The electrochemical CO 2 reduction reaction (CO 2 RR) using Cu-based catalysts holds great potential for producing valuable multi-carbon products from renewable energy. However, the chemical and structural state of Cu catalyst surfaces during the CO 2 RR remains a matter of debate. Here, we show the structural evolution of the near-surface region of polycrystalline Cu electrodes under in situ conditions through a combination of grazing incidence X-ray absorption spectroscopy (GIXAS) and X-ray diffraction (GIXRD). The in situ GIXAS reveals that the surface oxide layer is fully reduced to metallic Cu before the onset potential for CO 2 RR, and the catalyst maintains the metallic state across the potentials relevant to the CO 2 RR. We also find a preferential surface reconstruction of the polycrystalline Cu surface toward (100) facets in the presence of CO 2 . Quantitative analysis of the reconstruction profiles reveals that the degree of reconstruction increases with increasingly negative applied potentials, and it persists when the applied potential returns to more positive values. These findings show that the surface of Cu electrocatalysts is dynamic during the CO 2 RR, and emphasize the importance of in situ characterization to understand the surface structure and its role in electrocatalysis. 47 migrate. CO, which is a key intermediate in the CO 2 RR, has 48 been shown to exacerbate this reconstruction in near-ambient 49 pressure conditions. 15 Surface reconstructions can affect 50 product selectivity because the Cu(111) surface preferentially 51 yields CH 4 , whereas the Cu(100) surface produces C 2 H 4 with 52 a lower onset potential. 16 To probe the surface structure under 53 CO 2 RR conditions, electrochemical scanning tunneling mi-54 croscopy (ECSTM) has been utilized to image Cu surfaces 55 with atomic resolution and has successfully demonstrated that 56 polycrystalline Cu (hereafter referred to as Cu(pc)) 57 reconstructs into Cu(100) surfaces in N 2 -purged electrolytes. 17 58 However, one of the limitations of ECSTM is its limited field 59 of view, and it is unclear whether these changes occur globally. 60 Therefore, to understand the structural dynamics of Cu 61 surfaces more fully, it is imperative to elucidate both the local 62 atomic structure and long-range order under realistic CO 2 RR 63 conditions. Here, we characterize the near-surface structure of 64 a Cu(pc) thin film (50 nm thickness) under CO 2 RR 65 conditions by utilizing in situ grazing incidence X-ray 66 absorption spectroscopy (GIXAS) and X-ray diffraction 67 (GIXRD). The Cu(pc) thin film is utilized as an electrocatalyst 68 because it has been demonstrated that the roughness of the Cu 69 thin film is low enough to allow sensitivity to a few nm of the

The performance of battery electrode materials is strongly affected by inefficiencies in utilization kinetics and cycle life as well as size effects. Observations of phase transformations in these materials with high chemical and spatial resolution can elucidate the relationship between chemical processes and mechanical degradation. Soft X-ray ptychographic microscopy combined with X-ray absorption spectroscopy and electron microscopy creates a powerful suite of tools that we use to assess the chemical and morphological changes in lithium iron phosphate (LiFePO4) micro- and nanocrystals that occur upon delithiation. All sizes of partly delithiated crystals were found to contain two phases with a complex correlation between crystallographic orientation and phase distribution. However, the lattice mismatch between LiFePO4 and FePO4 led to severe fracturing on microcrystals, whereas no mechanical damage was observed in nanoplates, indicating that mechanics are a principal driver in the outstanding electrode performance of LiFePO4 nanoparticles. These results demonstrate the importance of engineering the active electrode material in next generation electrical energy storage systems, which will achieve theoretical limits of energy density and extended stability. This work establishes soft X-ray ptychographic chemical imaging as an essential tool to build comprehensive relationships between mechanics and chemistry that guide this engineering design.

Battery function is determined by the efficiency and reversibility of the electrochemical phase transformations at solid electrodes. The microscopic tools available to study the chemical states of matter with the required spatial resolution and chemical specificity are intrinsically limited when studying complex architectures by their reliance on two-dimensional projections of thick material. Here, we report the development of soft X-ray ptychographic tomography, which resolves chemical states in three dimensions at 11 nm spatial resolution. We study an ensemble of nano-plates of lithium iron phosphate extracted from a battery electrode at 50% state of charge. Using a set of nanoscale tomograms, we quantify the electrochemical state and resolve phase boundaries throughout the volume of individual nanoparticles. These observations reveal multiple reaction points, intra-particle heterogeneity, and size effects that highlight the importance of multi-dimensional analytical tools in providing novel insight to the design of the next generation of high-performance devices.

