Fast Oxygen Diffusion Research Articles

Layered Monoclinic Perrierite Oxo-Silicate La4Mn5Si4O22+Δ: A New Interstitial Oxide Ion Conductor for Low Temperature Applications

Oxide-ion conductors are important for various energy applications such as solid oxide fuel cells, solid oxide electrolyser cells, oxygen separation membranes, oxygen sensors, etc. State-of-the-art stable oxygen active materials often have adequate oxygen ion diffusion and chemical surface exchange only at high temperatures (> 700 oC). A promising strategy to improve the oxygen ion transport is to use the interstitial oxygen ion conductors as the interstitial diffusion barriers are often lower than vacancy-mediated diffusion barrier, potentially enabling reduced operation temperatures. However, due to the large size of the oxide ion, the formation of an adequate concentration of interstitials is difficult and hence the number of interstitial oxygen conductors is currently limited to just a handful of compounds, e.g., Ruddlesden-Popper, apatite, melilite, scheelite, fluorite and disordered hexagonal perovskites.We screened a large number of oxide materials using high-throughput ab initio methods (Please see separate poster from Jun Meng on this screening) and predicted stable formation and fast diffusion of interstitial oxygen in a new class of material La4Mn5Si4O22+δ (LMS), motivating us to synthesize this material and experimentally study its oxide ion transport properties. The room temperature X-ray diffraction study followed by Rietveld refinement confirmed its layered monoclinic perrierite structure. Electron probe micro-analysis (EPMA) and iodometric titration revealed the presence of the hyper stoichiometric oxygen anion (δ ~ + 0.5) confirming the interstitial oxygen ions within LMS lattice. Thermogravimetric analysis showed a small mass increment in LMS when heated at high temperatures suggesting the high temperature stability of interstitial oxygen ions. The measured ionic conductivity of LMS is higher than the yttria stabilized ZrO2, perovskite oxide La1-xSrxCo1-yFeyO3 and Ruddlesden-Popper oxide materials. Electrical conductivity relaxation studies demonstrated that self-diffusion and surface exchange coefficients of oxygen ion are comparable to or higher than many state-of-the-art oxide ion conductors. Finally, the high temperature stability of the synthesised material was confirmed using X-ray diffraction after each measurement.Overall, this experimental study confirms computational predictions that layered perrierite LMS is a new class of interstitial oxide ion conductors and suggests our overall approach may help the rational design of interstitial mediated oxide ion conductors-based devices suitable for efficient and stable applications at low temperature.

Using an ionomer as a size regulator in γ-radiation induced synthesis of Ag nanocatalysts for oxygen reduction reaction in alkaline solution

Ag nanoparticles (Ag NPs) are among the most promising candidates to replace Pt as the catalyst for the oxygen reduction reaction (ORR) in anion exchange membrane fuel cells (AEMFCs). However, synthesizing size-controlled Ag NPs with efficient catalytic performance is still challenging. Herein, uniform Ag NPs are produced through a γ-radiation induced synthesis route in aqueous solutions, using the ionomer PTPipQ100 as both an efficient size regulator in the synthesis and a conductor of hydroxide ions during the ORR process. The origin of the size control is mainly attributed to the affinity of the ionomer to metallic silver. The resulting Ag NPs covered with ionomer layers can be applied as model catalysts for ORR. The nanoparticles that were prepared using 320 ppm ionomer in the reaction solution turned out to be coated with a ∼ 1 nm thick ionomer layer and exhibited superior ORR activity as compared to other Ag NPs of similar size studied here. The improved electrocatalytic performance can be attributed to the optimal ionomer coverage that enables fast oxygen diffusion, as well as interactions at the Ag-ionomer interface which promote the desorption of OH intermediates from the Ag surface. This work demonstrates the advantage of using an ionomer as the capping agent to produce efficient ORR catalysts.

Nonstoichiometry, Defect Chemistry and Oxygen Transport in Fe-Doped Layered Double Perovskite Cobaltite PrBaCo2-xFexO6-δ (x = 0-0.6) Membrane Materials.

