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Active B5-sites on Ru catalysts can be exploited for various catalytic applications; the epitaxial formation of Ru NPs with hexagonal planar morphologies on hexagonal boron nitride sheets increases the number of active B5-sites along the nanoparticle edges.

Ruthenium is one of the most active catalysts for ammonia dehydrogenation and is essential for the use of ammonia as a hydrogen storage material. The B

The dehydrogenation mechanisms of ethylene diamine monoborane (EDMB) adducts and its derivatives having CH3, Cl, F, NH2, OCH3, CN, and H substituents at two sites on the ethylene backbone were investigated to explore their potential as liquid organic hydrogen carriers (LOHCs). Using density functional theory calculations, the thermodynamic parameters of the EDMB adducts and dehydrogenation reactions to form cyclic monomers, dimers, and trimers were calculated. In particular, we focused on the free energy barriers of EDMB adducts substituted with Cl/CN, Cl/OCH3, F/CN, F/OCH3, F/F, and NH2/H for cyclic monomer formation, H/CH3, H/CN, Cl/H, and NH2/H for cyclic dimer formation, and H/Cl, H/F, and NH2/H for cyclic trimer formation, which are promising candidates for chemical hydrogen storage. We also explored the formation of cyclic trimers from the selected cyclic monomers with CH3/CH3, H/CH3, and NH2/H substituents. As a result, the dehydrogenation pathways and transition states of the various adducts for the formation for the various cycles were identified, and electrostatic potential surfaces and frontier molecular orbitals calculations were calculated to understand the reaction further. The results obtained indicate the potential of these materials for hydrogen storage, and we hope that this work will encourage the experimental investigation of these materials.

Bimetallic Pd1Nix alloys supported on nitrogen-doped carbon (Pd1Nix/N–C, x = 0.37, 1.3 and 3.6) exhibit higher activities than Pd/N–C towards dehydrogenation of formic acid (HCO2H, FA). Density functional theory (DFT) calculations provided electronic and atomic structures, energetics and reaction pathways on Pd(111) and Pd1Nix(111) surfaces of different Pd/Ni compositions. A density of states (DOS) analysis disclosed the electronic interactions between Pd and Ni revealing novel active sites for FA dehydrogenation. Theoretical analysis of FA dehydrogenation on Pd1Nix(111) (x = 0.33, 1 and 3) shows that the Pd1Ni1(111) surface provides optimum H2-release efficiency via a favorable ‘HCOO pathway’, in which a hydrogen atom and one of the two oxygen atoms of FA interact directly with surface Ni atoms producing adsorbed CO2 and H2. The enhanced efficiency is also attributed to the blocking of an unfavorable ‘COOH pathway’ through which a C–O bond is broken and side products of CO and H2O are generated.

Experimental and first-principles studies were conducted to understand the adsorption mechanism of elemental mercury on FeCl3- and CuCl2-impregnated activated carbons. Activated carbon was impregna...

Herein, we report the significant effects of natural organic matter contained in natural zeolite (Z-NOM) on the physicochemical characteristics of a Ni/Fe@natural zeolite (NF@NZ) catalyst and its decontamination performance toward the dechlorination of trichloroethylene (TCE). Z-NOM predominantly consists of humic-like substances and has demonstrable utility in the synthesis of bimetallic catalysts. Compared to NF@NZ

