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Metal-free carbon materials are attractive Pt-based catalyst alternatives. However, despite efforts, the reaction mechanism remains elusive. Thus, we investigated the role of defects (dopant nitrogen and carbon vacancy) on the catalytic oxygen reduction reaction in a metal-free carbon material focusing on the effect of structural flexibility. Crucially, defects lower the energy barrier for the sp

Perovskite nanocrystals (NCs) are promising emissive materials for application in light-emitting diodes (LEDs) due to their high quantum efficiency and narrow full width at half maximum (FWHM). However, the ion bonding character of perovskite leads to their quick chemical decomposition under atmospheric moisture. Herein, we present CsPbBr3 perovskite NCs that achieved improved efficiency and stability with the addition of water during the synthesis process. The CsPbBr3 NCs synthesized with a controlled amount of water exhibited a quantum yield greater than 90%, sustained stability over 35 days and a much narrower FWHM than CsPbBr3 NCs that did not use water. Finally, water-added perovskite NC LEDs were fabricated and they showed a nearly 5-times improvement in current efficiency compared to the reference device.

For efficient electrochemical catalysts, several molecular-scale descriptors have been proposed for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Various descriptors of p...

Hydrogen peroxide production by enhanced electrocatalysts is an attractive alternative to the present commercial process. While the subnano/atomic dispersion in noble metal nanocatalysts is known to strongly enhance their catalytic efficiency and chemoselectivity, their excessive surface energy and consequent coarsening seriously compromise their physical/chemical stability. Here, we report a subnano/atomically dispersed Pt–Ag alloy (by a simply modified polyol process) that is resistant to agglomeration/Ostwald ripening. This catalyst does not follow a conventional four-electron oxygen reduction reaction (ORR) but selectively produces H2O2 without excessive degradation of its activity. We clarified the role of the alloying element, Ag, as follows: (1) selective activation of two-electron ORR by inhibiting O2 dissociation and (2) suppression of H2O2 decomposition by preventing the H2O2 adsorption. The present approach provides a convenient route for the direct generation of H2O2 as a simple byproduct of electricity generation by fuel-cell systems.

Maintaining the bandgap The bandgap of the black α-phase of formamidinium-based lead triiodide (FAPbI 3 ) is near optimal for creating high-efficiency perovskite solar cells. However, this phase is unstable, and the additives normally used to stabilize this phase at ambient temperature—such as methylammonium, caesium, and bromine—widen its bandgap. Min et al. show that doping of the α-FAPbI 3 phase with methylenediammonium dichloride enabled power conversion efficiencies of 23.7%, which were maintained after 600 hours of operation. Unencapsulated devices had high thermal stability and retained >90% efficiency even after annealing for 20 hours at 150°C in air. Science , this issue p. 749

A fast-charging battery that supplies maximum energy is a key element for vehicle electrification. High-capacity silicon anodes offer a viable alternative to carbonaceous materials, but they are vulnerable to fracture due to large volumetric changes during charge–discharge cycles. The low ionic and electronic transport across the silicon particles limits the charging rate of batteries. Here, as a three-in-one solution for the above issues, we show that small amounts of sulfur doping (, Silicon-based anodes are attractive for lithium ion batteries, but improvements in conductivity, ionic diffusion and structural stability would extend applications. Here the authors show that low sulfur-doping in a silicon anode leads to highly stable and fast battery cycling with a high energy density.

Tetracyclines (TCs) are the most widely used antibiotics for the prevention and treatment of livestock diseases, but they are toxic to humans and have frequently been detected in water bodies. In this study, the physical and chemical properties of the zirconium-based metal organic framework (MOF) UiO-66 and its NH2-functionalized congener UiO-66-NH2 were investigated along with batch TC adsorption tests to determine the effect of functionalization on TC removal. TC removal was highest at pH 3 and decreased with increasing pH. Pseudo-1st and pseudo-2nd-order kinetic models were used to study the adsorption equilibrium times, and Langmuir isotherm model was found to be more suitable than Freundlich model. The maximum uptake for UiO-66 and UIO-66-NH2 was measured to be 93.6 and 76.5 mg/g, respectively. Unexpectedly, the TC adsorption capacity of UiO-66-NH2 was observed to be lower than that of UiO-66. Density functional theory calculations revealed that the pore structures are irrelevant to TC adsorption, and that the –NH2 functional group could weaken the structural robustness of UiO-66-NH2, causing a reduction in TC adsorption capacity. Accordingly, robust MOFs with zirconium-based metal clusters can be effectively applied for the treatment of antibiotics such as TC in water.

