Concentration Of Surface Defects Research Articles

Carbon dots promoting surface defect and interphase high anion concentration for sodium-ion battery carbon anodes

The interphase chemistry of electrode/electrolyte significantly affects the electrochemical performance. This investigation explores the solid-liquid interphase alteration of an economical asphalt-derived carbon by incorporating multifunctional carbon dots, aiming to clarify the impact of interfacial properties on sodium-ion storage mechanisms. Enhanced by high density defects and carbonyl groups, the capacity, primarily within the sloping discharge, rise from 247 to 361 mA h g−1 in non-aqueous sodium ion batteries. Integrating experimental and computational methods reveals a marked improvement in PF6- anions absorption at the interface, refining the solvation structure and concentrating these anions. Consequently, a NaF/Na2CO3-dominated, inorganic-rich solid-electrolyte interphase (SEI) forms, attributed to the swift PF6- anion dissociation facilitated by the electrode's rapid electron mobility. This effect promotes sodium ion diffusion and accelerates the kinetics of sodium (de)intercalation. Beyond elucidating interfacial property contributions to the sodium storage in disordered carbon, this study highlights the genesis of irreversible capacity and draws connections between SEI's inorganic components and Coulombic efficiency. The insights offered furnish a pioneering perspective for engineering high-performance carbon anodes.

Doping with KBr to Achieve High-Performance CsPbBr3 Semitransparent Perovskite Solar Cells.

Wide-bandgap semitransparent perovskite photovoltaics are emerging as one of the ideal candidates for building-integrated photovoltaics (BIPV). However, surface defects in inorganic CsPbBr3 perovskite prepared by vapor deposition severely limit the optoelectronic performance of perovskite solar cells. To address this issue, a strategy of doping a trace amount of KBr into perovskite by vapor deposition is adopted, effectively improving the quality of the film, reducing surface defect concentration, and enhancing the transportation and extraction of charge carriers. Simultaneously, fully physical vapor deposition technology is employed to fabricate perovskite solar cells with an average visible light transmittance of 44%. These devices exhibited an ultrahigh open-circuit voltage of 1.55 V and a superior power conversion efficiency (PCE) of 7.28%, demonstrating excellent moisture and heat resistance. Moreover, the corresponding 5 cm × 5 cm modules achieve a PCE of 5.35% with great thermal insulation capability. This work provides an approach for fabricating highly efficient all-inorganic perovskite solar cells with high average visible light transmittance, demonstrating new insights into their application in building-integrated photovoltaics.

Systematic exploration of defect-rich 2D nanopetal assembled 3D ZnO nanoflowers for improved photocurrent generation and photocatalytic performance

Zinc Oxide (ZnO) stands as a highly significant metal oxide semiconductor with a large band gap of (3.2 eV), showcasing multifaceted properties. Significant findings of this study, designate the successful fabrication of 3D nanoflowers (NFs) with a specialized ZnO nanoarchitecture through a facile polyol process, considered by a notable presence of defect sites, as a photocatalyst for the deterioration of Rhodamine B (RhB). All ZnO NFs display increased absorption and a distinctive shift towards longer wavelengths, indicating a red shift phenomenon. Raman scattering, photoluminescence (PL), X-ray photoelectron spectroscopy (XPS), and electron spin resonance (EPR) unveiled that, the ZnO/24 hr, exhibited a notable abundance of defect states. The Brauner–Emmett–Teller (BET) analysis shows surface area of 55.14 m2g−1 for ZnO/24 hr resulted in a subsequent augmentation of the concentration of surface defects potentially enhancing the RhB photodegradation efficiency of 98%, surpassing the performance of other ZnO NFs samples, with a kinetic rate of 0.0638 min–1 under sunlight irradiation and better photocurrent response that improves the photogenerated separation of charge carriers. Hence, the findings from this investigation will offer novel perspectives for enhancing the photocatalytic and photoelectrochemical attributes of ZnO NFs grown over different durations.