Hydrogen energy is a potential next-generation energy source for fossil fuel replacement. The development of high-efficiency materials and catalysts for storage and transportation of hydrogen energy must be achieved to realize hydrogen economy. Recently, catalyst systems such as Pd nanoclusters (Pd NCs) supported on nickel hydroxide (Ni(OH)2) have been reported to have advantages, including effective suppression of CO production and efficiency enhancement of HCOOH dehydrogenation. However, the reaction mechanism and multi-metallic interface system design of such systems have not been elucidated. Therefore, various Ni(OH)2 surfaces supported on a graphene system were designed through density functional theory calculations, and the support material was combined with Pd38NC (Pd38NC/Ni(OH)2-G). Subsequently, the adsorption behavior of HCOOH dehydrogenation intermediates was analyzed. We found a new adsorption configuration in which HCOOH* (where * and a single underline indicates the adsorbed species and adsorbed atom, respectively) was adsorbed in a more stable manner (adsorption energy, Eads= −1.22eV) on the system than HCOOH* (Eads=−1.10eV) owing to the presence of Ni(OH)2-G. This affected the next step in HCOOH dehydrogenation, i.e., formation of HCOO* species, and showed a positive effect on the HCOOH dehydrogenation. To fundamentally understand this phenomenon, electronic structure (d-band center and density of states) and stability (vacancy formation energy) analyses were performed.

The objective of this study was to report the preparation of a highly efficient hematite nanorod photoanode by H2 treatment of the β-FeOOH nanorod with subsequent quenching in air at lower temperature activation for photoelectrochemical (PEC) water oxidation. The hematite nanorod photoanode (H650) prepared by thermally treating the β-FeOOH nanorod at 360 °C for 1 h under H2 flow and quenching at 650 °C for 10 min in air exhibited a remarkable photocurrent of 1.17 mA cm−2 at 1.23 V vs. RHE, which was 20 times higher than that of hematite quenched at the same temperature without H2 treatment. Such enhanced PEC performance was attributed to high Sn4+ diffusion from the fluorine doped SnO2 (FTO) substrate via H2 treatment and Sn4+ doping by subsequent lower temperature quenching. Our density functional theory (DFT) calculation supports our experimental results and proposed mechanism in that the Sn replacement reaction of magnetite (Fe3O4, H2-reduced β-FeOOH) occurs at a lower temperature and requires a smaller energy than that of akaganeite (β-FeOOH).

This study aims to identify the influence of attitude of nurses in a general hospital toward disaster preparedness and their clinical competence on disaster preparedness competence. Data were collected from 140 nurses working at a general hospital in B City from October 18 to 25, 2017. The frequency, percentage, average, and standard deviation were calculated and the t-test, ANOVA, Scheffѐ test, Pearson's correlation and stepwise multiple regression analyses were conducted using the SPSSWIN 23.0 program. Clinical competence showed a low level of correlation with disaster preparedness competence (r=.33, p

Syngas, a gaseous mixture of CO and H

To dramatically improve the performance of non-precious catalyst-based anion exchange membrane fuel cells (AEMFCs), a conceptual change in the structure of conventional electrocatalysts is needed. Here we report a novel work function tailoring of graphene via adopting a graphene shell-encapsulated Co nanoarchitecture to efficiently activate the graphitic carbon shell as an exclusive and main active site for the oxygen reduction reaction (ORR). Theoretical calculations and electrochemical analysis suggest that the charge transfer from core Co nanoparticles to the outer graphene shell results in a significant change in the electronic structure of the graphene shell and reduces its work function. The present catalyst shows high ORR catalytic activity but exceptionally enhanced durability compared to a Pt catalyst in alkaline media, which is attributed mainly to the reduced work function of the outer graphene shell and the 3D nanographene structure providing a large number of active carbon sites. The single cell using the graphene shell-encapsulated Co nanoparticles as a cathode catalyst produces a high maximum power density of 412 mW cm−2, making this among the best non-precious catalysts for the ORR reported so far. Therefore, our results demonstrate a promising strategy to rationally design inexpensive and durable oxygen reduction catalysts, and this hybrid concept will provide a new perspective for catalyst structures which can practically be used in AEMFCs.

Reversible formate (HCOO–) dehydrogenation and bicarbonate (HCO3–) hydrogenation would be desirable for the utilization and storage of hydrogen (H2) as an effective energy carrier. Carbon-supported Pd-based nanoparticles demonstrated enormous competitive advantages for these reactions. However, the fundamental mechanisms underlying these reversible reactions have not yet been elucidated. Herein, we report the reaction pathways for reversible reactions on a Pd-based catalyst using density functional theory (DFT) calculations and propose key factors for improving the reaction efficiency. As the first essential step, the difficulty in the conventional DFT modeling, that is simulation of an anion environment caused by HCOO–, was overcome by designing two-sided Pd12 nanoclusters supported on graphene (Pd12NC-G) with extra electrons. Using Pd12NC-G, we demonstrated that the key factor determining the potential limiting steps for the reversible reaction was desorption of hydrogen in HCOO– dehydrogenation (1.24 e...

