Oxygen reduction reaction (ORR) is an important cathodic reaction, but its slow reaction kinetics seriously hinders the application of clean energy devices such as fuel cells and metal-air batteries. Although platinum (Pt)-based catalysts possess excellent ORR activity, their high cost, scarce reserves, poor stability and tolerance make it difficult to commercialize current clean energy technologies. To address the above problems, it is urgent to develop new types of efficient and low-cost ORR catalysts. As an emerging carbon-based material, nanodiamond (ND) exhibits broad application prospects in ORR catalysis due to its advantages such as low cost, controllable functional group modification, high surface energy (>1000 mJ·m^-2), and unique π and σ bond configurations. This paper reviews the latest research progress of ND catalysts. Firstly, preparation methods such as detonation, chemical vapor deposition, pulsed laser ablation, and high-pressure high-temperature are introduced. Subsequently, modification strategies including heteroatom doping, surface functionalization, material composite, and morphology regulation are summarized, and their formation mechanism of active centers and regulation rules of reaction paths are analyzed, covering influence of different modification strategies on catalytic performance and comparison of relevant performance data. Finally, the challenges faced by current ND catalysts in catalytic mechanism, synthesis process, characterization technology, and design methods are analyzed to suggest the future development directions for the research and development of new carbon-based ORR catalysts.

Platinum-carbon (Pt/C) catalyst is one of the most promising cathode materials for proton exchange membrane fuel cells (PEMFCs). However, it faces significant durability challenges, primarily due to growth and agglomeration of platinum nanoparticles (Pt NPs), which results in increased Pt particle size and consequent loss of catalytic activity. In this study, an internally pearl-like mesoporous carbon (IPMC) support with beaded pore channels was constructed to investigate the deposition sites of Pt NPs within carbon supports. Through precisely confining Pt NPs within the pore channels by leveraging the unique pore architecture, efficient confinement and stabilization of Pt NPs were achieved. Average size of Pt NPs in IPMC increased by only 0.46 nm after 30000 cycles of accelerated durability test (ADT), significantly less than the growth (0.79 nm) observed in conventional solid carbon-supported catalysts. The IPMC-based catalyst also exhibited slower electrochemical performance decay. The electrochemical active area (ECSA) loss rate of the mesoporous carbon catalyst was 24.18%, significantly lower than 32.33% observed for solid carbon catalyst in comparative testing. This superior durability originates from unique pore structure of IPMC, which imposes spatial confinement effects that effectively suppress Ostwald ripening and migration of Pt NPs, thereby mitigating the degradation of oxygen reduction reaction (ORR) activity. This work delivers a precise structural blueprint for optimal carbon carriers of high-stability PEMFCs catalysts by revealing how beaded mesopores confine Pt NPs: interconnected pore channels with local constrictions form spatial barriers which hinder dissolved platinum species diffusion while anchoring particles.

NiMn-layered double hydroxide (NiMn-LDH) is a promising cathode material for hybrid supercapacitors (HSCs) due to its inherent environmental sustainability, exceptionally high theoretical specific capacitance, and robust cycling stability. However, its widespread practical application faces significant limitations due to its poor electronic conductivity, which results in low specific capacitance and rate capability. Particularly at mg·cm^-2 magnitude loading, the specific capacitance at high current densities of 50 A·g^-1 or above is much lower than 1500 F·g^-1, a performance threshold critically insufficient for the energy-power balance required in commercial HSC devices. To address this limitation, this work innovatively developed a novel NiMn_x-LDH@Ni₉₅Cu₅ electrode via a simple two-step electrodeposition strategy. Ni₉₅Cu₅ dendritric foams with hierarchical porous structure were prepared by hydrogen bubble template method, and NiMn-LDH was anchored to the Ni₉₅Cu₅ substrate by electrochemical deposition. By adjusting the Mn/Ni stoichiometric ratio in NiMn-LDH which was electrodeposited on the surface of Ni₉₅Cu₅ dendritic foam through variations of the metal ion ratios in electrodeposition solution, its influence on the composition, elemental valence state, crystal structure, morphology, energy band configuration, and electrochemical behavior of NiMn-LDH was investigated. As the Mn content in NiMn-LDH increases, the size of NiMn-LDH nanosheets decreases. The optimized NiMn_0.6-LDH@Ni₉₅Cu₅ electrode exhibits superior crystallinity, minimized charge-transfer resistance, the narrowest band gap, and synergistically exceptional electrochemical performance, delivering outstanding specific capacitances of 2365 F·g^-1 at a current density of 1 A·g^-1 and 1803 F·g^-1 at an ultrahigh current density of 50 A·g^-1, even under high mass loadings (>2 mg·cm^-2). Furthermore, it demonstrates remarkable cycling stability and retains 88.8% of its initial capacity after 3000 cycles at 20 A·g^-1. Collectively, this study confirms that the composition, crystallinity and energy band structure of LDH can be synergistically optimized by precisely tuning the bimetallic ratio, thus solving the problem of specific capacitance and multiplicity performance degradation of high-loading electrodes, and provides a new idea for the design of next-generation high-performance HSC electrodes.

