出版者・発行元：Materials Science and Engineering A  

Understanding and predicting mechanical properties such as proof stress (yield strength), ultimate tensile strength, elongation to failure, and reduction in area are essential for screening the application of austenitic stainless steels in adverse chemomechanical environments. However, experimental determination of these properties is time-consuming, labor-intensive, and costly—especially under extreme conditions, which requires advanced experimental capabilities. In this study, we leverage a large-scale, curated dataset comprising 2180 experimental entries of austenitic alloys to develop machine learning (ML) models capable of predicting these key mechanical properties as functions of composition, solution treatment condition, and testing temperature. We systematically evaluate a range of ML algorithms, namely linear regression, kernel ridge regression, extreme gradient boosting, and artificial neural network. Among these, the extreme gradient boosting achieves the highest predictive accuracy, with R² scores of 0.946 and 0.985 for proof stress and ultimate tensile strength, respectively. To further enhance model performance, we explore ensemble learning and transfer learning strategies. The transfer learning approach that leverages interdependencies between mechanical properties reduces the mean percentage error by 21.0% and increases R² score by 3.1% in predicting reduction in area, compared to the original artificial neural network model. Our results show that ML models trained on well-structured experimental data can serve as an efficient and reliable tool for exploring the effect of composition on screening metrics. This work highlights the potential of data-driven approaches to accelerate the design and optimization of high-performance austenitic alloys. Furthermore, obtaining feature importance and insights from extreme gradient boosting using Shapley Additive Explanation tool provides valuable understanding of how features contribute to the prediction of mechanical properties.

DOI： 10.1016/j.msea.2025.149714

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記述言語：英語   出版者・発行元：Beilstein Journal of Nanotechnology  

In this study, we employ the non-equilibrium Green’s function (NEGF) method combined with density functional theory (DFT) to compare electron transport through several layers of nanoscale graphene and hexagonal boron nitride (h-BN). Calculations were performed for one to six layers, corresponding to thicknesses of 0.5–3.0 nm, respectively. Electron transport was computed perpendicular to the layers in the stacking direction. We compared the decay of the current with the number of layers and evaluated the ability of h-BN to filter currents as a material coating. To investigate the effect of disorder, we included two major defects in the graphene lattice, namely, nitrogen doping and Stone–Wales defects. Nitrogen doping transforms graphene from a zero-bandgap semiconductor to a metal, while Stone–Wales defects open the bandgap. For h-BN, we considered Stone–Wales defects. A detailed comparison of electron transport through five materials, that is, multilayer nanoscale graphene, N-doped multilayer nanoscale graphene, Stone–Wales-defective multilayer nanoscale graphene, h-BN, and Stone–Wales-defective h-BN allowed us to understand the currents at the nanoscale and the chemical and structural control over the electron transport. The slopes of the current decay with thickness enabled us to extrapolate trends for electron transport in thicker multilayer carbon and h-BN materials.

DOI： 10.3762/bjnano.16.147

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記述言語：英語   出版者・発行元：Physical Chemistry Chemical Physics  

We study the mitigation of environmental hydrogen embrittlement of iron by ammonia impurities in the hydrogen gas using combined theoretical and experimental methods. The competitive and dissociative co-adsorption of gaseous ammonia and gaseous hydrogen on the iron surface was investigated using density functional theory. The surface adsorption and decomposition of ammonia, as well as the ammonia partial pressure, were considered as influential factors contributing to the control of atomistic hydrogen uptake into the material. To elucidate the mechanism of ammonia competing with hydrogen on the iron surface and of ammonia mitigating hydrogen embrittlement, we develop kinetic modeling that can estimate the reaction rate and the dynamic surface coverage of different adsorbed species on the iron surface. The reaction rates for hydrogen and ammonia co-adsorption and dissociation were calculated using transition state theory combined with the Langmuir adsorption model, and a fracture toughness test was conducted to validate theoretical results. The adsorption rate of ammonia on iron is significantly higher compared to hydrogen, thus, ammonia hinders the hydrogen adsorption on the iron surface. However, partial pressure dependent ammonia decomposition also provides hydrogen atoms, which induce hydrogen embrittlement. The theoretical results of this study were supported well by experimental fracture toughness test results.

DOI： 10.1039/d5cp02423d

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出版者・発行元：Corrosion Science  

As hydrogen emerges as a key energy carrier for carbon-neutral technologies, mitigating gaseous hydrogen embrittlement (GHE) in existing structural materials becomes a critical challenge for a seamless transition to a hydrogen economy, alongside the development of new hydrogen embrittlement-resistant materials. This work combined experimental studies and first-principles calculations to investigate the role of water vapor in mitigating GHE in the SCM435 low alloy steel. Fatigue crack growth (FCG) tests revealed that adding 991 vol ppm water vapor to a hydrogen environment markedly suppressed hydrogen-induced acceleration in the SCM435 steel. The crack growth rate in moist hydrogen was reduced by approximately 8 times compared to dry hydrogen for both strength levels, reaching levels comparable to those in air. Scanning electron microscopy analysis indicated that fracture surfaces in the moist hydrogen exhibited ductile transgranular fracture, contrasting with the quasi-cleavage and intergranular fracture features observed in dry hydrogen, confirming the protective effect of water vapor. Computational modeling showed that water molecules tended to adsorb on the clean Fe(110) surface in molecular form with an adsorption energy of −0.32 eV. Increasing water coverage raised the hydrogen dissociation barrier from 0 to 0.39 eV, reducing the dissociation rate constant by over 10⁷. These results suggest that trace amounts of water vapor can act as a practical GHE inhibitor, offering new perspectives for enhancing the reliability of structural materials in hydrogen-rich environments.

DOI： 10.1016/j.corsci.2025.113252

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出版者・発行元：Journal of Physical Chemistry C  

Rare-earth orthoferrites (ReFeO<inf>3</inf>) exhibit multifaceted properties, including weak ferromagnetism, potential ferroelectricity, and magnetoelectric coupling. This study systematically investigated Y<inf>1–x</inf>Gd<inf>x</inf>FeO<inf>3</inf>(x = 0.2–1.0) synthesized via hydrothermal methods to understand how Gd substitution tunes these multifunctional properties. X-ray diffraction confirms single-phase orthorhombic structures (Pnma) with lattice expansion proportional to the Gd content, while SEM analysis reveals morphology evolving from flattened rectangles to cubes with increasing substitution. Density functional theory calculations reveal complex bandgap evolution (2.30–2.31 eV) with nonlinear electronic structure changes upon Gd doping, attributed to varying magnetic ordering configurations in the G-type antiferromagnetic structure, validated by UV–visible reflectivity measurements. Magnetic characterization shows enhanced saturation magnetization from 1.87 emu/g (x = 0.2) to 3.53 emu/g (x = 1.0) due to Gd³⁺magnetic contributions while preserving canted antiferromagnetism. Notably, Y<inf>0.4</inf>Gd<inf>0.6</inf>FeO<inf>3</inf>exhibits excellent ferroelectric performance with remnant polarization of 6.23 μC/cm²at 100 kV/cm. These findings demonstrate effective property tuning through Gd doping, where the enhanced magnetization and tunable bandgap advance orthoferrites for magnetic memory applications and the observed ferroelectric properties enable multiferroic sensing capabilities.

