Search Results (142)

Hydrogen is a promising clean-energy carrier, but its low ignition energy, high diffusivity, and wide flammability range demand reliable leak detection. Chemiresistive sensors based on n-type metal oxide semiconductors are attractive owing to their simple architecture, low cost, large resistance modulation, thermal robustness, and compatibility with miniaturized devices. This review focuses on n-type metal oxide semiconductor nanomaterials for hydrogen sensing, particularly ZnO, SnO₂, In₂O₃, WO₃, TiO₂, and related mixed oxides. The fundamental sensing mechanisms are examined, including oxygen chemisorption, electron-depletion-layer modulation, grain-boundary barrier control, catalytic hydrogen spillover, and hydrogen-induced surface reduction or metallization, together with the way these mechanisms compete and cooperate under different operating conditions. Recent performance-enhancement strategies are organized around morphology and porosity control, noble-metal sensitization, defect and dopant engineering, n–n heterojunctions, molecular sieving, and low-temperature activation. Density functional theory is discussed as a design tool for evaluating adsorption energetics, vacancy formation, work-function shifts, band alignment, and interfacial charge transfer, along with its current limitations for modeling humid surfaces. Finally, key challenges and future directions, including humidity tolerance, standardized reporting, device integration, and emerging materials, are summarized to guide the development of high-performance hydrogen sensors. Full article

High-entropy alloys and the broader class of compositionally complex alloys have recently attracted significant attention as promising materials for solid-state hydrogen storage. Their potential arises not only from high configurational entropy but also from the possibility of tailoring phase composition, crystal structure, local chemical environment, and defect states that govern hydrogen sorption thermodynamics and kinetics. This review summarizes current understanding of hydrogen interaction mechanisms in HEAs and discusses the role of body-centered cubic (BCC), face-centered cubic (FCC), and Laves phases in determining hydrogen capacity, reversibility, and cyclic stability. The limitations of commonly used descriptors, including valence electron concentration (VEC), atomic size mismatch δ, enthalpy of mixing ΔH_mix, and Ω parameter, in predicting hydrogen storage behavior are critically analyzed. Particular attention is given to the effects of processing methods, phase transformations during hydrogenation/dehydrogenation, and the energetic heterogeneity of interstitial sites in multicomponent systems. The review highlights that future progress will depend on the transition from empirical alloy discovery toward physically informed multiparametric design integrating CALPHAD, DFT modeling, machine learning, and in situ/operando characterization techniques for the development of efficient and durable hydrogen storage materials. Full article

A comprehensive first-principles investigation of bulk and surface Cu defects in Zn-based chalcogenides (ZnO, ZnS, and ZnSe) is presented, aimed at assessing the effect of Cu doping on the optoelectronic properties of these materials and at addressing the photocatalytic activity towards the hydrogen evolution reaction (HER). Defect formation energies, adiabatic and optical charge-transition levels of the bulk materials are determined, and their dependence on growth conditions and Fermi-level position is analysed. The results indicate that, whereas ZnO supports both donor- and acceptor-like Cu defects with pronounced Jahn-Teller distortions, ZnS and ZnSe predominantly stabilise substitutional Cu as a mid-gap acceptor with weaker electron-lattice coupling and similar absolute transition levels. Calculated vertical transition energies rationalise the characteristic emission of Cu-doped samples in terms of defect-mediated optical cycles. The focus is then placed on surface energetics, which differ markedly from bulk behaviour and critically influence photocatalytic performance. Explicit modelling of HER demonstrates that Cu substitution dramatically reduces the overpotential on ZnS and ZnSe by tuning hydrogen adsorption toward the Sabatier optimum, while in ZnO the beneficial effect of Cu doping is diminished by the excessive strengthening of the adsorbate-surface interactions. Finally, the measured HER activities are rationalised by proposing a defect-mediated mechanism involving electron trapping at the surface Cu site, cooperative proton adsorption, and hydride formation. These findings establish defect thermodynamics and surface charge localisation as key design parameters for optimising materials engineering strategies in photocatalytic applications. Full article