Mixed conducting cobaltites PrBaCo2-xFexO6-δ (x = 0-0.6) with a double perovskite structure are promising materials for ceramic semi-permeable membranes for oxygen separation and purification due to their fast oxygen exchange and diffusion capability. Here, we report the results of the detailed study of an interplay between the defect chemistry, oxygen nonstoichiometry and oxygen transport in these materials as a function of iron doping. We show that doping leads to a systematic variation of both the thermodynamics of defect formation reactions and oxygen transport properties. Thus, iron doping can be used to optimize the performance of mixed conducting oxygen-permeable double perovskite membrane materials.

Calcium doping in double perovskite SmBa1−xCaxCo2O5+δ to enhance the electrochemical activity of solid oxide cell reversible oxygen electrode

Despite the remarkable reduction of carbon emissions due to COVID-19 pandemic during 2020, a reckless energy demand has compromised the 2050 agenda. In this scenario, reversible Solid Oxide Cells (rSOCs) could play a key-role due to their high fuel flexibility and versatility but there is still room for electrode stability and performance improvement. Lately, double perovskite materials have been widely studied due to their extraordinary fast oxygen diffusion rates and high conductivity mainly related to their layered ordering structure. In this work, the authors present the synthesis route and the electrochemical characterization of the A-site layered double perovskite structure SmBa1−xCaxCo2O5+δ in which calcium co-doping demonstrates a remarkable effect in the oxygen electrode activity. The best calcium doping corresponding to SmBa0.8Ca0.2Co2O5+δ displays a Rp reduction from 0.082 for the undoped material to 0.019 Ω·cm2 at 700 °C. Moreover, under anodic and cathodic operating conditions the electrocatalytic activity was further increased to 0.007 and 0.006 Ω·cm2 at η = ± 0.3 V, respectively. This behaviour demonstrates the suitability of the material to work as reversible oxygen electrode. Finally, the electrode material was subjected to a switching current aging test for over 100 h to prove the electrode stability under operating conditions.

Ca-Mg Multiple Deoxidation of Ti-50Al-2Cr-2Nb Intermetallic Compound Powder for Additive Manufacturing

In this study, we investigated Ca-Mg multiple deoxidation of Ti-50Al-2Cr-2Nb intermetallic compound powder for additive manufacturing. The crystal structure, surface morphology, and oxygen reduction rate of Ti-50Al-2Cr-2Nb powder before and after deoxidation according to particle size were observed through XRD, SEM, BET and O/N analyses. In addition, the oxide layer of the surface before and after deoxidation was observed through TEM analysis. In our previous study, Ti-48Al-2Cr-2Nb powder deoxidized by only calcium at 1,100 °C for 2 h showed the oxygen concentration of 320 ppm. Compared to the previous result, it was found that a low oxygen Ti-50Al-2Cr-2Nb intermetallic compound powder less than 155 ppm was obtained by Ca-Mg multiple deoxidation at 900 °C for 2 h. It is considered that the decrease in the deoxidation temperature from 1,100 °C to 900 °C for Ti-50Al-2Cr-2Nb powder was due to only existing γ-TiAl phase with a fast oxygen diffusion coefficient without α 2-Ti3Al phase at 900 °C. As a result, it was established that the oxygen reduction rate of the Ti-50Al-2Cr-2Nb powder depended on the specific surface area because the Ti-50Al-2Cr-2Nb powder without β-Ti phase was mainly deoxidized by oxygen reduction on the surface oxide layer more than interstitial oxygen.

Superconducting joining of YBCO coated conductors without a large critical current loss

Achieving superconducting joinings with large current capacities is a challenge for magnetic resonance imaging applications of YBa2Cu3O7-δ (YBCO) coated conductors (CCs). Here we report a novel method to fabricate a superconducting joining between two YBCO CCs using a joining strap consisting of YBCO, Ag, a buffer, and a substrate. The YBCO layer exfoliated from the buffer stack of a YBCO CC can retain more than 90% of its original critical current (Ic). This is particularly due to the Ag layer serving as a fast oxygen diffusion path to promote the recovery of superconductivity of the YBCO layer during oxygenation annealing. The atomic arrangement at the joined YBCO interface is well aligned along the (001) plane, enabling superior superconducting performance. The method reported here provides a practicable solution to achieve persistent current mode operation in second-generation high-temperature superconducting magnet applications.