DOI： 10.1021/acs.jpcc.5c03950

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出版者・発行元：Journal of Materials Chemistry A  

Theoretical design and experimental proof of photocatalytic performance of eosin Y (EY) on anatase TiO<inf>2</inf> with a pyridine linker were obtained for increasing the photobiocatalytic activity of water splitting using visible light. Comparative studies on the hybrid interface of anatase and EY with carboxyl and pyridine anchors were performed by using density functional theory (DFT), time-dependent density functional theory (TD-DFT) calculations and experimental photoreduction of methyl viologen (MV). The geometries, binding interactions between dyes and anatase, electronic structures and electron transfer as well as the effect of isomers (ortho, meta, and para) on the dye/anatase systems were investigated. Theoretical results indicated that EY with carboxyl and pyridine anchors had visible absorption and electron transfer from the dye to the anatase titania. Compared to carboxyl-para, which had the best optical performance among carboxyl groups, the adsorption strength of pyridine-ortho was close to that of carboxyl-para, while the oscillator strength increased significantly, which was more than 10 times higher than that of carboxyl-para. Corresponding with the theoretical estimation, EY pyridine linked TiO<inf>2</inf> is active to MV reduction under visible light irradiation by fast charge transfer, in particular, pyridine-ortho and para. Furthermore, high stability is also achieved for pyridine-para. An apparent quantum yield higher than 2.00% and 0.67% under 520 nm light was experimentally achieved in biocatalytic H<inf>2</inf> and NH<inf>3</inf> formation, respectively, for EY pyridine linked TiO<inf>2</inf>, which was correctly predicted by the DFT calculations.

DOI： 10.1039/d5ta05712d

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出版者・発行元：New Journal of Chemistry  

This work explores the feasibility of molecular oxygen activation and dissociation on the sp²-hybridized carbon surface of carbon-coated iron nanoparticles. Using density functional theory with a generalized gradient approximation, we elucidate the geometry and electronic structure of these nanoparticles, highlighting the nature of the C-Fe binding interactions and the resulting modifications to the carbon surface electronic states. The enhanced catalytic activity of carbon induced by the underlying iron core is attributed to core-shell electronic interactions within the nanoparticles. Activation of molecular oxygen to superoxo and peroxo species was investigated using the nudged elastic band method, with electron transfer processes analyzed in detail and linked to the core-shell characteristics of the system. Additionally, we examined the effects of nitrogen doping in the carbon shell on the structural and electronic properties of the nanoparticles. Potential degradation pathways, including parasitic reactions during oxygen activation, were also identified. This study offers new theoretical insights into the functional behavior of Fe-C-N catalysts.

DOI： 10.1039/d5nj02903a

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出版者・発行元：Engineering Failure Analysis  

The addition of trace amounts of oxygen (O<inf>2</inf>) to hydrogen gas (H<inf>2</inf>) can mitigate hydrogen embrittlement (HE) in steels by suppressing the hydrogen uptake. In this study, the influence of temperature on the HE mitigation effect of O<inf>2</inf> was investigated using fracture toughness tests of SCM440 low-alloy steel in H<inf>2</inf> environments containing volume ppm-levels of O<inf>2</inf> at 293 K and 277 K. Lowering the temperature from 293 K to 277 K enhanced the HE in pure H<inf>2</inf>. However, the addition of O<inf>2</inf> to the H<inf>2</inf> effectively mitigated the HE, with the mitigation effect becoming more pronounced at lower temperatures. This temperature-dependent mitigation is attributed to the different adsorption behaviors of H<inf>2</inf> and O<inf>2</inf> on the iron surface. O<inf>2</inf> adsorption onto iron occurs without an activation barrier, making it essentially temperature-independent. In contrast, H<inf>2</inf> adsorption requires overcoming an activation barrier and thus decreases with a lower temperature. Consequently, decreasing the temperature selectively suppresses H<inf>2</inf> adsorption while leaving O<inf>2</inf> adsorption unaffected, thus enhancing the relative effect of O<inf>2</inf>. Furthermore, the presence of O<inf>2</inf> increases the activation barrier for H<inf>2</inf> adsorption, which amplifies the temperature dependence of the H<inf>2</inf> adsorption. These dual effects contribute to the enhanced HE mitigation by O<inf>2</inf> at lower temperatures.

DOI： 10.1016/j.engfailanal.2025.109885

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出版者・発行元：Corrosion Science  

High temperature hydrogen attack (HTHA) is a form of degradation of carbon steels exposed to high temperature and high-pressure hydrogen whereby internal hydrogen reacting with carbides forms methane gas bubbles with an associated loss in strength and toughness due to decarburization. Grain boundary gas bubbles can grow and coalesce leading to microcrack formation and frequently to premature fracture. Current models mainly rely on the Grabke and Martin transient methane generation kinetics which is based on carburization/decarburization experiments on iron surface at temperatures between 600 °C and 800 °C, though those temperatures are much higher than those at which HTHA is observed in industrial processes. This work presents a coupled chemical kinetics and micromechanics model that addresses methane and hydrogen gas formation along with simultaneous decarburization and bubble growth over a wide temperature range. The energetics of the chemical reactions taking place at the ferrite-matrix/bubble interface are established through DFT calculations. Model calculations unveil the relationship between the rates of hydrogen migration to the bubble interface, carbon and hydrogen atom reactions for methane formation, and attendant volumetric bubble growth. The model predicts equilibrium methane bubble pressures that agree with those predicted by existing models at high temperatures. Significantly, the model predicts equilibrium methane pressures that are remarkably lower than the extrapolated predictions of the existing models at lower temperatures, e.g., 250 °C. In summary, the model establishes a methodology to understand and quantify methane pressure development and decarburization across the length and time scales that are relevant to hydrogen attack.

DOI： 10.1016/j.corsci.2025.112999

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出版者・発行元：Corrosion Science  

The influence of temperature on the hydrogen gas embrittlement (HGE) susceptibility of X80 is unclear. In this work, mechanical test results revealed the enhanced HGE susceptibility with the decreasing temperature ranging from 333 K to 263 K. At lower temperatures, quasi-cleavage characteristics appeared on crack surfaces and plasticity suppression was further enhanced. Increased dislocation trapping capacity with decreasing temperature was demonstrated by finite element analysis and first-principles molecular dynamics calculations. At the investigated temperature, hydrogen could be sufficiently supplied to dislocations. Therefore, hydrogen trapping sites exhibited a higher concentration than lattice hydrogen and played a dominant role in determining the overall hydrogen distribution within the material. The strong trapping ability of dislocations at lower temperatures could increase the hydrogen concentration in high-density dislocation regions, including the crack tip. It recommends that the HGE of X80 for hydrogen delivery shall be evaluated at a lower temperature instead of room temperature which usually be used.

DOI： 10.1016/j.corsci.2025.112928

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出版者・発行元：Journal of Materials Chemistry A  

To further enhance the performance of perovskite solar cells (PSCs), a more comprehensive analysis of the mechanisms through which organic molecules induce defect passivation and enhance hole extraction is essential. In this study, we employ several organic molecules with varying π-conjugation lengths to examine how factors such as their molecular desorption, energy levels, and radical-cation stability affect defect passivation, hole extraction, and the overall PSC performance. Our results show that passivation molecules with extended π-conjugation suppress molecular desorption from the perovskite surfaces during overlayer spin-coating and improve energy-level alignment at interfaces, thereby enhancing PSC efficiency through improved defect passivation and hole extraction. Additionally, extended π-conjugation improves radical-cation stability, contributing to greater device durability. Among the defect passivation materials studied, 2-(3-ethylamine)benzothieno[3,2-b]benzothiophene hydroiodide (BTBTAI) can provide the most significant improvements in these factors, increasing the initial efficiency from 22.7% to 24.6% and raising the efficiency retention from 61% to 85% after 1000 hours of continuous light illumination at 25 °C in formamidinium lead iodide-based PSCs. Reports on defect passivation from the perspectives of molecular desorption and cation stability are extremely limited. Therefore, these findings deepen the understanding of PSC operating mechanisms and offer valuable insights for developing design guidelines for future defect passivation materials with even higher device performance.

DOI： 10.1039/d5ta00754b

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出版者・発行元：International Journal of Hydrogen Energy  

This paper provides a comprehensive review of the authors’ recent achievements in mitigating hydrogen embrittlement (HE) in iron (Fe) and steels using carbon monoxide (CO) in gaseous H<inf>2</inf>. CO contained in H<inf>2</inf> gas preferentially adsorbs on the Fe surface, and effectively suppresses hydrogen dissolution into the material, resulting in mitigating HE. Fracture toughness test results under various conditions demonstrated the effectiveness of CO in mitigating HE, with its impact influenced by factors such as loading rate, gas pressure, strength, and chemical composition. The CO mitigation effect diminishes with the lower loading rate, higher gas pressure, higher strength, and increased chromium content. The mechanisms underlying the effects of these factors on the susceptibility to HE are theoretically elucidated based on the surface reactions of the H<inf>2</inf> and CO molecules with the Fe surface through density functional theory and molecular dynamics simulations.

