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We report ferromagnetism in 2H-Co$_{0.22}$TaS$_2$ single crystals where Co atoms are intercalated in the van der Waals gap, and a systematic study of its magnetic critical behavior in the vicinity of $T_c \sim 28$ K. The obtained critical exponents $\beta$ = 0.43(2), $\gamma$ = 1.15(1), and $\delta = 3.54(1)$ fulfill the Widom scaling relation $\delta = 1+\gamma/\beta$ and follow the scaling equation. This indicates that the spin coupling in 2H-Co$_{0.22}$TaS$_2$ is of three-dimensional Hersenberg type coupled with long-range magnetic interaction, and that the exchange interaction decays with distance as $J(r)\approx r^{-4.69}$. 2H-Co$_{0.22}$TaS$_2$ exhibits a weak temperature-dependent metallic behavior in resistivity and negative values of thermopower with dominant electron-type carriers, in which obvious anomalies were observed below $T_c$ as well as the anomalous Hall effect (AHE). The linear scaling behavior between the modified anomalous Hall resistivity $\rho_{xy}/\mu_0H$ and longitudinal resistivity $\rho_{xx}^2M/\mu_0H$ implies that the origin of AHE in 2H-Co$_{0.22}$TaS$_2$ should be dominated by the extrinsic side-jump mechanism.

A sodium borate glass containing both trivalent cerium oxide and tetravalent cerium oxide states nano particles of 2–5 nm in size was successfully prepared by doping the glass with varying amounts of cerium (IV) oxide with. X-ray absorption spectroscopy measurement was used to determine the coexistence of the multivalent state of cerium oxide in the borate glass. Significant changes in the trivalent and tetravalent cerium oxide concentrations were observed when the glass was melted using different melting parameters and different raw materials. Glass made with borax that contained of 0.05mols of CeO2 and melted at 1100 °C for 3 h had the highest concentration of trivalent cerium oxide. Transmission electron micrographs confirmed the release of trivalent Ce2O3 and tetravalent CeO2 nanoparticles from the glassy matrix. Fourier transform Infrared measurements suggest that the CeO2 in the glass acts as both a glass-former and glass modifier.

The synthesis of zeolite-supported Mo carbide species was studied by testing different reduction/carburization conditions applied to a zeolite-supported Mo oxide catalyst, with the aim to find the optimized treatment conditions necessary to form stable supported Mo carbide catalysts ex situ for application in methane dehydroaromatization reaction. Four types of treatment were performed and studied using temperature-programmed reduction and carburization profiles: (1) heating the catalyst in a reducing gas, H2, up to reaction temperature and switching to CH4; (2) heating the catalyst in a reducing gas, H2, mixed with dilute CH4; (3) heating the catalyst in CH4 up to reaction temperature; and (4) heating the catalyst in an inert gas (commonly He) up to reaction temperature and then switching to CH4 or to H2 followed by CH4 or to H2/CH4 mixture. Each of these processes were stopped at intermediate points to analyze the phases that were present in order to identify the structural evolution of the supported Mo carbides that originate from the supported Mo oxides. Once the supported carbides were formed, they were quenched under the same gas mixture, and then they were each tested in methane dehydroaromatization via previous heating to reaction temperature in He flow. Despite all of them showing only presence of Mo2C species on HZSM-5, the catalytic properties were dramatically different. Catalysts treated in H2 or CH4/H2 showed remarkably higher stability. These catalysts exhibited a higher Mo dispersion and thus exposure on the active surface.

Understanding the roles of metals and atomic structures in activating various elementary steps of electrocatalytic reactions can help rational design of binary or ternary catalysts for promoting activity toward desirable products via favorable pathways. Here we report on a newly developed ternary Au@PtIr core-shell catalyst for ethanol oxidation reaction (EOR) in alkaline solutions, which exhibits an activity enhancement of 6 orders of magnitude compared to AuPtIr alloy catalysts. Analysis of in situ infrared reflection absorption spectra for Au@PtIr and its bimetallic subsets, Au@Pt and PtIr alloy, found that monatomic steps and Au-induced tensile strain on PtIr facilitate C-C bond splitting via ethanol dissociative adsorption and Ir promotes dehydrogenation at low potentials. As evidenced by the CO band being observed only for the PtIr alloy that is rather inactive for ethanol dissociative adsorption, we propose that splitting the C-C bond at the earliest stage of EOR activates a direct 12-electron full oxidation pathway because hydrogen-rich fragments can be fully oxidized without CO as a poisoning intermediate. The resulting synergy of complementary effects of Au core and surface Ir leads to an outstanding performance of Au@PtIr for EOR as characterized by a low onset potential of 0.3 V and 8.3 A mg-1all-metals peak current with 57% currents generated via full ethanol oxidation.

Transition metal oxides have gained attention as promising oxygen evolution reaction (OER) electrocatalysts in alkaline electrolytes, but heterogeneities in typical catalyst samples often obscure k...

