Keywords: STXM, XAS, NEXAFS, XANES, ZIBs, ɑ-MnO 2 Zn-ion batteries (ZIBs) are considered promising alternatives to conventional Li-ion batteries, offering several advantages such as high operational voltage, cost-effectiveness, and enhanced safety. Among various cathode materials, manganese oxides, particularly ɑ-MnO 2 , are widely used as positive electrode materials in aqueous rechargeable ZIBs due to their natural abundance, low-cost, low toxicity, and relatively high reduction potentials [1]. However, the capacity of ɑ-MnO 2 -ZIBs is often limited by the dissolution of the active cathode material into the electrolyte and the formation of irreversible phases [1], [2]. The main redox mechanisms in ɑ-MnO 2 -ZIBs involve reversible Zn + intercalation/deintercalation alongside H + co-intercalation. Despite this, the detailed reaction mechanisms occurring during the charging and discharging processes, as well as the structural stability of the electrodes have not been fully addressed [3], [4]. Understanding how charge is effectively stored in ɑ-MnO 2 electrodes or across the electrode/electrolyte interface is crucial for the advancement of enhanced ɑ-MnO 2 -ZIBs electrodes. In this study, Scanning Transmission X-ray Microscopy (STXM) and X-ray Absorption Spectroscopy (XAS) techniques have been used to elucidate the charge storage mechanism of ɑ-MnO 2 -ZIBs. STXM is a synchrotron-based spectromicroscopic technique that provides speciation and high resolution (~30 nm) chemical mapping based on near-edge X-ray absorption fine structure contrast, typically obtained by measuring a sequence of images (stack) across an XAS edge. The hard X-ray spectra used in this study were measured with a lab-based QuantumLeap-H2000 (Sigray) [5]. Chemical state information was obtained through Mn, and Zn K-edge X-ray Absorption Near Edge Spectroscopy (XANES). STXM stacks of the microtome α-MnO 2 electrodes subjected to different charged/discharged cycles were measured at the Mn L 3 , O 1s, Zn L 2,3 , and C K-edges. Spatially resolved spectroscopy and quantitative chemical mapping at the Mn L 3 and O 1s edges demonstrated that MnO 2 is reduced to both Mn 3+ and Mn 2+ oxidation states in the discharged states through a reversible Mn 4+ ↔ Mn 3+ /Mn 2+ redox reaction. On the other hand, Zn L 2,3 measurements showed Zn signal in all electrode areas with 2-3 times larger amounts of Zn in the Mn(II)/Mn(III) area, than in the Mn(IV) area (particularly, after 100 cycles) (Fig.1) [6]. XANES measurements were very consistent with the STXM results indicating gradual decrease of the average oxidation state as the number of charge/discharge cycles increase (Fig. 2A) . Additionally, the Zn K-edge spectrum of the discharged states confirm the Zn intercalation (Fig. 2B) . These studies are helping better understand the redox and physico-chemical processes that take place at the surface or in the bulk of ɑ-MnO 2 ZIB electrodes. A more comprehensive understanding of α-MnO 2 -Zn ion batteries (ZIBs) requires the application of in-situ/operando STXM and XAS to elucidate the chemical and morphological changes occurring during charging/discharging processes under precisely controlled operational conditions. References Rubel, O., et al., Electrochemical stability of ZnMn 2 O 4 : Understanding Zn-ion rechargeable battery capacity and degradation. The Journal of Physical Chemistry C, 2022. 126 (27): p. 10957-10967. Alfaruqi, M.H., et al., Structural transformation and electrochemical study of layered MnO 2 in rechargeable aqueous zinc-ion battery. Electrochimica Acta, 2018. 276 : p. 1-11. Tran, T.N.T., et al., Reaction mechanisms for electrolytic manganese dioxide in rechargeable aqueous zinc-ion batteries. Scientific Reports, 2021. 11 (1): p. 20777. Zhao, Q., et al., Unravelling H + /Zn 2+ synergistic intercalation in a novel phase of manganese oxide for high ‐performance aqueous rechargeable battery. Small, 2019. 15 (47): p. 1904545. Srivatsan Seshadri, D.R.Q. and Lewis, S., XANES for Investigating Catalyst Chemical States (sigray.com) Haytham Eraky, James J. Dynes, Adam P. Hitchcock, Mn 2p and O 1s X-ray absorption spectroscopy of manganese oxides, Journal of Electron Spectroscopy and Related Phenomena, 2024. 274 : 147452. Figure 1

