Dissolution of a platinum catalyst is a major degradation mechanism of fuel cells, but the exact reaction mechanism has remained unclear. Here, electrochemical ambient pressure X-ray photoelectron spectroscopy (EC-APXPS) was utilized to provide direct information on chemical species on a single-crystal Pt(111) electrode under extremely low pH conditions. Measurements were conducted using a novel condensed electrolyte film electrochemical cell applying work function measurement as a loss-free probe for electrochemical potential. We show that platinum can dissolve chemically as Pt2+ ion during potential cycling and redeposit as Pt2+ at the onset potential for cathodic reactions. The dissolution of Pt does not require electrochemical oxidation via oxide place exchange. In contrast, the adsorption of oxygenated species (OH* or O*) at the onset potential for anodic reactions is a sufficient prerequisite to the dissolution. These results provide new insight into the degradation mechanism of Pt under extremely low pH conditions, predicted by the Pourbaix diagram, having practical applications to the durability of Pt-based catalysts in electrochemical energy conversion devices.

Electron-beam writer characterization is key to enable predictable product performance in a photomask shop. This is traditionally done by writing test patterns with one distinct tool on one blank Within this article, we introduce a method that reduces uncertainty caused by variation of blanks and process parameters, by using multiple, subsequent electron beam exposure steps with different same-of-a-kind tools. The method is demonstrated for the disentanglement of two of the most fundamental parameters in an e-beam tool, current density and blanker latency, which together determine the actual dose. Additional accuracy can be achieved by probing the same tool parameter with different methods, which is shown by comparing Critical Dimension Scanning Electron Microscopy of line-space patterns below the maximum shot size with Thin Film Optical Scatterometry of comparatively large pads. The multiple exposure method needs a proper correction of systematic effects caused by contact of exposed areas with air during mask transfer from one writer to another, which are presented and discussed.

We report on atom-specific activation of CO oxidation on Ru(0001) via resonant X-ray excitation. We show that resonant 1s core-level excitation of atomically adsorbed oxygen in the co-adsorbed phase of CO and oxygen directly drives CO oxidation. We separate this direct resonant channel from indirectly driven oxidation via X-ray induced substrate heating. Based on density functional theory calculations, we identify the valence-excited state created by the Auger decay as the driving electronic state for direct CO oxidation. We utilized the fresh-slice multi-pulse mode at the Linac Coherent Light Source that provided time-overlapped and 30 fs delayed pairs of soft X-ray pulses and discuss the prospects of femtosecond X-ray pump X-ray spectroscopy probe, as well as X-ray two-pulse correlation measurements for fundamental investigations of chemical reactions via selective X-ray excitation.

The dynamics of liquid water feature a variety of time scales, ranging from extremely fast ballistic-like thermal motion, to slower molecular diffusion and hydrogen-bond rearrangements. Here, we utilize coherent X-ray pulses to investigate the sub-100 fs equilibrium dynamics of water from ambient conditions down to supercooled temperatures. This novel approach utilizes the inherent capability of X-ray speckle visibility spectroscopy to measure equilibrium intermolecular dynamics with lengthscale selectivity, by measuring oxygen motion in momentum space. The observed decay of the speckle contrast at the first diffraction peak, which reflects tetrahedral coordination, is attributed to motion on a molecular scale within the first 120 fs. Through comparison with molecular dynamics simulations, we conclude that the slowing down upon cooling from 328 K down to 253 K is not due to simple thermal ballistic-like motion, but that cage effects play an important role even on timescales over 25 fs due to hydrogen-bonding.