Functional groups in natural organic matter have the potential to interact with and stabilize iron (Fe) redox species (ferric, ferrous) through complexation reactions. In this study, iron complexes with cysteine, arginine and histidine are used to investigate the extent to which specific functional groups present in these amino acids might hinder the oxidation of Fe2+ or promote the reduction of Fe3+. Iron complexes are synthesized by addition of ferrous or ferric salts to cysteine, arginine and histidine solutions at pH 7. The Fe-amino acid complexes are analysed using X-ray Absorption Spectroscopy (XAS), theoretical CTM4XAS (Charge Transfer Multiplet for XAS) calculations, and vibrational spectroscopy (FTIR and Raman). In addition, oxidation of the amino acids is determined by linear sweep voltammetry and chemical equilibrium modeling is used to predict the speciation of Fe in complexes with the amino acids. It is observed the extent of Fe redox transformation is affected by the electron donating capability of the ligand with which Fe reacts. In particular, the extent of Fe3+ reduction is related to the oxidation of the ligand with 80, 14 and 0% Fe3+ reduction by cysteine, arginine and histidine, respectively. Conversely, Fe2+ is preserved by cysteine (80%) > arginine (77%) > histidine (62%). The chemical forms of Fe in these mixed Fe oxidation-state systems include Fe-organic complexes and Fe precipitates. XAS and vibrational spectroscopy indicate thiol-S and amino-N bind Fe in complexes with cysteine. While amino-N and guanidyl-N functional groups of arginine bind Fe, carboxylate-O binding and the formation of Fe precipitates are only observed when Fe3+ is the predominant redox species. Whereas Fe precipitates seem to prevail in Fe(III)-histidine, distinct organic (Fe O/N C) and mineral (Fe O Fe) or mixed organic-mineral (Fe(O/N C)x(O Fe)y) coordination environments occur in Fe(II)-histidine with ∼60% Fe2+; in either case, Fe N(imidazole) binding is not evident. The ligand atoms to which Fe binds and the inherent reduction capacity of the ligand appear to mediate Fe redox transformations. The proportion of ferric iron (Fe3+) seems to determine whether a precipitate forms. Consistent with spectroscopic data, chemical equilibrium modeling using experimental solution conditions and fractional Fe2+ and Fe3+ concentrations obtained from CTM4XAS predict the formation of Fe(II)- and Fe(III)-amino acid complexes and hydrolyzed Fe species; these calculations however also predict the formation of Fe oxide precipitates in all Fe complexes. The results presented in this study help to explain the co-occurrence of Fe2+ and Fe3+ in natural environments where organic matter is present. They also highlight the role specific organic functional groups play on the formation and stabilization of Fe(II, III)-organic complexes and precipitates, and thus on the Fe redox cycle which affects Fe bioavailability and mobility in terrestrial and subsurface environments.

In this work, we have investigated a hierarchical CuO-derived inverse opal (CuO-IO) catalyst with high CO selectivity up to 80–90% and minimal H2 evolution at moderate potentials for CO2 electroreduction. The three-dimensionally (3D) structured, porous catalyst was composed of small CuO nanoparticles and exhibited a peak CO faradaic efficiency (FE) of 72.5% (±1.8), complete suppression of H2 formation, and good stability over 24 hours operation at −0.6 V versus the reversible hydrogen electrode (RHE). In situ Raman, X-ray absorption spectroscopy and X-ray diffraction measurements indicated reduction of the catalyst into metallic Cu0 oxidation state with dominant Cu(111) orientation under electrocatalytic conditions. We suggest that rapid depletion of CO2 and protons at the highly roughened catalyst surface likely increased the local pH during the electrolysis. The combination of C1 favoring Cu(111) surfaces and reduced local proton/CO2 availability facilitated selective conversion of CO2 into CO and reduced H2 and C2 products. Our work provides additional understanding of the structure–property relationships of 3D porous electrocatalysts for CO2 reduction applications by evaluating the crystallographic orientation, oxidation state, and crystallite size of a CO-selective CuO-IO catalyst under realistic working conditions.

We here present an innovative approach to increase the electron density of metallic Pd nanoparticles loaded on TiO2 photocatalysts by coordinating Pd with surface-anchored organic ligands. X-ray ph...

Van der Waals (vdW) ferromagnets are an important class of materials for spintronics applications. The recent discovery of atomically vdW magnets ${\mathrm{CrI}}_{3}$ and ${\mathrm{Cr}}_{2}{\mathrm{Ge}}_{2}{\mathrm{Te}}_{6}$ has triggered a renaissance in the area of two-dimensional (2D) magnetism. Herein we systematically studied 2H-${\mathrm{Mn}}_{0.28}{\mathrm{TaS}}_{2}$ single crystal, a 2D vdW ferromagnet with ${T}_{c}\ensuremath{\sim}82.3\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, and a large in-plane magnetic anisotropy. Mn $K$-edge x-ray absorption spectroscopy was measured to provide information on its electronic state and local atomic environment. The detailed magnetic isotherms measured in the vicinity of ${T}_{c}$ indicates that the spin coupling inside 2H-${\mathrm{Mn}}_{0.28}{\mathrm{TaS}}_{2}$ is of a 3D Heisenberg type coupled with the attractive long-range interaction between spins that decay as $J(r)\ensuremath{\approx}{r}^{\ensuremath{-}4.85}$. Both resistivity $\ensuremath{\rho}(T)$ and thermopower $S(T)$ exhibit anomalies near ${T}_{c}$, confirming that the hole-type transport carriers strongly interact with local moments. An unusual angle-dependent magnetoresistance is further observed, suggesting a possible field-induced novel magnetic structure.

