Single-atom catalysts (SACs) have garnered considerable attention owing to their profound potential in promoting the efficient utilization of metal resources and attaining atomic-level economy. Fe, Co, Ni SACs have demonstrated broad application prospects in electrocatalysis due to their tunable composition and structure, as well as their unique electronic properties. Firstly, the various preparation methods for Fe, Co, Ni SACs are outlined in this review, including high-temperature pyrolysis, impregnation, chemical vapor deposition, and atomic layer deposition. These methods not only enhance the utilization efficiency of metal atoms but also ensure the stability of the catalysts. Subsequently, this review summarizes the recent progress in the applications of Fe, Co, Ni SACs for electrocatalysis, with a particular focus on their efficacy in hydrogen evolution reaction, oxygen evolution reaction, oxygen reduction reaction, carbon dioxide reduction reaction, and nitrogen reduction reaction. Despite remarkable advancements, Fe, Co, Ni SACs still face challenges related to large-scale production, stability enhancement, comprehensive characterization, and mechanistic exploration. Finally, this review discusses these challenges and proposes strategies to address them in order to fully realize the potential of Fe, Co, Ni SACs as high-performance catalysts.

As a crucial renewable energy resource, biomass can be converted into high-value-added chemicals via unique catalytic routes, which facilitate the reduction of excessive dependency on fossil resources. However, the complex functional groups inherent in biomass and biomass-derived compounds enable considerable difficulties for their selective functionalization. The precise cleavage of special chemical bonds in biomass highly depended on the structure design of catalysts. Single-atom catalysts (SACs) have garnered significant attention in biomass valorization through the electrocatalytic and photoelectrocatalytic processes due to their maximal atom utilization efficiency, unique electronic structure, and tunable coordination environments. The present review outlines the latest research progress in this emerging field, focusing on the (photo)electrocatalytic application of SACs in biomass valorization, including cellulose-derived and hemicellulose-derived compounds and lignin. We also emphasize the innovative design and precise modulation of atomically dispersed metal active sites at the atomic level. Through state-of-the-art catalytic systems, we elaborately discuss the structure-activity relationship and elucidate the mechanisms of the (photo)electrocatalytic processes over SACs. Finally, we provide the prospects of SACs in (photo)electrocatalytic biomass valorization.

Carbon dioxide reduction reaction (CO₂RR) is an efficacious method to mitigate carbon emissions and simultaneously convert CO₂ into high-value carbon products. The efficiency of CO₂RR depends on the development of highly active and selective catalysts. Copper (Cu)-based catalysts can effectively reduce CO₂ to hydrocarbons and oxygen-containing compounds because of their unique geometric and electronic structures. Most importantly, Cu can reduce CO₂ to multiple carbon products (C₂₊). Therefore, this review aims to outline recent research progress in Cu-based catalysts for CO₂RR. After introducing the mechanism of this electroreduction reaction, we summarize the influence of the size, morphology, and coordination environment of single component Cu-based catalysts on their performance, especially the performance control of catalysts that contain nano Cu or Cu single-atom sites. Then, the synergistic regulation strategies of doping other metals into Cu-based catalysts are summarized. Finally, the research on the supports used for Cu-based catalysts is reviewed. The prospects and challenges of Cu-based catalysts are discussed.

Scanning electron microscopy (SEM) has been widely utilized in the field of materials science due to its significant advantages, such as large depth of field, wide field of view, and excellent stereoscopic imaging. However, at high magnification, the limited imaging range in SEM cannot cover all the possible inhomogeneous microstructures. In this research, we propose a novel approach for generating high-resolution SEM images across multiple scales, enabling a single image to capture physical dimensions at the centimeter level while preserving submicron-level details. We adopted the SEM imaging on the AlCoCrFeNi_2.1 eutectic high entropy alloy as an example. SEM videos and image stitching are combined to fulfill this goal, and the video-extracted low-definition images are clarified by a well-trained denoising model. Furthermore, we segment the macroscopic image of the eutectic high entropy alloy, and the area of various microstructures is distinguished. By combining the segmentation results and hardness experiments, we found that the hardness is positively correlated with the content of the body-centered cubic phase and negatively correlated with the lamella width. The whole procedure is also applied to a thermoelectric gradient material (PbSe-SrSe). Our work provides a feasible solution to generate macroscopic images based on SEM for further analysis of the correlations between the microstructures and spatial distribution, and can be widely applied to other types of microscopes.