Thermomagnetic refrigeration based on the Ettingshausen effect is a low-temperature solid-state cooling technology with advantages of precise temperature control, compact size and noiseless operation. In recent years, topological semimetals, which possess both electrons and holes as charge carriers and exhibit high carrier mobility, have shown excellent thermomagnetic performance at low temperatures, making them promising candidates for cryogenic applications. In this study, highly dense polycrystalline TaSb₂ was synthesized via solid-state reaction followed by spark plasma sintering, and its low-temperature thermomagnetic transport properties were systematically investigated. The results show that the Nernst thermopower (S_yx) peaks at around 27 K and increases with applied magnetic field. Under 9 T and 26 K, the Nernst power factor ((PF)_N) reaches 315.1 μW·cm^-1·K^-2, while under 9 T and 22 K, the Nernst figure of merit (z_N) is 7.1×10^-4 K^-1, both outperforming most reported polycrystalline thermomagnetic materials. Mechanistic analysis indicates that the high performance originates from the combined effects of strong bipolar effect, high carrier mobility and significant phonon-drag enhancement of thermopower. Moreover, magnetic fields markedly suppress the electronic contribution to thermal conductivity at low temperatures, making the total thermal conductivity predominantly determined by the lattice component. This work offers a new material option and design strategy for low-temperature solid-state cooling applications. The relatively high lattice thermal conductivity partially limits the thermomagnetic performance, and further reduction via phonon engineering could lead to substantial improvements.

Silicon carbide (SiC) is a promising material for nuclear reactor structures due to its excellent radiation resistance and high-temperature performance. The behavior of irradiation damage and the mechanisms of high-temperature recovery in SiC directly affect its service performance and longevity in nuclear environments. This study investigated effects of neutron irradiation on properties of 6H-SiC, with a particular focus on high-temperature recovery mechanisms of irradiation-induced defects. Specifically, defect evolution and thermodynamic responses in nitrogen-doped (N_D≈3.0×10¹⁹ cm^-3) 6H-SiC subjected to neutron irradiation at about 150 ℃ and a fluence of 2.58×10²⁰ n/cm² followed by isochronal annealing were examined. Integrated techniques and first-principles calculations were employed to comprehensively analyze its structural and property evolution. The key findings were as follows. (1) Significant lattice swelling was observed during the irradiation, with a swelling rate of 0.416% along the a-axis, 0.430% along the c-axis, and 1.310% in the unit cell volume, while all maintaining integrity of the single-crystalline structure. (2) A 14.7% increase in specific heat capacity was recorded, with 375.4 J/g of stored irradiation energy being released during heating from 100 ℃ to 500 ℃. (3) A four-stage defect recovery kinetic model was proposed based on the recovery of lattice parameters and the evolution of Raman spectra: Stage I (room temperature (RT)-600 ℃), primarily dominated by close-range recombination of carbon Frenkel pairs driven by migration energy (E_a) of 0.14 eV; Stage II (600-850 ℃), recombination of silicon Frenkel pairs and migration of carbon interstitials (E_a=0.26 eV); Stage III (850-1200 ℃), lattice reconstruction (E_a=0.65 eV); Stage IV (1200-1500 ℃), long-range diffusion of carbon vacancies (V_C) and dissociation of N_CV_Si complexes (E_a=1.50 eV). (4) The presence of nitrogen-stabilized N_CV_Si defect configurations was confirmed by a characteristic emission peak at 826 nm (634 cm^-1 Raman shift) when excited with 785 nm light. This study quantitatively reveals the defect recovery pathways and migration energies in neutron-irradiated 6H-SiC, providing a critical foundation for evaluating radiation damage, predicting performance, and optimizing annealing processes in nuclear-grade SiC materials.