A novel hierarchical corolla-like MnO2-decorated porous magnetic biochar composite (c-PMB/MnO2) was synthesized and used for the removal of As(V) and Cr(VI) from aqueous solutions. The experimental results indicated that the adsorption affinity order of c-PMB/MnO2 in the single-component system was As(V) (0.414 mmol/g) > Cr(VI) (0.185 mmol/g), which were more pronounced in sequential adsorption systems. XPS results revealed that all components of c-PMB/MnO2 (i.e., Fe3O4, MnO2, and biochar) contributed to As(V) and Cr(VI) adsorption, while the selective reduction of adsorbed Cr(VI) to Cr(III) occurred via the redox reaction between Fe3O4 and Cr(VI). Density functional theory calculations further indicated that As(V) and Cr(VI) compete for the available binding sites in binary-component system, although the presence of reduced Cr(III) as a majority species serves as a strong binding site for As(V) via the formation of covalent bonding between Cr(III) and the O atom in As(V) with binding energies of −123.1 and −125.6 kcal/mol, thereby enhancing competitive As(V) adsorption in binary-component and sequential adsorption systems. These results may provide important information to better understand the competitive adsorption mechanisms for the simultaneous removal of As(V) and Cr(VI) in water.

To realize the full performance of Zn-air batteries, the co-presence of a highly efficient oxygen reduction reaction (ORR) and an oxygen evolution reaction (OER) in the system is critical. Although copper and nickel are known to be bifunctional catalysts for ORR and OER, sluggish reactions as a result of the exceptionally strong O=O bond on the metal surface make it difficult to achieve high system efficiency. In this study, a metal carbide layer (CuCx and NiCx ) on dendritic copper and nickel is fabricated by a facile electrodeposition process to provide efficient catalytic active sites with moderate binding energy for easy electron transfer in both the OER and the ORR. The dendritic structure provides an enriched catalytic surface and the protective metal carbide layer offers an appropriate O binding energy and durability of Zn-air batteries. Owing to the presence of the stable metal carbide surface on the dendritic metal, the CuCx /Cu and NiCx /Ni catalysts exhibited well-defined limiting current densities of -5.19 and -5.11 mA cm-2 , respectively, and improved ORR and OER activities with lower polarization than the corresponding metal catalysts. Density functional theory revealed a 0.74 eV decrease in the overpotential of NiCx /Ni-catalyzed OER reactions compared with Ni-catalyzed OER reactions. The experimental and theoretical results prove that carbide layers on dendritic metal surfaces can greatly improve the activity of ORR and OER bifunctional electrocatalysts for Zn-air batteries.

Chromate is considered a toxic contaminant in various water sources because it poses a risk to animal and human health. To meet the stringent limits for chromium in water and wastewater, pyrrolic nitrogen structure was investigated as a chromate adsorbent for aqueous solutions, employing a polypyrrole coating on carbon black. The characteristics of the adsorbent were analyzed by high-resolution transmission electron microscopy, energy-filtered transmission electron microscopy, and X-ray photoelectron spectroscopy. Chromate was adsorbed as both Cr(III) and Cr(VI). The chromate adsorption capacity increased (from 50.84 to 174.81 mg/g) with increasing amounts of pyrrole monomers (from 50 to 86%) in the adsorbent. The adsorption capacity was well-correlated with the pyrrolic nitrogen content (from 2.06 to 6.57 at%) in the adsorbent, rather than other types of nitrogen. The optimized adsorption capacity (174.81 mg/g in the equilibrium batch experiment and 211.10 mg/g at an initial pH of 3) was far superior to those of conventional adsorbents. We investigated the mechanism behind this powerful chromate adsorption on pyrrolic nitrogen via physical/chemical analyses of the pH-dependent adsorption behavior, supported by first-principles calculation based on density functional theory. We found that Cr(III) and Cr(VI) adsorption followed different reaction paths. Cr(III) adsorption occurred in two sequential steps: 1) A Jones oxidation reaction (JOR)-like reaction of Cr(VI) with pyrrolic N that generates Cr(III), and 2) Cr(III) adsorption on the deprotonated pyrrolic N through Cr(III)–N covalent bonding. Cr(VI) adsorption followed an alternative path: hydrogen-bonding to the deprotonation-free pyrrolic N sites. The pH-dependent fractional deprotonation of the pyrrolic N sites by the JOR-like reaction in the presence of chromate played an important role in the adsorption.