Polymer electrolyte membrane (PEM) fuel cells produce clean energy using hydrogen and oxygen with water and heat as the only byproducts. However, their widespread adoption is still hindered by high cost and low efficiency. PEM fuel cells have a proton exchange membrane (ionomer) supported by platinum (Pt) catalyst layers to facilitate the hydrogen oxidation (anode) and the oxygen reduction (cathode) reactions. While sufficient membrane hydration is necessary to maintain proton conductivity, excess water in the catalyst layer can severely inhibit electrochemical reactions, limiting efficient fuel cell operation. To design high performance catalyst layer nanostructures, the formation of liquid water and the ionomer swelling with humidity in PEM fuel cell catalyst layers need to be investigated. In-situ hard X-ray techniques have been used to study the incipience of water; however, the high energy hard X-rays prevent spectroscopy of the low-Z membrane elements like carbon, fluorine, oxygen, and sulfur. Soft X-ray scanning transmission X-ray microscopy (STXM) and near edge X-ray absorption fine structure (NEXAFS) spectroscopy can uniquely perform high resolution (30 nm) imaging of the chemical constituents of catalyst layers with minimal radiation damage. In this work, we report a novel in-situ characterization of ionomer swelling with humidity in fuel cell catalyst layers using STXM and NEXAFS spectroscopy to reveal the nanoscale reactant and proton transport pathways in PEM fuel cell catalyst layers. Pristine catalyst coated membrane samples were cut using an ultramicrotome to obtain 300 nm thick sections and mounted in a custom cell to observe the in-situ effects of humidity. The thickness of liquid water in the membrane and catalyst layer as a function of relative humidity was obtained by performing in-situ imaging at the oxygen K-edge. We observed that at 55% relative humidity (RH), a through-plane water accumulation of 10-20 nm on the silica nanoparticles maintained the membrane proton conductivity and at 90% relative humidity, the hydration of the sulfonic acid sidechains of Nafion promoted nanoscale proton transport in the catalyst layers. Moreover, in-situ characterization of ionomer swelling with humidity was performed for the first time using NEXAFS at the fluorine K-edge. The ionomer volume fraction increased from 28% to 36% from dry (~6% RH) to humidified conditions (~90% RH) and resulted in higher nanoscale oxygen and water diffusion resistance. From these analyses, the effects of hydration on nanoscale mass transport and proton conductivity were quantified to inform the design of next-generation proton exchange membrane fuel cells. Figure 1

Thermally sprayed Al2O3 coatings containing graphene nano platelets (GNP) have been shown to exhibit improved wear resistance. To understand the positive influence of GNP on wear properties, scanning transmission X-ray microscopy (STXM) analyses were performed to determine the structural and chemical changes that occur on the GNP and alumina matrix after wear tests. STXM results acquired at the C K-edge showed that the GNP are aligned parallel to the specimen surface in the as-sprayed coatings. GNP flakes are also observed at the tribo-surface of the wear tested sample. The results obtained at the Al K-edge show that the aluminum oxide below the wear track becomes amorphous during the wear test and carbon is dissolved in it. Wear tests performed on thermally sprayed pure alumina samples (without GNP) and on sintered bulk alumina prove that neither the presence of GNP nor the porosity in the coating are responsible for the amorphization of the alumina matrix. The results discussed in this work advance the fundamental understanding of graphene-containing composites, which is considered very important to exploit the unique advantages of graphene in technological applications.