Sulfide minerals are important in immobilizing toxic contaminants in reducing environments. Iron sulfide (FeS) is ubiquitous in anoxic conditions and is a good scavenger of various organic and redox sensitive contaminants and heavy metals. Despite its contaminant removal capabilities, FeS has not been used as a practical adsorbent in contaminant removal due to its rapid oxidation under atmospheric conditions. To increase its applicability, we developed a method of modifying FeS by the addition of NaBH4 to form the less oxygen-sensitive NaBH4–FeS. We conducted oxidation tests using laboratory batch testing and real-time synchrotron X-ray absorption spectroscopy (XAS). The Fe K-edge XAS results showed that the oxidation rate of NaBH4–FeS was eight times slower than that of unmodified FeS while maintaining comparable contaminant removal capacities for Cr(VI) and As(III). The results of mechanistic density functional theory (DFT) calculations demonstrated that the oxidation of FeS occurred through electron transfer from sulfur of FeS to an oxidizing agent of oxygen, and that the hydride ion provided by NaBH4 retarded electron transfer from the FeS surface.

Zirconia supports were synthesized via a precipitation method, and the effects of crystalline structure and textural properties of ZrO2 on the methane combustion reaction were investigated using the Pd/ZrO2 catalysts. Upon increasing the digestion temperature, the crystalline structure of ZrO2 was transformed from the mixed phase (monoclinic and tetragonal) to the pure tetragonal phase, and these tetragonal ZrO2 supported Pd catalysts exhibited good hydrothermal stabilities. In addition, the BET surface areas of the tetragonal ZrO2 supports could also be tuned by varying the digestion time and calcination temperature, and the catalysts supported on ZrO2 having lower BET surface areas exhibited enhanced catalytic activities. Therefore, the Pd/ZrO2(85) catalyst, which had a tetragonal structure in addition to the smallest BET surface area, gave the optimal catalytic performance. This is likely due to larger PdO particles being formed on this ZrO2(85) support, thereby resulting in a highly reducible PdO species. Finally, variations in reducibility between the monoclinic and the tetragonal supported catalysts were clearly calculated by the density functional theory.

Highly dispersed Ptshell-Pdcore catalyst is synthesized via an electroless deposition and a galvanic displacement. From electrochemical analysis, the catalyst is confirmed to be active toward an ethanol oxidation reaction for a prolonged time, and is more resistive against COad-poisoning than a conventional Pt/C catalyst. The stable activity of Ptshell-Pdcore/C is ascribed to the modified electronic property of Pt over-layer, which leads to a weak CO-adsorption strength with a high affinity for OH. The weakened binding property of surface Pt with COad was experimentally confirmed by conducting a COad-stripping and by measuring an electrochemically active surface area of the catalyst over multiple cycles. The COad oxidation ability of as-synthesized catalyst is further proved by a computational method via density functional theory (DFT) calculation. The result presents a potential application of the catalyst for the efficient ethanol oxidation in a direct ethanol fuel cell.

In the attempt to reduce the high-cost and improve the overall durability of Pt-based electrocatalysts for the oxygen reduction reaction (ORR), density-functional theory (DFT) calculations have been performed to study the energetics of the elementary steps that occur during ORR on TiN(100)- and TiC(100)-supported single Pt atoms. The O2 and OOH* dissociation processes on Pt/TiN(100) are determined to be non-activated (i.e. “barrier-less” dissociation) while an activation energy barrier of 0.19 and 0.51 eV is found for these dissociation processes on Pt/TiC(100), respectively. Moreover, the series pathway (which is characterized by the stable OOH* molecular intermediate) on Pt/TiC(100) is predicted to be more favorable than the direct pathway. Our electronic structure analysis supports a strong synergistic co-operative effect by these non-oxide supports (TiN and TiC) on the reduced state of the single-atom Pt catalyst, and directly influences the rudimentary ORR steps on these single-atom platinized supports.