Gen IV nuclear reactors operate in extreme service environments characterized by high temperature and intense irradiation, imposing stringent demands on structural materials and thus necessitating the development of novel irradiation resistant materials. Titanium carbide (TiC_x) ceramic is considered as promising structural material for advanced nuclear reactors, attributed to its high melting point, excellent mechanical properties, and excellent corrosion resistance. In this study, TiC_x films with different stoichiometries were irradiated with 3 MeV Au²⁺, aiming to systematically investigate irradiation-induced changes in structural characteristics, surface morphology and mechanical properties under different irradiation fluences. The results revealed that structural disorder of TiC_x intensified with increasing irradiation fluence, while the substoichiometric TiC_x maintained superior structural stability after irradiation. Surface roughness of substoichiometric TiC_x showed no significant variation after irradiation, with no irradiation-induced crack. Additionally, both hardness and elastic modulus of TiC_x exhibited an increasing trend after irradiation, demonstrating that substoichiometric TiC_x enhanced resistance to irradiation compared to near-stoichiometric counterparts. The native carbon vacancies in substoichiometric TiC_x effectively suppress accumulation of irradiation-induced defects, thereby preserving excellent stability. This study provides critical insights into the relationship between stoichiometry and irradiation damage in TiC_x, while offering valuable guidance for designing new classes of irradiation-resistant ceramic materials.

Continuous alumina fiber-reinforced silica ceramic matrix composites exhibit excellent properties, such as high-temperature oxidation resistance, high strength and high toughness. As a dual-use material for both military and civilian applications, they hold broad prospects in numerous fields, including aviation, aerospace and energy. However, domestic research currently still remains on its initial stage and is characterized by a primarily qualitative understanding of their mechanical property failure mechanisms. In this study, an improved liquid-phase impregnation method, which integrated the process characteristics of the Sol-Gel method and slurry impregnation method, was adopted to prepare continuous alumina fiber-reinforced silica composites with tunable porosity. Microstructure and composition of the typical composite were comprehensively characterized using different techniques. Mechanical properties of these composites with different densification degrees were tested and analyzed. By integrating porosity data obtained from computed tomography (CT) test with simulation calculation, a relationship model linking mechanical property failure of the composites to porosity and pore size parameters was established. The results indicated that composites prepared via the improved liquid-phase impregnation method had significantly enhanced mechanical properties due to the presence of pore defects and weak interfacial bonding. Notably, as the composite porosity increased from 2.2% to 15.2%, the tensile strength decreased from 24.5 MPa to 17.8 MPa. Further modeling and simulation analysis revealed that, at a pore defect radius of 250 μm, an increase in porosity from 4.5% to 13.5% led to a corresponding reduction in tensile strength from 27.2 MPa to 20.6 MPa, thereby validating rationality of the simulation model. The law that the n-th power of tensile strength shows a negative linear correlation with porosity, and the tensile strength exponent factor n is negatively linearly correlated with the pore defect radius r. These findings provide a research basis for the performance optimization and practical application of continuous alumina fiber-reinforced silica composites.