Over the past decade advances in instrumentation and software have enabled development of spectro-ptychography (SP) as a higher spatial resolution extension of scanning transmission X-ray microscopy (STXM). Direct comparisons are made of same-area chemical state imaging of Cu nanoparticles using STXM and SP in order to compare and contrast the two approaches. We show that SP gives very similar chemical state information as STXM with significantly better spatial resolution and much higher quality images and chemical maps, on account of finer pixels in the reconstructed images. When defocused spot sizes are used (i.e., 1-3 mu m, as opposed to full-focus 30-50 nm) SP data acquisition is faster and the radiation dose delivered to the sample is smaller than the corresponding STXM measurement. The limitations of SP are primarily related to the time and complexity of the ptychographic reconstruction. We argue that these documented advantages mean that SP rather than STXM should be used for more complex studies such as tomography and in situ studies, especially when radiation damage is a concern. The main point of this manuscript is to illustrate, with scientifically relevant samples, the significant advantages of SP relative to conventional STXM, with the goal of encouraging greater use of SP.

This investigation is motivated by increasing interest in Mn3O4 as a promising alternative to MnO2 for supercapacitors with high active mass and the need for better understanding of charging and electrode activation mechanisms. High energy ball milling (HEBM) of chemically precipitated MnO2 and Mn3O4 in the presence of quercetin resulted in significant capacitance increase. The use of Mn2+ salts for Mn3O4 synthesis facilitated the application of quercetin as a new chelating capping agent for synthesis of Mn3O4, which showed higher capacitance, compared to HEBM Mn3O4. The capacitance of Mn3O4 prepared using quercetin was 6.0F cm -2 (149.50 F g-1) for cyclic voltammetry at 2 mVs- 1 and 8.03 F cm -2 (200.93 F g-1) for chronopotentiometry at 3 mA cm -2, which is on -par with the capacitance of MnO2. The time-consuming activation procedure, which limits Mn3O4 applications, was significantly accelerated for HEBM Mn3O4 and practically eliminated for Mn3O4 prepared using quercetin as a capping agent. Soft X-ray scanning transmission X-ray microscopy (STXM), an advanced synchrotron based analytical microscopy, was used at the O 1s and Mn 2p edges to identify and quantitatively map the Mn oxidation states present in Mn3O4 materials. Variable and fixed sweep rate electrochemical cycling procedures were used for the analysis of oxidation state of Mn and charging mechanism using STXM analysis coupled with electrochemical testing. The combination of STXM and electrochemistry provided valuable insights into the activation kinetics and charging mechanism. The STXM results showed that the tested materials contained mixtures of Mn2+, Mn3+ and Mn4+ oxides. A small amount of MnO phase in the tested samples indicated partial reduction. The higher content of MnO2 phase in the tested Mn3O4 prepared using quercetin as a capping agent, compared to HEBM Mn3O4, correlated with higher capacitance and the ability to eliminate the activation procedure.

Soft X-ray spectromicroscopy reveals the evolution of different phases in the formation of green alternative cements.

In situ electrochemistry on micron and submicron-sized individual particles and thin layers is a valuable, emerging tool for process understanding and optimization in a variety of scientific and technological fields such as material science, process technology, analytical chemistry, and environmental sciences. Electrochemical characterization and manipulation coupled with soft X-ray spectromicroscopy helps identify, quantify, and optimize processes in complex systems such as those with high heterogeneity in the spatial and/or temporal domain. Here we present a novel platform optimized for in situ electrochemistry with variable liquid electrolyte flow in soft X-ray scanning transmission X-ray microscopes (STXM). With four channels for fluid control and a modular design, it is suited for a wealth of experimental conditions. We demonstrate its capabilities by proving the reversible oxidation and reduction of individual microbial biofilm structures formed by microaerophilic Fe(II)-oxidizing bacteria, also known as twisted stalks. We show spectromicroscopically the heterogeneity of the redox activity on the submicron scale. Examples are also provided of electrochemical modification of liquid electrolyte species (Fe(II) and Fe(III) cyanides), and in situ studies of electrodeposited copper nanoparticles as CO2 reduction electrocatalysts under reaction conditions.