The ability of transition metal chitosan complexes (TMCs) of varying valence and charge to selectively adsorb As(III) and As(V) over their strongest adsorptive competitor, phosphate is examined. Fe(III)-chitosan, Cu(II)-chitosan, Al(III)-chitosan, Ni(II)-chitosan, and Zn(II)-chitosan are synthesized, characterized via Attenuated Total Reflectance-Fourier Transform Infrared spectroscopy (ATR-FTIR) and X-ray Diffractometry (XRD), and their selective sorption capabilities towards arsenite and arsenate over phosphate are evaluated. It was found that the stability of the metal-chitosan complexes varied, with Al(III)- and Zn(II)-chitosan forming unstable complexes resulting in precipitation of gibbsite, and Wulfingite and zincite, respectively. Cu(II)-, Ni(II)-, and Fe(III)- chitosan formed a mixture of monodentate and bidentate complexes. The TMCs which formed the bidentate complex (Cu(II)-, Ni(II)-, and Fe(III)-) showed greater adsorption capability for arsenate in competitive systems with phosphate. Using the binary separation factor ∝ t / c , it can be shown that only Fe(III)-chitosan is selective for As(V) and As(III) over phosphate. Density Functional Theory (DFT) modeling and extended X-ray absorption fine structure (EXAFS) determined that Fe(III)-chitosan and Ni(II)-chitosan adsorbed As(V) and As(III) via inner-sphere complexation, while Cu(II)-chitosan formed mainly outer-sphere complexes with As(V) and As(III). These differences in complexation likely result in the observed differences in selective adsorption capability towards As(V) and As(III) over phosphate.

We report discovery of new antiferromagnetic semimetal EuZnSb$_2$, obtained and studied in the form of single crystals. Electric resistivity, magnetic susceptibility and heat capacity indicate antiferromagnetic order of Eu with $T_N$ = 20 K. The effective moment of Eu$^{2+}$ inferred from the magnetization and specific heat measurement is 3.5 $\mu_B$, smaller than the theoretical value of Eu$^{2+}$ due to presence of both Eu$^{3+}$ and Eu$^{2+}$. Magnetic field-dependent resistivity measurements suggest dominant quasi two dimensional Fermi surfaces whereas the first-principle calculations point to the presence of Dirac fermions. Therefore, EuZnSb$_2$ could represent the first platform to study the interplay of dynamical charge fluctuations, localized magnetic 4$f$ moments and Dirac states with Sb orbital character., Comment: 9 pages, 4 figures

We carried out a comprehensive study of magnetic critical behavior in single crystals of ternary chalcogenide $\mathrm{Fe}{\mathrm{Cr}}_{2}{\mathrm{Te}}_{4}$ that undergoes a ferrimagnetic transition below ${T}_{c}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}$ 123 K. Detailed critical behavior analysis and scaled magnetic entropy change indicate a second-order ferrimagnetic transition. Critical exponents $\ensuremath{\beta}=0.30(1)$ with ${T}_{c}=122.4(5)\phantom{\rule{0.16em}{0ex}}\mathrm{K}, \ensuremath{\gamma}=1.22(1)$ with ${T}_{c}=122.8(1)\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, and $\ensuremath{\delta}=4.24(2)$ at ${T}_{c}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}123\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ suggest that the spins approach the three-dimensional Ising ($\ensuremath{\beta}=0.325, \ensuremath{\gamma}=1.24$, and $\ensuremath{\delta}=4.82$) model coupled with attractive long-range interactions between spins that decay as $J(r)\ensuremath{\approx}{r}^{\ensuremath{-}4.88}$. Our results suggest that the ferrimagnetism in $\mathrm{Fe}{\mathrm{Cr}}_{2}{\mathrm{Te}}_{4}$ is due to itinerant ferromagnetism among the antiferromagnetically coupled Cr-Fe-Cr trimers.

We here present a novel Ti

The 2D layered Ruddlesden-Popper crystal structure can host a broad range of functionally important behaviors. Here we establish extraordinary configurational disorder in a two dimensional layered Ruddlesden-Popper (RP) structure using entropy stabilization assisted synthesis. A protype A2CuO4 RP cuprate oxide with five components (La, Pr, Nd, Sm, Eu) on the A-site sublattice is designed and fabricated into epitaxial single crystal films using pulsed laser deposition. By comparing (La0.2Pr0.2Nd0.2Sm0.2Eu0.2)2CuO4 crystals grown under identical conditions but different substrates, it is found that heteroepitaxial strain plays an important role in crystal phase formation. When grown on a near lattice matched substrate, the high entropy oxide film features a T'-type RP structure with uniform A-site cation mixing and square-planar CuO4 units, however, growing under strong compressive strain results in a single crystal non-RP cubic phase consistent with a CuX2O4 spinel structure. These observations are made with a range of combined characterizations using X-ray diffraction, atomic-resolution scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray absorption spectroscopy measurements. Designing configurational complexity and moving between 2D layered RP and 3D cubic crystal structures in this class of cuprate materials opens many opportunities for new design strategies related to magnetoresistance, unconventional superconductivity, ferroelectricity, catalysis, and ion transport.