SiC_f/SiC composites exhibit advantages such as high-temperature resistance, oxidation resistance and high strength, making them a “star” candidate material in the field of aerospace thermal protection. Under operational conditions, these materials are subjected to prolonged multiple coupled fields such as heat, water and oxygen, exhibiting complex failure mechanisms and damage evolution patterns. This study investigated the integrated oxidation mechanism of the matrix/interface/fiber in Mini-SiC_f/BN/SiC composites under cyclic oxidation at 1100 ℃ in a water-oxygen coupled environment by using multi-scale macro/micro characterization techniques. The results showed that during the initial oxidation stage, an amorphous SiO₂ glass layer with relatively smooth morphology formed on the material surface. However, with an increase in crystallinity, localized spallation occurred in the oxide layer, causing the surface roughness to initial decrease and subsequent increase. X-ray microscope results showed that numerous micro-defects were generated within the material after cyclic oxidation, and the number of defects increased by orders of magnitude (about 107 fold). Majority of these micro-defects were mainly distributed on the matrix surface, and the oxidation products played a certain filling role in these defects. The tensile strength showed no significant variation before ((328.47±32.84) MPa) and after ((343.27±35.71) MPa) cyclic oxidation, indicating continued effectiveness of the synergistic toughening mechanism of “strong matrix-weak interface”. These observations indicate that an integrated oxidation protection mechanism involving matrix, interface and fiber exists in the Mini-SiC_f/BN/SiC, which is predicated on the filling of defects by SiO₂ and borosilicate glass generated by its interface layer and adjacent matrix with fibers in the direction parallel to the fiber axis. Dynamic “outer porous sacrificial layer-middle dense SiO₂-inner SiC matrix” is a three-dimensional protective barrier of the matrix in the direction perpendicular to the fiber axis. This dual-protection system substantially alleviates material degradation under cyclic thermal water oxidative conditions.

Under demanding service conditions, the operational requirements, namely high-temperature performance and structural weight reduction, in aero-engine hot section components continue to intensify. Silicon carbide fiber reinforced silicon carbide matrix (SiC/SiC) composites are widely recognized as exceptionally promising alternative materials owing to their outstanding high-temperature stability, substantially reduced density and superior corrosion resistance. However, in actual service environments, these composites inevitably experience complex vibrational loading spectra, which induce fatigue damage accumulation emerging as a critical limiting factor in their practical engineering implementation. In this study, 2D SiC/SiC plates were fabricated by chemical vapor infiltration. Specimens featuring bilateral arc-shaped notches were machined from the plates and subsequently subjected to narrow band random vibration fatigue tests under the first-order vibration mode. This experimental approach was undertaken specifically to investigate the progressive damage evolution process and the accompanying degradation patterns in tensile properties under vibrational fatigue loading. The experimental findings reveal that the normalized full time-domain characteristic curves of the 2D SiC/SiC plate structures exhibit progressive downward displacement while the applied equivalent stress amplitude increases. These curves concurrently manifest pronounced statistical dispersion throughout low-stress loading regime. Based on microstructural analyses, the damage evolution within the 2D SiC/SiC plate structure can be classified into three distinct and sequential stages: the initial matrix damage stage, the subsequent interface damage stage, and the final fiber damage stage. Quantitatively, the damage progression rate follows a distinct correlated three stage evolution—commencing with rapid progression, then transitioning to reduced propagation velocity, and lastly culminating in accelerated damage advancement. Residual tensile properties demonstrate that the tensile characteristics of the 2D SiC/SiC plate structure follow an exponential decline trend. At a resonance frequency reduction of 31.9%, the tensile strength, proportional limit stress, elastic modulus, and resilience modulus have degraded to 270.0 MPa, 64.1 MPa, 106.3 GPa, and 0.020 MJ/m³, respectively, all falling below 70% of the corresponding values in the as-fabricated pristine state. Subsequent analyses of the tensile fracture surface reveal matrix cracking and pronounced fiber wear as the dominant damage mechanisms responsible for the significant degradation observed in the tensile properties of the vibration fatigued composite structure. These findings provide a critical experimental basis for assessing the service reliability of 2D SiC/SiC plate structures under vibrational service conditions.

BN ceramic fibers exhibit significant potential for applications in high-temperature wave-transparent and semiconductor fields, due to their excellent resistance to high temperatures and thermal conductivity, as well as their outstanding wave-transparent performance. However, the low crystallinity observed in BN ceramic fibers inhibits complete realization of their potential superior properties associated with the h-BN crystal structure. In this work, based on the mechanism that inorganic nanofillers could act as heterogeneous nucleating agents to accelerate matrix crystallization, three lateral sizes (0.5, 2 and 4 μm) of amino-functionalized BN nanosheets (BNNSs) were prepared utilizing a one-step ball milling method. BNNSs were chemically bonded to molecular chain of polyborazine to synthesize hybrid BNNS/polyborazine precursors, which were finally derived into high-performance BN ceramic fibers with high crystallinity. This investigation thoroughly explored the scale effects of BNNS on the molecular structure of hybrid precursor, as well as their physicochemical properties and melt spinning performance. Relationship among the BNNSs’ size, microstructure and mechanical properties was elucidated. Increasing BNNSs size could enhance the ceramic yield of precursor (up to 64.1%), but destroy the viscosity-time stability. Moreover, it was demonstrated that BNNS scale could evidently regulate crystal structure of BN ceramic fibers. Relationship among the BNNSs’ lateral sizes, crystal structure and mechanical performance was determined to be non-linear. BN ceramic fibers containing 2 μm BNNS displayed the highest crystallinity (94%), grain size (12.5 nm) and density (2.00 g/cm³). However, surface defects associated with 2 μm BNNS resulted in a non-optimal average tensile strength (0.90 GPa). BN ceramic fibers doped with 0.5 μm BNNS exhibited the best average tensile strength (0.94 GPa), attributed to the favorable combination of high crystallinity and smooth surface. This work could provide crucial references for fine regulation of microstructure and preparation of high-performance BN ceramic fibers.