Thin films of n-type γ-Cu 3 V 2 O 8 are prepared with high phase purity via reactive co-sputtering deposition. Complementary X-ray spectroscopic methods are used to reveal that the valence band maximum consists of O 2p states, while the conduction band minimum is primarily composed of Cu 3d states. Therefore, γ-Cu 3 V 2 O 8 is classified as a charge transfer insulator, in which the 1.80 eV indirect band gap corresponds to the O 2p → Cu 3d transition. Through photoelectrochemical measurements, the surface of γ-Cu 3 V 2 O 8 photoanodes is found to display intrinsic activity for catalyzing water oxidation that is stable with time. The combination of a small optical band gap, suitable valence band energy, and excellent photoelectrochemical stability suggests that γ-Cu 3 V 2 O 8 could be a promising photoanode material. However, it is found that the charge extraction efficiency from these semiconductor photoanodes is strongly limited by a short (20−40 nm) hole diffusion length. Characterization of the electronic structure and transport properties of γ-Cu 3 V 2 O 8 photoanodes suggests strategies for improving energy conversion efficiency and provides fundamental insights that can be used for understanding and evaluating function in a broader class of emerging ternary metal oxides.

Understanding Fe deposition in fluid catalytic cracking (FCC) catalysis is critical for the mitigation of catalyst degradation. Here we employ soft X-ray ptychography to determine at the nanoscale the distribution and chemical state of Fe in an aged FCC catalyst particle. We show that both particle swelling due to colloidal Fe deposition and Fe penetration into the matrix as a result of precracking of large organic molecules occur. The application of ptychography allowed us to provide direct visual evidence for these two distinct Fe-based deactivation mechanisms, which have so far been proposed only on the basis of indirect evidence.

Grazing incidence cell probes catalyst surface during high current operation with improved mass transport.

High spatial resolution magnetic x-ray spectromicroscopy at x-ray photon energies near the cobalt L3 resonance was applied to probe an amorphous 50 nm thin SmCo5 film prepared by off-axis pulsed laser deposition onto an x-ray transparent 200 nm thin Si3N4 membrane. Alternating gradient magnetometry shows a strong in-plane anisotropy and an only weak perpendicular magnetic anisotropy, which is confirmed by magnetic transmission soft x-ray microscopy images showing over a field of view of 10 μm a primarily stripe-like domain pattern but with local labyrinth-like domains. Soft x-ray ptychography in amplitude and phase contrast was used to identify and characterize local magnetic and structural features over a field of view of 1 μm with a spatial resolution of about 10 nm. There, the magnetic labyrinth domain patterns are accompanied by nanoscale structural inclusions that are primarily located in close proximity to the magnetic domain walls. Our analysis suggests that these inclusions are nanocrystalline Sm2Co17 phases with nominally in-plane magnetic anisotropy.

A nano-high performance liquid chromatography-inductively coupled plasma mass spectrometry (nano-HPLC-ICPMS) method is developed, using a demountable direct injection high efficiency nebulizer (d-DIHEN), to reduce sample and mobile phase consumption, minimize organic waste generation, decrease analysis time, and enhance separation efficiency. A HPLC column (50 mm  0.3 mm id), packed with 3.5 mm C 18 material, is explored for chromatographic separation of five arsenic species naturally present in the environment or introduced as a pollutant: sodium (meta)arsenite [As(III)], arsenic acid [As(V)], dimethylarsenic acid (DMA), disodium methylarsenate (MA), and p-arsanilic acid (p-ASA). A fast chromatographic separation of five arsenic species is achieved in less than 12 min at a solution flow rate of 0.9 mL min À1 using a 50 nL sample injection. The HPLC-ICPMS interface provides well defined flow injection profiles at various concentrations, giving a correlation coefficient of 0.999 for each individual arsenic species calibration curve. Precision values for peak height and area of five arsenic species range from 0.5 to 6.5% RSD and absolute detection limits are within 0.4 to 5.4 pg arsenic, which are comparable to previously reported data at higher solution uptake rates (20 mL min À1 to 1 mL min À1 ) and larger sample injection volumes (20-100 mL).