Pt-based binary alloys (Pt-M, M = transition metal) with optimal electronic and geometric properties may be used to secure the economic feasibility of fuel cells by reducing Pt content and increasing cathodic efficiency. Herein, the oxygen reduction reaction (ORR) on Pt-M alloys (Pt3M and PtM, M = Co, Ni, Mn, and Ir) was probed by density functional theory calculations to reveal that the oxygen dissociation pathway is optimal for Pt(1 1 1), Pt3M(1 1 1), and PtM(1 1 1) surfaces. However, as the above alloys were inferior to Pt catalysts, Pt/Pt-M alloys were designed by the addition of a single Pt skin layer at the top of Pt-M alloys, which enhanced ORR performance by decreasing the adsorption strengths of key intermediates (O* and OH*) to values below those observed for the Pt catalyst. Pt/PtNi and Pt/PtCo catalysts, which offer the benefit of decreased Pt content, showed particularly high performances. The results of electronic structure analysis demonstrated that the above decrease in adsorption strength was due to the inhibition of the high activity of the Pt-M(1 1 1) surface by the Pt skin layer. Finally, simple descriptors (optimal d-band center position and adsorption strength) were established to enable the further search for better fuel cell catalysts.

Syngas, a gaseous mixture of CO and H2, is a critical industrial feedstock for producing bulk chemicals and synthetic fuels, and its production via direct CO2 electroreduction in aqueous media constitutes an important step toward carbon-negative technologies. Herein, we report controlled syngas production with various H2/CO ratios via the electrochemical CO2 reduction reaction (CO2RR) on specifically formulated Au25 and PtAu24 nanoclusters (NCs) with core-atom-controlled selectivities. While CO was predominantly produced from the CO2RR on the Au NCs, H2 production was favored on the PtAu24 NCs. Density functional theory calculations of the free energy profiles for the CO2RR and hydrogen evolution reaction (HER) indicated that the reaction energy for the conversion of CO2 to CO was much lower than that for the HER on the Au25 NC. In contrast, the energy profiles calculated for the HER indicated that the PtAu24 NCs have nearly thermoneutral binding properties; thus, H2 production is favored over CO formation. Based on the distinctly different catalytic selectivities of Au25 and PtAu24 NCs, controlled syngas production with H2/CO ratios of 1 to 4 was demonstrated at a constant applied potential by simply mixing the Au25 and PtAu24 NCs based on their intrinsic catalytic activities for the production of CO and H2.

First-principles study explores the catalytic performance of the Cu(1 1 1) and Cu/G catalysts for the electrochemical CO2 reduction using computational hydrogen electrode model. Two different pathways, determined based on the initially generated intermediates (COOH* and HCOO*), as well as successive intermediates and the end products, were investigated. Although the two catalysts promote both pathways, Cu(1 1 1) surface favors “COOH pathway” and Cu/G catalyst strongly promotes the “HCOO pathway” with an free energy barrier of 0.83 eV (CO* → CHO*) and 0.87 eV (HCOO* → H2COO*). Electronic properties and binding nature of the final intermediate (CH3O*) on both catalysts sheds light on the fundamental reason for the selective end products (CH4 on the Cu(1 1 1) surface and CH3OH on the Cu/G catalyst). CH3OH is predominantly produced with the Cu/G catalyst because the C O bond of CH3O* is stronger than the bond between the single Cu atom and O of CH3O*, given that the energy of the d-band center of the single Cu atom is relatively highly negative. The current study explores the different electrochemical reduction pathways on the Cu(1 1 1) and Cu/G catalyst, providing insight for the design of highly efficient catalysts that afford selective end products.