Electrochemical CO2 conversion offers a route to use renewable sources of electricity to convert CO2 into valuable carbon-based fuels and chemicals, including carbon monoxide, ethanol and ethylene. For electrochemical CO2 conversion technologies to become a viable component of future sustainable energy infrastructures, improved performance materials (catalysts, electrodes, membrane electrode assemblies) are needed to achieve high conversion rates, selectivity and single-pass utilization of CO2. This talk will focus on the development of techniques to characterize the properties of electrochemical CO2 conversion materials under reaction conditions. These in-situ methods are producing results which will guide the design of next generation materials and reactors. The talk will focus primarily on in situ transmission electron microscopy (TEM) and related spectroscopic techniques (energy dispersive X-ray analysis and selected area electron diffraction), along with synchrotron-based methods including in-situ soft X-ray scanning transmission X-ray microscopy (STXM).

Soft X-ray spectro-ptychography of nickel-nitrogen-carbon electrocatalysts containing atomically dispersed Nibased active sites were measured at the Ni L3 edge. Samples prepared with two different loadings of Ni precursors were investigated and compared to the results of an earlier study using scanning transmission X-ray microscopy (STXM) [Zhang et al., ACS Catalysis 12 (2022) 8746]. The ptychography data sets were measured using a defocused probe (1-3 & mu;m). The spatial resolution was improved from-60 nm (STXM) to-20 nm (ptychography). Spectro-ptychography stacks were measured at 4 component-specific energies (4-E stack) and at many energies across the full Ni L3 edge (34-E stack). Maps of three key chemical components (Ni metal, Ni3S2, and atomically dispersed N-coordinated Ni catalyst sites) were derived by fits of suitable reference spectra to absorption signals derived from the amplitude images from ptychographic reconstruction. The spectroptychography 4-E and 34-E stacks gave chemical mapping similar to each other and to the earlier STXM results. The phase signals obtained from the same data set and reconstruction were also found to be analyzable using reference phase spectra extracted from the phase stack, which generated chemical maps similar to those based on ptychography amplitude data. By using a defocused probe, the radiation dose and acquisition times for spectro-ptychography are comparable to conventional STXM, but significantly improved spatial resolution was achieved. This study highlights the added value of spectro-ptychography relative to STXM for studies of electrocatalysts.

We report a scanning transmission X-ray microscopy (STXM) study of hematite nanorods, prototypical photoanode used in solar water splitting. Hematite nanorods were obtained by hydrothermal growth from aqueous solutions using FeCl3 as precursor. Potentials for onset of water splitting are smaller using this synthesis method, compared to values reported for hematite photoanodes obtained by epitaxial growth. STXM revealed the presence of a hexahydrate iron chloride phase at the surface of the nanorods, which is linked to the low onset potential values. We detail the quantification approach that revealed the specific microstructure of individual hematite nanorods.

Polymer electrolyte membrane (PEM) water electrolysis is a promising green hydrogen generation technology to mitigate the effects of anthropogenic climate change. To achieve stable cell voltages, a conditioning procedure is typically required, where current or voltage cycling is applied until stable performance is achieved. Previous studies have demonstrated that a decrease in voltage occurs within the first few hours of operation [1], but this conditioning period has not been extensively studied for PEM electrolyzers, despite a variety of standard conditioning protocols available for PEM fuel cells in the literature. Previous works additionally suggest that changes in performance may be induced due to structural changes in the anode catalyst layer (CL) caused by large gas bubble evolution during the first few hours of operation [2]. However, to establish and optimize a conditioning procedure for PEMWEs, the specific structural changes caused by conditioning on the anode CL must be elucidated and correlated with the electrochemical performance parameters. In this work, we applied scanning transmission X-ray microscopy (STXM) to PEMWE catalyst layers to reveal pore and ionomer distributions in pristine and conditioned commercial CL samples. Prior to imaging, CL samples were embedded in epoxy and cut to 50 nm thick slices using an ultramicrotome. Using near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, Carbon 1s and Fluorine 1s absorption edges were probed to reveal pore and ionomer distributions, respectively. After image acquisition, the image stacks were processed to obtain the ionomer and epoxy spectra to enable spectral fitting and thresholding. Through this analysis, we quantified various morphological properties of catalyst layers (including CL thickness, porosity, pore size distribution, agglomerate distribution, and ionomer content) and compared these properties to those of pristine CLs to explain changes in cell performance. The insights gained from this work will aid in the development of efficient conditioning protocols and identify optimal post-conditioned anode CL morphology to inform the design of next-generation catalyst materials. A. Weiß et al., J Electrochem Soc, 166, F487–F497 (2019). O. Panchenko et al., Mater Today Energy, 16, 100394 (2020).