The electrochemical carbon dioxide reduction reaction (CO2RR) allows the storage of energy in readily available chemicals such as ethylene and other hydrocarbons, while contributing to the abatement of CO2. Copper is the only pure metal able to perform CO2RR with appreciable activity and selectivity towards multi-carbon products, due to optimal binding of the key intermediate CO,1 especially when the electrode is nanostructured and derived from an oxide.2 Oxide-derived copper (OD-Cu) electrodes exhibit activity and ethylene selectivity higher than pristine copper during the carbon dioxide reduction reaction (CO2RR), and the presence of residual subsurface oxygen in OD-Cu is associated with such improvement.3 In order to establish a structure-activity relationship for the catalyst during reaction, operando investigation is necessary. Using in situ x-ray photoelectron spectroscopy (XPS), quasi in situ electron energy-loss spectroscopy (EELS) in a transmission electron microscope (TEM) and quasi in situ positron annihilation spectroscopy (PAS), we show that oxygen is primarily concentrated in an amorphous 1-2 nm thick layer on the OD-Cu surface (see Figure), it is stable during CO2RR for up to 1 hour at -1.15 V vs RHE and is associated with a high density of defects in the OD-Cu structure.4 Corroborated with density functional theory (DFT) calculations on copper nanoclusters we show that both the low-coordination of the amorphous OD-Cu surface and the presence of subsurface oxygen that withdraws charge from the copper d-band selectively enhance the binding energy of CO without altering that of other reaction intermediates, therefore breaking the scaling relation between d-band center vs CO binding energy.4,5 (1) Peterson, A. A.; Nørskov, J. K. Activity Descriptors for CO2 Electroreduction to Methane on Transition-Metal Catalysts. J. Phys. Chem. Lett. 2012, 3 (2), 251–258. (2) Roberts, F. S.; Kuhl, K. P.; Nilsson, A. High Selectivity for Ethylene from Carbon Dioxide Reduction over Copper Nanocube Electrocatalysts. Angew. Chemie 2015, 127, 5268–5271. (3) Eilert, A.; Cavalca, F.; Roberts, F. S.; Osterwalder, J.; Liu, C.; Favaro, M.; Crumlin, E. J.; Ogasawara, H.; Friebel, D.; Pettersson, L. G. M.; et al. Subsurface Oxygen in Oxide-Derived Copper Electrocatalysts for Carbon Dioxide Reduction. J. Phys. Chem. Lett. 2017, 8 (1), 285–290. (4) Cavalca, F.; Ferragut, R.; Aghion, S.; Eilert, A.; Diaz-Morales, O.; Liu, C.; Koh, A. L.; Hansen, T. W.; Pettersson, L. G. M.; Nilsson, A. Nature and Distribution of Stable Subsurface Oxygen in Copper Electrodes During Electrochemical CO 2 Reduction. J. Phys. Chem. C 2017, acs.jpcc.7b08278. (5) Liu, C.; Lourenço, M. P.; Hedström, S.; Cavalca, F.; Diaz-Morales, O.; Duarte, H. A.; Nilsson, A.; Pettersson, L. G. M. Stability and Effects of Subsurface Oxygen in Oxide-Derived Cu Catalyst for CO 2 Reduction. J. Phys. Chem. C 2017, acs.jpcc.7b08269. Figure 1

Copper electrocatalysts derived from an oxide have shown extraordinary electrochemical properties for the carbon dioxide reduction reaction (CO2RR). Using in situ ambient pressure X-ray photoelectron spectroscopy and quasi in situ electron energy-loss spectroscopy in a transmission electron microscope, we show that there is a substantial amount of residual oxygen in nanostructured, oxide-derived copper electrocatalysts but no residual copper oxide. On the basis of these findings in combination with density functional theory simulations, we propose that residual subsurface oxygen changes the electronic structure of the catalyst and creates sites with higher carbon monoxide binding energy. If such sites are stable under the strongly reducing conditions found in CO2RR, these findings would explain the high efficiencies of oxide-derived copper in reducing carbon dioxide to multicarbon compounds such as ethylene.

The knowledge of the particle content is essential for the improvement of nanocomposites, for instance with respect to mechanical strengthening. However, the demand of evaluating the fraction of nanodiamonds in Ni-P coatings, i.e. nano-sized light element particles in a heavy metal alloy matrix is a crucial task. Results obtained by means of high performance wavelength dispersive X-ray fluorescence analysis, energy dispersive X-ray spectroscopy and quantitative metallography are compared. On the basis of calculated fractions of incorporated particles as a function of their size and distance, the differing results are discussed. Best confidence has been achieved for composites with a fairly uniform particle distribution providing best features for application as functional materials in any case.The particle fraction can be provided at least as an approximate range regardless of the applied method.