Highly efficient water-oxidation catalysts (WOCs) were readily prepared through the simple heat treatment of cobalt-containing polyoxometalate [Co4(H2O)2(PW9O34)2]10− (POM). The annealing of soluble POM molecules at high temperatures in air led to the formation of insoluble nanoparticles, of which the crystal structure and catalytic activity can be controlled by the annealing temperature. POMs were converted to amorphous and crystalline CoWO4 nanoparticles when annealed at 400 and 500 °C, respectively. Interestingly, amorphous CoWO4 nanoparticles exhibited excellent catalytic activity near the neutral pH of pH 8.0, making them superior to both pristine POM and POM-derived crystalline CoWO4 nanoparticles. X-ray absorption and photoelectron spectroscopies combined with density functional theory (DFT) calculations revealed that their outstanding performance was resulted from the generation of large amounts of oxygen vacancies upon annealing, leading to the optimum distance between the nearest Co ions for the Langmuir-Hinshelwood (LH) mechanism. Based on these findings, we could readily immobilize CoWO4-based WOCs on the surfaces of various electrodes for efficient electrochemical and photoelectrochemical water oxidation through the annealing of POMs pre-adsorbed onto the desired electrode surface. This study may provide insights not only for the synthesis of efficient electrocatalysts derived from POMs but also for their immobilization onto the desired electrode surface for practical applications.

Mechanically sinterable sulfide Na+ superionic conductors are key to enabling room-temperature-operable all-solid-state Na-ion batteries (ASNBs) for large-scale energy storage applications. To date, few candidates can fulfill the requirement of a high ionic conductivity of ≥1 mS cm–1 using abundant, cost-effective, and nontoxic elements. Herein, the development of a new Na+ superionic conductor, Ca-doped cubic Na3PS4, showing a maximum conductivity of ∼1 mS cm–1 at 25 °C is described. Complementary analyses using conductivity measurement by the AC impedance method, 23Na nuclear magnetic resonance spectroscopy, and density functional theory calculations reveal that the aliovalent substitution of Na+ in Na3PS4 with Ca2+ renders a cubic phase with Na vacancies, which increases the activation barriers but drastically enhances Na-ion diffusion. It is demonstrated that TiS2/Na–Sn ASNBs employing Ca-doped Na3PS4 exhibit a high charge capacity of 200 mA h g–1 at 0.06C, good cycling performance, and higher rate ca...

Owing to its mass-production capability and simple process, liquid-phase exfoliation (LPE) of layered bulk materials is commonly used for synthesizing two-dimensional materials, such as graphene or transition metal dichalcogenides (TMDs). Surfactants are often used in LPE process to improve the exfoliation efficiency and dispersion stability of target materials. However, during the surfactant-mediated exfoliation process, the as-applied surfactant typically forms strong covalent/noncovalent bonds with target materials, thereby deteriorating the properties of starting materials. Rinsing the surfactants can also be problematic because the decreased dispersion of the exfoliated flakes leads to restacking. Therefore, the contradictory phenomenon between maintaining the dispersion stability and preserving the material property has been a demanding issue in the LPE process of two-dimensional materials. Herein, a surfactant-assisted LPE of molybdenum disulfide (MoS2) using Nafion as the surfactant in environment...

Tetraethylenepentamine (TEPA), consisting mainly of primary and secondary amines, exhibits a high CO2 sorption capacity; however, its poor thermal stability hampers practical utilization in the temperature swing adsorption process for CO2 capture. Here, a facile functionalization of TEPA with 1,2-epoxybutane (EB) substantially enhanced its thermal stability as well as the CO2 adsorption kinetics. Our careful analysis on the liquid-state 13C NMR disclosed the amine state distribution of EB-functionalized TEPA (EB-TEPA). Although the increase in tertiary amine portion induced by EB-functionalization reduced CO2 sorption capacity, the 0.64EB-TEPA (i.e., TEPA functionalized with EB with a TEPA/EB molar ratio of 1:3)/SiO2 showed an excellent long-term stability over the 10 consecutive cycles of adsorption/desorption processes with a CO2 swing capacity of 2.0 mmol CO2 g–1 under dry CO2/N2 (15/85 mol/mol) feed conditions. Also, the first-principles calculation identified the configuration of modified TEPA molecu...

We investigate the application of the onion-like carbon (OLC) as an electrocatalyst for [VO]2+/[VO2]+ redox flow reaction; its performance (electrocatalytic activity and reversibility) strongly increases with the synthesis to peak at 1800 °C in 1000–2000 °C range. The dopant/modification-free, optimized redox performances of the OLC is comparable to some of the best data in the literature of various types of carbon materials with post-synthesis modifications or doping. Mechanism behind such performance optimization is investigated employing various physical/electrochemical analyses as well as the first-principles calculations. We demonstrate that the carbon dangling bonds or the crystalline defects, generated by an inherent mechanism unique to the OLC, played a pivotal role in determining the electrocatalytic performances.