The conversion of carbon dioxide (CO2) into usable hydrocarbon fuels is important for recycling carbon resources and mitigating environmental problems. However, converting CO2, which is a stable compound, requires a high additional energy. Therefore, it is essential to understand the electrochemical reduction mechanisms of CO2 and develop more efficient catalysts. In this study, density functional theory calculations were performed to examine electrochemical CO2 reduction on copper nanoclusters (NCs) (Cu13 NCs and Cu55 NCs) and the Cu(1 1 1) surface to verify the effect of the surface geometry and size of the NCs on the conversion of CO2 into CH4. The highest energy barriers to CO2 reduction (i.e., the potential-limiting step) on the Cu13 NCs (0.64 eV), Cu55 NCs (0.83 eV), and Cu(1 1 1) surface (0.86 eV) lie in the CO∗ → CHO∗ step. The formation of an adsorbed CHO intermediate depending on the catalyst surface geometry may significantly influence the energy barrier, as demonstrated by analyses of the electronic properties, such as the density of states, charge density difference, and highest occupied molecular orbital and lowest unoccupied molecular orbital band gap.

Ni(x)/Al2O3 (x=wt%) catalysts with Ni loadings of 5–25 wt% were prepared via a wet impregnation method on an γ-Al2O3 support and subsequently applied in the reductive amination of ethanol to ethylamines. Among the various catalysts prepared, Ni(10)/Al2O3 exhibited the highest metal dispersion and the smallest Ni particle size, resulting in the highest catalytic performance. To reveal the effects of reaction parameters, a reductive amination process was performed by varying the reaction temperature (T), weight hourly space velocity (WHSV), and NH3 and H2 partial pressures in the reactions. In addition, on/off experiments for NH3 and H2 were also carried out. In the absence of NH3 in the reactant stream, the ethanol conversion and selectivities towards the different ethylamine products were significantly reduced, while the selectivity to ethylene was dominant due to the dehydration of ethanol. In contrast, in the absence of H2, the selectivity to acetonitrile significantly increased due to dehydrogenation of the imine intermediate. Although a small amount of catalyst deactivation was observed in the conversion of ethanol up to 10 h on stream due to the formation of nickel nitride, the Ni(10)/Al2O3 catalyst exhibited stable catalytic performance over 90 h under the optimized reaction conditions (i.e., T=190 °C, WHSV=0.9 h−1, and EtOH/NH3/H2 molar ratio=1/1/6).

Pt shells were synthesized on Pd-based alloy-cores via the chemical reduction method. Pt shells containing 1, 2, or 3 layers were prepared by controlling the amounts of Pt precursor used during synthesis. The thicknesses of Pt shell layers were calculated using the difference in the particle size between core and core-shell nanocatalysts, as determined from Cs-corrected scanning transmission electron microscopy (Cs-STEM) data. The shape and elemental distribution in the core-shell structured nanoparticles were analyzed using line profiles and elemental mapping from Cs-STEM. High-resolution X-ray diffraction and X-ray photoelectron spectroscopy analyses suggested that the structural and electronic properties of core-shell nanocatalysts were dependent on the number of shell layers. The activity and durability of the core-shell nanocatalysts were analyzed by the electrochemical method. Accelerated durability tests (ADT) were conducted in the potential range of 0.6–1 V for 10000 cycles, and the mass and specific activities of ADT were shown to be stable for the carbon-supported core-shell nanocatalyst with two Pt shell layers (core@Pt[2](*)/C). In addition, excellent electrochemical performance was observed for the core@Pt[2]/C sample before and after the ADT compared to the commercial samples as well as other samples prepared in this study. Importantly, the optimized Pt usage demonstrated in this study would significantly contribute to the commercialization of proton exchange membrane fuel cells.