Photothermal‐Assisted Triphase Photocatalysis Over a Multifunctional Bilayer Paper

AbstractPhotocatalysis as one of the future environment technologies has been investigated for decades. Despite great efforts in catalyst engineering, the widely used powder dispersion and photoelectrode systems are still restricted by sluggish interfacial mass transfer and chemical processes. Here we develop a scalable bilayer paper from commercialized TiO2 and carbon nanomaterials, self‐supported at gas‐liquid‐solid interfaces for photothermal‐assisted triphase photocatalysis. The photogeneration of reactive oxygen species can be facilitated through fast oxygen diffusion over triphase interfaces, while the interfacial photothermal effect promotes the following free radical reaction for advanced oxidation of phenol. Under full spectrum irradiation, the triphase system shows 13 times higher reaction rate than diphase controlled system, achieving 88.4 % mineralization of high concentration phenol within 90 min full spectrum irradiation. The bilayer paper also exhibits high stability over 40 times cycling experiments and sunlight driven feasibility, showing potentials for large scale photocatalytic applications by being further integrated into a triphase flow reactor.

Photothermal-Assisted Triphase Photocatalysis Over a Multifunctional Bilayer Paper.

Photocatalysis as one of the future environment technologies has been investigated for decades. Despite great efforts in catalyst engineering, the widely used powder dispersion and photoelectrode systems are still restricted by sluggish interfacial mass transfer and chemical processes. Here we develop a scalable bilayer paper from commercialized TiO2 and carbon nanomaterials, self-supported at gas-liquid-solid interfaces for photothermal-assisted triphase photocatalysis. The photogeneration of reactive oxygen species can be facilitated through fast oxygen diffusion over triphase interfaces, while the interfacial photothermal effect promotes the following free radical reaction for advanced oxidation of phenol. Under full spectrum irradiation, the triphase system shows 13 times higher reaction rate than diphase controlled system, achieving 88.4 % mineralization of high concentration phenol within 90 min full spectrum irradiation. The bilayer paper also exhibits high stability over 40 times cycling experiments and sunlight driven feasibility, showing potentials for large scale photocatalytic applications by being further integrated into a triphase flow reactor.

A dual-biomimetic photocatalytic fuel cell for efficient electricity generation from degradation of refractory organic pollutants

Energy recovery from wastewater treatment is attracting tremendous research interests since the environmental and energy issues can be simultaneously addressed. Photocatalytic fuel cell (PFC) provides a sustainable way for water purification and electricity generation, but its performance has been restricted by the poor mass and charge transfer. Herein, we demonstrated an integrated PFC platform by mimicking the metabolic processes in human body. Inspired by the purification of metabolites in the microstructure of liver lobules, flow-through TiO2 photoanode with numerous microchannels was developed. Compared to traditional PFC with planar photoanode, the biomimetic microflow PFC exhibited 3 to 5-fold enhancements in the removal efficiencies of various organic pollutants, including perfluorooctanoic acid, 4-chlorophenol, bisphenol A, methylene blue, and amoxicillin. To mimic the breathing process in alveoli, an ultrathin air cathode was fabricated by sputtering Pt (loading as small as 0.01 mg cm−2) on nanoporous polyethylene film, contributing to fast oxygen diffusion and abundant gas-liquid-solid three-phase reactive sites. The construction of this dual-biomimetic PFC system resulted in an open circuit voltage of 0.92 V and a record-high power output of 500 μW cm−2 under simulated solar light. The series connection of modularized reactors allowed for the successive purification of wastewater by self-generated electricity. Thus, this work opens up new opportunities of biomimetic photocatalytic system for addressing the water-energy nexus.

A high-entropy manganite in an ordered nanocomposite for long-term application in solid oxide cells

The implementation of nano-engineered composite oxides opens up the way towards the development of a novel class of functional materials with enhanced electrochemical properties. Here we report on the realization of vertically aligned nanocomposites of lanthanum strontium manganite and doped ceria with straight applicability as functional layers in high-temperature energy conversion devices. By a detailed analysis using complementary state-of-the-art techniques, which include atom-probe tomography combined with oxygen isotopic exchange, we assess the local structural and electrochemical functionalities and we allow direct observation of local fast oxygen diffusion pathways. The resulting ordered mesostructure, which is characterized by a coherent, dense array of vertical interfaces, shows high electrochemically activity and suppressed dopant segregation. The latter is ascribed to spontaneous cationic intermixing enabling lattice stabilization, according to density functional theory calculations. This work highlights the relevance of local disorder and long-range arrangements for functional oxides nano-engineering and introduces an advanced method for the local analysis of mass transport phenomena.