The facile tuning of the gate size and the chemical functionalization of zeolitic imidazolate frameworks (ZIFs) have been considered efficient strategies for various potential applications including gas membranes, sensors, and catalysts. Herein, we demonstrate the synthesis of amine-functionalized ZIF-8 (ZIF8-A) with 3-amino-1,2,4-triazole (Atz) by postsynthetic modification (PSM) towards two objectives: (1) CO2 selective adsorption by a combination of chemical interactions and controlled gate sizes and (2) potential for further chemical modifications. The acquired ZIF8-A substantially enhanced CO2/N2 and CO2/CH4 selectivity at 35 °C compared to ZIF-8 since the Atz conversion enhanced chemical interactions with CO2 due to the introduction of amine moieties while reducing both the surface area and pore volume. The gate size control of ZIF-8 by the replacement of Atz was thoroughly investigated by extensive transport experiments and density functional theory (DFT)-based computational simulations. In addition, the vinyl-functionalized ZIF-8, another versatile starting material, was successfully prepared by further chemical modifications of ZIF8-A with either methacrylic anhydride or glycidyl methacrylate through nucleophilic substitution reactions. As such, we believe that our current work can provide promising platforms for designing ZIF-based materials with versatile properties including precise control of the gate size and the incorporation of various functional groups.

Hollow particles of N,B co-doped carbon were synthesized at different temperatures and used as electrocatalysts for the oxygen reduction reaction (ORR). The particles were synthesized by chlorinating Ti(C 0.3 N 0.7 ) and TiB 2 powders, with the sample formed at 800 °C showing the highest ORR activity, which was comparable to a commercial Pt/C catalyst. The catalyst electron transfer number of 3.94 was close to 4, indicating high selectivity for the ORR. The excellent ORR performance arose from the particle structure that facilitated mass transport, including the hollow shape with well-developed micro and macro pores, and various active nitrogen functional groups on the surface. Boron also played an important role along with the nitrogen, improving the activity for the ORR through a synergistic effect. These properties make these materials promising for the ORR and other electrochemical applications.

Adsorption is a simple and effective method for the removal of hexavalent chromium (Cr(VI)) from contaminated water. Several amino silane–graphene oxide (GO) composites with different species of amino groups (pN-GO, psN-GO, and pssN-GO; p: primary, s: secondary, N: amine) were evaluated to investigate their adsorption capacity and the effects of primary and secondary amines on Cr(VI) adsorption. We conducted a quantitative analysis to reveal the difference between primary and secondary amines in terms of Cr(VI) removal efficiency. A synergic effect was observed between the neighboring secondary amines in pssN-GO. From the Langmuir model prediction, we found that the composite with pssN-GO exhibited the highest maximum adsorption capacity (260.74 mg/g), followed by those with psN-GO (208.22 mg/g) and pN-GO (189.47 mg/g). Monolayer adsorption was more dominant when using pssN-GO, with the pseudo-second-order model best fitting the kinetic experiment results, whereas multilayer adsorption was dominant when using psN-GO and pN-GO.

Because of the surface depolarization field, there is a critical thickness for ferroelectricity in ultrathin ferroelectric films, hindering miniaturization of high-density nonvolatile memory storage devices. A controllable Rashba effect by external electric field via switchable dipole moment could be a promising way to control and manipulate the spin degrees of freedom in spintronics. Here, based on first principles calculations, we show that non-planar Ag

We are proposed that a possible mechanism for Cr(VI) removal by functionalized mesoporous silica. Mesoporous silica was functionalized with (3-aminopropyl)trimethoxysilane (APTMS) using the post-synthesis grafting method. The synthesized materials were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), N2 adsorption-desorption analysis, Fourier-transform infrared (FT-IR), thermogravimetric analyses (TGA), and X-ray photoelectron spectroscopy (XPS) to confirm the pore structure and functionalization of amine groups, and were subsequently used as adsorbents for the removal of Cr(VI) from aqueous solution. As the concentration of APTMS increases from 0.01 M to 0.25 M, the surface area of mesoporous silica decreases from 857.9 m2/g to 402.6 m2/g. In contrast, Cr(VI) uptake increases from 36.95 mg/g to 83.50 mg/g. This indicates that the enhanced Cr(VI) removal was primarily due to the activity of functional groups. It is thought that the optimum concentration of APTMS for functionalization is approximately 0.05 M. According to XPS data, NH3+ and protonated NH2 from APTMS adsorbed anionic Cr(VI) by electrostatic interaction and changed the solution pH. Equilibrium data are well fitted by Temkin and Sips isotherms. This research shows promising results for the application of amino functionalized mesoporous silica as an adsorbent to removal Cr(VI) from aqueous solution.