Transition metal nitrides possessing superior electrical conductivity and outstanding oxidation and corrosion resistance have been described as good substitutes for carbon support materials which are vulnerable during proton exchange membrane fuel cell (PEMFC) operation due to corrosion and poor life cycles. A closer theoretical inspection of the stability and electronic properties of titanium nitride-supported Pt in comparison with carbon-supported Pt (using graphite and graphene) has been conducted using density functional theory calculations. A single Pt atom adsorbed more strongly to the TiN surface than to both graphite and graphene, causing a larger degree of charge transfer between Pt and TiN.

Carbon-based nanomaterials are frequently used as a support for proton exchange membrane fuel cell (PEMFC) catalysts, due to their high electrical conductivity and large surface area; however, the limited long-term stability of carbon-based catalysts under PEMFC operation causes huge problems in practical applications. Here we report the use of vanadium nitride (VN) nanofiber membrane as a highly durable catalyst support for oxygen reduction reaction (ORR). Nanofibrous VN was prepared using a simple electrospinning process, followed by sequential heat treatments in air and NH 3 . The NH 3 treatment temperature affected the crystallinity as well as the crystal size of VN, which ultimately affected the catalytic ORR activity of Pt-decorated catalysts. The optimized Pt/VN catalysts exhibited excellent ORR activity and durability in acid electrolyte. Much higher durability of Pt/VN than Pt/C was verified by chrono-amperometry analysis. Density functional theory (DFT) calculations provided further evidence of the strong interaction of Pt and VN, which contributed to the high stability of the catalyst.

Poly(dibenzylated benzimidazolium) bromides (Bz-PBI-Br) were converted successfully to OH− ion conducting poly(dibenzylated benzimidazolium) hydroxides (Bz-PBI-hydroxides) by the treatment of KOH. The Bz-PBI-hydroxides obtained in this study showed an excellent alkali tolerance compared to previously synthesized poly(dimethylated benzimidazolium) hydroxides (Me-PBI-hydroxides). According to 1H-NMR analysis, Me-PBI-hydroxides were decomposed during KOH treatment. In order to find out the reason, density functional theory (DFT) calculations of two benzimidazolium structures, e.g., dimethylated benzimidazolium (Me-BI+) and dibenzylated benzimidazolium (Bz-BI+), were performed. Bz-BI+ showed lower electron affinity and OH−-binding energies at the C2 position of the benzimidazolium ring than Me-BI+. These DFT results strongly confirm that Bz-BI+ is less vulnerable to an OH− attack than Me-BI+; this contributes to the enhanced stability and OH− ion conductivity of the Bz-PBI-hydroxides.

Conversion of carbon dioxide (CO 2 ) into methane (CH 4 ) on copper (Cu) surfaces were investigated to understand the fundamental mechanism of CO 2 reduction, and to suggest a key factor for designing promising catalysts for CO 2 conversion into hydrocarbon fuels. The density functional theory calculations revealed the lowest-energy reaction pathways on Cu(1 0 0), Cu(1 1 0), and Cu(1 1 1) planes, and determined that the potential limiting step for CO 2 reduction lies between the reaction intermediates CO ∗ and CHO ∗ ( ∗ denotes the state adsorbed on the catalyst surface). The energy barrier to the potential limiting step is lowered in the following order: Cu(1 1 0) 2 reduction by designing a Cu thin film on a supporting material with larger lattice constant than Cu. To demonstrate this, we evaluated the energy barriers to the potential limiting step on a single Cu thin layer supported on both palladium (Pd) and silver (Ag), and confirmed that the Pd supporting material can enlarge the interatomic distance of the single Cu(1 1 1) layer by 8.7% and thereby lower the energy barrier from 0.97 to 0.63 eV.