Room temperature oxygen exchange and diffusion in nanometer-thick ZrO2 and MoO3 films

The diffusion of oxygen in thin films of ZrO2 and MoO3 was investigated with atomic 18O as a tracer using low energy ion scattering sputter depth profiling. 3 nm amorphous and 20 nm polycrystalline films were prepared by reactive magnetron sputtering and exposed to atomic oxygen species at room temperature. Exposure results in a fast diffusion of oxygen to a limited depth of ~1 nm and ~2.5 nm for ZrO2 and MoO3, respectively, and surface exchange limited to a maximum of 65% to 75%. The influence of the crystalline structure of the films on exchange and diffusion was negligible. We propose that the transport of oxygen in oxides at room temperature is dominated by a field-induced drift, generated by the chemisorption of reactive oxygen species. The maximum penetration of oxygen is limited by the oxide space charge region, determined by the oxide electrical properties. We applied a drift–diffusion model to extract values of surface potential and kinetic parameters of oxygen exchange and diffusion. The developed experimental analysis and modelling suggest that the electric field and consequent distribution of charged species are the main factors governing exchange rates and species diffusion in an oxide thin film at room temperature.

Achievement of Low-Resistivity Diffusion Joint of REBCO Coated Conductors by Improving the Interface Connection of Ag Stabilizer

The achievement of low-resistance connection in REB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-z</sub> (REBCO, RE = Y, Gd) coated conductors (CCs) has become one of the strategic factors for magnet applications. In this letter, we fabricated low-resistivity (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sj</sub> = 4.9 nΩ·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) Ag-diffusion joints of REBCO CC by improving the interface connection of the Ag stabilizer. The effective contact area at the interface between two Ag stabilizers can be increased by polishing the surface of the Ag stabilizers, which can reduce joint resistance (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">j</sub> ). Compared with a traditional diffusion temperature (400 °C), diffusion bonding of the Ag stabilizers at higher temperatures (800 or 850 °C, typical connection temperatures for superconducting joint) can promote interface connection between two Ag stabilizers. The oxygen content in REBCO will be reduced due to diffusion bonding at higher temperatures. Therefore, we etched some microchannels that serve as the fast oxygen diffusion paths on the surface of the Ag stabilizers to help restore the oxygen content, thereby recovering critical current (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) and reducing R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">j</sub> . The connection mechanism of the interface between two Ag stabilizers was investigated through the cross-sectional analysis and delamination of the joint part. In addition, the REBCO layer can be completely peeled off and almost retain the original I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> by diffusion bonding of the Ag stabilizers at higher temperatures. This fabrication technique is a unique practicable solution to reduce the R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">j</sub> for the CC with thin Ag stabilizers and improve the peeling quality of the REBCO layer for efficiently fabricating the superconducting joint.

Zr0.92Y0.08O1.92‐La0.6Sr0.4Co0.2Fe0.8O3–δ Asymmetric Dual‐phase Oxygen Transport Membrane for Simultaneously Methane Partial Oxidation and Water Splitting▴

AbstractOxygen transport membrane (OTM) allows O2− to transport from oxygen donation side to partial oxidation side without the contact of oxidant and fuel, providing an efficient pathway for the fuel conversion. OTM with high oxygen permeability are crucial for OTM‐involved processes, and the asymmetric dual‐phase OTM is one of the promising materials with desirable oxygen permeability and stability. Herein, we fabricated a Zr0.92Y0.08O1.92‐La0.6Sr0.4Co0.2Fe0.8O3−δ (YSZ‐LSCF) asymmetric dual‐phase OTM for the methane partial oxidation and water splitting. It exhibits highest oxygen permeation flux of 0.151 mL cm−2 min−1 at 900 °C among all membranes due to the fast oxygen diffusion kinetic. In water splitting experiments driven by different reducing atmospheres (CO and CH4), all the membranes are reactive. The YSZ‐LSCF asymmetric dual‐phase membrane reveals a favorable performance for the partial oxidation of methane to syngas with a H2/CO molar ratio close to 2 and simultaneously water splitting to produce hydrogen. The membrane maintains high stability during the experiments, and the clear dual phases, grain boundaries and porous structure are visible. Owing to its desired oxygen permeability and stability, YSZ‐LSCF asymmetric dual‐phase membrane developed in the present study provides an efficient process for the methane partial oxidation and water splitting.