DOI： 10.1016/j.ijhydene.2024.04.071

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記述言語：英語   出版者・発行元：Inorganic Chemistry  

High-valent iron oxido species, central to many enzymatic and biomimetic catalyzed organic oxidative transformations, can be generated by direct electrochemical oxidation, circumventing high-energy O atom donor reagents. Electrochemical generation necessitates knowledge of the redox potentials involved, which is hindered by the lack of well-defined Fe(III)/Fe(IV) redox waves in the voltammetry of many iron-based catalysts. Hence, other approaches including chemical oxidation and bulk spectro(electro)chemical methods need to be taken. In the case of the well-studied oxidation catalyst, (Formula presented), where N<inf>4</inf>Py is 1,1-bis(pyridin-2-yl)-N,N-bis(pyridin-2-ylmethyl)methanamine, estimates of the Fe(III/IV) redox potentials range from 0.4 to 1.3 V vs SCE. Here, we show that electrochemical surface-enhanced Raman scattering spectroscopy reveals “hidden” redox waves, and hence redox potentials, when coupled with cyclic voltammetry. Rapid spectral acquisition (>2 Hz) of surface-enhanced Raman spectra at electrochemically roughened gold electrodes enables real-time spectral acquisition during cyclic voltammetry. We show that the Fe(III)/Fe(IV) redox potential of (Formula presented) is close to that determined earlier by chemical redox titrations (0.85 V vs SCE). Furthermore, comproportionation and adsorption processes are shown to impact the rates of electron transfer observed, which rationalizes the absence of a distinct Fe(III)/Fe(IV) redox wave in its cyclic voltammetry.

DOI： 10.1021/acs.inorgchem.5c01017

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記述言語：英語   出版者・発行元：Physical Chemistry Chemical Physics  

CeO<inf>2</inf> supported with Ni nanoparticles has emerged as a promising catalyst for enhancing the efficiency of dry reforming of methane (DRM) reaction. Methane dissociation (CH<inf>4</inf> → CH<inf>3</inf> + H) was reported as one of the rate-determining steps in the DRM reaction. We elucidated the reaction mechanism and explored methods for reducing the activation energy using density functional theory (DFT) calculations, where the activation energy of methane dissociation was determined at multiple Ni<inf>4</inf> cluster sites on CeO<inf>2</inf>. In parallel, we experimentally evaluated methane dissociation based on the methane consumption rate in the DRM reaction using newly developed flower-like Ni-supported CeO<inf>2</inf> catalyst (Ce(F)). The experimental activation energy was determined to be 0.69 eV (15.91 kcal mol⁻¹), closely matching the DFT-calculated value of 0.80 eV (18.45 kcal mol⁻¹) for the Ni<inf>4</inf> cluster model, validating our theoretical predictions. Additionally, we discovered that positively charging the Ni<inf>4</inf> can lower the activation energy of methane dissociation. These findings contribute to a deeper understanding of how to control the activation energy of the methane dissociation reaction in DRM.

DOI： 10.1039/d4cp01324g

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記述言語：英語   出版者・発行元：Physical Chemistry Chemical Physics  

Self-assembled monolayers (SAMs), especially those based on thiol containing compounds on gold, are of both practical and fundamental interest. Thiols and thiolates can bind to gold in several ways due to the presence of holes and edges on the surfaces. The variety of binding motifs is increased by the presence of adatoms, i.e. gold atoms present on the surface, that sit between the thiolate and the surface. Although these motifs bind strongly to gold surfaces, they are sufficiently mobile to allow for self-assembly of thiols, either by movement across the surface or by desorption/re-adsorption. The motifs have been investigated primarily in the context of high surface coverage, with some attention given to the mobility of these motifs. Here we focus on the binding in the low-coverage regime, i.e. the initial stage of SAM formation, using theoretical methods. We determine the relative stability of the motifs formed with methane thiolate in the low-coverage regime, and rationalize their relative mobilities. Methane thiolate is used to minimize contributions of intermolecular interactions. Competition between the rates of adsorption, movement, and formation of the motifs can influence the formation of SAMs. In this work we expand the understanding of the early stages of monolayer formation and conclude that the type of motif formed initially depends strongly on the availability of gold adatoms and defects (edges and holes) on the surface at the point of adsorption.

DOI： 10.1039/d4cp03709j

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出版者・発行元：Journal of Materials Chemistry A  

Oxide perovskites, such as SrCoO<inf>3</inf>, are considered to be promising air electrode catalysts for solid oxide cells. SrCoO<inf>3</inf> is composed of non-precious elements and possesses catalytic activity for various reactions, including an oxygen reduction and an oxygen evolution reaction. However, the catalytic activity of this material is typically limited at reduced temperatures. In this study, the catalytic activity of SrCoO<inf>3</inf> was improved by co-doping of cerium (Ce) and samarium (Sm) at the A site (Sr site) of SrCoO<inf>3</inf>. Although Ce was considered the B-site dopant in terms of ionic size and coordination number, a small amount of Ce was successfully substituted at the Sr site, simultaneously with Sm. Oxygen reduction and evolution activity were significantly increased by substitution of a small amount of cerium (∼2.5 mol%) at the A-site. At 973 K, the maximum power density generated from the LaGaO<inf>3</inf>-supported cell with Ce-Sm co-doped SrCoO<inf>3</inf> as an air electrode was 0.62 W cm⁻² in fuel cell mode, and the current density in steam electrolysis mode at 1.5 V was 0.93 A cm⁻². The increased air electrode activity could be assigned to the improvement in the surface active sites and electrical conductivity of SrCoO<inf>3</inf> by simultaneous substitution of Ce with Sm at the A site.

DOI： 10.1039/d4ta08181a

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記述言語：英語   出版者・発行元：Analytical Chemistry  

Accurate, label-free quantification of proteins, and more specifically albumin, is essential in studies aimed at monitoring transport across biological barrier tissues in vitro. Surface-enhanced Raman scattering (SERS) can deliver the sensitivity and specificity needed for such studies at physiologically relevant conditions, however, direct detection of albumin is not typically feasible at such concentrations. Here we use a small-molecule reporter (pyrazine-2-carbonitrile, PCN) that can interact both with albumin and a SERS substrate to facilitate albumin quantification. The nanoparticle surface/PCN and albumin/PCN interactions are sufficiently balanced to yield the sensitivity and specificity needed for in vitro tissue studies. The major challenge in using SERS for such assays is that the spectra of analytes can differ from their nonresonant Raman spectra, due to distinct species forming at and near the surface of the nanoparticles. Specifically, the binding of PCN to gold nanoparticles, formation of Au-PCN complexes, as well as PCN itself, contribute to the SERS spectra. We elucidate the nature of these interactions through concentration dependence studies and computational methods. Ultimately, we show that understanding these different interactions is key to quantification of albumin, at physiologically relevant albumin concentrations ranging from 0.4 to 4.4 μM using SERS spectroscopy. These data compare well with the state-of-the-art spectroscopic method, i.e., the transport of fluorescently labeled albumin across cell layers. We anticipate that this assay will stimulate analysis in in vitro models, such as organ-on-a-chip models and flow systems.