The Oxygen Evolution Reaction (OER) is the bottleneck in the water splitting reaction since it involves four intermediate steps, constituting the adsorption–desorption of oxygen-based radical groups, and not all of them are energetically favorable. Rapidly growing research interest is focusing on carbon-based materials as novel, highly active and durable non-precious electrocatalysts for the OER, representing a valuable alternative to precious and rare materials with electrochemical properties tuned by defect creation. In this work, we propose a facile and green methodology based on the modification of graphene oxide by laser irradiation to obtain an alternative OER catalyst. GO flakes were chemically and physically modified using pulsed laser irradiation at $532\mathrm{nm}$ with fluences of $1.5\mathrm{J}/{\mathrm{cm}}^2$ and $2.5\mathrm{J}/{\mathrm{cm}}^2$. Different analyses were carried out to correlate the electrochemical performance with the structural, optical, and morphological properties; after that, we correlated the improvements in the OER with respect to the pristine GO with the increase in OH functional groups obtained by laser treatment. The best-performing sample exhibited an overpotential of $380\mathrm{mV}$, comparable to that of catalysts reported in the literature but with the advantage of not being a precious or rare material. Full article

Local chemical heterogeneity is a typical feature of selective laser melted (SLM) austenitic stainless steel and is closely related to its hydrogen-assisted deformation behavior. In this work, molecular dynamics simulations are performed to investigate the effects of local segregation on stacking fault energy, hydrogen diffusion, and dislocation motion in austenitic stainless steel. Three representative alloy compositions, Fe₇₁Cr₁₇Ni₁₂, Fe₇₁Cr₂₃Ni₆, and Fe₇₁Cr₁₁Ni₁₈, are used to describe local composition variation associated with segregation in SLM-relevant austenitic stainless steel. The results show that Ni-rich regions exhibit relatively higher stacking fault energy and faster hydrogen diffusion, whereas Cr-rich regions show lower stacking fault energy and reduced hydrogen mobility. Hydrogen further decreases the stacking fault energy in all three alloy models and exerts a stronger influence on local defect energetics than composition variation alone. Shear simulations indicate that elemental segregation itself has only a limited direct effect on dislocation motion, whereas its interaction with hydrogen leads to a more evident retardation of partial dislocation propagation within the segregation region. These findings highlight the coupled roles of local composition variation and hydrogen in governing defect evolution and local deformation behavior in segregation-containing regions. Full article

To enhance the thermal decomposition properties of glycidyl azide polymer energetic thermoplastic elastomer (GAP-ETPE), the effects of nano-CuO supported on different carbon carriers (GO and CNT) were systematically investigated in this study. The structural characteristics and catalytic performances were comprehensively analyzed using XRD, Raman, XPS, UPS, BET, SEM, and TEM, coupled with thermal analysis techniques including TG-DSC and TG-MS. The results indicate that the catalytic performance follows the descending order of CuO/CNT > CuO/GO > CuO. Notably, CuO/CNT exhibits the optimal catalytic activity, advancing the exothermic peak temperature of the azide groups by approximately 33 °C and resulting in a more concentrated heat release process. The superior synergistic catalytic effect of CuO/CNT is attributed to the following: the three-dimensional network constructed by CNT effectively overcomes the agglomeration of CuO nanoparticles and the restacking defects typical of GO nanosheets, thereby significantly reducing the gas–solid mass transfer resistance. Simultaneously, the highly graphitized sp² conjugated skeleton of CNT provides an exceptional electron transport capability, facilitating rapid electron migration. These findings demonstrate that the structure of carbon supports profoundly influences the synergistic catalytic effect of CuO, offering valuable insights into the design of highly efficient catalysts for energetic binders. Full article