Reacting CO2 and ethane to synthesize value-added oxygenate molecules represents opportunities to simultaneously reduce CO2 emissions and upgrade underutilized ethane in shale gas. Herein, we propose a strategy to produce C3 oxygenates using a tandem reactor. This strategy is achieved with a Fe3Ni1/CeO2 catalyst (first reactor at 600–800 °C) for CO2-assisted dehydrogenation and reforming of ethane to produce ethylene, CO, and H2, and a RhCox/MCM-41 catalyst (second reactor at 200 °C) enabling CO insertion for the production of C3 oxygenates (propanal and 1-propanol) via the heterogeneous hydroformylation reaction at ambient pressure. In-situ characterization using synchrotron spectroscopies and density functional theory (DFT) calculations reveal the effect of Rh–Co bimetallic formation in facilitating the production of C3 oxygenates. The proposed strategy provides an opportunity for upgrading light alkanes in shale gas by reacting with CO2 to produce aldehydes and alcohols. Reacting CO2 and ethane to achieve value-added C3 oxygenates offers opportunities to simultaneously reduce CO2 emissions and upgrade underutilized ethane in shale gas. Here, the authors report a successful oxygenate production strategy enabled by inserting CO2-derived CO into ethane-derived ethylene using a tandem reactor.

Renewable production of ammonia, a building block for most fertilizers, via the electrochemical nitrogen reduction reaction (ENRR) is desirable; however, a selective electrocatalyst is lacking. Here we show that vanadium nitride (VN) nanoparticles are active, selective, and stable ENRR catalysts with an ENRR rate and a Faradaic efficiency (FE) of 3.3 × 10

This study presents a single-atom Pt catalyst that achieves efficient C–F bond activation, which is a challenging reaction in both chemical synthesis and environmental remediation of recalcitrant fluorinated hydrocarbons. Up to 1.6 wt % Pt was loaded as a single-atom on SiC substrate (Pt1/SiC) using a facile, scalable wet-chemical method developed based on anchor-site and photoreduction techniques. The high catalytic activity of Pt1/SiC for hydrodefluorination of perfluorooctanoic acid, which is a select perfluorinated pollutant of significant environmental concern, is attributed to the effective hydrogen spillover from isolated Pt onto the SiC surface where the resulting Si–H bond further redistributes with the C–F bond to accomplish hydrodefluorination.

We present a comprehensive investigation of the anisotropic magnetic and magnetocaloric properties of quasi-two-dimensional weak itinerant ferromagnet trigonal ${\mathrm{Cr}}_{5}{\mathrm{Te}}_{8}$ single crystals. Magnetic-anisotropy-induced satellite transition ${T}^{*}$ is observed at low fields applied parallel to the $ab$ plane below the Curie temperature (${T}_{c}\ensuremath{\sim}230\phantom{\rule{4pt}{0ex}}\mathrm{K}$). ${T}^{*}$ is featured by an anomalous magnetization downturn, similar to that in structurally related ${\mathrm{CrI}}_{3}$, which possibly stems from an in-plane antiferromagnetic alignment induced by out-of-plane ferromagnetic spins canting. Magnetocrystalline anisotropy is also reflected in magnetic entropy change $\mathrm{\ensuremath{\Delta}}{S}_{M}(T,H)$ and relative cooling power. Given the high Curie temperature, ${\mathrm{Cr}}_{5}{\mathrm{Te}}_{8}$ crystals are materials of interest for nanofabrication in basic science and applied technology.

The structure-activity relationship between the ORR performance and the surface electronic structure of Pd is constructed and the ORR performance are rationally modified via the structural transition from disordered face centered cubic phase (fcc, D-PdFe/C) to ordered intermetallic tetragonal phase (fct, O-PdFe/C). When the small amount of Pt atoms decorated on O-PdFe/C surface forming O-PdFe@Pt/C core-shell structure, the sublayer of Pd and Fe atoms may cause the lattice contraction of surface Pt and then weak the bonding energy on O-PdFe@Pt/C catalyst relative to bulk Pt/C, which is further illustrated by density functional theory (DFT) calculation. The weakened oxygen affinity results in the enhancement of ORR performance on O-PdFe@Pt/C. For a practical application, the well-constructed O-PdFe@Pt/C exhibits higher voltage and peak power density than D-PdFe@Pt/C and Pt/C when applied as the air-breathing cathode material in Zn-air battery.

A Pd-promoted Re/SiO2 catalyst was prepared by sequential impregnation and compared to monometallic Pd/SiO2 and Re/SiO2. All samples were characterized by electron microscopy, H2 and CO chemisorption, H2 temperature-programmed reduction, and in-situ X-ray absorption spectroscopy at the Re LIII and Pd K-edges. The samples were also tested in the reduction of propionic acid to 1-propanol and propionaldehyde at 433 K in 0.1-0.2 MPa H2. Whereas monometallic Pd was inactive for carboxylic acid reduction, monometallic Re catalyzed aldehyde formation, but only after high-temperature pre-reduction that produced metallic Re. When Pd was present with Re in a bimetallic catalyst, Pd facilitated the reduction of Re in H2 to ~4+ oxidation state at modest temperatures, producing an active catalyst for the conversion of propionic acid to 1-propanol. Under the conditions of this study, the orders of reaction in propionic acid and H2 were approximately zero and one, respectively. Transient kinetic analysis of the carboxyl...