DOI： 10.1021/acs.analchem.4c05906

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記述言語：英語   出版者・発行元：Advanced Materials  

Exploiting the self-assembled molecules (SAMs) as hole-selective contacts has been an effective strategy to improve the efficiency and long-term stability of perovskite solar cells (PSCs). Currently, research works are focusing on constructing SAMs on metal oxide surfaces in p-i-n PSCs, but realizing a stable and dense SAM contact on halide perovskite surfaces in n-i-p PSCs is still challenging. In this work, the hole-selective molecule for n-i-p device is developed featuring a terephthalic methylammonium core structure that possesses double-site anchoring ability and a matching diameter (6.36 Å) with the lattice constant of formamidinium lead iodide (FAPbI<inf>3</inf>) perovskite (6.33 Å), which facilitates an ordered and full-coverage SAM atop FAPbI<inf>3</inf> perovskite. Moreover, theoretical calculations and experimental results indicate that compared to the frequently used acid or ester anchoring groups, this ionic anchoring group with a dipolar charge distribution has much larger adsorption energy on both organic halide terminated and lead halide terminated surfaces, resulting in synergistic improvement of carrier extraction and defect passivation ability. Benefiting from these merits, the efficiency of PSCs is increased from 21.68% to 24.22%. The long-term operational stability under white LED illumination (100 mW cm⁻²) and at a high temperature of 85 °C is also much improved.

DOI： 10.1002/adma.202414576

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出版者・発行元：International Journal of Hydrogen Energy  

This study investigated the pressure-dependent CO<inf>2</inf> effect on the hydrogen embrittlement of X80 and GB20# pipeline steels by combining experiments and first-principles calculations. Results revealed that the CO<inf>2</inf> effect enhanced the fatigue crack growth for GB20# steel in 10 MPa CO₂-enriched hydrogen mixtures. However, the improved degree by the CO₂ effect at 10 MPa was less pronounced than at 0.4 MPa, which was found for the first time. This was attributed to the decreased adsorption rate of CO₂ on iron as hydrogen pressure increased. Therefore, in high-pressure CO₂-enriched hydrogen mixtures, CO<inf>2</inf> could not significantly accelerate the inherent rapid hydrogen uptake at high pressure.

DOI： 10.1016/j.ijhydene.2024.10.032

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出版者・発行元：Materials Advances  

The direct conversion of methane to methanol has attracted increasing interests, owing to the necessity for an abundant low-carbon source of energy. However, numerous challenges are encountered in attaining a high conversion rate and selectivity using the existing approach and catalysts. One of them is the need for a reaction halt and a reactivation of the catalyst using an oxidant at high temperature, which makes the whole process non-cyclic. In this study, we employ density functional theory calculations to evaluate rutile-type IrO<inf>2</inf>(110), β-PtO<inf>2</inf>(110), and β-MnO<inf>2</inf>(110) surfaces not only for cleaving the H-CH<inf>3</inf> bond but also for forming methanol. We find that IrO<inf>2</inf>(110) and β-PtO<inf>2</inf>(110) thermodynamically and kinetically favor the C-H activation on the bridging μO-atom terminations via a heterolytic pathway. However, the formation of strong Ir-C and Pt-C bonds, which initially help the C-H bond scission, hinders the methanol formation. In the β-MnO<inf>2</inf>(110) case, in contrast, the Mn-C interaction is quite weak, and the Mn(μ-O)Mn active site is electrophilic, thus allowing the formation of a stable ˙CH<inf>3</inf> radical intermediate state that becomes the driving force for a low-barrier homolytic C-H bond scission as well as a low-barrier and highly exothermic formation of methanol. This first cycle of methane oxidation results in a reduced β-MnO<inf>2</inf>(110) surface, where no more μ-O active sites are available for the subsequent cycles of methane activation. Nonetheless, this reduced surface can also oxidize methane to methanol when the H<inf>2</inf>O<inf>2</inf> oxidant is inserted in the mid-way reaction and forms new active sites of μ-OH. The second reaction is also highly exothermic although the C-H activation barrier is not as low as that for the fresh stoichiometric surface. This study suggests the β-MnO<inf>2</inf>(110) surface as a potential catalyst for the cyclic oxidation of methane to methanol using the H<inf>2</inf>O<inf>2</inf> oxidant without halting for reactivation.

DOI： 10.1039/d4ma00827h

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出版者・発行元：Accounts of Materials Research  

Conspectus Carbon nanotubes are classified into single-walled carbon nanotubes (SWNTs), double-walled carbon nanotubes and multiwalled carbon nanotubes. Among these, SWNTs have remarkable electronic, mechanical, optical, chemical and thermal properties, which are derived from their one-dimensional extended π-conjugated structures, and thus, they demonstrate a high potential toward the development of the next-generation nanoelectronics, (nano)bio, and energy and environmental materials and devices. As-produced SWNTs are a mixture of semiconducting (sem-) and metallic (met-)-SWNTs; thus, chirality sorting is highly important. So far various methods have been presented for such a separation including (i) use of chemical adsorbents such as polyfluorenes (PFOs) and their analogues and (ii) physical methods including surfactant-aided density gradient ultracentrifugation (DGU), gel chromatography techniques, and the surfactant-aided aqueous two-phase extraction method. However, such methods are not simple, and the removal of the wrapped adsorbents on the SWNTs is very difficult. Thus, the development of a method to remove the adsorbent from the sorted SWNTs is highly important to obtain adsorbent-free pure sem-SWNTs. In this Account, we provide a summary of a one-pot highly efficient sem-SWNT sorting using a solubilizer and removal of the wrapped solubilizer/adsorbent from the surfaces of the sorted tubes to provide highly pure adsorbent-free sem-SWNTs, in which the design and synthesis of adsorbents that selectively sorts sem-SWNTs from as-produced SWNTs, a mixture of sem-SWNTs and met-SWNTs, with easy removal property by a suitable method are described. In particular, we demonstrate a solubilizer-free sem-SWNT sorting based on supramolecular chemistry. The development of easy/simple and an efficient adsorbent-free sem-SWNT sorting method is highly important for proper fundamental use and application of SWNTs in industry. In addition, we describe computer simulations for selective sem-SWNT sorting based on a DFT method; in particular, we summarize our density functional theory (DFT) approach for helical wrapping of flavin molecules on the (8,6)-SWNT, leading to successful SWNT chirality separation. Finally, the introduction of a machine learning approach for SWNT solubilization is summarized.

DOI： 10.1021/accountsmr.4c00113

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担当区分：最終著者  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   出版者・発行元：Journal of Physical Chemistry A  

Cyclization and cycloreversion of organic compounds are fundamental kinetic processes in the design of functional molecules, molecular machines, nanoscale sensors, and switches in the field of molecular and nanoelectronics. We present a fully automatic computational platform for the design of a class of five- and six-membered ring lactones by optimizing the ring-opening reaction rate. Starting from a minimal initial parent set, our algorithm generates iteratively cascades of pools of candidate lactone derivatives where optimization and down-selection are performed without human supervision. We employ the density functional theory combined with the transition state theory to elucidate the exact mechanism leading to the lactone ring-opening reaction. On the basis of the analysis of the reaction pathway and the frontier molecular orbitals, we identify a simple descriptor that can easily correlate with the reaction rate. Consequently, we can omit computationally expensive transition state calculations and deduce the reaction rate from simple ground-state and ionic calculations. To accelerate the platform, we use a data set of the order of 800 molecules to train machine learning models for the prediction of targeted chemical properties, reducing the computational time by a 90% factor. We developed an evolutionary algorithm capable of generating data sets 3 orders of magnitude larger than the initial parent set. Thus, we can explore a large domain of chemical space using minimal computational effort. Our entire platform is modular, and our current implementation for lactone can be further generalized to more complex systems via substitution of the quantum chemical and fingerprinting modules.

DOI： 10.1021/acs.jpca.3c05887

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出版者・発行元：Solid State Ionics  

Mullite-phase bismuth gallate (Bi<inf>2</inf>Ga<inf>4</inf>O<inf>9</inf>) was successfully synthesized with partial substitution of bismuth with alkaline-earth cation, Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺. The effect of this substitution on the electrical conductivity was investigated. In this study, substitution with Ca²⁺ of Bi site was further studied for increasing the ionic conductivity as well as the phase stability in reducing atmospheres. Substitution with Ca²⁺ was found to be the most effective and with 12.5 mol% of Ca²⁺ as the optimized doping amount. Conductivity and stability in reducing atmospheres was increased down to p<inf>O2</inf> ≤ 10⁻¹⁹ atm while keeping the conductivity of σ = 2.6 × 10⁻² S·cm⁻¹ at 973 K largely independent of oxygen partial pressure. Oxygen permeation analysis estimates 76% of theoretical oxygen permeation rate at 973 K suggesting main charge carrier is oxide ion. Partial electronic conductivity was measured with the ion blocking method. Oxide ion conductivity is dominated over wide p<inf>O2</inf> range excepting for hole conduction at high p<inf>O2</inf>. Density functional theory (DFT) analysis on oxide ion diffusion route suggests oxygen hoping through lattice vacancy is main pathway for oxide ion conductivity in this doped Bi<inf>2</inf>Ga<inf>4</inf>O<inf>9</inf>. Despite the low oxide ion conductivity in Mullite-phase oxide, it was found that Ca doped Bi<inf>2</inf>Ga<inf>4</inf>O<inf>9</inf> shows good oxide ion conductivity over wide p<inf>O2</inf> range.