KTb₃F₁₀ (KTF) crystal, characterized by its high Tb³⁺ ion concentration, low thermo-optic coefficient and low phonon energy, exhibits significant potential for efficient laser emission in the green and yellow wavelength ranges. However, challenges such as incongruent melting behavior, hygroscopicity of raw materials, high-temperature compositional volatility, and corrosive nature of fluorides have severely hindered the growth of high-quality KTF crystals. This study aims to develop an effective approach to address these issues, achieve the growth of high-quality KTF crystals, and characterize their optical properties. An optimized vertical Bridgman method integrated with a laser-sealed platinum crucible technique under vacuum was employed. This innovative approach effectively shielded the raw materials from water and oxygen contamination while suppressing compositional deviation during crystal growth through a sealed environment. As a result, blank KTF crystals with dimensions of φ16 mm×30 mm were successfully grown, and their relevant spectral properties were characterized. X-ray rocking curve of the (111) plane showed a full width at half maximum of 0.08°, indicating high crystalline perfection. Thermal analysis indicated significant volatilization of KTF at high temperatures. Spectral tests revealed an average transmittance of >90% in the 400-1600 nm range and an absorption coefficient of <0.007 cm^-1 at 1064 nm, demonstrating minimal optical loss suitable for high-power laser applications. Fluorescence lifetime was 4.82-4.99 ms for the Tb³⁺ ion at the ⁵D₄ energy level, which is 3-5 times longer than that in oxide matrices. This superiority is attributed to the suppression of non-radiative relaxation by the low-phonon fluoride matrix, enhancing the energy storage efficiency for laser emission. Based on above data, this study has successfully established a viable growth method for KTF crystals, providing a new technical pathway for the controllable synthesis of KTF and other ternary fluoride materials. All these results provide valuable insights for the high-efficiency application of KTF crystals in yellow-green laser emission.

Two-dimensional (2D) gallium nitride (GaN) exhibits broad application prospects in the field of ultraviolet optoelectronics due to its dual characteristics of wide-bandgap semiconductor and quantum confinement effect. However, conventional synthesis methods for 2D GaN, such as metal-organic chemical vapor deposition and molecular beam epitaxy, typically require high growth temperatures, prolonged processing time, and relatively high costs. To address these critical challenges, this work leverages the intrinsic properties of liquid metal gallium, including its low melting point and ease of oxidation to develop an efficient and relatively low-temperature synthesis strategy for 2D GaN. The core of this strategy includes following steps. Firstly, utilizing a straightforward spin-coating exfoliation technique to directly extract an amorphous gallium oxide (Ga₂O₃) from the surface of liquid gallium. Subsequently, subjecting the amorphous Ga₂O₃ to a nitridation treatment process at a relatively low temperature of 850 ℃, successfully achieved its conversion into high-crystalline-quality GaN. Characterization results demonstrate that the synthesized 2D GaN possesses a thickness of approximately 2.2 nm, a lateral dimension on the centimeter scale, and a hexagonal wurtzite crystal structure. Furthermore, based on the prepared 2D GaN, a photoconductive ultraviolet photodetector is constructed. Performance characterization results reveal that under a 5 V bias voltage and illumination by 325 nm ultraviolet light, the device exhibits a responsivity of 4.14 A/W and a high detectivity of 1.02×10¹³ Jones. This study demonstrates the successful preparation of large-area 2D GaN material based on liquid gallium metal, providing a valuable reference for the development of low-dimensional and high-performance ultraviolet photodetectors.