Synergism of defect and band engineering in ultra-thin metal free organic C(CN)3 nanosheet for efficient photocatalytic CO2 reduction

Photocatalytic CO2 conversion is an effective and promising strategy for alleviating carbon emissions and energy crisis. Herein, an aqueous ultrasonic method is applied to exfoliate bulk half metallic C(CN)3 into ultra-thin atomic layered C(CN)3 nanosheets. It found that after 20 h of ultrasonic treatment, the as-obtained C(CN)3-20 presents a significantly improved photocatalytic CO2 reduction activity. The CO production rate reaches 285.3 μmol g−1 h−1, fiftyfold of the bulk C(CN)3. The significant improvement in photocatalytic performance can be attributed to the following factors: (1) exfoliation reduces the particle size and increases the specific surface areas of the material. Thus, the atomic utilization efficiency is improved; (2) the bandgap of the material is enlarged after exfoliation, while suitable bandgap further promotes photocatalytic CO2 conversion; (3) the optimized surface defect concentration enhances the separation efficiency of photogenerated electrons and holes. This study demonstrates the synergistic effect of defect regulation and band engineering on photoelectric property modulation for metal-free organic C(CN)3, enabling highly selective and efficient CO2 photoconversion.

Studies on the Cooperative Influence of Cr and Mo on the Pitting Corrosion Resistance of Super Austenitic Stainless Steels

The effects of varying Cr and Mo concentrations on the pitting corrosion resistance of super austenitic stainless steels in Cl− solutions were investigated using a combination of immersion experiments, electrochemical measurements, X-ray photoelectron spectroscopy, and first-principles computational simulations. The surface characteristics, impedance, and defect concentration of the passive film were changed, and this eventually resulted in a decrease in the number of pitting pits. Due to a decrease in active sites within the passive film, a delayed beginning of pitting, and the combined effect of MoO42− inhibitors, it was discovered that an increasing Mo concentration slows the rate of pitting extension, resulting in reduced maximum pitting area and depth. Additionally, Mo increased the adsorption energy of nearby atoms, whereas Cr raised the adsorption energy of itself. Interestingly, compared with individual doping, co-doping of Cr and Mo increased work function and adsorption energy, indicating a synergistic impact in enhancing resistance to Cl− corrosion.

Interfacial States in Au/Reduced TiO2 Plasmonic Photocatalysts Quench Hot-Carrier Photoactivity.

Understanding the interface of plasmonic nanostructures is essential for improving the performance of photocatalysts. Surface defects in semiconductors modify the dynamics of charge carriers, which are not well understood yet. Here, we take advantage of scanning photoelectrochemical microscopy (SPECM) as a fast and effective tool for detecting the impact of surface defects on the photoactivity of plasmonic hybrid nanostructures. We evidenced a significant photoactivity activation of TiO2 ultrathin films under visible light upon mild reduction treatment. Through Au nanoparticle (NP) arrays deposited on different reduced TiO2 films, the plasmonic photoactivity mapping revealed the effect of interfacial defects on hot charge carriers, which quenched the plasmonic activity by (i) increasing the recombination rate between hot charge carriers and (ii) leaking electrons (injected and generated in TiO2) into the Au NPs. Our results show that the catalyst's photoactivity depends on the concentration of surface defects and the population distribution of Au NPs. The present study unlocks the fast and simple detection of the surface engineering effect on the photocatalytic activity of plasmonic semiconductor systems.

3D snowflake graphene modified α-MnO2 Catalyst: Enhancing the Low-Temperature catalytic activity for VOCs degradation

Manganese oxide is a promising catalyst for volatile organic compounds oxidation with merits of low cost, abundant valence states, diverse crystal forms and morphology, however, its catalytic activity at low temperature (<200 °C) is limited due to the poor dispersion and inferior electron transfer. To solve these problems, a novel 3D snowflake graphene is doped into α-MnO2 to fabricate rGO@α-MnO2 catalyst to enhance the catalytic activity at low temperature. Compared with α-MnO2, the rGO@α-MnO2 catalysts present larger specific surface area and pore volume, which facilitates the adequate contact reaction between active component and VOCs. The unique graphene electronic bridge promotes the electron transfer on rGO@α-MnO2, which results in higher concentration of surface defects and more surface adsorbed oxygen to the catalyst. The performance tests show that the catalyst doped with 4% 3D snowflake graphene has the best activity, which can achieve 90% toluene conversion at 155 °C, and even 100% toluene conversion with 80% CO2 selectivity at 200 °C. In particular, 4%rGO@α-MnO2 demonstrates excellent catalytic stability and moisture resistance, presenting similar catalytic performance after 5 cycles for both the dry and high relative humidity (RH = 85%) conditions. The excellent activity of 4%rGO@α-MnO2 can be attributed to the enhancement of toluene adsorption energy after graphene doping and the defect induced by the interface effect between graphene and (211) facet. In general, 3D snowflake graphene doping provides a convenient and cost-effective method to enhance the low-temperature activity of the α-MnO2 catalyst, presenting great application potential.