Shallow Iodine Defects Accelerate the Degradation of α-Phase Formamidinium Perovskite

Summary Shallow defects are mostly benign in covalent semiconductors, such as silicon, given that they do not constitute non-radiative recombination sites. In contrast, the existence of shallow defects in ionic perovskite crystals might have significant repercussions on the long-term stability of perovskite solar cells (PSCs) because of the metastability of the ubiquitous formamidinium lead triiodide (FAPbI3) perovskite and the migration of charged point defects. Here, we show that shallow iodine interstitial defects ( I i ) can be generated unintentionally during commonly used post-fabrication treatments, which can lower the cubic-to-hexagonal transformation barrier of FAPbI3-based perovskites to accelerate its phase degradation. We demonstrate that concurrently avoiding the generation of I i and the more effective passivation of iodine vacancies ( V I ) can improve the thermodynamic stability of the films and operational stability of the PSCs. Our most stable PSC retained 92.1 % of its initial performance after nearly 1,000 h of continuous illumination operational stability testing.

New insight into the formation and oxygen barrier mechanism of carbonaceous oxide interlayer in a multicomponent carbide

ABSTRACTEarly transition metal carbides are considered to be superior candidate materials for oxidizing environments at temperatures exceeding 2000°C. Generally, the remarkable oxidation resistance is largely attributed to a carbonaceous oxide interlayer (eg, Hf–O–C, Zr–O–C, and Ta–O–C), located at the interface between the external oxide layer and internal carbide (eg, HfC, ZrC, and TaC), acting as the primary oxygen barrier. However, the oxygen barrier mechanism of the carbonaceous oxide interlayer remains unclear. Herein, through studying the oxidation behavior of a novel multicomponent carbide Hf0.5Zr0.3Ti0.2C in oxidizing environments up to 2500°C, the oxygen barrier mechanism of the carbonaceous oxide was recently revealed. We found that the oxygen barrier resulted from the slow oxygen diffusion through the inner grains of Hf‐Zr–Ti–O due to the presence of carbon formed at the grain boundaries because of the existence of compact external oxide layer, beneath which the Hf–Zr–Ti–O–C interlayer possesses much lower oxygen activity and temperature that allow carbon to exist stably. This as‐formed carbon strongly retarded the fast diffusion of oxygen along the grain boundaries of oxides. Additionally, desirable synergisms of the designed multicomponent system, particularly, the outward short‐circuit diffusion of Ti, lead to the self‐healing of the external oxide layer, evidently enhancing integral protection performance against oxidizing environments.

2D diffusion of oxygen in Ln10Mo2O21 (Ln = Nd, Ho) oxides

Ln molybdates are promising materials for hydrogen/oxygen separation membranes. This work aims at elucidating features of oxygen transport in Ln10Mo2O21 (Ln = Nd, Ho) oxides using novel 2D diffusion models. Nd10Mo2O21 and Ho10Mo2O21 were synthesized by the mechanical activation followed by sintering in the 1600–1650 °C temperature range and characterized by XRD as a complex rhombohedral phase and fluorite one, respectively. Oxygen transport features were studied by the oxygen isotope heteroexchange with C18O2 in a flow reactor using temperature-programmed and isothermal modes.According to numerical analysis, isotope exchange in Ln10Mo2O21 cannot be described by a single diffusion coefficient, which is explained by nonuniformity of the oxygen diffusion pathways. The mathematical model including equations for a faster diffusion along grain boundaries and a slower diffusion within grain bulk (2D diffusion model) gives the best fit. The same accuracy was achieved using the model including 2D diffusion and exchange between grain bulk oxygen forms with different M-O bonds strength. The values of oxygen tracer diffusion coefficient are ~10−7–10−6 cm2/s and ~10−11–10−8 cm2/s at 700 °C along grain boundaries and within grain bulk, respectively. Hence, new 2D models were developed to describe oxygen diffusion in polycrystalline oxides. A fast oxygen diffusion demonstrated for Ln10Mo2O21 oxides makes them promising for design of hydrogen/oxygen separation membranes.

