Synchrotron-based Spectroscopy Research Articles

Activating 2D MoS2 by loading 2D Cu–S nanoplatelets for improved visible light photocatalytic hydrogen evolution, drug degradation, and CO2 reduction

Finding reliable photocatalysts capable of driving reactions using only sunlight is more needed than ever. A variety of strategies to harvest sunlight and convert it into chemical energy have been successfully utilized such as synthesizing nanostructures, using metal nanoparticles, doping, and others. In this work, we discover a facile way to anchor CuS nanoplatelets on 2D MoS2 by the solvothermal method using ethylene glycol (EG) as both a reduction agent and an exfoliating agent of bulk MoS2. Using CuS as a co-catalysis on MoS2 with their huge surface areas, led to improved photocatalytic activity for three different applications including H2 evolution, CO2 reduction, and endosulfan degradation. Specifically, Cu–S@MoS2 3% nanocomposite produced 9.86 μmol g−1 h−1 of H2, 0.48 μmol g−1 h−1 of CO and full decomposition of endosulfan within 6 h. The Cu-loaded MoS2 nanocomposites were thoroughly characterized by spectroscopic (including synchrotron-based spectroscopy) and microscopic methods to understand the formation of Cu–S during the solvothermal process. Moreover, the role of the EG during the synthetic procedure was revealed experimentally and studied theoretically via DFT simulations.

Microbiological and geochemical characterization of As-bearing tailings and underlying sediments

Over the past 100 years, extensive oxidation of As-bearing sulfide-rich tailings from the abandoned Long Lake Gold Mine (Canada) has resulted in the formation of acid mine drainage (pH 2.0–3.9) containing high concentrations of dissolved As (∼400 mg L−1), SO42-, Fe and other metals. Dissolved As is predominantly present as As(III), with increased As(V) near the tailings surface. Pore-gas O2 is depleted to < 1 vol% in the upper 30–80 cm of the tailings profile. The primary sulfides, pyrite and arsenopyrite, are highly oxidized in the upper portions of the tailings. Elevated proportions of sulfide-oxidizing prokaryotes are present in this zone (mean 32.3% of total reads). The tailings are underlain by sediments rich in organic C. Enrichment in δ34S-SO4 in pore-water samples in the organic C-rich zone is consistent with dissimilatory sulfate reduction. Synchrotron-based spectroscopy indicates an abundance of ferric arsenate phases near the impoundment surface and the presence of secondary arsenic sulfides in the organic-C beneath the tailings. The persistence of elevated As concentrations beneath the tailings indicates precipitation of secondary As sulfides is not sufficient to completely remove dissolved As. The oxidation of sulfides and release of As is expected to continue for decades. The findings will inform future remediation efforts and provide a foundation for the long-term monitoring of the effectiveness of the remediation program.

Atomic Layer Grown Zinc–Tin Oxide as an Alternative Buffer Layer for Cu2ZnSnS4-Based Thin Film Solar Cells: Influence of Absorber Surface Treatment on Buffer Layer Growth

Zn1-x Sn x O y (ZTO) deposited by atomic layer deposition has shown promising results as a buffer layer material for kesterite Cu2ZnSnS4 (CZTS) thin film solar cells. Increased performance was observed when a ZTO buffer layer was used as compared to the traditional CdS buffer, and the performance was further increased after an air annealing treatment of the absorber. In this work, we study how CZTS absorber surface treatments may influence the chemical and electronic properties at the ZTO/CZTS interface and the reactions that may occur at the absorber surface prior to atomic layer deposition of the buffer layer. For this, we have used a combination of microscopy and synchrotron-based spectroscopies with variable information depths (X-ray photoelectron spectroscopy, high-energy X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy), allowing for an in-depth analysis of the CZTS near-surface regions and bulk material properties. No significant ZTO buffer thickness variation is observed for the differently treated CZTS absorbers, and no differences are observed when comparing the bulk properties of the samples. However, the formation of SnO x and compositional changes observed toward the CZTS surface upon an air annealing treatment may be linked to the modified buffer layer growth. Further, the results indicate that the initial N2 annealing step integrated in the buffer layer growth by atomic layer deposition, which removes Na-CO x species from the CZTS surface, may be useful for the ZTO/CZTS device performance.