Selective hydrogenation of crotonaldehyde over Ir/TiO2 catalysts: Unraveling the metal-support interface related reaction mechanism

For the supported catalysts for the selective hydrogenation of α, β - unsaturated aldehyde with H2, tailoring of metal - support interfacial effect to improve reaction performance is a significant but challenging subject. In this work, we regulated both the size regimes of the Ir deposits (single atom, nanocluster and nanoparticle) and the crystal plane of anatase TiO2 (TiO2(101), TiO2(100) and TiO2(001)) so as to alter the Ir-TiOx interfacial properties, in order to unravel reaction mechanism of selective hydrogenation of crotonaldehyde over the Ir/TiO2 catalysts. Both the activity and selectivity to crotyl alcohol increased as the Ir size grew from single atom to nanoparticle, ascribed to high Ir0 content, high concentration of surface defects and prominent H-spillover effect on the Ir nanoparticles. Moreover, the in situ Fourier transform infrared spectroscopy (FTIR) and density functional theory (DFT) calculations demonstrated that an end-on CO adsorption mode for crotonaldehyde molecule was favored at the Ir-TiOx interface particularly at high H coverage, which thus facilitated the hydrogenation of CO bond to form crotyl alcohol. Moreover, the highest reactivity of the Ir nanoparticles was evidenced by the lowest reaction barrier. These results explicitly demonstrate that larger metal nanoparticles and adsorption geometry of the reactant at the metal - support interface are vital for improved catalytic performance, which would shed light on the ingenious catalyst design.

Surface Decorations on Mixed Ionic and Electronic Conductors: Effects on Surface Potential, Defects, and the Oxygen Exchange Kinetics.

The oxygen exchange kinetics of epitaxial Pr0.1Ce0.9O2-δ electrodes was modified by decoration with submonolayer amounts of different basic (SrO, CaO) and acidic (SnO2, TiO2) binary oxides. The oxygen exchange reaction (OER) rate and the total conductivity were measured by in situ PLD impedance spectroscopy (i-PLD), which allows to directly track changes of electrochemical properties after each deposited pulse of surface decoration. The surface chemistry of the electrodes was investigated by near-ambient pressure XPS measurements (NAP-XPS) at elevated temperatures and by low-energy ion scattering (LEIS). While a significant alteration of the OER rate was observed after decoration with binary oxides, the pO2 dependence of the surface exchange resistance and its activation energy were not affected, suggesting that surface decorations do not alter the fundamental OER mechanism. Furthermore, the total conductivity of the thin films does not change upon decoration, indicating that defect concentration changes are limited to the surface layer. This is confirmed by NAP-XPS measurements which find only minor changes of the Pr-oxidation state upon decoration. NAP-XPS was further employed to investigate changes of the surface potential step on decorated surfaces. From a mechanistic point of view, our results indicate a correlation between the surface potential and the altered oxygen exchange activity. Oxidic decorations induce a surface charge which depends on their acidity (acidic oxides lead to a negative surface charge), affecting surface defect concentrations, any existing surface potential step, potentially adsorption dynamics, and consequently also the OER kinetics.

Optimisation of melt pouring temperature and low superheat casting of Al-15Mg2Si-4.5Si composite

ABSTRACT In this study, a computational fluid dynamics (CFD) model is employed to optimise the melt pouring temperature during Low superheat casting (LSC) of the Al-15 Mg2Si-4.5Si composite. The die cavity considered to perform the die filling simulations corresponds to the as-cast tensile specimens, as per ASTM B557 guidelines. The findings of the study include melt temperature distribution, solid fraction distribution during filling as well as during solidification, velocity distribution of the melt and surface defect concentration. Experimentation is performed to develop low superheat cast composite based on the numerically estimated optimum melt pouring temperature of 650°C. Mixture of irregular dendritic, polygonal and equiaxed shaped primary Mg2Si grains are observed within the cast parts, whereas primary Al grains are found to be of dendritic morphology with occasional presence of spheroids. Marked improvements in microstructure and mechanical properties have been evidenced in the LSC composite compared to its conventional cast counterpart.