Methane (CH₄), as both a greenhouse gas and a crucial energy source, plays an important role in achieving China’s carbon peaking and carbon neutrality goals. The significant concentration differences of CH₄ from various sources influence the selection of relevant conversion technologies. However, little research has addressed the impact of CH₄ concentration variation on catalytic performance, and studies focusing on the catalytic pyrolysis of methane for carbon material production are especially scarce. In this work, molten salt catalytic pyrolysis was employed as the core strategy to systematically investigate the catalytic decomposition behavior of CH₄ with varying concentrations (20%-100%) and the morphology control mechanisms of carbon products in a CuCl₂-NaCl molten salt system. The results revealed that the formation of graphene films was attributed to the two-dimensional assembly of carbon atoms on bubble surfaces at high CH₄ concentrations, followed by subsequent film growth. High CH₄ concentration in the CuCl₂-NaCl system favored the formation of well-ordered graphene structures, while low concentrations primarily produced fragmented carbon. Furthermore, various molten salt systems yielded different carbon morphologies, including graphite sheets, short rod-like carbon nanotubes, and film-like carbon. Comprehensive characterizations demonstrated that the CH₄ concentration determined growth mode of the carbon products. This study elucidates morphology control mechanisms of the carbon products driven by the CH₄ concentration gradient in molten salt systems, providing a theoretical basis for the environmentally friendly synthesis of high-value-added carbon materials and development of low-carbon technologies.

Commercial phosphor-converted white LEDs (pc-WLEDs) face two inherent limitations, namely blue light hazard and low color rendering index, due to the use of blue LEDs as excitation source. To address these challenges, violet LEDs are proposed as an alternative solution. Currently, phosphors that can be efficiently excited by violet light (with wavelengths from 400 to 420 nm) remain under development still. In this study, we utilize large language models to construct a comprehensive database of Eu²⁺ and Ce³⁺ doped phosphors for discovering novel violet-excited phosphors. A total of 822 phosphor data entries, including elemental compositions, crystal structures and excitation/emission wavelengths, have been extracted and validated from 9551 research papers. Compared with Ce³⁺ doped phosphors, the Eu²⁺ are in general more suited for violet-excited phosphors, as well as red-emitting phosphors. In particular, Eu²⁺ doped nitrides and sulfides are worth of exploration for violet-excited phosphors. This database is expected to be useful in the future development of phosphors for pc-WLEDs based on artificial intelligence methods. The datasets in this article are listed in Science Data Bank at http://doi.org/10.57760/sciencedb.34314.

Carbon fiber-reinforced carbon aerogel (C/CA) composites are one of the most promising candidates for applications requiring both thermal insulation and load bearing capabilities. The preparation of anti-oxidation coatings on C/CA to address its susceptibility to oxidation is a feasible approach to promote its application in oxidative environments. However, the currently reported coatings on C/CA mainly focus on improving the ablation performance and coating preparation process typically necessitating high-temperature heat treatment. This procedure can increase its thermal conductivity and reduce its thermal insulation ability. In this study, a series of ceramic-resin coatings were fabricated on C/CA through a simple slurry brushing-drying approach at room temperature. The effects of phenolic resin content on the coating structure, residual stress, thermal shock, and oxidation behaviors were investigated. Due to the adhesive properties and curing-induced shrinkage, the PR-7.5 coating (containing 7.5% (in mass) phenolic resin in the slurry) exhibits bonding strength close to fracture strength of the substrate and residual compressive stress of 0.853 GPa, which is beneficial for resisting thermal shock cracking. However, excessive resin content (PR-10.0 containing 10.0% (in mass) phenolic resin in the slurry) induces tensile stress due to uneven curing shrinkage, thereby leading to thermal shock cracking. Meanwhile, oxidation tests reveal significantly reduced weight losses for PR-7.5 (17.46% at 800 ℃/100 min, 8.15% at 1000 ℃/120 min, 3.15% at 1200 ℃/120 min) versus uncoated C/CA’s 44.60% loss at 800 ℃/20 min. This work provides a brand-new and simple approach to improving the anti-oxidation performance of C/CA and expands its application in mild oxidative environments.