Band alignment determination in few-layer exfoliated MoSe2/SiO2 interface using Synchrotron-based photoemission spectroscopy

Band alignment determination in few-layer exfoliated MoSe2/SiO2 interface using Synchrotron-based photoemission spectroscopy

Electronic Properties of Fully Strained La1-x Sr x MnO3 Thin Films Grown by Molecular Beam Epitaxy (0.15 ≤ x ≤ 0.45).

The structural, electronic, and magnetic properties of Sr-hole-doped epitaxial La1–xSrxMnO3 (0.15 ≤ x ≤ 0.45) thin films deposited using the molecular beam epitaxy technique on 4° vicinal STO (001) substrates are probed by the combination of X-ray diffraction and various synchrotron-based spectroscopy techniques. The structural characterizations evidence a significant shift in the LSMO (002) peak to the higher diffraction angles owing to the increase in Sr doping concentrations in thin films. The nature of the LSMO Mn mixed-valence state was estimated from X-ray photoemission spectroscopy together with the relative changes in the Mn L2,3 edges observed in X-ray absorption spectroscopy (XAS), both strongly affected by doping. CTM4XAS simulations at the XAS Mn L2,3 edges reveal the combination of epitaxial strain, and different MnO6 crystal field splitting give rise to a peak at ∼641 eV. The observed changes in the occupancy of the eg and the t2g orbitals as well as their binding energy positions toward the Fermi level with hole doping are discussed. The room-temperature magnetic properties were probed at the end by circular dichroism.

A Review of State of the Art in Phosphine Ligated Gold Clusters and Application in Catalysis.

Atomically precise gold clusters are highly desirable due to their well‐defined structure which allows the study of structure–property relationships. In addition, they have potential in technological applications such as nanoscale catalysis. The structural, chemical, electronic, and optical properties of ligated gold clusters are strongly defined by the metal–ligand interaction and type of ligands. This critical feature renders gold–phosphine clusters unique and distinct from other ligand‐protected gold clusters. The use of multidentate phosphines enables preparation of varying core sizes and exotic structures beyond regular polyhedrons. Weak gold–phosphorous (Au–P) bonding is advantageous for ligand exchange and removal for specific applications, such as catalysis, without agglomeration. The aim of this review is to provide a unified view of gold–phosphine clusters and to present an in‐depth discussion on recent advances and key developments for these clusters. This review features the unique chemistry, structural, electronic, and optical properties of gold–phosphine clusters. Advanced characterization techniques, including synchrotron‐based spectroscopy, have unraveled substantial effects of Au–P interaction on the composition‐, structure‐, and size‐dependent properties. State‐of‐the‐art theoretical calculations that reveal insights into experimental findings are also discussed. Finally, a discussion of the application of gold–phosphine clusters in catalysis is presented.

Infrared phonon spectroscopy on the Cairo pentagonal antiferromagnet Bi2Fe4O9 : A study through the pressure-induced structural transition

Magnetic and crystallographic transitions in the Cairo pentagonal magnet ${\mathrm{Bi}}_{2}{\mathrm{Fe}}_{4}{\mathrm{O}}_{9}$ are investigated by means of infrared synchrotron-based spectroscopy as a function of temperature (20--300 K) and pressure (0--15.5 GPa). One of the phonon modes is shown to exhibit an anomalous softening as a function of temperature in the antiferromagnetic phase below 240 K, highlighting spin-lattice coupling. Moreover, under applied pressure at 40 K, an even larger softening is observed through the pressure-induced structural transition. Lattice dynamical calculations reveal that this mode is indeed very peculiar as it involves a minimal bending of the strongest superexchange path in the pentagonal planes, as well as a decrease in the distances between second-neighbor irons. The latter confirms the hypothesis made by Friedrich et al., [J. Phys.: Condens. Matter 24, 145401 (2012)] about an increase in the oxygen coordination of irons being at the origin of the pressure-induced structural transition. As a consequence, one expects a new magnetic superexchange path that may alter the magnetic structure under pressure.