DOI： 10.1016/j.ssi.2023.116343

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出版者・発行元：Journal of Physical Chemistry C  

The high oxide-ion transport in three fluorite-structured oxide electrolytes is examined by using density functional theory. Our study elucidates the oxide-ion diffusion mechanism in yttrium (Y)-doped ZrO<inf>2</inf>, Y-doped CeO<inf>2</inf>, δ-Bi<inf>2</inf>O<inf>3</inf>, and α-Bi<inf>2</inf>O<inf>3</inf>, including the major change in oxygen mobility that occurs in Bi<inf>2</inf>O<inf>3</inf> at the δ-α phase transition. This research focuses on the partial covalent interactions, often neglected in atomistic simulations, and their effect on the migrating oxygen ion. We found a direct relationship between the degree of hybridization (i.e., partial covalent interactions) in the resting state, transition state, and the activation barrier for oxygen migration. From this, we can understand the oxygen-ion migration energetics by analyzing the resulting electron density. The oxide ions migrate nonlinearly between two adjacent lattice sites to maximize partial covalent interactions with the neighboring cations. We also provide an explanation for the enhanced oxide-ion conductivity of δ-Bi<inf>2</inf>O<inf>3</inf> compared to α-Bi<inf>2</inf>O<inf>3</inf>, related to the electron density due to different 6s lone-pair orientations. The disordered δ-phase has a complex lone-pair orientation, which also changes as the oxygen ion is migrating, resulting in a very low barrier to oxygen-ion migration. In contrast, α-Bi<inf>2</inf>O<inf>3</inf>, a material with exactly the same stoichiometry, has a well-ordered lattice, and the lone-pair orientation is always arranged to hinder the oxygen diffusion pathway.

DOI： 10.1021/acs.jpcc.3c03050

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出版者・発行元：Advanced Energy Materials  

The versatility of the spinel (AB<inf>2</inf>O<inf>4</inf>) oxides means they are of great interest for a variety of catalysis and energy conversion applications, involving gas reactions and reforming. CuFe<inf>2</inf>O<inf>4</inf> spinel is identified as a highly efficient fuel electrode for CO<inf>2</inf>/H<inf>2</inf>O co-electrolysis due to its promising electrocatalytic activity. To identify the actual active sites, the electrochemical characteristics, composition, chemical state, and microstructure are systematically investigated while optimizing the electrolysis performance by varying the feed gas composition. Markedly enhanced electrolysis current density is achieved under a CO<inf>2</inf>-enriched composition of 50%CO<inf>2</inf>/10%H<inf>2</inf>O-Ar. This promising performance is attributed to the in situ exsolution of heterostructural “Cu/Fe<inf>3</inf>O<inf>4</inf>” nanoparticles on the parent CuFe<inf>2</inf>O<inf>4</inf> surface during co-electrolysis. Interestingly, a strong correlation of the electrolysis performance with the amount of the formed heterostructural cermet is observed. The exsolved cermet heterostructure plays a crucial role in CO<inf>2</inf>/H<inf>2</inf>O electroreduction, as also confirmed by density-functional-theory studies. The self-exsolved Cu/Fe<inf>3</inf>O<inf>4</inf> nanoparticles present exceptional strength due to a strong interaction between the formed metallic Cu and Fe<inf>3</inf>O<inf>4</inf>, enabling the electrode to remain active and stable under such high electrical polarization. The excellent durability and stability of the self-exsolved heterostructural nanoparticles are clearly confirmed by long-term operation at high-working voltage with an outstanding Faradaic efficiency (nearly 100%).

DOI： 10.1002/aenm.202301042

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記述言語：英語   出版者・発行元：Nanotechnology  

The effect of defects, nitrogen doping, and hydrogen saturation on the work function of graphene is investigated via first principle calculations. Whilst Stone-Wales defects have little effect, single and double vacancy defects increase the work function by decreasing charge density in the π-electron system. Substitutional nitrogen doping in defect-free graphene significantly decreases the work function, because the nitrogen atoms donate electrons to the π-electron system. In the presence of defects, these competing effects mean that higher nitrogen content is required to achieve similar reduction in work function as for crystalline graphene. Doping with pyridinic nitrogen atoms at vacancies slightly increases the work function, since pyridinic nitrogen does not contribute electrons to the π-electron system. Meanwhile, hydrogen saturation of the pyridinic nitrogen atoms significantly reduces the work function, due to a shift from pyridinic to graphitic-type behavior. These findings clearly explain some of the experimental work functions obtained for carbon and nitrogen-doped carbon materials in the literature, and has implications in applications such as photocatalysis, photovoltaics, electrochemistry, and electron field emission.

DOI： 10.1088/1361-6528/ac7ecf

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出版者・発行元：International Journal of Fracture  

High temperature hydrogen attack (HTHA) is degradation of steels exposed to hydrogen gas at high temperatures and pressures. Hydrogen in steels reacts with carbon from carbides to produce methane gas bubbles typically on grain boundaries which grow and coalesce, leading to loss of strength and fracture toughness. Current design practice against HTHA is based on the Nelson curves which define the conditions for safe operation in a temperature/hydrogen-partial-pressure diagram. Nelson curves are phenomenological in nature and do not account for the underlying failure mechanism(s), material microstructure, carbide stability, and applied stresses. In light of experimental evidence of predominant cavitation ahead of cracks reported by Martin et al. (Acta Mater 140:300–304, 2017), it is expected that void growth is accelerated by the triaxial stresses associated with microstructural flaws. To this end, we propose a three-dimensional, axisymmetric, constraint-based void-growth model extending the “one-dimensional” model of Dadfarnia et al. (Int J Fract 219:1–17, 2019). The present model is shown to yield satisfactory agreement with the available experimental data from hydrogen attack of 2¼Cr–1Mo steel at temperatures ranging from 500 to 600 °C. In addition, the model is used to construct Nelson type curves in the temperature/hydrogen-partial-pressure diagram. These curves represent failure times for given applied stresses and triaxiality. The proposed methodology can be viewed as providing a step toward improving the current design practice against HTHA while maintaining the simplicity of the original Nelson curve approach.

DOI： 10.1007/s10704-023-00739-2

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

出版者・発行元：Bulletin of the Chemical Society of Japan  

Earth-abundant non-precious metal-coordinated eco-friendly catalysts with high oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) performances were designed and created. The development of a cost-effective, efficient, and durable bifunctional ORR and OER electrochemical catalyst is a key for future batteries. So far, precious metals, e.g., Pt and Ir, have been used as efficient catalysts for the ORR and OER, respectively. However, they are expensive and their deposits on earth are limited, which are the major drawbacks of these metals, along with the sluggish reactions of ORR and OER. Since electroconductivity of promising metal-free catalyst candidates are poor, good electronic supporting materials are needed. Due to their high conductivity, stability and easy handling, carbon nanotubes are a most promising material. Recent advances in carbon nanotube/nanocarbon-based ORR and OER catalysts, metal oxide and others/nanocarbon catalysts for ORR, OER, HER and Zn-air electrodes, as well as computational study for such catalyst reactions, are discussed.