Insights into the pivotal role of surface defects on anatase TiO2 nanosheets with exposed {001} facets for enhanced photocatalytic activity

The surface defects on the TiO2 nanosheets with high energy {001} facets were controlled. The surface adsorbed O increased with the increased hydrothermal temperature, while that for TiO2–400 decreased. PALS results TiO2–160 exhibits larger oxygen vacancy clusters and a low ratio of bulk defects to surface defects. The photocatalytic activity of TiO2–160 significantly enhances 26.48 times higher than P25. And TiO2–160 presents the highest photocurrent, lowest PL emission, and longest fluorescence lifetime. The pivotal role of surface defects on anatase TiO2 nanosheets with exposed high energy {001} facets has been revealed. It was the larger oxygen vacancy clusters on the {001} surface, coupled with a considerable concentration of surface defects that guaranteed the greatly promoting photocatalytic activity. Larger oxygen vacancy clusters provide pathway to facilitate the activation and transportation of active oxygen species, while a considerable surface defects can significantly decrease the recombination of photogenerated charge carriers in bulk defects.

Analysis of Experimental Results of Defect Concentraions in the Surface Layer of Acceptor Doped Ceria

Recent experimental results of the dependence on oxygen partial pressure, P(O2), of the small polarons concentration in the monomolecular surface layer of doped ceria, are interpreted theoretically. Two different, experimental conditions are examined. First, the highly reduced surface of Sm0.2Ce0.8O1.9 – δ (SDC) is treated and the [Ce3+]s--P(O2) relations are evaluated. The experimental data are explained by a metallic surface layer, approximately neutral, i.e. with negligible transfer of charge to the bulk. The surface is metallic as the outer electrons on Ce3+ ions, which are small polarons when under low concentration, lose their localization under high concentration. Second, the surface of Pr0.1Ce0.9O2 – δ (PCO) is examined. The experimental data of [Pr3+]s--P(O2) relations are explained by a semiconducting, negatively charged, monomolecular surface layer forming a double layer with a positive bulk. In both SDC and PCO the surface defect concentration dependence on P(O2) is different from that of the bulk.

Probing size-dependent defects in zinc oxide using synchrotron techniques: impact on photocatalytic efficiency.

In the present study, synchrotron-based X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS) and X-ray excited optical luminescence (XEOL) have been used to investigate the induced defect states in metal oxide nanomaterials. Specifically, two synthesis approaches have been followed to develop unique nano-sized peanut-shaped (N-ZnO) nanostructures and micron-sized hexagonal rods (M-ZnO). XANES analysis at the Zn K-edge revealed the presence of defect states with a divalent oxidation state of zinc (Zn2+) in a tetrahedral structure. Furthermore, XAS measurements performed at the Zn L3,2-edge and O K-edge confirm higher oxygen-related defects in M-ZnO, while N-ZnO appeared to have a higher concentration of surface defects due to size confinement. Moreover, the in-line XEOL and time dependent-XEOL measurements exposed the radiative excitonic recombination phenomena occurring in the band-tailing region as a function of absorption length, X-ray energy excitation, and time. Based on the chronology developed in the defect state improvement, a possible energy band diagram is proposed to accurately locate the defect states in the two systems. Furthermore, the increased absorption intensity at the Zn L3,2-edge and the O K-edge under the UV lamp suggests delayed recombination of electrons and holes, highlighting their potential use as photo catalysts. The photocatalytic activity degrading the rhodamine B dye established M-ZnO as a superior catalyst with a rapid degradation rate and significant mineralization. Overall, this work provides valuable insights into ZnO defect states and provides a foundation for efficient advanced materials for environmental or other optoelectronic applications.

Role of Alkylamines in Tuning the Morphology and Optical Properties of SnS2 Nanoparticles Synthesized by via Facile Thermal Decomposition Approach.