Exploring new materials with earth-abundant and low-toxicity elements has been a long-standing goal in thermoelectrics. Hexaferrites, a family of environmentally friendly oxides, exhibit complex and tunable structures and excellent magnetic properties, but receive limited attention as potential thermoelectric materials. Here in this study, we systematically investigated the thermoelectric transport properties of W-type hexaferrites BaFe₂Fe₁₆O₂₇ and the cobalt-substituted derivatives prepared by sintering in the nitrogen atmosphere. These materials exhibit an n-type conduction behavior and cobalt substitution can tune the electrical transport properties effectively. Low-temperature specific heat capacity analysis unravels the existence of low-energy optical phonons that contribute to damping the heat transport. Low room temperature thermal conductivity of 1.27 W m^-1 K^-1 is obtained, and the role of cobalt substitution on the thermal conductivity reduction is rationalized by the Debye-Callaway model. This study ‌enlightens the investigation of the thermoelectric transport properties of W-type hexaferrites BaFe₂Fe₁₆O₂₇ and extends the scope of new thermoelectric compounds.

Two-dimensional organic-inorganic hybrid halide perovskites have garnered much attention owing to their outstanding stability alongside unique quantum-well structures and anisotropic properties, leading to improved charge dynamics. Two-dimensional perovskites can be divided into three phases including Ruddlesden-Popper, Dion-Jacobson, and Alternating cations in the interlayer space phase. Each phase of these perovskites shows distinguished phase-dependent structural and optoelectrical properties. Tuning their properties by designing the materials can be a key strategy to enhance the device performance in optoelectrical applications. Configuration of spacer cations and the control of octahedral layer numbers (n) can be important parameters in material design, enabling the tuning of dielectric properties, exciton binding energy, and bandgaps, as well as materials structures, thereby influencing stability and charge transport behaviors. In this point, two-dimensional perovskite single crystals can play essential roles in not only understanding phase-dependent intrinsic natures but also enhancing performance of optoelectronic applications, specifically owing to their long carrier diffusion length and enhanced stability with little grain boundaries and low trap density. This review will deliver the strategy of phase-dependent materials design with an understanding of their anisotropic properties and charge dynamics for optoelectronic applications, including photodetectors and X-ray detectors.

Focused ion beam lift-out has become an essential technique for fabricating small-scale specimens in atom probe tomography (APT). By using a rotatable micromanipulator, we developed methods that can precisely extract the regions of interest for APT samples with challenging-to-prepare geometries. Combining this function with pre-milling and pre-tilt operations, we prepare three typically challenging APT specimens: nanoparticles, nanowires, and thin films. This combination can effectively decrease the sample preparation time and increase the accuracy of focused ion beam lift-out specimen preparation.

In thermoelectrics, optimizing both carrier and phonon transport is crucial for enhancing thermoelectric performance. Strontium titanate, a representative N-type oxide thermoelectric material, often exhibits inferior figure of merit (zT) due to its large band gap that limits carrier concentration, and high lattice thermal conductivity, attributed to strong Ti-O covalent bonds. Conventional approaches, such as aliovalent doping to increase carrier concentration or introducing structural defects to reduce lattice thermal conductivity, are insufficient as they fail to decouple the interdependent electrical and thermal properties. Herein, we introduce a high-pressure synthesis technique that concurrently modulates both the band gap and microstructure. This approach effectively enhances the carrier concentration by narrowing the band gap and increases the effective mass of the density of states through enhanced solubility limit of rare earth elements, significantly improving the power factor. Additionally, high-pressure condition induces microstructural defects, including point defects, dislocations, lattice distortions, and nanoscale grains, which promote broad-wavelength phonon scattering and minimize lattice thermal conductivity. Consequently, a peak zT value of 0.25 at 973 K is attained in high-entropy (Sr_0.2La_0.2Nd_0.2Sm_0.2Eu_0.2)TiO₃ synthesized at 5 GPa, representing a 5.3-fold improvement over undoped strontium titanate. This work highlights the pivotal role of high-pressure synthesis in decoupling the carrier and phonon transport in thermoelectrics.