Atomically dispersed Co(II) cations coordinated to nitrogen in a carbon matrix (Co-N-C) catalyze oxidative dehydrogenation of benzyl alcohol in water with a specific activity approaching that of supported Pt nanoparticles. Whereas Cu(II) cations in N-doped carbon also catalyze the reaction, they are about an order of magnitude less active compared with Co(II) cations. Results from X-ray absorption spectroscopy suggest that oxygen is also bound to N-coordinated Co(II) sites but that it can be partially removed by H2 treatments at 523–750 K. The N-coordinated Co(II) sites remained cationic in H2 up to 750 K, and these stable sites were demonstrated to be active for propane dehydrogenation. In situ characterization of Cu(II) in N-doped carbon revealed that reduction of the metal in H2 started at about 473 K, indicating a much lower thermal stability of Cu(II) in H2 relative to Co(II). The demonstrated high catalytic activity and thermal stability of Co-N-C in reducing environments suggests that this material...

Doping with a transition metal was recently shown to greatly boost the activity and durability of PtNi/C octahedral nanoparticles (NPs) for the oxygen reduction reaction (ORR), but its specific roles remain unclear. By combining electrochemistry, ex situ and in situ spectroscopic techniques, density functional theory calculations, and a newly developed kinetic Monte Carlo model, we showed that Mo atoms are preferentially located on the vertex and edge sites of Mo–PtNi/C in the form of oxides, which are stable within the wide potential window of the electrochemical cycle. These surface Mo oxides stabilize adjacent Pt sites, hereby stabilizing the octahedral shape enriched with (111) facets, and lead to increased concentration of Ni in subsurface layers where they are protected against acid dissolution. Consequently, the favorable Pt3Ni(111) structure for the ORR is stabilized on the surface of PtNi/C NPs in acid against voltage cycling. Significantly, the unusual potential-dependent oxygen coverage trend o...

Single-atom catalysts have emerged as an exciting paradigm with intriguing properties different from their nanocrystal counterparts. Here we report Ni single atoms dispersed into graphene nanosheets, without Ni nanoparticles involved, as active sites for the electrocatalytic CO2 reduction reaction (CO2RR) to CO. While Ni metal catalyzes the hydrogen evolution reaction (HER) exclusively under CO2RR conditions, Ni single atomic sites present a high CO selectivity of 95% under an overpotential of 550 mV in water, and an excellent stability over 20 hours’ continuous electrolysis. The current density can be scaled up to more than 50 mA cm−2 with a CO evolution turnover frequency of 2.1 × 105 h−1 while maintaining 97% CO selectivity using an anion membrane electrode assembly. Different Ni sites in graphene vacancies, with or without neighboring N coordination, were identified by in situ X-ray absorption spectroscopy and density functional theory calculations. Theoretical analysis of Ni and Co sites suggests completely different reaction pathways towards the CO2RR or HER, in agreement with experimental observations.

Tuning the hydrogen adsorption energy (EH) by controlling the surface electronic structure of Pt is essential for enhancing the hydrogen oxidation reaction (HOR) performance in alkaline media. This could be achieved by forming a Pt skin on PdFe/C nanoparticles with structurally ordered intermetallic (O-PdFe@Pt/C) or disordered alloy (D-PdFe@Pt/C). The HOR activity on O-PdFe@Pt/C exhibits an exchange current density of 1.49 A mgPt−1, which is 3.87 and 7.56 times higher than that on D-PdFe@Pt/C (0.385 A mgPt−1) and Pt/C (0.197 A mgPt−1), respectively. The excellent electrocatalytic HOR performance on O-PdFe@Pt/C can be ascribed to the attenuation of EH on the Pt shell induced by the structurally ordered PdFe core, where the EH on O-PdFe@Pt surface is 0.18 eV smaller than that on Pt according to DFT calculations.

Rechargeable sodium-ion batteries with earth-abundant Fe/Mn based cathodes are a promising choice for grid-scale applications. However, the key candidate, P2-type Fe-based materials, suffers from severe voltage decay during battery operation due to Fe3+ migration to the neighboring tetrahedral sites. In this study, two Fe-based layered oxides, Na0.7[Cu0.15Fe0.3Mn0.55]O2 and Na0.7[Cu0.2Fe0.2Mn0.6]O2, were prepared. With a combination of in situ XRD, X-ray PDF, and hard and soft X-ray absorption, we demonstrate that the voltage decay in Fe-based layered oxides has dynamic origins. Drastic phase transition can be triggered by higher upper voltage limit, while partially irreversible Fe migration leads to voltage fading. With excess Cu doped into the crystal lattice, Fe migration can be considerably mitigated and therefore, structural stability can be maintained. Furthermore, Cu introduction brings about extra capacity via the correlation between transition metal elements and ligand oxygen, which may well compensate for capacity loss from inert impurity doping. Possible strategies for suppressing the detrimental voltage decay in battery cathodes can be proposed accordingly.