Arsenic in water and wastewater is considered to be a critical contaminant as it poses harmful health risks. In this regard, to meet the stringent regulation of arsenic in aqueous solutions, nitrogen doped carbon-based materials (CN) were prepared as adsorbents and tested for the removal of arsenic ion from aqueous solutions. Nitrogen-doped carbon (CNs) synthesized by chlorination exhibited well-developed micro- and small meso-pores with uniform pore structures. The structure and characteristics of the adsorbents thus developed were confirmed by field-emission scanning electron microscopy, transmission electron microscopy, Brunauer-Emmett-Teller analysis, X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. Among the CNs developed, CN700 exhibited high adsorption capacity for arsenic (31.08 mg/g). The adsorption efficiency for arsenic ion was confirmed to be affected by pyrrolic nitrogen and micro-pores. These results suggest that CNs are useful adsorbents for the treatment of arsenic, and in particular, CN700 demonstrates potential for application as an adsorbent for the removal of anionic heavy metals from wastewater and sewage.

It is essential and important to determine the adsorption mechanism as well as removal efficiency when using an adsorption technique to remove toxic heavy metals from wastewater. In this research, the removal efficiency and mechanism of chromium removal by a silica-based nanoparticle were investigated. A PEI-silica nanoparticle was synthesized by a one-pot technique and exhibited uniformly well-dispersed PEI polymers in silica particles. The adsorption capacity of chromium ions was determined by a batch adsorption test, with the PEI-silica nanoparticle having a value of 183.7 mg/g and monolayer sorption. Adsorption of chromium ions was affected by the solution pH and altered the nanoparticle surface chemically. First principles calculations of the adsorption energies for the relevant adsorption configurations and XPS peaks of Cr and N showed that Cr(VI), [HCrO4]− is reduced to two species, Cr(III), CrOH2+ and Cr3+, by an amine group and that Cr(III) and Cr(VI) ions are adsorbed on different functional groups, oxidized N and NH3+.

Hematite is a promising semiconductor for photoelectrochemical water splitting owing to its ideal band gap, nontoxicity, abundance, and chemical stability. However, the conversion efficiency remains less than its theoretical limit, which is in part due to a low carrier density. Although efforts have been made to increase the carrier density by incorporating appropriate donor dopants, structural instability caused by high donor doping has restricted the enhancement achieved and the resulting photocatalytic performance. Herein, we used density functional theory calculations to show that an enhanced carrier density and photocatalytic performance can be achieved without causing structural instability by using a donor–donor codoping strategy to introduce a 3d transition metal (Ti/V) and Si into hematite. Despite the Coulombic repulsion among the electrons from donors, the Coulombic attraction between donors with an oxidation number of +4 (Ti4+/V4+) and negatively charged small polarons contribute to a strong binding energy. The compensatory binding energy stabilizes the crystal structure and thus increases the density of carriers, most of which are small polarons. We also suggest that the carrier density can be further enhanced by increasing the ratio of Si interstitial doping, which produces four times more polarons than Si substitutional doping under experimental conditions of high temperature and low oxygen partial pressure. Our findings pave a way for an environment-friendly and efficient photocatalysis toward improvement of hydrogen fuel generation.

Direct or indirect emissions of phosphate from point or non-point sources into aquatic ecosystem may pose serious adverse risks to human life and environmental sustainability. Owing to their environmental and economic benefits, biochar-based adsorption processes have recently emerged as an ideal approach. However, the surface of biochar is normally negatively charged, thus limiting its binding affinity toward anionic contaminants. Herein, in order to address this weakness and further improve adsorption performance, we developed rice husk (RH)-derived biochar functionalized with Mg/Al-calcined layered double hydroxides (RHB/MgAl-CLDHs) via the co-pyrolysis of MgAl-LDH preloaded RH, and we examined its phosphate adsorption properties in aqueous environments. Multiple analyses and phosphate adsorption experiments revealed that the Mg:Al molar ratio (2:1–5:1) and co-pyrolysis temperature (300–700 °C) control the physicochemical properties of synthesized samples and their phosphate adsorption affinities. The molar ratio affects the charge density, whereas the co-pyrolysis temperature determines the surface functionality and porosity. Specifically, RHB/MgAl-CLDHs(2:1/500) (molar ratio = 2:1, co-pyrolysis temperature = 500 °C) exhibited the highest phosphate removal of 97.6% due to the conversion of RH into biochar, decomposition of interlayer water/nitrate, transformation of LDH structures to mixed metal oxides (layered double oxides), and improved porosity, favoring stronger adsorption and intercalation of phosphate. Spectroscopic solid-phase analyses demonstrated that the adsorption mechanism involves the “memory effect” and the formation of both outer- and inner-sphere surface complexes via attractive electrostatic interactions and monodentate/bidentate complexations. In conclusion, considering its high selectivity and excellent recyclability, RHB/MgAl-CLDHs(2:1/500) is a promising material for mitigating eutrophication.