We investigated the adsorption and reaction of pyridine on flat Pt(111) and stepped Pt(355) surfaces via high-resolution in situ x-ray photoelectron spectroscopy. The surfaces were exposed to pyridine at temperatures between 112 and 300 K while simultaneously recording XP spectra. Subsequently, the crystals were annealed and the temperature dependencies of the N 1s and C 1s core levels were studied again in a continuous and quantitative way. Various surface species were found, namely, physisorbed, flat-lying and end-on pyridine, α-pyridyl species on the terraces and on the steps and several unidentified high temperature species. We were able to show an influence of the steps of Pt(355) by pre-adsorbing silver next to the step, which selectively suppresses the step adsorption.

Nanostructured copper cathodes are among the most efficient and selective catalysts to date for making multicarbon products from the electrochemical carbon dioxide reduction reaction (CO2RR). We report an in situ X-ray absorption spectroscopy investigation of the formation of a copper nanocube CO2RR catalyst with high activity that highly favors ethylene over methane production. The results show that the precursor for the copper nanocube formation is copper(I)-oxide, not copper(I)-chloride as previously assumed. A second route to an electrochemically similar material via a copper(II)-carbonate/hydroxide is also reported. This study highlights the importance of using oxidized copper precursors for constructing selective CO2 reduction catalysts and shows the precursor oxidation state does not affect the electrocatalyst selectivity toward ethylene formation.

In the present study, the possibility of extracting biogenic silica from various European biomass materials was investigated. High-purity biogenic silica (>90 wt % SiO2) was obtained from energy crops (miscanthus), agro wastes (wheat straw), and other crop residues (cereal remnant pellets). Three different morphological forms of biogenic silica materials (ash) were obtained by a thermo-chemical treatment of these biomass sources. The wet biomass materials were leached using 5 M sulfuric acid for a defined period of time. After washing and drying the biomass materials, the leached samples were subjected to a heat treatment in a furnace with three sequential temperatures and time stages to determine the minimum combustion temperature of the organic compounds in the biomass materials. The final products were characterized by X-ray diffraction, X-ray fluorescence, carbon content analysis, differential thermal analysis, low temperature nitrogen adsorption, mercury intrusion porosimetry, and scanning electron microscopy. The obtained silica materials had a microstructure composed of accessible, interconnected, and intraparticle meso- and macropores with sizes ranging from 3 to 1500 nm.

In this study Egyptian diatomaceous earth from Kasr El-Sagha locality in El Fayium province, Egypt was used. A highly purified diatomite has been prepared successfully by using a two stage process. In the first stage, samples of Egyptian diatomite were subjected to several mechanical techniques (attrition scrubbing and hydrocyclone classification) to remove most of the accompanied gangue minerals like inorganic carbonate, silica sand, and clay. The fraction with a particle size of −45μm was then submitted to a thermo-chemical treatment. This second stage started with a calcination of the diatomite samples at 1023K for 1h. Three modified forms of diatomite were then prepared by hot acidification of the calcined diatomite samples with aqua regia (5M HCl+5M HNO3), 5M sulphuric acid or 5M hydrochloric acid. The refined products were characterized by X-ray diffraction, X-ray fluorescence, low temperature nitrogen adsorption, mercury intrusion and scanning electron microscopy. Silica materials with high purity (>96wt.% SiO2) and an accessible and interconnected mesopore structure could be obtained. Additionally, all samples displayed a large amount of macropores of about 1μm diameter and a broad distribution of larger interstitial macropores. The treatment with hydrochloric acid led to products with a specific surface area between 120 and 150m2g−1 and 63wt.% of amorphous phase.

This study presents two routes to produce amorphous silica from an Egyptian rice husk under conditions optimized for least environmental impact and low cost. The first route includes thoroughly washing of the husk sample with water, dry milling and leaching with citric acid. The leaching process was applied in two stages, that is, at 323K for 180min and then at 353K for 60min. After washing and drying, the leached sample was subjected to a heat treatment in a muffles furnace at four sequential steps. The second route includes all the previously mentioned steps, except the citric acid leaching. The final products were characterized using x-ray fluorescence analysis, carbon content analysis, x-ray diffraction, differential thermal analysis, nitrogen adsorption, mercury intrusion, and scanning electron microscopy. The results show that the citric acid leaching has many advantages with respect to silica yield and porosity as well.