The present study reported the synthesis of SnS2 nanoparticles by using a thermal decomposition approach using tin chloride and thioacetamide in diphenyl ether at 200 °C over 60 min. SnS2 nanoparticles with novel morphologies were prepared by the use of different alkylamines (namely, octylamine (OCA), dodecylamine (DDA), and oleylamine (OLA)), and their role during the synthesis was explored in detail. The synthesized SnS2 nanostructures were characterized using an array of analytical techniques. The XRD results confirmed the formation of hexagonal SnS2, and the crystallite size varied from 6.1 nm to 19.0 nm and from 2.5 to 8.8 nm for (100) and (011) reflections, respectively. The functional group and thermal analysis confirmed the presence of organics on the surface of nanoparticles. The FE-SEM results revealed nanoparticles, nanoplates, and flakes assembled into flower-like morphologies when dodecylamine, octylamine, and oleylamine were used as capping agents, respectively. The analysis of optical properties showed the variation in the bandgap and the concentration of surface defects on the SnS2 nanoparticles. The role of alkylamine as a capping agent was explored and discussed in detail in this paper and the mechanism for the evolution of different morphologies of SnS2 nanoparticles was also proposed.

Influence of oxygen vacancies of CeO2 on reverse water gas shift reaction

Catalytic CO2 hydrogenation on metal oxides is attractive to realize carbon neutrality initiatives. Understanding roles of oxygen vacancies of oxide-based catalysts is critical for the catalytic mechanism of CO2 hydrogenation. Herein, we used CO2 hydrogenation as model reaction on CeO2 to investigate the effects of oxygen vacancies and provided direct spectroscopic evidence for redox mechanism via in-situ DRIFTS and isotope switch experiments. A volcano-type activity curve was found for CO2 hydrogenation to CO on CeO2 upon the continuous variation of the surface defect concentration of oxygen vacancy. Kinetic analysis and ex-situ techniques indicate that surface oxygen contributes to H2 activation and oxygen vacancy accelerates the dissociation of CO2, emphasizing the unique roles of surface oxygen and oxygen vacancies, respectively. These results enrich the understanding of surface defect chemistry of CeO2 and lay an important theory foundation for design of oxide-based catalysts for hydrogenation.

Effect of inert ambient annealing on structural and defect characteristics of coaxial N-CNTs@ZnO nanotubes coated by atomic layer deposition

The structure and intrinsic defects of ZnO determine the photogeneration of electron-hole pairs. The control of these characteristics allows for improving the activity of photocatalytic nanostructures. The intrinsic defects of ZnO atomic layer deposited around carbon nanotubes, coaxial N-CNT@ZnO, and its evolution after annealing in a nitrogen atmosphere are studied. TEM showed that the coaxial N-CNT@ZnO structure is preserved up to 500 °C; some damage is seen at 600 and 700 °C. Raman and XPS reveal a low surface defect concentration for as-grown ZnO, increasing to a maximum for the 600 °C annealed sample. Cathodoluminescence shows a broad low-intensity green emission associated with oxygen vacancies of ZnO. The surface defects improved the photocatalytic degradation of amaranth dye, however, damage to the coaxial structure lowers the catalytic activity.

Surface defects engineered Bi4Ti3O12 nanosheets for photocatalytic degradation of antibiotic levofloxacin

Surface defects have a significant effect on the photocatalytic reaction of Bi4Ti3O12, but the mechanism is unclear. In addition, when surface defects and highly exposed facets exist at the same time, which factor plays the main role in photocatalytic activity is also controversial. Herein, it is found that Bi4Ti3O12 with adjustable concentrations of surface defects and percentage of exposed {001} facets can be prepared by using titania of different crystal types and sizes as raw materials, which is extremely beneficial for exploring the above problems. The photocatalytic activity of Bi4Ti3O12 nanosheets with surface defects and exposed {001} facets was the same as that of Bi4Ti3O12 nanosheets with surface defects alone (about 72.5% of photodegradation levofloxacin under 10 min of simulated sunlight irradiation). Based on the experimental results and density functional theory calculations, the influence mechanism of surface defects was deeply studied. The surface defects resulting from partial exfoliation of the external (Bi2O2)2+ layers changed band structure of Bi4Ti3O12. More importantly, surface defects with high concentration became hole trapping sites, which was conducive to the faster participation of holes in the photocatalytic oxidation process.