Transition metal dichalcogenides (TMDs) have shown promising potential as electrocatalyst materials for the hydrogen evolution reaction (HER). However, the low catalytic activity in the basal planes of TMDs results in only limited HER activity, and several strategies to overcome this bottleneck have been proposed, involving various post-synthesis treatments such as introducing chalcogen vacancies or applying mechanical strain. Herein, we demonstrate in-situ modulation of chalcogen vacancy sites during the chemical vapor deposition synthesis of molybdenum diselenides (MoSe2) for application in the HER. We demonstrate for the first time that the Tafel reaction can be activated via in-situ vacancy-engineered MoSe2, resulting in improved onset potential and an exceptionally low Tafel slope, which exhibits one of the lowest values reported for TMDs to date in our knowledge. Density functional theory calculations revealed that vacancy coalescence in the MoSe2 lattice reduced the hydrogen adsorption free energy and diffusion barrier to activate the Tafel reaction. Our approach could contribute to the development of high-performance TMDs-based electrocatalysts with relatively simple processability to make hydrogen production more viable.

As the development of noble metal free catalysts became important in the biomass conversion, catalytic hydrogenation of furfural (FAL) is investigated over ordered mesoporous cobalt oxide (m-Co3O4). When m-Co3O4 is reduced at 350 and 500 °C in hydrogen, the original crystal structure of Co3O4 is changed to CoO and Co, respectively. Here we examine the effect of the structure, porosity, and oxidation state of m-Co3O4 to identify catalytically active species for hydrogenation of FAL. Among cobalt oxide catalysts having different crystal structures and symmetry, m-CoO having p6mm symmetry exhibits the highest activity. In product selectivity, the CoO phase induces FAL hydrogenolysis by selective production of 2-methyl furan (MF), while the Co3O4 and Co phases promote preferential hydrogenation of side chain (carbonyl group) of FAL to furfuryl alcohol. Density functional theory calculations also reveal that the adsorption of FAL on CoO(111) is higher than Co(111). Overall, these studies demonstrate that CoO as the most active phase is responsible for the high FAL conversion and the distinct pathway of FAL to MF.

This article briefly summarizes the research activities in the field of hydrogen storage in sorbent materials and reports our recent works and future directions for the design of such materials. Distinct features of sorption-based hydrogen storage methods are described compared with metal hydrides and complex chemical hydrides. We classify the studies of hydrogen sorbent materials in terms of two key technical issues: ( i ) constructing stable framework structures with high porosity, and ( ii ) increasing the binding affinity of hydrogen molecules to surfaces beyond the usual van der Waals interaction. The recent development of reticular chemistry is summarized as a means for addressing the first issue. Theoretical studies focus mainly on the second issue and can be grouped into three classes according to the underlying interaction mechanism: electrostatic interactions based on alkaline cations, Kubas interactions with open transition metals, and orbital interactions involving Ca and other nontransitional metals. Hierarchical computational methods to enable the theoretical predictions are explained, from ab initio studies to molecular dynamics simulations using force field parameters. We also discuss the actual delivery amount of stored hydrogen, which depends on the charging and discharging conditions. The usefulness and practical significance of the hydrogen spillover mechanism in increasing the storage capacity are presented as well.

We present a theoretical model capable of identifying multiple adsorption sites in a gas storage material with different binding energies and different amounts of adsorbed molecules. By applying this model to experimental data on the hydrogen storage in MOFs, we extract hydrogen adsorption properties of MOFs with coexisting strong and weak adsorption sites.

Fabricating perovskite oxide/carbon material composite catalysts is a widely accepted strategy to enhance oxygen reduction reaction/oxygen evolution reaction (ORR and OER) catalytic activities. Herein, synthesized, porous, perovskite-type Sm0.5 Sr0.5 CoO3-δ hollow nanofibers (SSC-HF) are hybridized with cross-linked, 3D, N-doped graphene (3DNG). This rationally designed hybrid catalyst, SSC-HF-3DNG (SSC-HG), exhibits a remarkable enhancement in ORR/OER activity in alkaline media. The synergistic effects between SSC and 3DNG during their ORR and OER processes are firstly revealed by density functional theory calculations. It suggests that electron transport from 3DNG to O2 and SSC increases the activity of electrocatalytic reactions (ORR and OER) by activating O2 , increasing the covalent bonding of lattice oxygen. This electron transfer-accelerated catalysis behavior in SSC-HG will provide design guidelines for composites of perovskite and carbon with bifunctional catalysts.