In this study, we have conducted an investigation on the structural characteristics and electronic properties of van der Waals heterostructures (vdWHs) composed of Gallium selenide (GaSe) and MoSi₂N₄. The analysis was carried out using first-principles methods. The findings indicate that the heterostructure exhibits stability at standard room temperature and possesses characteristics of an indirect bandgap semiconductor. Interestingly, we observed that the band edges of the heterostructure of monolayer GaSe and MoSi₂N₄ were able to form a type-I band alignment. Therefore, in the field of optoelectronic devices, GaSe/MoSi₂N₄ vdWHs can be widely used in light-emitting devices such as diodes. In addition, through the application of an external electric field and in-plane strain, the band edges of GaSe/MoSi₂N₄ vdWHs can be separated from the GaSe and MoSi₂N₄ layers, forming a transition from the type-I to type-II band alignment, which is very favorable for realizing effective electron-hole separation. Therefore, GaSe/MoSi₂N₄ vdWHs have great potential as an adjustable material in optoelectronic applications.

The lack of sufficient uniform deformation ability of body-centered cubic (BCC) high-entropy alloys (HEAs) is the obstacle to their applications as structural materials. Here we present a grain refinement strategy to achieve excellent uniform ductility of a BCC non-equal atomic ratio Ti-Zr-V-Nb-Al (TZ) alloy. The uniform elongation and yield strength of the fine-grained TZ alloy with a grain size of 15 µm are as high as ~12% and 840 MPa, respectively. The outstanding uniform deformability of the fine-grained TZ alloys is due to the frequent cross-slip events and abundant dislocation tangles. Grain refinement can increase the probability of dislocation entanglement, thereby promoting a rise in the work-hardening rate. The good plasticity and high work-hardening rate can improve the uniform deformation ability. Our results will give new insights into enhancing uniform ductility while maintaining high strength in the BCC HEAs.

Mechanochromic colloidal photonic crystals (PCs), which typically integrate a self-assembled PC array with a highly elastic medium, exhibit the ability to reversibly respond to external mechanical stimuli by altering the periodicity of PC structures. Nowadays, leveraging visible indications and optical signals for mechanical forces, mechanochromic colloidal PCs have been widely used in reflecting body motion, health monitoring, and communications in daily life. However, despite their extensive applications on land, it is vital to explore the potential of mechanochromic sensing applications underwater, where message transmission mainly relies on body gestures and motions. This review comprehensively examines recent advancements in mechanochromic colloidal PCs and their underwater applications. The first part introduces the response mechanism of mechanochromic colloidal PCs, emphasizing the main principles that facilitate sensing on the microscale. The second part describes the fabrication strategies for constructing these PCs, demonstrating various approaches to establish optical sensors with specific functionalities. The final section discusses the confronted challenges and summarizes the potential opportunities in developing mechanochromic colloidal PCs for underwater sensing applications.

Halide perovskites (HPs) have found wide-ranging applications in photovoltaic and optoelectronic devices, achieving remarkable success due to their unique crystal structure and properties. Given the sensitivity of perovskite materials to external stimuli, it is crucial to understand the intrinsic changes in structure and chemical composition during operational conditions. This understanding could assist researchers in exploring new strategies to enhance the photoelectrical properties and stability of these materials. While many in situ methods, such as in situ X-ray diffraction and in situ photoluminescence, have been employed to investigate the properties of perovskite materials in real-time, in situ transmission electron microscopy (TEM) stands out as an unparalleled technique for observing subtle changes at the micro and even atomic scale. In this review, we summarize recent advancements in studying HPs using in situ TEM. We first introduce studies on the crystallization process of HP crystals through in situ TEM observation, and then categorize research works on the degradation process of HPs driven by different external stimuli, including electron beam, heat, electrical bias, light, and ambient atmosphere. Finally, we highlight several challenges that still need to be addressed in the future. This review aims to present a thorough summary of the existing research and lay the groundwork for future inquiries in this captivating area.