The speciation of iron (Fe) in organic matter (OM)-rich environments under in situ variable redox conditions is largely unresolved. Peatlands provide a natural setting to study Fe–OM interactions. Utilizing chemical, spectroscopic and theoretical modeling approaches, we report the chemical forms, oxidation states and local coordination environment of naturally occurring Fe in the vertically redox-stratified Manning peatlands of western New York. In addition, we report dominant carbon, sulfur and nitrogen species that can potentially stabilize the various Fe species present in these peatlands. Our results provide clear direct and indirect evidence for the co-occurrence of ferrous (Fe2+) and ferric (Fe3+) iron species in peats under both oxic and anoxic conditions. Iron is mostly present within the operationally defined organic and amorphous (i.e., short range ordered, SRO) fractions; ferric iron primarily as magnetically isolated paramagnetic Fe3+ in Fe(III)-organic complexes, but also in mineral forms such as ferrihydrite; ferrous iron in tetrahedral coordination in Fe(II)-organic complexes with minor contribution from pyrite. All of the Fe species identified stabilize Fe(III) and/or Fe(II) in anoxic and oxic peats. Fundamental differences are also observed in the relative proportion of C, S and N functionalities of OM in oxic and anoxic peats. Aromatic C C, ester, phenol and anomeric C (R O C O R), as well as thiol, sulfide and heterocyclic N functionalities are more prevalent in anoxic peats. Collectively, our experimental evidence suggests iron forms coordination complexes with O-, S- and N-containing functional groups of OM. We posit the co-occurrence of organic and mineral forms of Fe(II) and Fe(III) in both oxic and anoxic peat layers results from dynamic complexation and hydrolysis-precipitation reactions that occur under variable redox conditions. Our findings aid in understanding the crucial role OM plays in determining Fe species in soils and sediments.

We demonstrate the key features of an interference cathode using both simulations and experiments. We deposit Cs3Sb photocathodes on Ag to produce an interference enhanced photocathode with 2–5× quantum efficiency (QE) enhancement using a robust procedure that requires only a smooth metal substrate and QE monitoring during growth. We grow both an interference cathode (Ag substrate) and a typical photocathode (Si reference substrate) simultaneously to confirm that the effects are due to optical interactions with the substrate rather than photocathode composition or surface electron affinity differences. Growing the cathodes until the QE converges shows both the characteristic interference peaks during growth and the identical limiting case where the cathode is “infinitely thick,” in agreement with simulations. We also grow a cathode until the QE on Ag peaks and then stop the growth, demonstrating broadband QE enhancement.

Die Umwandlung von Methan in Alkohole unter milden Reaktionsbedingungen ist eine vielversprechende Technologie fur die Nutzung abgelegener Methanvorkommen. Die flussigen Alkohole konnen in Pipelines transportiert und zu wertvolleren Chemikalien weiterverarbeitet werden. Hier wird gezeigt, dass ein Katalysator aus Nickeloxidpartikeln auf einen Ceroxid-Zirconiumoxid-Trager (NiO/CZ) Methan in einem einzigen, kontinuierlich betriebenen Reaktor zu Methanol und Ethanol umwandeln kann. Die Reaktion geschieht bei milden Temperaturen (723 K) mit O2 als Oxidationsmittel. Die Produktion von Alkoholen erfordert die Gegenwart von Wasserdampf, um die vollstandige Oxidation zu CO2 zu unterdrucken. Die Synergie zwischen Lewis-aciden NiO-Partikeln und dem redoxaktiven Ceroxid-Zirconiumoxid-Trager ermoglicht die ungewohnliche Reaktivitat dieses Katalysators.

The surface electronic structures of catalysts need to be carefully engineered in CO2 reduction reaction (CO2RR), where the hydrogen evolution side reaction usually takes over under a significant overpotential, and thus dramatically lowers the reaction selectivity. Surface oxides can play a critical role in tuning the surface oxidation state of metal catalysts for a proper binding with CO2RR reaction intermediates, which may significantly improve the catalytic activity and selectivity. Here, we demonstrate the importance of surface-bonded oxygen on silver nanoparticles in altering the reaction pathways and improving the CO2RR performances. A comparative investigation on air-annealed Ag (Air-Ag) catalyst with or without the post-treatment of H2 thermal annealing (H2-Ag) was performed. In Air-Ag, the subsurface chemically bonded O species (O–Agδ+) was identified by angle resolved X-ray photoelectron spectroscopy and X-ray absorption spectroscopy techniques, and contributed to the improved CO selectivity rat...

The start of operations at the National Synchrotron Light Source II (NSLS-II) at Brookhaven National Laboratory heralded a new beginning for photon-science-based research capabilities in catalysis. This new facility builds on many years of pioneering work that was conducted at the NSLS synergistically by many scientists from academia, government labs, and industry. Over several decades, numerous discoveries in catalysis were driven through the emergence of an arsenal of tools at the NSLS that exploited the power of emerging X-ray methods encompassing scattering, spectroscopy, and imaging. In-situ and operando methodologies that coupled reactor environments directly with advanced analytical techniques paved a rapid path towards realizing an improved fundamental understanding at the frontiers of chemical science challenges of the day.