Because of the surface depolarization field, there is a critical thickness for ferroelectricity in ultrathin ferroelectric films, hindering miniaturization of high-density nonvolatile memory storage devices. A controllable Rashba effect by external electric field via switchable dipole moment could be a promising way to control and manipulate the spin degrees of freedom in spintronics. Here, based on first principles calculations, we show that non-planar Ag2Te monolayer, which has been recently predicted to be a topological insulator, possess a switchable out-of-plane electric dipole moment. The switching of the dipole can be realized by the penetration of Te atoms through the hexagonal Ag-plane. Additionally, non-planar Ag2Te shows a giant Rashba spin-splitting ([Formula: see text] eV A) due to the out-of-plane electric dipole moment. Our tight binding model indicates that the origin of such large [Formula: see text] is the large inversion symmetry breaking term ([Formula: see text] eV), which is one order of magnitude larger in non-planar Ag2Te monolayer compared with other Rashba materials. Interestingly, the Rashba effect can be turned on/off by the phase transition from non-planar to planar structure via Te displacement. Moreover, the spin-texture can be completely reversed because of switchable electric dipole moment. Our work shows a new way to realize ferroelectric-like dipole moment switching and consequently switchable Rashba spin-splitting, which may facilitate a nonvolatile electrical control of the spin degrees of freedom, down to the monolayer thickness, promising potential applications to electrically controlled spintronic devices.

We developed a two-step doping strategy for chemical modification of covalent organic frameworks (COFs) as hydrogen storage materials. The first step was the boron (B) doping of organic building units, suppressing the clustering of subsequent metal dopants on frameworks. The second step was the doping of metal atoms, forming trapping centers for H2 molecules on B-doped COFs. Using ab initio calculations, we explored the doping processes and studied the dependence of the structural stability and electronic properties of doped building units on the B concentration. In organic building units of COF-1, two-B para substitution was energetically more favorable than other B substitutions. The clustering of Sc, Ti, and Ca was suppressed on such B-doped COF-1. Sc and Ti preferred the double-sided adsorption, while Ca only favored the single-sided adsorption, due to their different interactions with the substrates. Each Sc and Ti atom bound four H2 molecules through the Kubas interaction, while each Ca atom could a...

Highly sensitive and selective chemiresistive sensors based on graphene functionalized by metals and metal oxides have attracted considerable attention in the fields of environmental monitoring and medical assessment because of their ultrasensitive gas detecting performance and cost-effective fabrication. However, their operation, in terms of detection limit and reliability, is limited in traditional applications because of ambient humidity. Here, the enhanced sensitivity and selectivity of single-stranded DNA-functionalized graphene (ssDNA-FG) sensors to NH3 and H2S vapors at high humidity are demonstrated and their sensing mechanism is suggested. It is found that depositing a layer of ssDNA molecules leads to effective modulation of carrier density in graphene, as a negative-potential gating agent and the formation of an additional ion conduction path for proton hopping in the layer of hydronium ions (H3O+) at high humidity (>80%). Considering that selectively responsive chemical vapors are biomarkers associated with human diseases, the obtained results strongly suggest that ssDNA-FG sensors can be the key to developing a high-performance exhaled breath analyzer for diagnosing halitosis and kidney disorder.

Silicene is a two-dimensional honeycomb lattice made of silicon atoms, which is considered to be a new Dirac fermion system. Based on first-principles calculations, we examine the possibility of the formation of solitonlike topological domain walls (DWs) in silicene. We show that the DWs between regions of distinct ground states of the buckled geometry should bind electrons when a uniform electric field is applied in the perpendicular direction to the sheet. The topological origin of the electron confinement is demonstrated based on numerical calculations of the valley-specific Hall conductivities, and possible experimental signatures of the quantum valley Hall effects are discussed using simulated scanning tunneling microscopy images. Our results strongly suggest that silicene could be an ideal host for the quantum valley Hall effect, thus providing a pathway to the valleytronics in silicon-based technology.

We present results of $Re (A_0)$ and $Re (A_2)$ calculated using HYP staggered fermions on the lattice of $16^3 \times 64$ at $\beta=6.0$. These results are obtained using leading order chiral perturbation in quenched QCD. Buras's original RG evolution matrix develops a removable singularity for $N_f=3$. This subtlety is resolved by finding a finite solution to RG equation and the results are presented.