Bioactive glass (BG) degrades in vivo, releasing therapeutic ions and forming an apatite-like phase to repair hard tissues. While many BG-derived materials have been employed clinically, researchers continue to work on improving the physicochemical properties and biological functions of BG due to its inappropriate degradation rate and unsatisfactory bone repair effects. Our previous work revealed that the incorporation of chlorine (Cl) into BG expanded the glass structure, facilitating glass degradation and rapid hydroxyapatite formation. Chloride-containing bioactive glasses (GPCl) showed good osteogenesis effects in vitro and in vivo. However, the fast degradation rate of GPCl may cause a mismatch between bone formation and glass degradation, limiting its bone repair efficacy. This study incorporated various amounts of magnesium (Mg, 0-20 mol%) into GPCl to regulate its degradation behavior and enhance its bone regeneration ability. Four glasses were synthesized using a melt-quench method. The in vitro glass bioactivity was evaluated in Minimum Essential Medium-α (α-MEM), while the in vivo osteogenic effect of Mg-doped chloride-containing bioactive glasses (GPMgCl) was investigated on a rat skull critical-size defect and compared with the commercially available bone substitute (Bio-Oss^®). Additionally, the blood and main organs of rats were collected to assess the biocompatibility of GPMgCl. Our results demonstrated that Mg delayed the degradation rate of GPCl and the rate of hydroxyapatite formation while maintaining excellent bioactivity in α-MEM. GPMgCl promoted the expression of osteogenic genes osteocalcin (OCN), bone morphogenetic protein 2 (BMP2), and vascular endothelial growth factor (VEGF), and facilitated the formation of the mineralized nodules. Moreover, it exhibited superior osteogenic effects compared to Bio-Oss^® in vivo, with GPMg10Cl showing optimal bone regeneration ability. Blood biochemical analyses, blood cell tests, and hematoxylin-eosin staining of organs confirmed the excellent biocompatibility of GPMgCl. Incorporating Mg into GPCl is a promising approach to regulate degradation behavior and enhance osteogenic performance, making GPMgCl a promising bone substitute material to meet future bone repair needs.

Secondary lithium-carbon dioxide (Li-CO₂) batteries possess great application potential for CO₂ fixation and electrochemical energy storage. Nevertheless, the formation of stable and insulating discharge intermediates and the complexity of multiphase interfacial reactions lead to large potential polarization and inferior redox reversibility. In this review, we systematically discuss the charge/discharge mechanisms of Li-CO₂ redox reaction. Latest research achievements about cathode architecture and active site engineering are summarized in detail. In particular, representative engineering strategies (i.e., morphological modulation, dimensional hybridization, defect, single atoms, heterostructure, and synergy engineering) of cathode materials for high-performance Li-CO₂ batteries are systematically introduced. Lastly, the current research progress is briefly summarized and the future challenge and potential opportunities for further development of advanced Li-CO₂ batteries are proposed.

The application of nanotopographic structures is considered a promising strategy for improving outcomes in tissue engineering. Nanotopographic structures-mediated immune responses have a more profound influence than the direct modulation of functional cell responses. However, the reported immunomodulatory effects of different nanotopographic structures are inconsistent and unpredictable. Therefore, it is necessary to further understand the general or fundamental biological mechanisms underlying nanotopographic structures-mediated immune regulation to fabricate structures with the desired immunomodulatory properties. Compared to the effects on protein absorption and physiochemical signals, the mechanical forces induced by nanotopographic structures play a more pivotal role in determining immune responses. Elucidating the mechanotransduction mechanisms by which mechanical forces from nanotopographic structures are converted into intracellular biochemical signals in immune cells is crucial. This understanding is essential for the precise regulation of immune responses mediated by nanotopographic structures and for guiding the development of nanotopographic structures with advanced immunomodulatory properties. This review elucidates the impact of nanotopographic structures on cellular mechanical forces and the subsequent activation of mechanosensors. The ensuing mechano-regulatory effects on immune responses are reviewed, and mechanoimmunomodulation is proposed as a strategy for designing nanotopographic structures to modulate immunity. This review contributes to revolutionizing the strategy for developing nanotopographic structures and promotes the application of nanotopographic structures with the mechanoimmunomodulatory property in tissue engineering.

With modern science and technology developing, the concentration of atmospheric carbon oxide (CO₂) has increased substantially. CO₂ electroreduction reaction (CO₂RR) can efficiently utilize sustainable power to produce value-added chemicals and implement energy storage. Previous researches have proved bismuth metal and bismuth-based materials can transfer CO₂ to formate selectively. However, in this paper, the latest progress in the synthesis of advanced electrocatalysts with bismuth-based CO₂RR catalysts is reviewed from the aspects of catalyst material design, synthesis, reaction mechanism and performance verification/optimization. Some methods of designing catalysts are discussed and analyzed from different angles, including catalyst morphology, defects and heterogeneous structures. In particular, the application of in situ characterization technique in catalyst characterization is introduced. Subsequently, some views and expectations regarding the current challenges and future potential of CO₂RR research are presented.