DOI： 10.1246/bcsj.20230051

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出版者・発行元：Journal of Physical Chemistry C  

A rechargeable Zn-air battery is expected as a large capacity battery alternative to the Li ion battery; however, short cycle life is the current issue. In this study, it was found that the addition of 3,3-diaminodipropylamine was effective for preventing the formation of a Zn dendrite in the anode resulting in a long cycle life with more than 300 cycles and a discharge capacity larger than 700 mAh/g (>85% Zn used for discharge) when Ni<inf>0.8</inf>Fe<inf>0.2</inf>Co<inf>2</inf>O<inf>4</inf> and 8 M KOH-H<inf>2</inf>O were used for the air electrode and electrolyte, respectively. The increased cycle stability could be assigned to the change in the solvated structure of Zn²⁺ in the electrolyte by the strong interaction between 3,3-diaminodipropylamine and solvated water, which is suggested by Raman and Fourier transform infrared spectroscopic analyses. Ab initio molecular dynamics simulations suggest that the amine is strongly interacted with OH of solvated water molecules and changes the coordination number of Zn²⁺, and as result, the size of the solvated Zn²⁺ cluster was increased, resulting in enhanced Zn²⁺ mobility in the electrolyte for the uniform deposition of Zn on the anode during charge by increased mobility.

DOI： 10.1021/acs.jpcc.2c08682

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出版者・発行元：Communications Materials  

Oxynitrides are promising materials for visible light-driven water splitting. However, limited information regarding their electron-momentum resolved electronic structure exists. Here, with the advantage of the enhanced probing depth and chemical state specificity of soft-X-ray ARPES, we determine the electronic structure of the photocatalyst oxynitride LaTiO<inf>2</inf>N and monitor its evolution as a consequence of the oxygen evolution reaction. After the photoelectrochemical reactions, we observe a partial loss of Ti- and La-N 2p states, distortions surrounding the local environment of titanium atoms and, unexpectedly, an indication of an electron accumulation layer at or near the surface, which may be connected with either a large density of metallic surface states or downward band bending. The distortions and defects associated with the titanium 3d states lead to the trapping of electrons and charge recombination, which is a major limitation for the oxynitride LaTiO<inf>2</inf>N. The presence of an accumulation layer and its evolution suggests complex mechanisms of the photoelectrochemical reaction, especially in cases where co-catalysts or passivation layers are used.

DOI： 10.1038/s43246-023-00344-9

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   出版者・発行元：Journal of Physical Chemistry A  

In this study we employ density functional theory to investigate the binding interaction between polydimethylsiloxane and CO<inf>2</inf> for application in gas separation membranes. The binding strength has been studied systematically as a function of the monomer conformational rotations in the polymer chain. Our work identified major differences between the CO<inf>2</inf> interaction with the helical conformation and the linear conformation of polydimethylsiloxane polymer chains. We have further estimated dependence between the CO<inf>2</inf> binding strength and the polydimethylsiloxane polymer chain curvature by systematically evaluating the CO<inf>2</inf> binding to cyclic polydimethylsiloxane oligomers. The enhanced CO<inf>2</inf> interaction with helical chains and cyclic oligomers was attributed to cooperative, confinement effects, and local electron density distribution at the Si-O-Si fragments. The binding modes were identified using vibration frequency analysis.

DOI： 10.1021/acs.jpca.2c07001

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

出版者・発行元：Proceedings of the International Offshore and Polar Engineering Conference  

Carbon monoxide (CO) contained in hydrogen gas mitigates hydrogen embrittlement (HE). This CO effect can be affected by the chemical composition of the steel surface. This study investigated the effect of chromium (Cr) on Cr-rich and Cr-low materials. During the fracture toughness test, the CO effect was significantly less for the SUS430 ferritic stainless steel (16.17% Cr) compared to that for the A333 carbon steel (0.03% Cr). The mechanism that Cr reduced the CO mitigation effect was considered by DFT calculations of the interaction of CO with the steel surface. It revealed that the CO adsorption on the Fe site is greater than that on the Cr site.

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出版者・発行元：ACS Catalysis  

Hydroxide-derived copper (OH/Cu) electrodes exhibit excellent performance for the electrocatalytic CO<inf>2</inf> reduction reaction (CO<inf>2</inf> RR). However, the role of hydroxide (OH) in CO<inf>2</inf> RR remains controversial; therefore, the origin of the selectivity enhancement emerging on OH/Cu has not been fully understood. In the present work, we quantitatively evaluated surface OH by electroadsorption and established a direct correlation between the OH amount and selectivity for the production of CH<inf>4</inf> and C<inf>2+</inf> on OH/Cu with the help of computational investigations concerning work functions of the surface. Based on these findings, we demonstrated variable selectivity using OH/Cu electrodes having a controlled OH amount; three OH/Cu electrodes realized their distinct selectivity such as Faradic efficiency (FE) for the production of CH<inf>4</inf> (CH<inf>4</inf> FE) of 78%, C<inf>2+</inf> FE of 71%, and the ratio of C<inf>2+</inf> -To-CH<inf>4</inf> >355. The proposed simple strategy for selectivity control would contribute to further quantity synthesis of value-Added chemicals using CO<inf>2</inf> RR.

DOI： 10.1021/acscatal.2c03650

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出版者・発行元：Materialia  

Proton-conducting oxides are promising for applications in solid oxide fuel cells and steam electrolysis at intermediate temperatures (400–600 °C). The hydration reaction requires oxide ion vacancies and the protonic conductive species originate from this reaction. Increasing the proton concentration leads to higher proton conductivity but also expands the lattice volume, known as chemical expansion, which may lead to the mechanical failure of the oxide. Thus, it is important to clarify the factors that decrease the chemical expansion. A previous study suggested that chemical expansion could be suppressed by a large bulk modulus. Although this was only a qualitative argument, our study quantitatively clarifies the effect of the bulk modulus experimentally and theoretically. To examine the difference between Ce and Zr, which are typical elements in proton-conducting oxides, 6.25 mol% Y-doped SrZrO<inf>3</inf> and SrCeO<inf>3</inf> were prepared, and their bulk moduli were quantitatively evaluated. Y-doped SrZrO<inf>3</inf> had a larger bulk modulus than Y-doped SrCeO<inf>3</inf>. Our results support the previous finding that proton-conducting oxides with large bulk modulus suppress chemical expansion. In addition, our theoretical calculations of the force constants showed that the difference in bulk modulus was caused by the Zr-O bonds being more rigid than the Ce-O bonds. Our results should provide useful guidelines for suppressing chemical expansion in proton-conducting oxides.

DOI： 10.1016/j.mtla.2022.101616

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出版者・発行元：Materials Advances  

As efficient electrodes in energy conversion and storage devices, we focus on the development of a polymer-type non-precious metal-coordinated eco-friendly catalyst with high performance, which is of importance in flexible wearable energy storage electronic devices with adaptable shapes. In the present study, we describe the design and synthesis of a nickel (Ni)-coordinated poly(thiourea-formaldehyde) polymer, then a nanocarbon (Vulcan, porous nanocarbon CNovel™, 2-different multi-walled carbon nanotubes, or single-walled carbon nanotubes) as the conducting support was combined to prepare seven different molecular catalysts. The chemical structure of the Ni-coordinated polymer was characterized by elemental analysis, ¹³C NMR, FT-IR and XPS. Furthermore, EXAFS studies and theoretical calculations revealed that this polymer consists of two Ni-O (2.17 Å) and two Ni-S (2.17 Å) coordination bonds. This Ni-coordination polymer was stable in an oxidative and reductive environment in an alkaline medium over a long term due to its strong Ni-coordination. The catalysts were found to act as an efficient catalyst for an oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Especially, among the catalysts, the CNovel™-based catalyst showed the highest oxygen electrode performance for the ORR: E<inf>1/2</inf>: 0.81 V vs. RHE, and OER: 1.57 V vs. RHE at 10 mA cm⁻². The catalyst acted as an efficient and durable cathode for a rechargeable Zn-air battery (charge-discharge overpotential gap of 0.45 V). Such outstanding air-cathode performance is explained by the cooperative mechanism between water on the axial site of the Ni in the polymer and superoxide ion on the porous carbon. The present study is of importance for the development of advanced energy materials in batteries and molecular catalysts.