Interfacial electronic coupling and band alignment of P3HT and exfoliated black phosphorous van der Waals heterojunctions

The band alignment and the interfacial electronic coupling of van der Waals heterojunctions formed by the Poly[3-hexylthiophene-2,5-diyl] (P3HT) semiconductor polymer and the mechanically exfoliated black phosphorous (BP) multilayers were investigated using different spectroscopies techniques. The energy band alignment was assessed using Ultraviolet (UPS) and X-ray (XPS) photoelectron spectroscopies. The result of this analysis shows that the P3HT-BP interface presents a type I band alignment with conduction band minimum and the valence band maximum located in the BP layer. A valence band offset of 0.45 eV and a conduction band offset of 1.25 eV parameters were found. Near-Edge X-ray Absorption Fine Structure (NEXAFS) and resonant Auger (RAS) synchrotron-based spectroscopies were used to investigate the interfacial electronic coupling between BP and P3HT. Interfacial charge transfer times obtained from core hole clock approach and using the S1s core–hole lifetime as a reference time were used as quantitative parameters to measure the degree of electronic coupling. We found that the π*(SC) electronic state is the faster electron delocalization pathway from the P3HT to the BP conduction band and therefore there is a strong electronic coupling between these states. This result was supported from density functional theoretical calculations.

(Invited) From Atomic-Scale Understanding to Design of Advanced Electrocatalyst Materials

Increasing concerns regarding the environmental impact of power generation and the reduction of carbon emissions have become a major motivation for the use of sustainable electrical power. In this perspective, renewable energy sources are expected to take up an important part of electric energy produced in the near future. Since renewable sources such as wind and solar are intermittent in nature, their increased installation will result in either excessive or insufficient power generation at times. A large variety of concepts for using this surplus power is currently under development.Acidic water electrolysis is an attractive environmentally-safe solution for the conversion and storage of excess electricity into hydrogen and oxygen. The large scale application of water electrolysis systems is currently hindered by low efficiency and instability of catalysts during long term operation [1]. This is especially crucial for the anodic oxygen evolution reaction (OER) which catalyzed by Iridium based alloys and oxides making the issues related to efficiency of catalyst utilization and durability even more critical. The development of catalyst materials with superior performance demands a deep understanding of the OER itself as well as electrocatalysts degradation mechanisms. Although a large number of possible OER mechanisms have been proposed [2], the topic remains a subject of intensive debates across the scientific literature, since the intermediates and their possible interrelations are in most cases unknown. Additional challenges in mechanistic studies are related to the changes in the composition of the catalyst and its degradation triggered by OER. Though the existence of experimental correlation between the structure, activity of OER catalyst and its dissolution was numerously reported and discussed [2,3], reports addressing all these aspects in one study are rare. This indicates that further research efforts are required to reveal reaction intermediates and products by means, for instance, of mass spectrometry at the atomic scale by atom probe tomography, that complement spectroscopic insight from synchrotron-based experiments, ideally in operando conditions.In this presentation, the main fundamental limitations that hinder the current understanding of the reactions mechanisms occurring in water electrolysis will be discussed. It will be stressed that only the combination of insights enables the establishing of reliable structure-function relationships in electrocatalyst materials. We present our approach to investigate complex processes in electrocatalysis with a combination of independent methods like online electrochemical mass spectrometry, atom probe tomography and synchrotron-based spectroscopy [4,5]. In particular, we discuss approaches to resolving the reaction mechanism on constantly evolving surfaces; present our recent results on the interplay between the nature of the active sites in Ir-based oxides and their stability towards the OER and establish structure–function relationships between the reactivity and the atomic-scale surface structure [5]. Finally, using the new insights gained in our recent studies [4-6], we discuss potential design strategy for Ir-based OER catalysts with high catalytic activity and long-term stable performance.[1] S. Cherevko et al., Catalysis Today 2016, 262, 170-180[2] T. Reier, H.N. Nong, D. Teschner, R. Schlögl, P. Strasser, Adv. Energy Mater. 2017, 7(1), 1601275.[3] O. Kasian, J.P. Grote, S. Geiger, S. Cherevko, K.J.J. Mayrhofer, Angew. Chem. Int. Ed. 2018, 57, 2488 –2491.[4] K. Schweinar, R.L. Nicholls, C.R. Rajamathi, P. Zeller, M. Amati, L. Gregoratti, D. Raabe, M. Greiner, B. Gault, O. Kasian, J. Mater. Chem. A 2020, 8(1), 388-400.[5] O. Kasian, S. Geiger, T. Li, J-P. Grote, K. Schweinar, S. Zhang, C. Scheu, D. Raabe, S. Cherevko, B. Gault, K. Mayrhofer, Energy Environ. Sci. 2019, 12(12), 3548-3555.[6] K. Schweinar, I. Mouton, B. Gault, O. Kasian, J. Phys. Chem. Lett. 2020, submitted.