Eddy-current inspection of anisotropic composites, such as aeronautical CFRP, demands models that ensure mathematical rigor, tensorial consistency, and clear energetic interpretation. This work presents a novel unified variational framework with a multiplicative tensor perturbation for the time-harmonic eddy-current problem in anisotropic media with defective regions. The formulation is posed in the natural spaces $H(\mathrm{curl};\Omega )\times H^1\left({\Omega }_c\right)$, and the well-posedness is established via the Lax–Milgram theorem under physically consistent assumptions on permeability and conductivity. The sesquilinear form admits a Hermitian decomposition that separates dissipative and reactive contributions, revealing the energetic structure of the weak formulation. Defects are modeled through multiplicative modifications of the baseline anisotropic conductivity tensor. This congruence-based approach preserves symmetry and positive definiteness, ensuring non-negative Joule losses and structural stability, allowing a modular representation of subsurface delamination, fiber breakage, conductive inclusions, and distributed porosity within a single tensorial framework. A central result of the present formulation is the reconstruction of the complex power functional from the evaluation of the weak form at the solution, showing that the active dissipated power and the magnetic reactive power arise directly from the same integral terms. Through the complex Poynting theorem, the quadratic form is linked to the internal complex power, establishing a direct connection between the variational formulation and measurable quantities such as probe impedance variations. Simulations of realistic layered CFRP configurations, including single- and multi-defect scenarios, confirm that, compared with additive perturbations, the multiplicative model provides enhanced energetic contrast, particularly in strongly anisotropic and interacting defect conditions. Agreement with experimental measurements, supported by a quantitative comparison of dissipated power variations obtained from controlled EC experiments, corroborates the physical relevance and robustness of the proposed complex power functional. Full article

Perovskite oxide photoanodes are attractive for alkaline water oxidation but are commonly limited by interfacial recombination and sluggish charge transfer. Here we enhance anisotropic SrTiO₃ (STO) photoelectrodes via Al doping by simple yet effective one-step hydrothermal method and identify an optimal composition at 4% Al. In 0.1 M NaOH (pH 13) under simulated AM 1.5G illumination, 4% Al:STO exhibits 2 times enhancement in photocurrent density and 80% increase in electrochemically active surface area compared with the pristine SrTiO₃, as evidenced by the reduced charge-transfer resistance and enlarged light–dark photocurrent gap. together with a markedly reduced interfacial impedance, indicating accelerated charge extraction and transfer. Band-structure analysis shows a positive shift in flat-band potential and slight band-gap narrowing after Al doping, providing more favorable carrier energetics. Steady-state and time-resolved photoluminescence further demonstrate strong PL quenching and a prolonged carrier lifetime for 4% Al:STO. ECSA analysis suggests increased electrochemically accessible surface sites at the optimal doping level. Overall, moderate Al doping synergistically tunes defects, band energetics, and interfacial kinetics to improve STO photoanodes for solar water splitting. Full article

Junction spectroscopy techniques (JSTs) are powerful tools for investigating electrically active defects in semiconductors. Originally developed to study point-like defects in bulk semiconductors, JSTs have since been extended to increasingly complex systems, providing valuable insights into defect energetics and interactions. This review paper outlines the fundamental principles of JSTs and critically examines their application to emerging materials, such as perovskite solar cells and two-dimensional (2D) materials. By highlighting both the capabilities and limitations of JSTs in these non-classical systems, the review demonstrates their continued relevance and important role in advancing next-generation semiconductor materials and devices. Full article

This study presents a unified first-principles investigation of CO₂, NO₂, SO₂, and H₂O adsorption on Al₂O₃ (001), TiO₂ (001), and SiO₂ (001) surfaces, establishing the first cross-material, chemically consistent benchmark for oxide–gas interactions. Calculated adsorption energies reveal strong chemisorption of SO₂ and NO₂ on Al₂O₃ and TiO₂, moderate H₂O binding—particularly on TiO₂ where hydroxylation is favored—and generally weak CO₂ interactions across all surfaces. Bader charge analysis provides atom-resolved insight into these trends, showing substantial electron transfer and pronounced oxygen-site polarization for strongly adsorbing gases, in contrast to the minimal charge redistribution characteristic of physisorbed CO₂. These charge-transfer signatures distinguish binding mechanisms, clarify the origins of material-specific selectivity, and link adsorption to expected variations in surface conductivity and sensor response. The combined energetic and electronic analysis also reveals competitive effects between humidity and CO₂ on surface hydroxylation and local electronic structure, a phenomenon critical for realistic sensing environments but previously unaddressed. Overall, this work delivers a rigorous comparative framework for understanding gas interactions with technologically relevant oxides and provides a solid foundation for future studies involving defects, dopants, surface reconstructions, and advanced functionalization strategies for environmental monitoring and energy-conversion devices. Full article