A micro-chip based three-electrode electrochemical reactor enabling controlled, variable electrolyte flow, rapid electrolyte change and applied electrode potentials was used for in-situ soft X-ray spectro-ptychography of Cu particle catalysts under electrochemical CO2 reduction (CO2R) conditions. In comparison to scanning transmission X-ray microscopy (STXM), the spatial resolution was improved by a factor of three through measuring patterns of diffracted photons via spectro-ptychography. We present here a detailed study of how individual cubic Cu particles change morphology and oxidation state as a function of applied potential during CO2R. Quantitative chemical mapping by in-situ spectro-ptychography demonstrated that as-deposited, primarily mixed Cu(I) and Cu(0) particles were completely reduced to pure Cu(0) at an electrode potential of -0.2 VRHE, above the potential at which CO2R commences. At increasingly negative potentials, in the regime of CO2R, these Cu(0) particles underwent morphological changes, losing the initial cubic structure and forming irregular dendritic-like structures. This initial demonstration of in-situ soft X-ray spectro-ptychography sheds insight on the morphological and chemical structural changes of Cu particles in the CO2R regime and paves the way for more detailed in-situ studies of electrochemical materials and processes.

Supercapacitors (SCs) as energy storage devices provide higher energy density than conventional capacitors and higher power density than batteries1. Understanding how charge is efficiently stored in the electrodes or across the electrolyte/electrode interface is key to developing advanced SC electrodes. Scanning transmission x-ray microscopy (STXM) studies2 have been used to investigate MnO2 based supercapacitor electrodes using a novel three-electrode based in-situ flow electrochemical device (Fig. 1)3, 4. Near-edge X-ray absorption fine structure (NEXAFS) spectra of MnO2 films in-situ deposited and subjected to several different electrochemical processes were measured with high spatial resolution at the Mn L3 and O K edges (Fig. 2) at both working electrode (WE) and counter electrode (CE) regions. In this work, the redox state changes associated with pseudocapacitance during charging/discharging processes in a potential window of -0.5 VAu to +0.9 VAu (+0.1 VRHE to +1.5 VRHE) have been investigated. The spectroscopic data and quantitative chemical mapping by in-situ STXM measurements demonstrated that an as-electrodeposited MnO2 film was reduced to both Mn3+ and Mn2+ oxidation states through a reversable Mn4+ ↔ Mn3+/Mn2+ redox reaction. A significant change from a quasi-uniform MnO2 film to a dendritc MnO2 structure was observed during discharging at +1.5 VRHE (Fig. 3, Fig. 4) corresponding to redeposition of Mn2+ dissolved into electrolyte during the reduction process5. In-situ STXM measurements at the CE showed there is deposition of MnO2 during the reduction reaction (charging process) at +0.1 VRHE. Mn L3 features of Mn2+ appeared in the electrolyte region during the reduction process and disappeared during the oxidation process, confirming the dissolution/redeposition mechanism. We have developed a novel and versatile platform for in situ studies of electrochemical processes, including supercapacitors, batteries, and electro-catalysts3, 4. References A. G. Olabi, Q. Abbas, A. Al Makky, and M. A. Abdelkareem, Energy, 248 123617 (2022). K. V. Kaznatcheev, C. Karunakaran, U. D. Lanke, S. G. Urquhart, M. Obst, and A. P. Hitchcock, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 582 (1), 96-99 (2007). A. P. Hitchcock, C. Zhang, H. Eraky, L. Shahcheraghi, F. Ismail, and D. Higgins, Microscopy and Microanalysis, 27 (S2), 59-60 (2021). C. Zhang, N. Mille, H. Eraky, S. Stanescu, S. Swaraj, R. Belkhou, D. Higgins, and A. Hitchcock, (2023). T.-H. Wu, Y.-Q. Lin, Z. D. Althouse, and N. Liu, ACS Applied Energy Materials, 4 (11), 12267-12274 (2021). Figure 1