Demand on the practical synthetic approach to the high performance electrocatalyst is rapidly increasing for fuel cell commercialization. Here we present a synthesis of highly durable and active intermetallic ordered face-centered tetragonal (fct)-PtFe nanoparticles (NPs) coated with a "dual purpose" N-doped carbon shell. Ordered fct-PtFe NPs with the size of only a few nanometers are obtained by thermal annealing of polydopamine-coated PtFe NPs, and the N-doped carbon shell that is in situ formed from dopamine coating could effectively prevent the coalescence of NPs. This carbon shell also protects the NPs from detachment and agglomeration as well as dissolution throughout the harsh fuel cell operating conditions. By controlling the thickness of the shell below 1 nm, we achieved excellent protection of the NPs as well as high catalytic activity, as the thin carbon shell is highly permeable for the reactant molecules. Our ordered fct-PtFe/C nanocatalyst coated with an N-doped carbon shell shows 11.4 times-higher mass activity and 10.5 times-higher specific activity than commercial Pt/C catalyst. Moreover, we accomplished the long-term stability in membrane electrode assembly (MEA) for 100 h without significant activity loss. From in situ XANES, EDS, and first-principles calculations, we confirmed that an ordered fct-PtFe structure is critical for the long-term stability of our nanocatalyst. This strategy utilizing an N-doped carbon shell for obtaining a small ordered-fct PtFe nanocatalyst as well as protecting the catalyst during fuel cell cycling is expected to open a new simple and effective route for the commercialization of fuel cells.

The competitive adsorption between phosphate and arsenic (As) in natural soil and mineral systems is important for controlling subsurface contaminants. Phosphate is known to adsorb more strongly than As in Fe(III) oxide-based mineral systems. Here, X-ray absorption spectroscopy (XAS) and density functional theory (DFT) were employed to understand the fundamental reaction mechanisms of As and phosphate on an FeS surface. The competitive effect of phosphate in As(V)-contaminated soil systems differed with changing FeS concentrations. In soil batches with high FeS contents, As(V) was more strongly adsorbed than phosphate, and no additional As release was observed in the aqueous phase, in the presence of phosphate. Through the XAS measurement of laboratory batch samples, the reaction mechanisms could be comprehensively understood, including the reduction of As(V) to As(III), the secondary precipitation of sulfide minerals, and the adsorption mechanism of As(V) on the surface of FeS. The DFT calculations revealed the relative adsorption strengths on the FeS surface were As(V) > phosphate > As(III). Comparing the adsorption energies revealed that As(V) reacted more strongly with FeS than phosphate and As(III), and that the effect of phosphate co-occurrence was negligible in the FeS–As system, in line with the experimental measurements.

In the present work, we have accomplished morphology-controlled synthesis of ternary Pt–Pd–Cu alloy nanoparticles, particularly for efficient electrocatalytic oxygen reduction reactions. By controlling over the degree of galvanic displacement at room temperature, we selectively introduced porous and hollow architectures into Pt-decorated Pd–Cu alloy nanoparticles. Porous morphology was accompanied with partially facilitated Pt substitution reaction while hollow shape was exclusively achieved when the galvanic reaction was coupled with additional pre-treatment process which could eventually make the following displacement reaction more facile. Not only the both porous and hollow Pt@PdCu/C catalysts exhibited enhanced ORR performances compared to commercial Pt/C, but also they displayed outstanding durability. In addition, we investigated the alloying effects between Pt and Pd–Cu composite and the presumable influences of lattice strain through preliminary theoretical calculation to account for the enhanced ORR efficiency and durability of the present catalysts.

Structure effects of NiS and Ni3S2 nanoparticles were investigated for their electrocatalytic activity in the hydrogen evolution reaction in both acid and alkaline media. Owing to the different atomic configurations and crystalline structures, there is a hydrogen adsorption energy difference, which induces a difference in the activity. From density functional theory calculations and experimental observations, the importance of designing an electrocatalyst with an appropriate atomic configuration is evident.

