Combination of atom probe tomography, isotope-labelling and online electrochemical mass spectrometry provides direct correlation of atomic scale structure of Ir oxide catalysts with the mechanism of oxygen formation from the lattice atoms.

The development of efficient acidic water electrolyzers relies on understanding dynamic changes of the Ir-based catalytic surfaces during the oxygen evolution reaction (OER). Such changes include degradation, oxidation, and amorphization processes, each of which somehow affects the material’s catalytic performance and durability. Some mechanisms involve the release of oxygen atoms from the oxide’s lattice, the extent of which is determined by the structure of the catalyst. While the stability of hydrous Ir oxides suffers from the active participation of lattice oxygen atoms in the OER, rutile IrO2 is more stable and the lattice oxygen involvement is still under debate due to the insufficient sensitivity of commonly used online electrochemical mass spectrometry. Here, we revisit the case of rutile IrO2 at the atomic scale by a combination of isotope labeling and atom probe tomography and reveal the exchange of oxygen atoms between the oxide lattice and water. Our approach enables direct visualization of the electrochemically active volume of the catalysts and allows for the estimation of an oxygen exchange rate during the OER that is discussed in view of surface restructuring and subsequent degradation. Our work presents an unprecedented opportunity to quantitatively assess the exchange of surface species during an electrochemical reaction, relevant for the optimization of the long-term stability of catalytic systems.

Porosity of shales is an important parameter that impacts rock strength for seal or wellbore integrity, gas-in-place calculations for unconventional resources or the diffusional solute and gas transport in these microporous materials. From a well section obtained from the Mont Terri Underground Rock Laboratory in St Ursanne, Switzerland, we determined porosity, pore size distribution and specific surface areas on a set of 13 Opalinus Clay samples. The porosity methods employed are helium-pycnometry, water and mercury injection porosimetry, liquid saturation and immersion, and low pressure N2 sorption, as well as small-angle to ultra-small-angle neutron scattering (SANS–USANS). These were used in addition to mineralogical and geochemical methods for sample analysis that comprise X-ray diffraction, X-ray fluorescence, total organic carbon content and cation exchange capacity. We find large variations in total porosity, ranging from approximately 23% for the neutron-scattering method to approximately 10% for mercury injection porosimetry. These differences can partly be related to differences in pore accessibility, while no or negligible inaccessible porosity was found. Pore volume distributions between neutron scattering and low-pressure sorption compare very well but differ significantly from those obtained from mercury porosimetry: this is realistic since the latter provides information on pore throats only, and the two former methods on pore throats and pore bodies. Finally, we find that specific surface areas determined using low-pressure sorption and neutron scattering match well.

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The anodic oxygen evolution reaction (OER) has significant importance in many electrochemical technologies. In proton exchange membrane water electrolyzers it plays a pivotal role for electrochemical energy conversion, yet sluggish kinetics and the corrosive environment during operation still compel significant advances in electrode materials to enable a widespread application. Up-to-date Iridium is known as the best catalyst material for the OER in acidic media due to its relatively high activity and long-term stability. However, scarcity of iridium drives the development of strategies for its efficient utilization. One promising way would be the formation of mixtures in which the noble catalyst element is dispersed in the non-noble matrix of more stable metals or metal oxides. A promising valve metal oxide is TiOx, yet the degree to which performance can be optimized by composition is still unresolved. Thus, using a scanning flow cell connected to an inductively coupled plasma mass spectrometer, we examined the activity and stability for the OER of an oxidized Ir–Ti thin film material library covering the composition range from 20–70 at.% of Ir. We find that regardless of the composition the rate of Ir dissolution is observed to be lower than that of thermally prepared IrO2. Moreover, mixtures containing at least 50 at.% of Ir exhibit reactivity comparable to IrO2. Their superior performance is discussed with complementary information obtained from atomic scale and electronic structure analysis using atom probe tomography and x-ray photoelectron spectroscopy. Overall, our data shows that Ir–Ti mixtures can be promising OER catalysts with both high activity and high stability.

The pore space of shales and mudrocks ranges from molecular dimensions to micrometers in length scale. This leads to great variation in spatial characteristics across many orders of magnitude, which poses a challenge for the determination of a representative microscopic pore network for such systems. Standard characterization techniques generally provide volumeaveraged properties while high-resolution imaging techniques do not assess a representative range of pore sizes because of limitations in the spatial resolution over the field of view. Due to this complexity, open questions remain regarding the role of the pore network in retention and transport processes, which in turn control oil and gas production. Volume-averaged but spatially resolved information is obtained for pores of size from 2 to 150 nm by applying scanning small-and wide-angle X-ray scattering (SAXS and WAXS) microscopy. Scattering patterns are collected in a scanning microscopy mode, such that microvoxels are sampled sequentially, over a total of 2 × 2 mm 2 raster area on specifically prepared thin sections with a thickness of 10−30 μm. Spatially resolved variations of porosity, pore-size distribution, orientation, as well as mineralogy are derived simultaneously. Aiming at a full characterization of the shale pore network, the measurements and subsequent matrix porosity analysis are integrated in a multiscale imaging workflow involving FIB-SEM, SEM, and μ-CT analysis.

The use of N 2 physisorption for the characterization of the pore structure of shales is assessed by addressing some common pitfalls and misconceptions related to the interpretation of physisorption data. In addition, N 2 physisorption is compared to other methods used to characterize shales. For this purpose a set of pore-structure and total-porosity data from N 2 physisorption, He-pycnometry, Hg-intrusion porosimetry, fluid saturation (Archimedes) methods, and (ultra) small-angle neutron scattering was obtained from measurements on samples of Opalinus Clay.

The structural changes of copper hexacyanoferrate (CuHCF), a Prussian blue analogue, which occur when used as a cathode in an aqueous Zn‐ion battery, are investigated using electron microscopy techniques. The evolution of ZnxCu1−xHCF phases possessing wire and cubic morphologies from initial CuHCF nanoparticles are monitored after hundreds of cycles. Irreversible introduction of Zn ions to CuHCF is revealed locally using scanning transmission electron microscopy. A substitution mechanism is proposed to explain the increasing Zn content within the cathode material while simultaneously the Cu content is lowered during Zn‐ion battery cycling. The present study demonstrates that the irreversible introduction of Zn ions is responsible for the decreasing Zn ion capacity of the CuHCF cathode in high electrolyte concentration.