Corrosion mechanism investigation of TiN/Ti coating and TC4 alloy for aircraft compressor application

It is imperative to develop multifunctional erosion and corrosion resistant coatings for compressor blades of aircraft engines in harsh environment. PVD (Physical Vapor Deposition) technology has the advances in processing erosion-resistant coatings; however, the performance of PVD coatings to combat corrosion depends on various coating defects. Determining and comparing the corrosion performances of PVD TiN/Ti coating and uncoated TC4 alloy was the main objective of present work. The 960 h salt spray corrosion and 116 h hot corrosion tests were conducted to simulate the grounding and working environments of the aircraft compressors. The corrosion mechanisms due to the coating defects such as pinhole, columnar boundary and large grain were analyzed based on the OM, Confocal microscope, electrochemical measurements, SEM, XRD and EDS results. Owing to the disordered state associated with the columnar boundary and the coating defect, nitrogen could be easily replaced by oxygen in the hot corrosion process, these structures were channels for fast diffusion of oxygen. Moreover, the Gibbs energy changes of Ti oxidation and TiN oxidation were thermodynamically calculated according to the working condition of aircraft compressors, and considerable research effort was focused on mapping out the phase diagram of Ti, TiN and high pressure gases. The findings of this research can provide insights into developing multifunctional coatings for future aircraft engines.

Study of Superconductivity in YBa2Cu3O7-x/SrTiO3 Composites

Superconducting properties of YBa2Cu3O7-x (YBCO)/SrTiO3 (STO) polycrystalline composites were investigated. The composites were obtained by rapid thermal processing of the 20% YBCO–80% STO mixtures in the air in the temperature range 700–1000 °C for 2 min. Magnetization measurements showed that the superconducting critical temperature (Tc) is practically not changed if optimally doped YBCO is used in YBCO/STO composites. In contrast, a strong increase of Tc from 65 to 90 K was found in the case of underdoped YBCO. This increase of Tc can be explained by unusually fast diffusion of oxygen from STO to YBCO grains in sintered composites. Obtained results show that the YBCO oxidation process can be significantly accelerated in underdoped YBCO/STO composites during rapid high-temperature processing.

High yield of H2O2 and efficient S recovery from toxic H2S splitting through a self-driven photoelectrocatalytic system with a microporous GDE cathode

In this paper, the toxic H2S was transformed efficiently into valuable S and H2O2 and its chemical reaction energy was converted into electric energy through a self-driven photoelectrocatalytic(PEC) system, which consisted of a microporous gas diffusion electrode(GDE) and a self-bias photoanode. In the cathode region, high yield of H2O2 up to 0.8 mmol/L/h, was achieved because of the fast gas diffusion and direct two-electron reduction of molecular oxygen on the microporous GDE cathode. In the anodic region, H2S was completely converted into S without persulfide based on a I−/I3− redox system and the production rate of S recovery was about 0.60 mmol/h, 42 times higher than before. The remarkable catalytic efficiency also benefited from the self-bias design of photoanode, which included a front photoanode of WO3 and a rear Si photovoltaic cell (Si PVC). The constituted self-driven PEC system could accelerate the charges separation and increase the electron transfer rate of PEC cell. In addition, electricity was generated simultaneously, with a maximum power density of 0.19 mW/cm2. The proposed self-driven PEC cell system offers an efficient, complete and sustainable way for H2S resourcization.

First-principles prediction of oxygen diffusivity near the [formula omitted] twin boundary in titanium

We study the diffusivity of oxygen interstitials around a (101¯2) twin boundary in Titanium. First, we identify all possible stable interstitial sites around the twin boundary and compute the corresponding site energies and transition energy barriers for jumps between these sites, using density functional theory. We show that the site energies and the barriers are consistently lower than in bulk, suggesting the higher tendency of oxygen to segregate to the twin boundary region. Using the site and transition energies and an exact solution to the master equation, we then compute the diffusivity of oxygen in the presence of the twin boundary and find enhanced diffusivity around the boundary in all directions. Enhanced diffusivity towards the boundary determines the feasibility of oxygen segregation to favorable sites at the boundary, while increased diffusivity in the boundary plane provides a path for fast diffusion of oxygen. This result reveals the underlying mechanism governing the slow growth of (101¯2) twin by pinning at the segregated oxygen interstitials.