Biomass, as an emerging environmental and renewable resource derived from various green sources, is increasingly being recognized for its inherent structural characteristics that are conducive to the production of high-value chemicals. The complicated structure and oxygen-rich nature of biomass and its derivatives necessitate high-value targeted conversion, typically involving liquid-phase hydrogenation or the addition of acidic or basic environments. These processes impose stringent requirements on the efficiency and durability of the catalysts. Recently, the innovation of single atom catalysts (SACs) with individual catalytic sites dispersed on various supports has demonstrated high catalytic efficiency and good selectivity. Owing to their high atomic utilization and cost-efficiency, SACs have emerged as one of the most promising heterogeneous catalysts. This review summarizes current progress on the catalytic conversion of biomass mediated by SACs. Significant emphasis is placed on the unique active sites and reaction mechanisms of SACs in various kinds of catalytic methods (thermocatalysis, electrocatalysis, photocatalysis). In order to facilitate comparison, the various reactions are categorized according to the type of raw material (cellulose, hemicellulose, lignin, etc.). Especially, the developing strategies for preparing SACs are summarized to better satisfy industrial requirements. Finally, we provide an anticipatory outlook of future developments in this field, focusing on biomass utilization and advanced catalytic systems.

With the over-consumption of non-renewable energy, green and clean renewable energy is inevitably the choice in modern society. In particular, lithium-ion batteries (LIBs) have been widely used in automobiles, aviation and other fields due to their high energy density and other advantages. However, lithium reserves are limited, and LIBs have safety hazards, so the development of alternative rechargeable batteries cannot be delayed. Aqueous zinc ion batteries (AZIBs) have a high theoretical specific capacity while ensuring safety, and have been intensively investigated in recent years. The advancement of cathode materials is essential for AZIBs. In this article, the recent development of non-oxide manganese and vanadium cathode materials such as MnS, MnHCF, VN, VSe₂ and VS₂ for AZIBs is critically reviewed. The emerging strategies for modifying these cathode materials for enhanced electrochemical performance are critically analyzed. Finally, some important achievements of this research field are summarized, and the challenges and future research directions are presented. We hope that this article can shed light on the development of AZIBs.

Dislocations in perovskite oxides have an important influence on their macroscopic performances. In this work, we report abundant dislocations in PbZrO₃-based antiferroelectric (AFE) ceramics, which manifest themselves mainly as dislocation arrays with Burgers vectors along the <110> direction. We demonstrate that these dislocation arrays were emitted from the grain boundaries and exhibit a pure screw character with glide systems of <110>{$$ 1\bar{1} 0 $$}. The in situ transmission electron microscopy investigations indicate that dislocations are beneficial for stabilizing the AFE phase in the heating process and serve as nucleation sites for the AFE phase during cooling. Meanwhile, the stress field of dislocation arrays also plays a critical role in the growth of AFE domains, which can be applied for regulating domain size and orientation. These findings provide the basis for dislocation engineering in AFE ceramics.

Conductive polymer composites used to develop stretchable strain sensors have great potential for a wide range of applications, but engineering such a sensor with high sensitivity and durability remains very challenging. In this study, we propose a hydrothermal approach coupled with a freeze-drying technique to fabricate durable and stretchable strain sensors based on polydopamine-functionalized halloysite nanotube/reduced graphene oxide/polydimethylsiloxane (PDA@HNT/rGO/PDMS) aerogel composites. These sensors exhibit exceptional sensing performance, enhanced stretchability, linearity range, and stability. A comparative analysis of graphene oxide at different concentrations demonstrates that the flexible PDA@HNT/rGO/PDMS composites exhibit a significantly broader sensing range when the graphene oxide concentration is reduced to 2.5 mg/mL, in contrast to the higher concentration of 5.0 mg/mL. Specifically, the synergistic effect of both PDA and natural fiber HNTs results in aerogel composite strain sensors with a desirable gauge factor and a linearity sensing range as evidenced by the theoretical analysis, which demonstrates great potential for wearable electronics and human motion detection. The synergy between PDA and HNTs enhances the properties of aerogel composite strain sensors by improving interfacial adhesion, uniformly dispersing reinforcing agents, and maintaining conductive pathways, resulting in a highly sensitive, broad-range, and durable device. The development of conductive PDA@HNT/rGO/PDMS aerogel composites for flexible strain sensors represents an important advancement in the field of wearable technology and has the potential to revolutionize the way we monitor and respond to mechanical stress in various applications.