DOI： 10.1039/d2ma00450j

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記述言語：英語   出版者・発行元：Rsc Advances  

Biomass discharged from primary industries can be converted into methane by fermentation. This methane is used for generating electricity with solid oxide fuel cells (SOFCs). This methane fermentation provides H<inf>2</inf>S, which reduces the efficiency of SOFCs even at a level as low as a few parts per million. It has been experimentally reported that a nitrogen (N)-doped graphene-based material known as pyridinic N removes H<inf>2</inf>S via an oxidation reaction compared with another graphene-based material known as oxidized N. To understand this experimental result, we investigated H<inf>2</inf>S adsorption on pyridinic N and oxidized N by a density functional theory analysis and further examined the activation barrier of dissociation reactions. We found that the adsorption of H<inf>2</inf>S on pyridinic N is more stable than that on oxidized N. In addition, the H<inf>2</inf>S dissociation reaction occurs only on pyridinic N.

DOI： 10.1039/d2ra00898j

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PubMed

出版者・発行元：Journal of Physical Chemistry C  

Near-infrared photoluminescence (NIR PL) at regions over 1000 nm is used by advanced optical technologies such as quantum communication and deep tissue bioimaging. We demonstrate that covalent attachment of a diarylethene derivative to single-walled carbon nanotubes (SWCNTs) introduces sp3 carbon defects into the crystalline sp2 carbon networks of SWCNTs through chemical functionalization by which red-shifted and bright NIR PL band at 1142 nm appears. Moreover, its PL wavelength switching is achieved reversibly and repeatedly based on photoisomerization of the diarylethene moieties on the nanotubes. The photoswitching phenomena confirmed by spectroscopic measurements and theoretical calculations reveal that the band gaps for PL change according to the diarylethene isomerization on the nanotubes.

DOI： 10.1021/acs.jpcc.2c02977

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出版者・発行元：Journal of Physical Chemistry C  

The development of a facile method to sort semiconducting single-walled carbon nanotubes (s-SWCNTs) and their enantiomer recognition are still great challenges. We here describe a finding that a commercially available, safe, and cost-effective hydrophobic riboflavin analogue (riboflavin tetrabutyrate; RTB) efficiently sorts only s-SWCNTs by a one-pot method (bath-type sonication for 30 min followed by ultracentrifugation) and recognizes their enantiomers (left- and right-handed s-SWCNTs). The solubilization behavior of the SWCNTs strongly depends on the concentration of RTB; namely, with the decrease in the concentration of RTB, the s-SWCNT (n,m)-chiral selective sorting efficiency is enhanced. When using RTB = ∼0.4 mM (SWCNTs = 1 mg/3 mL toluene), two (n,m) chiralities of the s-SWCNTs with (n,m) = (8,6) and (8,7) were efficiently sorted. Furthermore, when using RTB = 0.5-1 mM, the SWCNT enantiomer recognition was observed. In addition, the X-ray photoelectron spectroscopic study revealed that the adsorbed RTB molecules on the s-SWCNTs were readily removed by simple rinsing with acetone to provide adsorbent-free pure s-SWCNTs. On the basis of the experimentally obtained data using Raman, photoluminescence, and visible-near-IR absorption spectroscopy techniques and computational density functional theory (DFT) approaches, we have revealed a possible mechanism for this unique s-SWCNT selective sorting and their enantiomer recognition. The supramolecular orientation of RTB into the helical superlattice with its own chirality provides a mechanism for chirality recognition. The study demonstrates one-pot sorting of s-SWCNTs and their enantiomer recognition using a cost-effective, safe molecule. Such a study is important for s-SWCNT separation science and its application in nanoscience and engineering areas.

DOI： 10.1021/acs.jpcc.2c00959

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出版者・発行元：Machine Learning with Applications  

Materials chemistry is being profoundly influenced by the uptake of machine learning methodologies. Machine learning techniques, in combination with established techniques from computational physics, promise to accelerate the discovery of new materials by elucidating complex structure–property relationships from massive material databases. Despite exciting possibilities, further methodological developments call for a greater synergism between materials chemists, physicists, and engineers on one side, with computer science and math majors on the other. In this review, we provide a non-exhaustive account of machine learning in materials chemistry for computer scientists and applied mathematicians, with an emphasis on molecule datasets and materials chemistry problems. The first part of this review provides a tutorial on how to prepare such datasets for subsequent model building, with an emphasis on the construction of feature vectors. We also provide a self-contained introduction to density functional theory, a method from computational physics which is widely used to generate datasets and compute response variables. The second part reviews two machine learning methodologies which represent the status quo in materials chemistry at present – kernelized machine learning and Bayesian machine learning – and discusses their application to real datasets. In the third part of the review, we introduce some emerging machine learning techniques which have not been widely adopted by materials scientists and therefore present potential avenues for computer science and applied math majors. In the final concluding section, we discuss some recent machine learning-based approaches to real materials discovery problems and speculate on some promising future directions.

DOI： 10.1016/j.mlwa.2022.100265

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出版者・発行元：Journal of Physical Chemistry C  

Density functional theory calculations were performed to elucidate the origin of catalytic activity of the pristine LnO-terminated surfaces of two Ruddlesden-Popper phase oxides of industrial interest. The direct comparison of molecular oxygen interaction with La<inf>2</inf>NiO<inf>4</inf>and Pr<inf>2</inf>NiO<inf>4</inf>allowed us to evaluate the electronic effect on the oxygen reduction reaction energetics. We have further addressed the surface catalytic activity as a function of interstitial oxygen occupancy in the rock salt layer and provided a possible explanation for the limits of the interstitial oxygen concentration. The oxide ion transport in the rock salt layer was compared for La<inf>2</inf>NiO<inf>4.125</inf>and Pr<inf>2</inf>NiO<inf>4.125</inf>. The diffusion difference was attributed to the electronic structure of the valence shells of Pr and La. The different polarizability of those elements would lead to the opposite effect on the transition state stability. In-depth understanding of the La<inf>2</inf>NiO<inf>4</inf>and Pr<inf>2</inf>NiO<inf>4</inf>(including La<inf>2</inf>NiO<inf>4.125</inf>and Pr<inf>2</inf>NiO<inf>4.125</inf>) electronic properties allowed us to refer electronic and hole conductivities to the computed band gaps and the electronic structure of the valence bands. Our study shows that while La<inf>2</inf>NiO<inf>4</inf>and Pr<inf>2</inf>NiO<inf>4</inf>share a similar crystallographic structure, the most important properties, such as surface catalytic activity, ionic diffusivity, and electron transport, are a direct consequence of the valence shell structure of the Ln cations: La and Pr.

DOI： 10.1021/acs.jpcc.2c00480

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出版者・発行元：International Journal of Hydrogen Energy  

The effect of ammonia (NH<inf>3</inf>) contained in hydrogen (H<inf>2</inf>) gas on hydrogen environment embrittlement (HEE) of SCM440 low-alloy steel was studied in association with the NH<inf>3</inf> concentration, loading rate, and gas pressure. NH<inf>3</inf> worked as both mitigator of the HEE and inducer of hydrogen embrittlement (HE) depending on the testing conditions. The mitigation of the HEE was achieved by the deactivation of the iron (Fe) surface for H<inf>2</inf> dissociation caused by the preferential adsorption of NH<inf>3</inf> on the Fe surface, which is enhanced by the increase in the NH<inf>3</inf> concentration and decrease in the H<inf>2</inf> gas pressure. NH<inf>3</inf> induced HE was caused due to creating hydrogen by the NH<inf>3</inf> decomposition. Since the NH<inf>3</inf> decomposition rate is low, the induction effect was observed when the loading rate was low. The effect of NH<inf>3</inf> was determined by the competition of the mitigation and induction effects.