NiFe-layered double hydroxide (LDH) is thought of as a promising bifunctional water-splitting catalyst, owing to its excellent performances for alkaline oxygen evolution reactions (OERs). However, it shows extremely poor activity toward hydrogen evolution reactions (HERs) due to the weak hydrogen adsorption. We demonstrated that the integration of Rh species and NiFe-LDH can dramatically improve its HER kinetics without sacrificing the OER performance. The Rh species were initially integrated into NiFe-LDH as oxidized dopants and metallic clusters (< 1 nm). In 1 M KOH electrolyte, an overpotential of 58 mV is needed to catalyze 10 mA cm-2 HER current density. Furthermore, this catalyst only requires 1.46 V to drive an electrolyzer at 10 mA cm-2. A strong interaction between metallic Rh clusters and NiFe hydroxide during the HER process is revealed. The theoretical calculation shows the Rh ions replace Fe ions as the major active sites that are responsible for OERs.

Rational designing of catalysts to promote the sluggish kinetics of the cathode oxygen reduction reaction in proton exchange membrane fuel cells is still challenging, yet of crucial importance to its commercial application. In this work, on the basis of theoretical DFT calculations which suggest that order structured fct-phased PtFe (O-PtFe) with an atomic Pt shell exhibits superior electrocatalytic performance towards the ORR, the desired structure was prepared by using a scalable impregnation–reduction method. The as-prepared O-PtFe delivered enhanced activity (0.68 A mg−1Pt) and stability (73% activity retention after 10 000 potential cycles) compared with the corresponding disordered PtFe alloy (D-PtFe) and Pt. To confirm the excellent durability, in situ X-ray absorption fine structure spectroscopy was conducted to probe the local and electronic structure changes of O-PtFe during 10 000 cycle accelerated durability testing. We hope that this facile synthesis method and the in situ XAFS experiment could be readily adapted to other catalyst systems, facilitating the screening of highly efficient ORR catalysts for fuel cell application.

Shifting electrochemical oxygen reduction towards 2e– pathway to hydrogen peroxide (H2O2), instead of the traditional 4e– to water, becomes increasingly important as a green method for H2O2 generation. Here, through a flexible control of oxygen reduction pathways on different transition metal single atom coordination in carbon nanotube, we discovered Fe-C-O as an efficient H2O2 catalyst, with an unprecedented onset of 0.822 V versus reversible hydrogen electrode in 0.1 M KOH to deliver 0.1 mA cm−2 H2O2 current, and a high H2O2 selectivity of above 95% in both alkaline and neutral pH. A wide range tuning of 2e–/4e– ORR pathways was achieved via different metal centers or neighboring metalloid coordination. Density functional theory calculations indicate that the Fe-C-O motifs, in a sharp contrast to the well-known Fe-C-N for 4e–, are responsible for the H2O2 pathway. This iron single atom catalyst demonstrated an effective water disinfection as a representative application., Hydrogen peroxide can be produced alternatively using green inputs such as air, water, and sunlight but this requires a selective catalyst. Here the authors report an iron single atom catalyst that can convert oxygen into hydrogen peroxide with a selectivity of above 95% in both alkaline and neutral pH.

Due to its chemical stability, titania (TiO2) thin films increasingly have significant impact when applied as passivation layers. However, optimization of growth conditions, key to achieving essent...

The utilization of CO2 as a C1 feedstock for synthesis of value-added chemicals and fuels could both mitigate the negative effects associated with increasing CO2 emissions and decrease dependence on fossil fuels as part of a future circular carbon economy. Co-based catalysts have been well-developed for Fischer-Tropsch synthesis (FTS), but replacing the CO reactant with CO2 (CO2-FTS) typically results in low selectivity toward desirable light olefins. To better understand the structure-property relationships of Co-based catalysts, and extend promising FTS results to CO2-FTS, we have studied the effect of a potassium promoter and acidic properties of ZSM-5 on catalytic performance. The selectivity of FTS and CO2-FTS is shown to be a strong function of Si/Al ratio in co-impregnated catalysts, with findings supported by in situ XAFS and FTIR, demonstrating light olefin selectivity can be tuned by Si/Al ratio and the method of introducing the K promoter.

The Pechini synthesis was used to prepare nickel aluminate catalysts with the compositions NiAl4O7, NiAl2O4, and Ni2Al2O5. The samples have been characterized by N2 physisorption, temperature-programmed reduction (TPR), temperature-programmed oxidation (TPO), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and X-ray absorption spectroscopy (XAS). Characterization results indicate unique structural properties and excellent regeneration potential of nickel aluminates. Prepared samples were tested when unreduced and reduced prior to reaction for methane dry reforming and methane steam reforming reactivity. NiAl2O4 in the reduced and unreduced state as well as NiAl4O7 in the reduced state are active and stable for methane dry reforming due to the presence of 4-fold coordinated oxidized nickel. The limited amount of metallic nickel in these samples minimizes carbon deposition. On the other hand, the presence of metallic nickel is required for methane ste...