Constructing single-atomic nickel sites in carbon nanotubes for efficient CO2 electroreduction

Electrochemical CO2 reduction (ECR) has been considered as the most promising route to convert CO2 into fuels, but suffers inferior conversion efficiency and product selectivity due to the lack of effective electrocatalysts. Herein, the N-coordinated single-atomic Ni active sites embedded in porous carbon nanotubes (Ni/N-CNTs) are constructed through one-pot pyrolysis strategy as an efficient ECR electrocatalyst. The Zn source in pyrolysis plays a key role in the formation of bamboo-like CNTs, and increased concentrations of surface defects and single-atomic Ni sites of the electrocatalyst. All these benefits endow the electrocatalyst with excellent ECR performance, achieving a large CO Faradaic efficiency (FECO) up to 98% and turnover frequency up to 304.5 h−1 at a relatively low potential of −0.65 V vs. RHE. Furthermore, over 80% FECO can be maintained in a wide potential range from −0.57 to −0.81 V. In addition, the electrocatalyst also shows high operation stability for 20 h without obvious FECO and jCO decay. We believe this study will shed a new light on the design of highly efficient M/N–C catalyst for ECR systems.

Shed light on defect induced enhanced visible-light photocatalysis activity of rutile TiO2 nanoparticles: effects of annealing on blue-gray to light–gray transition

Preparation of the defective TiO2 nanoparticles (NPs) have been recently in particular interest for its outstanding applications in visible-light active photocatalysis. In order to make TiO2 visible-light absorber, optical band gap should be modified especially via introducing structural defects like oxygen vacancies as an effective pathway. In this research, we prepared defective rutile TiO2 NPs with highly efficient photocatalytic activity under visible light. The NPs were synthesized by electric arc discharge in water as a cost-effective and environmentally friendly method with capability of defect formation which followed by heat treatment. The photocatalytic activity improvement mechanisms based on oxygen vacancies were supported by TEM, XPS, XRD, PL and optical spectroscopy characterizations. Spherical TiO2 NPs with average size of 23, 28, 38, and 50 nm were obtained for pristine, and annealed samples at 300, 500 and 700 °C respectively. The optical band gaps of NPs decreased from 2.9 to 2.0 eV with annealing temperature, and a concurrent color change from blue-gray to light-gray. The XPS results confirm the presence of vacant oxygen and surface OH defects in all TiO2 samples. The results reveal that concentration of surface defects and mostly the oxygen vacancies play a crucial role in visible light photoactivity of gray TiO2 nanostructures. In the synthesized TiO2 NPs, the sample with the lowest concentration of non-lattice oxygen exhibit better degradation efficiency than other samples. The results provide a flexible method for synthesis of defective rutile TiO2 as a highly efficient visible active photocatalyst nanomaterial.

Enhanced defect emission of TiO2-doped transparent glass-ceramics embedding ZnO quantum dots with optimized heat-treatment schedule

This work mainly concentrated on the structural and optical properties of TiO 2 -doped transparent glass-ceramics embedding ZnO quantum dots (QDs). The results show that the concentration of non-bridging oxygen and related defects in the glasses increases and thermal parameters decreases by the introduction of TiO 2 . The surface defect concentration of ZnO QDs is greatly improved and the size of ZnO QDs is reduced by heat treatment below the T g and the introduction of TiO 2 . The green emission of glasses is mainly derived from oxygen vacancy defects and the yellow emission of glass-ceramics primarily originated from oxygen interstitial defects which show a tendency of enhancing first and then reducing with the increase of TiO 2 content. Among them, the optimal content for the strongest emission intensity of TiO 2 -doped glasses and glass-ceramics was determined to be 1.0 mol%, and the relative exceeds 10 times and 5.4 times that of TiO 2 -free glasses and glass-ceramics, respectively. The average size of ZnO QDs (∼2.1 nm) remarkably close to its exciton Bohr radius is successfully prepared by the optimal heat treatment condition (630 °C/8 h, below the T g ). The results show that these glass-ceramics embedding ZnO QDs are good yellow emission materials and have application prospects in WLEDs.