DOI： 10.1016/j.ijhydene.2022.03.006

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Density functional theory calculations were performed to elucidate the origin of catalytic activity of the pristine LnO-terminated surfaces of two Ruddlesden–Popper phase oxides of industrial interest. The direct comparison of molecular oxygen interaction with La2NiO4 and Pr2NiO4 allowed us to evaluate the electronic effect on the oxygen reduction reaction energetics. We have further addressed the surface catalytic activity as a function of interstitial oxygen occupancy in the rock salt layer and provided a possible explanation for the limits of the interstitial oxygen concentration. The oxide ion transport in the rock salt layer was compared for La2NiO4.125 and Pr2NiO4.125. The diffusion difference was attributed to the electronic structure of the valence shells of Pr and La. The different polarizability of those elements would lead to the opposite effect on the transition state stability. In-depth understanding of the La2NiO4 and Pr2NiO4 (including La2NiO4.125 and Pr2NiO4.125) electronic properties allowed us to refer electronic and hole conductivities to the computed band gaps and the electronic structure of the valence bands. Our study shows that while La2NiO4 and Pr2NiO4 share a similar crystallographic structure, the most important properties, such as surface catalytic activity, ionic diffusivity, and electron transport, are a direct consequence of the valence shell structure of the Ln cations: La and Pr.

記述言語：英語   出版者・発行元：Advanced Materials  

The oxygen evolution reaction (OER) is a critical element for all sorts of reactions that use water as a hydrogen source, such as hydrogen evolution and electrochemical CO<inf>2</inf> reduction, and novel design principles that provide highly active sites on OER electrocatalysts push the limits of their practical applications. Herein, Au-cluster loading on unilamellar exfoliated layered double hydroxide (ULDH) electrocatalysts for the OER is demonstrated to fabricate a heterointerface between Au clusters and ULDHs as an active site, which is accompanied by the oxidation state modulation of the active site and interfacial direct O-O coupling (“interfacial DOOC”). The Au-cluster-loaded ULDHs exhibit excellent activities for the OER with an overpotential of 189 mV at 10 mA cm⁻². X-ray absorption fine structure measurements reveal that charge transfer from the Au clusters to ULDHs modifies the oxidation states of trivalent metal ions, which can be active sites on the ULDHs. The present study, supported by highly sensitive spectroscopy combining reflection absorption infrared spectroscopy and modulation-excitation spectroscopy and density functional theory calculations, indicates that active sites at the interface between the Au clusters and ULDHs promote a novel OER mechanism through interfacial DOOC, thereby achieving outstanding catalytic performance.

DOI： 10.1002/adma.202110552

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出版者・発行元：Journal of Physics and Chemistry of Solids  

The effect of the partial covalent character of cations on their ionic diffusivity in La<inf>x</inf>Sr<inf>1-x</inf>Ga<inf>y</inf>Mg<inf>1-y</inf>O<inf>3-δ</inf>, a perovskite with A<inf>x</inf>A'<inf>x-1</inf>B<inf>y</inf>B'<inf>y-1</inf>O<inf>3-δ</inf> general formula, is determined computationally using plane wave, periodic, pseudopotential density functional theory. The diffusion of ions is assumed to take place by a vacancy-mediated transport mechanism. Using Vineyard's transition state theory, diffusion coefficients for each ion are obtained. The results of the calculations show that at temperature of 1000 K the diffusivity of the oxide ion is greater than that of the A-site cations by at least ten orders of magnitude, and the diffusivities of the A-site cations are greater then the diffusivities of B-site cations by at least eight orders of magnitude. Those results are related to local ionic mobilities and are not representative for macroscopic ionic diffusion. The diffusivities of rather covalent, polarizable, cations (La and Ga) were found to be lower than those of more ionic, hard, cations (Sr and Mg) despite the fact that La and Ga have smaller ionic radii than Sr and Mg, respectively. The migration pathway of the B-site cations is curved for different possible locations of the necessary oxygen vacancies and the calculations revealed that the curved pathway is not caused by steric hindrance of an intervening oxide ion but rather the driving force to maximize the electronic interactions of the B cation with surrounding oxide ions along the entire migration pathway.

DOI： 10.1016/j.jpcs.2021.110393

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

The effect of the partial covalent character of cations on their ionic diffusivity in LaxSr1-xGayMg1-yO3-δ, a perovskite with AxA'x-1ByB'y-1O3-δ general formula, is determined computationally using plane wave, periodic, pseudopotential density functional theory. The diffusion of ions is assumed to take place by a vacancy-mediated transport mechanism. Using Vineyard's transition state theory, diffusion coefficients for each ion are obtained. The results of the calculations show that at temperature of 1000 K the diffusivity of the oxide ion is greater than that of the A-site cations by at least ten orders of magnitude, and the diffusivities of the A-site cations are greater then the diffusivities of B-site cations by at least eight orders of magnitude. Those results are related to local ionic mobilities and are not representative for macroscopic ionic diffusion. The diffusivities of rather covalent, polarizable, cations (La and Ga) were found …

出版者・発行元：Metallurgical and Materials Transactions A Physical Metallurgy and Materials Science  

The addition of a small volume fraction of carbon monoxide (CO) gas to pure gaseous H<inf>2</inf> potentially mitigates the susceptibility of steel to hydrogen environment embrittlement (HEE). The effect of environmental gas pressure on the mitigation of HEEs by a mixture of H<inf>2</inf> and CO was examined in this study. Fracture toughness tests of an ASTM A106 pipe carbon steel were carried out in H<inf>2</inf> gas containing CO. The environmental gas pressures at which the fracture toughness tests were conducted were 0.6, 1.0 and 4.0 MPa. The addition of a certain concentration of CO to H<inf>2</inf> gas completely prevented HEE. The CO concentration achieving complete HEE prevention increased with an enhancement of the environmental gas pressure. Molecular dynamics (MD) simulations were further conducted to interpret the experimental results based on the interactions of H<inf>2</inf> and CO with the Fe surface in conjunction with the effect of gas pressure. The MD simulations revealed that the dissociation rate of dihydrogen molecules to atomic hydrogen on the Fe surface significantly increased with an elevation of the gas pressure, whereas the adsorption rate of CO on the Fe surface was almost independent of the gas pressure. These results suggest that the increase in the gas pressure relatively promotes hydrogen uptake into the material in the presence of CO, which accounts for the experimental results showing that the CO concentration achieving complete HEE prevention increased with the elevation of the gas pressure.

DOI： 10.1007/s11661-021-06491-3

Web of Science

Scopus

出版者・発行元：Proceedings of the International Offshore and Polar Engineering Conference  

The mitigation effect of carbon monoxide (CO) on hydrogen embrittlement (HE) was studied in terms of the loading rate dependence by fracture toughness tests, fatigue crack growth tests, and density functional theory (DFT) simulations. The experimental results demonstrated that the mitigation effect is reduced with a decreasing loading rate in the lower crack growth rate region. The DFT simulations revealed that this is caused by the incomplete coverage of the iron surface by CO. Oppositely, the mitigation effect increased with the decreasing loading rate in the higher crack growth rate region due to a lack of CO adsorption on the iron surface.

Scopus

出版者・発行元：Bulletin of the Chemical Society of Japan  

Current greenhouse gas emissions suggest that keeping global temperature increase below 1.5 degrees, as espoused in the Paris Agreements will be challenging, and to do so, the achievement of carbon neutrality is of utmost importance. It is also clear that no single solution can meet the carbon neutral challenge, so it is essential for scientific research to cover a broad range of technologies and initiatives which will enable the realization of a carbon free energy system. This study details the broad, yet targeted research themes being pioneered within the International Institute for Carbon-Neutral Energy Research (I2CNER). These approaches include hydrogen materials, bio-mimetic catalysts, electrochemistry, thermal energy and absorption, carbon capture, storage and management and refrigerants. Here we outline the state of the art for this suite of technologies and detail how their deployment, alongside prudent energy policy implementation can engender a carbon neutral Japan by 2050. Recognizing that just as no single technological solution will engender carbon neutrality, no single nation can expect to achieve this goal alone. This study represents a recognition of conducive international policy agendas and is representative of interdisciplinary, international collaboration.

DOI： 10.1246/bcsj.20210323

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）