A high-throughput, operando-ready X-ray absorption spectroscopy catalytic reaction cell consisting of 4 parallel reactors was designed to collect X-ray absorption near edge structure and extended fine structure spectra under reaction conditions. The cell is capable of operating at temperatures from ambient conditions up to 773 K and pressures from ambient to 2 MPa in a variety of gas environments. The cell design is mechanically simple, and programmable operation at beamline 8-ID (NSLS-II, Brookhaven National Laboratory) makes it straightforward to use. Reactor tube parts were available as-fabricated from commercial sources, while the heating jacket and cell mounting required custom machining.

NH3 synthesis by the electrocatalytic N2 reduction reaction (NRR) under ambient conditions is an appealing alternative to the currently employed industrial method-the Haber-Bosch process-that requires high temperature and pressure. We report single Mo atoms anchored to nitrogen-doped porous carbon as a cost-effective catalyst for the NRR. Benefiting from the optimally high density of active sites and hierarchically porous carbon frameworks, this catalyst achieves a high NH3 yield rate (34.0±3.6 μg NH 3 h-1 mgcat. -1 ) and a high Faradaic efficiency (14.6±1.6 %) in 0.1 m KOH at room temperature. These values are considerably higher compared to previously reported non-precious-metal electrocatalysts. Moreover, this catalyst displays no obvious current drop during a 50 000 s NRR, and high activity and durability are achieved in 0.1 m HCl. The findings provide a promising lead for the design of efficient and robust single-atom non-precious-metal catalysts for the electrocatalytic NRR.

This work was supported by Rice University. This research used the 8-ID (ISS) beamline of the National Synchrotron Light Source II and the Center for Functional Nanomaterials, US Department of Energy Office of Science User Facilities operated for the DOE Office of Science by Brookhaven National Laboratory under contract no. DE-SC0012704. Q.J. and H.N.A. acknowledge the support from King Abdullah University of Science and Technology (KAUST).

We report the development, testing, and demonstration of a setup for modulation excitation spectroscopy experiments at the Inner Shell Spectroscopy beamline of National Synchrotron Light Source - II. A computer algorithm and dedicated software were developed for asynchronous data processing and analysis. We demonstrate the reconstruction of X-ray absorption spectra for different time points within the modulation pulse using a model system. This setup and the software are intended for a broad range of functional materials which exhibit structural and/or electronic responses to the external stimulation, such as catalysts, energy and battery materials, and electromechanical devices.

We report a study of Co-doped berthierite Fe$_{1-x}$Co$_x$Sb$_2$S$_4$ ($x$ = 0, 0.1, and 0.2). The alloy series of Fe$_{1-x}$Co$_x$Sb$_2$S$_4$ crystallize in an orthorhombic structure with the Pnma space group, similar to FeSb$_2$, and show semiconducting behavior. The large discrepancy between activation energy for conductivity, $E_\rho$ (146 $\sim$ 270 meV), and thermopower, $E_S$ (47 $\sim$ 108 meV), indicates the polaronic transport mechanism. Bulk magnetization and heat capacity measurements of pure FeSb$_2$S$_4$ ($x$ = 0) exhibit a broad antiferromagnetic (AFM) transition ($T_N$ = 46 K) followed by an additional weak transition ($T^*$ = 50 K). Transition temperatures ($T_N$ and $T^*$) slightly decrease with increasing Co content $x$. This is also reflected in the thermal conductivity measurement, indicating strong spin-lattice coupling. Fe$_{1-x}$Co$_x$Sb$_2$S$_4$ shows relatively high value of thermopower (up to $\sim$ 624 $\mu$V K$^{-1}$ at 300 K) and thermal conductivity much lower when compared to FeSb$_{2}$, a feature desired for potential applications based on FeSb$_{2}$ materials.

We report the anomalous Hall effect (AHE) in single crystals of a quasi-two-dimensional ${\mathrm{Fe}}_{3\ensuremath{-}x}{\mathrm{GeTe}}_{2}$ ($x\ensuremath{\approx}0.36$) ferromagnet grown by the flux method which induces defects on the Fe site and bad metallic resistivity. Fe $K$-edge x-ray absorption spectroscopy was measured to provide information on the local atomic environment in such crystals. The dc and ac magnetic susceptibility measurements indicate a second-stage transition below 119 K in addition to the paramagnetic to ferromagnetic transition at 153 K. A linear scaling behavior between the modified anomalous Hall resistivity ${\ensuremath{\rho}}_{xy}/{\ensuremath{\mu}}_{0}{H}_{\mathrm{eff}}$ and longitudinal resistivity ${\ensuremath{\rho}}_{xx}^{2}M/{\ensuremath{\mu}}_{0}{H}_{\mathrm{eff}}$ implies that the AHE in ${\mathrm{Fe}}_{3\ensuremath{-}x}{\mathrm{GeTe}}_{2}$ should be dominated by the intrinsic Karplus-Luttinger mechanism rather than the extrinsic skew-scattering and side-jump mechanisms. The observed deviation in the linear-$M$ Hall conductivity ${\ensuremath{\sigma}}_{xy}^{A}$ below 30 K is in line with its transport characteristic at low temperatures, implying the scattering of conduction electrons due to magnetic disorder and the evolution of the Fermi surface induced by a possible spin-reorientation transition.