Non-Equilibrium Lattice Heterogeneity As the Unified Kinetic Hurdle of Ni-Rich Layered Cathode for Ultrafast Lithium Ion Batteries

The significantly reduced capacity at a fast cycling rate is one of the most serious bottlenecks that prevent the large-scale application of Ni-rich layered oxide cathode for electrical vehicle batteries. Figuring out the capacity decline mechanism is crucial to addressing such hurdle and developing ultrafast lithium ion batteries. In this work, with operando synchrotron-based spectroscopy, we captured the formation of non-equilibrium separated phases during the extremely fast cycling of various Ni-rich layered oxides, in contrast to their solid-solution structural evolution pathway at slow cycling rate. Further, such non-equilibrium phase heterogeneity was demonstrated to be an effective capacity retention descriptor for Ni-rich layered oxide cathode: the capacity retention ratio is liner inversely proportional to the lattice heterogeneity at an extremely fast cycling rate (e.g., 10C), regardless of the composition and Ni content. Those detrimental non-equilibrium phase heterogeneity could be eliminated by raising the operation temperature, contributing to much higher lithium ion transport kinetics and better capacity retention during ultrafast cycling

Mechanisms of Pyrite Formation Promoted by Sulfate-Reducing Bacteria in Pure Culture

Pyrite, or iron disulfide, is the most common sulfide mineral at Earth’s surface and is widespread through the geological record. Because sulfides are mainly produced by sulfate-reducing bacteria (SRB) in modern sedimentary environments, microorganisms are assumed to drive the formation of iron sulfides, in particular pyrite. However, the exact role played by microorganisms in pyrite formation remains unclear and, to date, the precipitation of pyrite in microbial cultures has only rarely been achieved. The present work relies on chemical monitoring, electron microscopies, X-ray diffraction and synchrotron-based spectroscopy to evaluate the formation of iron sulfides by sulfate-reducing bacteria Desulfovibrio desulfuricans as a function of the source of iron, either provided as dissolved Fe2+ or as FeIII-phosphate nanoparticles. Dissolved ferrous iron led to the formation of increasingly crystalline mackinawite (FeS) with time, encrusting bacteria cell walls, hence preventing further sulfate reduction upon day 5 and any evolution of iron sulfides into more stable phases, e.g. pyrite. In contrast, ferric phosphate was transformed into a mixture of large flattened crystals of well crystallized vivianite (Fe3(PO4)2 . 8 H2O) and a biofilm-like thin film of poorly crystallized mackinawite. Although being hosted in the iron sulfide biofilm, most cells were not encrusted. Excess-sulfide delivered by the bacteria and oxidants (such as polysulfides) promoted the evolution of mackinawite into greigite (Fe3S4) and the nucleation of pyrite spherules. These spherules were several hundreds nanometer wide and occurred within the extracellular polymeric substance (EPS) of the biofilm after only 1 month. Altogether, the present study demonstrates that the mineral assemblage induced by the metabolic activity of SRB strongly depends on the source of iron, which has strong implications for the interpretation of the presence of pyrite and vivianite in natural environments.