In this study, an enzyme-free electrochemical sensor based on zinc oxide (ZnO) nanorods synthesized by the thermal decomposition of zinc acetate is presented. The suggested approach ensures simplicity, environmental friendliness, and scalability of the process without the use of an autoclave or high pressure. The morphology and structure of the samples are studied using SEM, TEM, XRD, Raman, FTIR, XPS, PL, and UV-Vis spectroscopy. It is found that heat treatment at 450 °C increases the degree of crystallinity, increases the size of crystallites, and reduces the concentration of surface defects, which leads to improved optical and electrochemical characteristics of the material. Beyond conventional sensitivity metrics, our study demonstrates that the selective detection of ascorbic acid (AA) and uric acid (UA) can be achieved by controlling the applied potential on a single ZnO electrode, an approach that leverages differences in redox energetics and surface interaction dynamics rather than complex surface functionalization. It is shown in this work that the synthesized ZnO samples subjected to heat treatment in air at 450 °C exhibit high sensitivity to ascorbic acid (9951.87 μA·mM⁻¹·cm⁻²; LoD = 1.11 μM) at a potential of 0.2 V and to uric acid (5762.48 μA·mM⁻¹·cm⁻²; LoD = 1.71 μM) in a phosphate buffer solution (pH 7) at a potential of 0.4 V with a linear range of 3 mM, offering a way to create simplified multicomponent electrochemical biosensors based on potential-controlled selectivity. Full article

The field of developing effective catalysts for heterogeneous catalysis has recently focused on controlling the structures of catalysts themselves to optimise the density and energy of crystal lattice defects. This can significantly influence catalytic activity in terms of both reaction rates and reaction mechanisms, and thus the selective production of desired substances as well. In many cases, these crystal lattice defects manifest themselves as so-called electron traps (ETs) and thus significantly influence charge transfer between the catalyst and reactants. ETs provide the missing electronic link between atomic-scale defects and macroscopic performance in heterogeneous catalysis. Therefore, the importance of ETs for catalysis is particularly evident in areas where charge transfer plays a fundamental role in the reaction mechanism, such as photocatalysis and electrocatalysis. In the field of thermally initiated reactions, the importance of ETs in heterogeneous catalysis has not yet been fully appreciated. However, several studies have already addressed the importance of ETs for this type of reaction. This review consolidates and extends the concept of ETs to purely thermal-initiated reactions, with a focus on CO₂ hydrogenation using typical transition metal catalysts. Firstly, in this review, ETs are defined as band gap states associated with internal and external defects, and their depth, density, spatial location, and dynamics are then coupled with key steps in thermocatalytic cycles, including charge storage/release, reactant activation, intermediate stabilisation, and redox turnover. Secondly, electron trap detection is reviewed based on advanced spectroscopic techniques, including reversed double-beam photoacoustic spectroscopy (RDB-PAS), thermally stimulated current (TSC), deep-level transient spectroscopy (DLTS), thermoluminescence (TL), electron paramagnetic resonance (EPR), and photoluminescence (PL), highlighting how each method describes trap energetics and populations under realistic operating conditions. Finally, case studies on the application of metal oxides and supported metals are discussed, as these are typical catalysts for the reaction mentioned above. This review highlights how oxygen vacancies (OVs), polarons, and metal–support interfacial sites act as robust electron reservoirs, lowering the barriers for CO₂ activation and hydrogenation. By reframing thermocatalysts through the lens of ET chemistry, this review identifies ETs as actionable targets for the rational design of next-generation materials for CO₂ hydrogenation and related high-temperature transformations. Full article