Spectro-ptychography offers improved spatial resolution and additional phase spectral information relative to that provided by scanning transmission X-ray microscopes. However, carrying out ptychography at the lower range of soft X-ray energies (e.g. below 200 eV to 600 eV) on samples with weakly scattering signals can be challenging. Here, results of soft X-ray spectro-ptychography at energies as low as 180 eV are presented, and its capabilities are illustrated with results from permalloy nanorods (Fe 2p), carbon nanotubes (C 1s) and boron nitride bamboo nanostructures (B 1s, N 1s). The optimization of low-energy X-ray spectro-ptychography is described and important challenges associated with measurement approaches, reconstruction algorithms and their effects on the reconstructed images are discussed. A method for evaluating the increase in radiation dose when using overlapping sampling is presented.

Ptychography is a coherent diffraction imaging technique that measures diffraction patterns at many overlapping points on a sample and then uses an algorithm to reconstruct amplitude and phase images of the object and probe. Here, we report imaging, spectroscopy and linear dichroism ptychographic measurements at the carbon K-edge. This progress was achieved with a new generation of scientific Complementary Metal Oxide Semiconductor (sCMOS) X-ray cameras with an uncoated image sensor which has fast image transfer and high quantum efficiency at the carbon K-edge. Reconstructed amplitude and phase contrast images, C 1s spectral stacks, and X-ray linear dichroism of carbon nanotubes at the carbon K-edge were measured with ptychography. Ptychography and conventional Scanning Transmission X-ray Microscopy (STXM) are compared using results acquired from the same area. Relative to STXM, ptychography provides both improved spatial resolution and improved image quality. We used defocus ptychography, with an X-ray beam spot size of 1.0 micron, in order to reduce radiation damage and carbon deposition. Comparable spatial resolution was achieved to that of ptychography performed with a focused beam. Ptychography at the carbon K-edge offers unique opportunities to perform high resolution spectromicroscopy on organic materials important in medicine, biology, environmental science and energy materials.

Mineral-associated organic matter is an integral part of soil carbon pool. Biological processes contribute to the formation of such organo-mineral complexes when soil microbes, and in particular soil fungi, deposit a suite of extracellular metabolic compounds and their necromass on the mineral surfaces. While studied in bulk, micro- to nanoscale fungal-mineral interactions remain elusive. Of particular interest are the mutual effects at the interface between the fungal exometabolites and proximal mineral particles. In this work, we have grown saprotrophic and symbiotic fungi in contact with two soil minerals with contrasting properties: quartz and goethite, on top of X-ray transparent silicon nitride membrane windows and analyzed fungal hyphae by synchrotron-based scanning transmission X-ray microscopy in combination with near edge X-ray fine structure spectroscopy at C(K) and Fe(L) absorption edges. In the resultant chemical maps, we were able to visualize and differentiate organic compounds constituting the fungal cells, their extracellular metabolites, and the exometabolites adsorbing on the minerals. We found that the composition of the exometabolites differed between the fungal functional guilds, particularly, in their sugar to protein ratio and potassium concentration. In samples with quartz and goethite, we observed adsorption of the exometabolic compounds on the mineral surfaces with variations in their chemical composition around the particles. Although we did not observe clear alteration in the exometabolite chemistry upon mineral encounters, we show that fungal-mineral interaction result in reduction of Fe(III) in goethite. This process has been demonstrated for bulk systems, but, to our knowledge, this is the first observation on a single hypha scale offering insight into its underlying biological mechanisms. This demonstrates the link between processes initiated at the single-cell level to macroscale phenomena. Thus, spatially resolved chemical characterization of the microbial-mineral interfaces is crucial for an increased understanding of overall carbon cycling in soil.