Synchrotron-based spectroscopy and imaging reveal changes in the cell-wall composition of barley leaves in defence responses to Blumeria graminis f. sp. tritici

Plant cell walls (CW) are composed mainly of cellulose–hemicellulose networks embedded in a pectin matrix. CW apposition, including papilla formation, is often associated with plant defence responses to infection by fungal pathogens. In this study, synchrotron-based Fourier transform infrared (sFTIR) spectroscopy and focal plane array (FPA) imaging were explored to characterize changes in CW chemical composition of barley leaf epidermis inoculated with the powdery mildew fungus of wheat that was unable to infect the barley cultivar ‘CDC Silky’ successfully. Spectroscopic results showed increased intensity of peaks representing asymmetric and symmetric stretching vibrations that correspond to fatty acid groups, phenolics/lignin, cellulose, hemicellulose, pectins and glucans. sFTIR spectral data separated the inoculated samples (with papillae formation) from non-inoculated controls, based on CW components including lignin/phenolics, polysaccharides and glucans. These results were further verified with FPA imaging. This is the first report on using sFTIR spectroscopy and FPA imaging to analyse in situ composition of plant cell wall components in relation to host defence responses. These findings, especially the changes in cellulose, hemicelluloses, pectins and glucans, lend support to a proposed structure of effective papillae, as well as to callose-cellulose networks associated with the defence response of barley against powdery mildew. Increases in phenolics likely help strengthen CW, in addition to direct effects on pathogens. The results also demonstrate that sFTIR and FPA analyses can be useful to study plant–pathogen interactions, especially in determining the role of cell wall apposition in response to fungal infection.

Fe-incorporated TiO2 nanotube arrays: Electronic structure and magnetic response

Incorporating Fe atoms into the lattice is shown to significantly alter electronic and magnetic properties of $\mathrm{Ti}{\mathrm{O}}_{2}$ nanotubes synthesized by electrochemical anodization of Ti-Fe alloy sheets. The effects of Fe incorporation on the nanotube morphology, crystallinity, crystal structure, magnetic behavior and electronic structure were investigated with crystallographic and magnetic probes, including synchrotron-based spectroscopy. Results indicate that the iron cations predominately adopt the $\mathrm{F}{\mathrm{e}}^{3+}$ configuration, leading to a large increase of the electronic density of states at the Fermi energy. This increase is anticipated to provide enhanced catalytic action, for instance, in the degradation of water and of air pollutants. These results provide insight for tailoring the functionality of these nanostructures for energy-related applications.

Single-Crystal Nitrogen-Rich Two-Dimensional Mo5N6 Nanosheets for Efficient and Stable Seawater Splitting.

Transition metal nitrides (TMNs) have great potential for energy-related electrocatalysis because of their inherent electronic properties. However, incorporating nitrogen into a transition metal lattice is thermodynamically unfavorable, and therefore most of the developed TMNs are deficient in nitrogen. Consequently, these TMNs exhibit poor structural stability and unsatisfactory performance for electrocatalytic applications. In this work, we design and synthesize an atomically thin nitrogen-rich nanosheets, Mo5N6, with the help of a Ni-inducing growth method. The as-prepared single-crystal electrocatalyst with abundant metal-nitrogen electroactive sites displays outstanding activity for the hydrogen evolution reaction (HER) in a wide range of electrolytes (pH 0-14). Further, the two-dimensional Mo5N6 nanosheets exhibit high HER activity and stability in natural seawater that are superior to other TMNs and even the Pt benchmark. By combining synchrotron-based spectroscopy and the calculations of electron density of state, we find that the enhanced properties of these nitrogen-rich Mo5N6 nanosheets originates from its Pt-like electronic structure and the high valence state of its Mo atoms.

Ultrahigh-vacuum organic molecular-beam deposition system for in situ growth and characterization.