Here we report the preparation of hollow microspheres with a thin shell composed of mixed cobalt nitride (Co–N) and cobalt oxide (Co–O) nanofragments encapsulated in thin layers of nitrogen-doped carbon (N–C) nanostructure (Co–N/Co–O@N–C) arrays with enhanced bifunctional oxygen electrochemical performance. The hybrid structures are synthesized via heat treatment of N-doped hollow carbon microspheres with cobalt nitrate, and both the specific ratio of these precursors and the selected annealing temperature are found to be the key factors for the formation of the unique hybrid structure. The as-obtained product (Co–N/Co–O@N–C) presents a large specific surface area (493 m2 g−1), high-level heteroatom doping (Co–N, Co–O, and N–C), and hierarchical porous nanoarchitecture containing macroporous frameworks and mesoporous walls. Electronic interaction between the thin N–C layers and the encapsulated Co–N and Co–O nanofragments efficiently optimizes oxygen adsorption properties on the Co–N/Co–O@N–C and thereby triggers bifunctional oxygen electrochemical activity at the surface. The Co–N/Co–O@N–C nanohybrid exhibited a high onset potential of 0.93 V, and a limiting current density of 5.6 mA cm−2 indicating 4-electron oxygen reduction reaction (ORR), afforded high catalytic activity for the oxygen evolution reaction (OER) and even exceeded the catalytic stability of the commercial precious electrocatalysts; furthermore, when integrated into the oxygen electrode of a regenerative fuel cell device, it exhibited high-performance oxygen electrodes for both the ORR and the OER.

The mobility of heavy metalloids including As, Sb, Mo, W, and Cr in soil was investigated under both reducing and oxidizing conditions. The effects of soil mineralogy and the presence of competitive anions were studied as important factors affecting the mobility of these contaminants. Batch experiments conducted with the addition of oxidized and fresh FeS exhibited enhanced sorption rates for As and W under oxidizing conditions, and for Mo under reducing conditions. The inhibitory effect of phosphate on the sorption rates was most apparent for As and Mo under both oxidizing and reducing conditions, while only a small phosphate effect was observed for Sb and W. For Sb and W mobility, pH was determined to be the most important controlling factor. The results of long-term batch experiments revealed that differences in the mobility of metalloids, particularly As, were also influenced by microbial activity in the oxidizing and reducing conditions.

Transition metals, such as iron (Fe)- or cobalt (Co)-based nanomaterials, are promising electrocatalysts for oxygen reduction reactions (ORR) in fuel cells due to their high theoretical activity and low cost. However, a major challenge to using these metals in place of precious metal catalysts for ORR is their low efficiency and poor stability, thus new concepts and strategies should be needed to address this issue. Here, we report a hybrid aciniform nanostructures of Fe nanofragments embedded in thin nitrogen (N)-doped graphene (Fe@N-G) layers via a heat treatment of graphene oxide-wrapped iron oxide (Fe2O3) microparticles with melamine. The heat treatment leads to transformation of Fe2O3 microparticles to nanosized zero-valent Fe fragments and formation of core-shell structures of Fe nanofragments and N-doped graphene layers. Thin N-doped graphene layers massively promote electron transfer from the encapsulated metals to the graphene surface, which efficiently optimizes the electronic structure of the graphene surface and thereby triggers ORR activity at the graphene surface. With the synergistic effect arising from the N-doped graphene and Fe nanoparticles with porous aciniform nanostructures, the Fe@N-G hybrid catalyst exhibits high catalytic activity, which was evidenced by high E1/2 of 0.82 V, onset potential of 0.93 V, and limiting current density of 4.8 mA cm−2 indicating 4-electron ORR, and even exceeds the catalytic stability of the commercial Pt catalyst.

The effect of alloying with transition metals (Ni, Co, Fe) on the adsorption strength of phosphoric acid on Pt alloy surfaces was investigated using electrochemical analysis and first-principles calculations. Cyclic voltammograms of carbon-supported Pt3M/C (M = Ni, Co, and Fe) electrocatalysts in 0.1 M HClO4 with and without 0.01 M H3PO4 revealed that the phosphoric acid adsorption charge density near the onset potential on the nanoparticle surfaces was decreased by alloying with transition metals in the order Co, Fe, Ni. First-principles calculations based on density functional theory confirmed that the adsorption strength of phosphoric acid was weakened by alloying with transition metals, in the same order as that observed in the electrochemical analysis. The simulation suggested that the weaker phosphoric acid adsorption can be attributed to a lowered density of states near the Fermi level due to alloying with transition metals.