Initial stage of oxynitridation process of Si substrate is of crucial importance in fabricating the ultrathin gate dielectric layer of high quality in advanced MOSFET devices. The oxynitridation reaction on a relaxed Si(001) surface is investigated via reactive molecular dynamics (MD) simulation. A total of 1120 events of a single nitric oxide (NO) molecule reaction at temperatures ranging from 300 to 1000 K are statistically analyzed. The observed reaction kinetics are consistent with the previous experimental or calculation results, which show the viability of the reactive MD technique to study the NO dissociation reaction on Si. We suggest the reaction pathway for NO dissociation that is characterized by the inter-dimer bridge of a NO molecule as the intermediate state prior to NO dissociation. Although the energy of the inter-dimer bridge is higher than that of the intra-dimer one, our suggestion is supported by the ab initio nudged elastic band calculations showing that the energy barrier for the int...

Low-temperature specific heat, $C$, in magnetic fields up to ${H}_{c}$${}_{2}$ is reported for underdoped Ba(Fe${}_{0.955}$Co${}_{0.045}$)${}_{2}$As${}_{2}$ (${T}_{c}$ = 8 K) and for three overdoped samples Ba(Fe${}_{1\ensuremath{-}x}$Co${}_{x}$)${}_{2}$As${}_{2}$ ($x$ = 0.103, 0.13, and 0.15; ${T}_{c}$ = 17.2, 16.5, and 11.7 K, respectively). Previous measurements of thermal conductivity (as a function of temperature and field) and penetration depth on comparable-composition samples gave some disagreement as to whether there was fully gapped/nodal behavior in the under-/overdoped materials, respectively. The present work shows that the measured behavior of the specific heat \ensuremath{\gamma} (\ensuremath{\propto}$C/T$ as $T$ \ensuremath{\rightarrow} 0, i.e., a measure of the electronic density of states at the Fermi energy) as a function of field approximately obeys \ensuremath{\gamma} \ensuremath{\propto} ${H}^{0.5\ifmmode\pm\else\textpm\fi{}0.1}$, similar to the Volovik effect for nodal superconductors, for both the underdoped and the most overdoped Co samples. However, for the two overdoped compositions $x$ = 0.103 and 0.13, the low-field ($H$ \ensuremath{\le} 10 T) data show a Volovik-like behavior of \ensuremath{\gamma} \ensuremath{\propto} ${H}^{0.3\ensuremath{-}0.4}$, followed by an inflection point, followed at higher fields by \ensuremath{\gamma} \ensuremath{\propto} ${H}^{1}$. We argue that, within the two-band theory of superconductivity, an inflection point may occur if the interband coupling is dominant.

Using density functional theory electronic structure calculations, we investigate the calcium-hydroxyl group complex for potential applications to the hydrogen storage at near ambient temperature and pressure. The Ca atom is bound to the hydroxyl group with a binding energy comparable to the cohesive energy of bulk Ca, and we find that each Ca atom binds up to seven ${\text{H}}_{2}$ molecules in the molecular form. Binding of an unexpectedly large number of ${\text{H}}_{2}$ molecules is attributed to the fact that $d$ orbitals of Ca positive ions are downshifted and partially occupied, thereby validating the empirical 18-electron rule as in the transition metal atoms. The binding energy turns out to be $\ensuremath{\sim}0.1\text{ }\text{eV}/{\text{H}}_{2}$, somewhat smaller than the requirement $(\ensuremath{\ge}0.2\text{ }\text{eV}/{\text{H}}_{2})$ of the room-temperature application. We also show that an important bonding mechanism of ${\text{H}}_{2}$ molecules on Ca is the polarization, namely, the electric dipole moment of ${\text{H}}_{2}$ induced by the partially ionized Ca. Based on this result, the possibility of the organic material functionalized with hydroxyl groups for a hydrogen storage medium is discussed.

We present results of the one-loop corrections originating from the penguin diagrams for the improved staggered fermion operators constructed using various fat links such as Fat7, Fat7+Lepage, $\bar{\rm Fat7}$, HYP (I) and HYP (II). The main results include the diagonal/off-diagonal mixing coefficients and the matching formula between the continuum and lattice operators., Comment: 4 figures, Contribution to Lattice 2003

We investigate the hydrogen storage capacity of the light transition metal (TM)-decorated metal organic frameworks (MOFs) by performing ab initio density functional theory calculations. We find that among all the light TM elements, divalent Ti and Fe are suitable for decorating MOFs to enhance the hydrogen uptake, considering the H2 binding energy on the TM atom and the reversibly usable number of H2 molecules attached to the metal site. In general, the magnetization of metal atoms undergoes a high-spin to low-spin state transition when H2 molecules are adsorbed, which helps to stabilize the system energetically. By analyzing the projected density of states on each TM atom, it is shown that the d-level shift induced by the ligand field of the adsorbed H2 molecules contributes substantially to the H2 binding strength. We also study the stability of selected TM-decorated nanostructures against the attack of foreign molecules by examining the energetics of those contaminating molecules around the metal sites.