A compact ultrahigh-vacuum molecular-beam deposition system has been developed for the in situ synthesis of organic thin films and multilayers. The system incorporates all the features (heater, thickness monitor, evaporators) necessary for controlled organic thin-film growth. It can be used independently, or it can be docked to the in situ growth system and transferred to other instruments of the PGM beamline, thus allowing extensive film preparation and characterization. A manipulator dedicated to specimen preparation and organic-film deposition with temperature control between 200 K and ∼800 K has been developed. The design and performance of the system are reported with emphasis on a novel solution of masks developed to achieve position-dependent film deposition. To demonstrate the enhanced capabilities of the PGM beamline in the growth and in the characterization of electronic-structure studies of organic molecular films and their heterostructures through synchrotron-based spectroscopies, this paper presents some preliminary results of a study of Fe-phthalocyanine growth on Si substrates and on in situ prepared La0.67Sr0.33MnO3 buffer layers on SrTiO3 single crystal.

Far-infrared synchrotron-based spectroscopy of CH3SH from 50 to 560 cm−1: Near-free-rotor torsion-rotation structure and torsion-vibration interactions

Analysis of torsion-rotation structure in the far-infrared Fourier transform synchrotron spectrum of CH332SH recorded from 50 to 560 cm−1 at the Far-Infrared Beamline of the Canadian Light Source has been extended to higher near-free rotor torsional states reaching up into the region of the small-amplitude vibrations. A variety of sub-bands has been assigned for torsional quantum number up to vt = 5, expanding the database of ground-state energy term values to higher K and vt levels to provide a broad foundation for associated investigations of the vibrational spectrum. The origins of the high-vt sub-states fit quite well to a pattern of free-rotor parabolic curves as a function of K, but with a lower value of the torsional constant F than obtained from previous global analysis of lower-vt data. Numerous resonances perturbing and mixing coupled near-degenerate sub-states have been observed, arising from interactions both within the ground state and between ground and excited vibrational levels.

Probing the interaction between 2,2'-bithiophene-5-carboxylic acid and TiO2 by photoelectron spectroscopy: A joint experimental and theoretical study.

The interaction between 2,2'-bithiophene-5-carboxylic acid (PT2) sublimed under ultra-high vacuum conditions and anatase (101) and rutile (110) TiO2 single crystal surfaces is investigated by studying the electronic spectral density near the Fermi level with synchrotron-based spectroscopy. The experimental results are compared to density functional theory calculations of the isolated PT2 molecule and of the molecule adsorbed on an anatase TiO2 (101) cluster. The relative concentrations of Ti, C, and S atoms indicate that the adsorbed molecule remains intact upon deposition, which is typical of a Stranski-Krastanov growth mode. The analysis of the O1s spectrum suggests a predominant bidentate geometry of the adsorption with both rutile and anatase surfaces, as supported by previous theoretical simulations. It is also theoretically and experimentally demonstrated that the PT2 adsorption causes the appearance of new electronic states in the gap near the TiO2 valence band. A pinning effect of the LUMO level of the dye is also theoretically predicted.

Fundamental interplay between anionic/cationic redox governing the kinetics and thermodynamics of lithium-rich cathodes

Reversible anionic redox has rejuvenated the search for high-capacity lithium-ion battery cathodes. Real-world success necessitates the holistic mastering of this electrochemistry’s kinetics, thermodynamics, and stability. Here we prove oxygen redox reactivity in the archetypical lithium- and manganese-rich layered cathodes through bulk-sensitive synchrotron-based spectroscopies, and elucidate their complete anionic/cationic charge-compensation mechanism. Furthermore, via various electroanalytical methods, we answer how the anionic/cationic interplay governs application-wise important issues—namely sluggish kinetics, large hysteresis, and voltage fade—that afflict these promising cathodes despite widespread industrial and academic efforts. We find that cationic redox is kinetically fast and without hysteresis unlike sluggish anions, which furthermore show different oxidation vs. reduction potentials. Additionally, more time spent with fully oxidized oxygen promotes voltage fade. These fundamental insights about anionic redox are indispensable for improving lithium-rich cathodes. Moreover, our methodology provides guidelines for assessing the merits of existing and future anionic redox-based high-energy cathodes, which are being discovered rapidly.

