competitive energy density, and low cost. However, the hardly reported anodic polarization seriously deteriorates the lifespan and energy density of SZBs at a high current density. Here, we develop an integrated acid-assisted confined self-assembly method (ACSA) to elaborate a two-dimensional (2D) mesoporous zincophilic sieve (2DZS) as the kinetic interface. The as-prepared 2DZS interface presents a unique 2D nanosheet morphology with abundant zincophilic sites, hydrophobic properties, and small-sized mesopores. Therefore, the 2DZS interface plays a bifunctional role in reducing the nucleation and plateau overpotential: (a) accelerating the Zn²⁺ diffusion kinetics through the opened zincophilic channels and (b) inhibiting the kinetic competition of hydrogen evolution and dendrite growth via the significant solvation-sheath sieving effect. Therefore, the anodic polarization is reduced to 48 mV at 20 mA cm^-2, and the full-battery polarization is reduced to 42% of an unmodified SZB. As a result, an ultrahigh energy density of 866 Wh kg_sulfur^-1 at 1 A g^-1 and a long lifespan of 10,000 cycles at a high rate of 8 A g^-1 are achieved.

Catalytically Active Advanced Two-Dimensional Ultrathin Nanomaterials for Sustainable Energy

Advanced two-dimensional (2D) ultrathin nanomaterials’ unique structural and electronic properties and their applications in the photo-, photoelectro-, and electro-catalysis fields present timely topics related to the development of sustainable energy. This critical review briefly summarizes the state-of-the-art progress on 2D ultrathin nanomaterials. In this mini review, we started with the synthesis of 2D ultrathin nanomaterials. Then, various strategies for tailoring the electronic and configuration structures of these nanomaterials in the new energy catalysis field are surveyed, where the emphasis is mainly on structure-activity relationships. The advancements of versatile 2D ultrathin nanomaterials in the fields of hydrogen evolution, carbon dioxide conversion, and dinitrogen fixation for sustainable energy were also discussed. Finally, the existing challenges and future research directions in this promising field are presented.