Nanomaterial-based hole transport layers (HTLs) play a vital role in regulating interfacial charge extraction and recombination in perovskite solar cells (PSCs). To improve PSC efficiency, hydrothermally synthesized CeO₂@MoS₂ nanocomposites (CM NCs) were incorporated as an interfacial buffer layer into a NiO_X/MeO-2PACz HTL. The introduction of CM NCs induces strong interfacial interactions, where Mo sites in MoS₂ interact with NiO_X, modulating the Ni²⁺/Ni³⁺ ratio and reducing the interfacial trap density. Moreover, CeO₂ promotes the formation of oxygen vacancies, collectively improving the conductivity and hole transport capability of the NiO_X HTL. The MoS₂-grafted CeO₂ interlayer effectively tailors the interfacial energetics and creates an effective channel for hole transfer, thereby reducing open-circuit voltage (V_OC) loss and enhancing device performance. This interface modification efficiently enhances hole extraction, and non-radiative recombination is effectively suppressed at the NiO_X/MeO-2PACz/perovskite interface. Thereby, incorporating 2 vol% CM NCs into PSCs achieved a power conversion efficiency (PCE) of 17.93%, compared to 17.50% for a 1 vol% CM NCs-based device and 17.01% for the unmodified control device. The enhanced performance at the optimized CM NCs concentration is attributed to effective defect passivation, reduced V_OC loss, and improved interfacial band alignment, which together facilitate hole extraction and suppress non-radiative recombination. However, excessive CM NCs incorporation (4 vol%) leads to increased interfacial resistance, partial hole blocking effects associated with the n-type nature of CeO₂, and aggravated recombination, resulting in degraded device performance. These results demonstrate that precise control over CM NCs interlayer thickness and concentration is critical for maximizing device performance, providing a robust strategy for designing high-efficiency and stable NiO_X-based PSCs and advancing nanocomposite-enabled interfacial engineering for photovoltaic applications. Full article

Piezochromic nanomaterials, whose optical responses can be reversibly tuned by mechanical stimuli, have recently gained prominence as versatile platforms for strain-programmable light–matter interactions. Their mechanically responsive band structures, excitonic states, and defect energetics have enabled a wide range of optoelectronic demonstrations—including pressure-tunable emitters, reconfigurable photonic structures, and adaptive modulators—which collectively highlight the unique advantages of mechanical degrees of freedom for controlling optical functionality. These advances naturally suggest new opportunities in photovoltaic technologies, where experimentally validated phase stabilization and defect reorganization under low-strain thin-film conditions could address long-standing limitations in solar absorbers and device stability. Meanwhile, stress-mediated bandgap tuning—largely inferred from high-pressure laboratory studies—presents a conceptual blueprint for future adaptive spectral response and structural self-monitoring. However, the application of these mechanisms faces a major challenge in bridging the magnitude gap between GPa-level high-pressure phenomena and the low-strain regimes of realistic operational environments. Future development requires advances in low-threshold responsive materials, innovative strain-amplifying device architectures, and the pursuit of intelligent, multi-functional system integration. Full article

The interaction between laser irradiation and energetic materials is critically influenced by microstructural void defects that determine local energy deposition and initiation sensitivity. In this work, a three-dimensional finite-difference time-domain (3D-FDTD) method was employed to investigate the modulation effects of void defects on optical field distributions and hot spot formation in RDX energetic crystals. The influences of void geometry, spatial position, and void number on the modulation of the incident laser beam were systematically analyzed. It reveals that void defects exhibit strong focusing and scattering behavior, leading to localized high-intensity regions both inside RDX bulk crystals and in void defects. For a single void defect, increasing either the width or depth can significantly enhance the peak electric field and thus the laser sensitivity of RDX crystals. When two voids are present, the number of high-intensity spots first increases and then decreases with increasing separation distance, and the strongest modulation effects are obtained at separations of 0.75λ–3λ. Furthermore, as the number of void defects increases, the modulation effect intensifies, promoting the formation of more hot spots. These findings provide quantitative insight into how void structures govern laser–matter interactions in energetic crystals, offering guidance for understanding and controlling laser initiation behavior. Full article