(Invited) Elucidating Oxygen Evolution on Model Oxide Electrodes

It is particularly challenging to catalyse oxygen evolution under the acidic conditions of polymer electrolyte membrane (PEM) electrolysers. All compounds, apart from IrO x and RuO x , are catalytically inactive or unstable. I will present a series of model studies where we aim to elucidate the factors that control oxygen evolution. Using thin films of RuO2, we showed that continuous mass losses occur in parallel to oxygen evolution, even when the electrochemical response is stable.1 This finding demonstrates that short term electrochemical measurements are an insufficient measure of long term stability. Our experiments on mass-selected Ru and RuOx particles revealed the high sensitivity of the oxygen evolution performance of nanoparticulate catalysts to the exact oxidation treatment.2,3 X-ray absorption measurements, taken in-operando, provide spectroscopic evidence for the potential dependent coverage of the reaction intermediates. Moreover, tests on oriented thin films indicate that the “coordinatively unsaturated” surface site is responsible for the activity of RuO2.4 Our very recent studies suggest that the dissolution rate of RuO2 is also highly dependent on the orientation. The scarcity of RuOx and IrOx could limit the scalability of PEM electrolysers. An alternative strategy could be utilise non-precious metal oxides to catalyse oxygen evolution in acid. However, most non-precious metal oxides exhibit poor stability. Theoretical calculations predicted that MnO x could be stabilised against corrosion by the presence of TiO x at its surface, without affecting the catalytic activity. Our experiments on sputter-deposited thin films verify this notion. 5 The catalysts under investigation include model-size selected nanoparticles, commercial high surface area catalysts, sputtered films and oriented thin films. We have probed these surfaces with electrochemical measurements, ultra-high vacuum based surface science methods, electron microscopy, synchrotron-based spectroscopy and density functional theory calculations. 1 Frydendal, R., Paoli, E. A., Knudsen, B. P., Wickman, B., Malacrida, P., Stephens, I. E. L. & Chorkendorff, I. ChemElectroChem 1, 2075, (2014). 2 Paoli, E. A., Masini, F., Frydendal, R., Deiana, D., Malacrida, P., Hansen, T. W., Chorkendorff, I. & Stephens, I. E. L. Catal. Today 262, 57, (2016). 3 Paoli, E. A., Masini, F., Frydendal, R., Deiana, D., Schlaup, C., Malizia, M., Hansen, T. W., Horch, S., Stephens, I. E. L. & Chorkendorff, I. Chemical Science 6, 190, (2015). 4 Stoerzinger, K. A., Diaz-Morales, O., Kolb, M., Rao, R. R., Frydendal, R., Qiao, L., Wang, X. R., Halck, N. B., Rossmeisl, J., Hansen, H. A., Vegge, T., Stephens, I. E. L., Koper, M. T. M. & Shao-Horn, Y. ACS Energy Letters , 876, (2017). 5 Frydendal, R., Paoli, E. A., Chorkendorff, I., Rossmeisl, J. & Stephens, I. E. L. Adv. Energy Mater. 5, 1500991, (2015).

Effects of plant growth and time on phosphorus speciation in a manure-amended Prairie soil under controlled conditions

The fate of phosphorus (P) added as manure to soils is affected by the presence of plants and time. A growth chamber study was conducted to determine how the presence of canola (B. napus) plants influences the forms and distribution of P in a typical cultivated prairie (Saskatchewan, Canada) soil at 1, 3, and 5 weeks after addition of solid cattle manure (SCM) and liquid hog manure (LHM). Techniques used for speciation of soil P included sequential chemical extraction and synchrotron-based spectroscopy. Manure addition, especially SCM, increased P concentration in the labile fractions, with similar patterns of change in P fractions over time and effects of plant uptake on fractions in both manured and non manured soils. The concentrations of most P forms were decreased in the presence of plants, especially labile P (resin-P and NaHCO3-P) in the SCM soil after 5 weeks of plant growth. A significant increase in NaOH extractable inorganic P and more stable HCl extractable P was observed over time along with significant decrease of resin-P and NaOH organic P forms. The X-ray absorption near-edge structure (XANES) spectroscopy results indicated that no large changes in the bulk speciation or P crystallinity in the manured soil were occurring over the five-week period. This suggests that plant growth drew from all soil P pools relatively equally during this study.