When studying the stability of electrocatalysts, scientists often focus primarily on surface evolution, as surface reactions are directly linked to catalytic activity. However, electrocatalytic processes can also induce profound transformations within the bulk of the material, altering its electronic structure, mechanical integrity, and overall stability.

In my talk, I will discuss bulk transformations in electrocatalysts caused by intercalation reactions under oxidative conditions and during oxygen evolution reaction (OER). I will demonstrate how the intercalation of ions can trigger volumetric expansion, chemo-mechanical coupling, anion redox activity, and ultimately lattice instability in oxide and hydroxide systems. To capture the nanoscale evolution of these materials, we combined advanced characterization techniques such as resonant inelastic X-ray scattering (RIXS), operando scanning transmission X-ray microscopy, electron microscopy (S/TEM), and atomic force microscopy (AFM), and used single-crystalline materials and model electrocatalysts. Our findings highlight the crucial role of ion insertion and de-insertion dynamics in governing the stability and performance of electrocatalysts.

Coupled benchtop EPR-NMR provides a powerful platform for studying reactions that contain both radical and organic species. NMR monitoring approaches typically rely on the 1D ¹H spectra, but interpreting these signals on benchtop NMR systems can be complicated due to substantial spectral overlap, arising from the instrument’s low magnetic field and limited sensitivity. To address this limitation, we employed Multivariate Curve Resolution-Alternating Least Squares (MCR-ALS) analysis, a rigorous chemometric deconvolution approach that can extract pure component spectra from overlapping signals and track their concentration profiles over time.

Here for the first time, we established a robust analytical framework for mechanistic investigations into the electrochemical TEMPO mediated lignin conversion by integrating MCR-ALS with our operando benchtop EPR–NMR platform. The complex lignin model compound and product signal can be deconvoluted and identified in benchtop NMR spectra. Therefore, it provides detailed mechanistic insight like the kinetics, TEMPO regeneration pathway.

Magnetic resonance methods, including nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR), are non-invasive, atom-specific, quantitative, and are applicable for liquid and solid-state materials. These features make magnetic resonance ideal tools for operando measurement of an electrochemical device, and for establishing structure-function relationships under device-operating conditions.  

For the first part of my talk, I will present how we develop and apply coupled NMR and EPR methods to unravel molecular-level physical and chemical processes in redox flow batteries. I will present case studies on viologen-based RFBs and demonstrate how we monitor the state of charge, unravel degradation reaction mechanisms as well as ion transport through membranes. For the second part, I will present new in situ NMR methods for studying Li-mediated ammonia synthesis, and the direct observation of lithium plating and its concurrent corrosion, nitrogen splitting on lithium metal and protonolysis of lithium nitride. Built upon these insights, we have developed a new alkaline electrochemical ammonia synthetic method. By the end of this talk, I hope to show that operando magnetic resonance is powerful and general, and can be applied for understanding various energy storage and conversion chemistries. 

References

1. Zhao E W, Liu T, Jónsson E, Lee J, Temprano I, Jethwa B J, Wang A, Smith H, Carretero-González J, Song Q, Grey C P “In situ NMR metrology reveals reaction mechanisms in redox flow batteries” Nature 2020, 579, 224-228.

2. Zhao E W, Jónsson E, Jethwa B J, Hey D, Lyu D, Brookfield A, Klusener P A A, Collison D, Grey C P “Coupled in situ NMR and EPR studies reveal the electron transfer rate and electrolyte decomposition in redox flow batteries” J. Am. Chem. Soc. 2021, 143, 1885-1895.

3. Luo R, Janssen H J W G, Kentgens A P M, Zhao E  W “A parallel line probe for spatially selective electrochemical NMR spectroscopy” J. Magn. Reson. 2024, 361, 107666 (Front cover; Special Issue: New Voices in Magnetic Resonance; Invited).

4. Silva Testa A G, Damhuis M A, Elemans J A A W, Zhao E W “Coupled benchtop NMR and EPR spectroscopy reveals the electronic structure of viologen radicals in a redox flow battery” ACS Electrochemistry, 2025, 1, 1977-1982 (Front cover).

5. Luo R, Gunnarsdóttir A B, Aspers R. L. E. G., Zhao E W “In situ NMR guided design of alkaline electrochemical ammonia synthesis” Science Advances, Accepted. Preprint 10.26434/chemrxiv-2024-cpf4j

Understanding how local reaction environments control product selectivity is essential for advancing bicarbonate-fed CO₂ electrolyzers, which directly integrate CO₂ capture and conversion. In a bicarbonate electrolyzer, protonation of HCO₃^- enables the in-situ release of CO₂ (i-CO₂) for electroreduction. Enabling C-C products is challenging in these systems due to the lower availability of reactive CO₂ compared to the gas fed systems.

In a bicarbonate electrolyzer, the overall performance of the system is determined by the interplay of three key factors: the proton flux, the chemical potential of HCO₃^- in the electrolyte and the chemical potential of surface bound hydroxide (OH^-). The proton flux is proportional to the current density and determines the CO₂ generated at the interface of membrane and electrolyte. In addition to being the effective CO₂ feed, HCO₃^- is a proton buffer that limits the local pH increase at the surface hindering CO₂ reduction reaction efficiency. Since the bulk chemical potential of HCO₃^- and proton flux are externally controlled input variables, we focus on the role of surface bound OH^- and its impact on C₂ product selectivity.

Here, we employ operando Raman spectroscopy to directly monitor the evolution of surface-bound OH- as a function of current density and bicarbonate concentrations, enabling the first real-time visualization of so OH^- behaviour under industrially relevant operating currents (>200 mA·cm^-2). These measurements reveal the conditions under which OH^- accumulation is either suppressed by bicarbonate buffering or amplified to create highly alkaline microenvironments conducive to C-C coupling. Analysis of OH^- band position and intensity further uncover how the local interfacial environment interacts with bulk electrolyte chemistry, defining the operating boundaries for maximising C₂ selectivity in bicarbonate electrolysis.

By functionally modifying the cathode catalyst, we observe distinct OH^- dynamics that directly correlate with improved ethylene faradaic efficiencies, demonstrating that bypassing the bicarbonate buffer can sustain the high local pH required for C₂ pathways.

Complementary galvanostatic electrochemical impedance spectroscopy (EIS) provides an additional handle on interfacial processes, with equivalent-circuit fits supporting the Raman-derived picture of how OH^- behaviour governs product selectivity.

Together, these results provide the first operando spectroscopic evidence linking OH^- interfacial dynamics to C₂ formation in bicarbonate electrolyzers, offering mechanistic insight and design principles for next-generation reactive-capture CO₂ conversion systems.

The electrochemical reduction of carbon dioxide (CO₂R) offers a sustainable pathway for converting CO₂ into value-added chemicals and fuels, contributing to industrial decarbonization. However, achieving high selectivity and stability at industrially relevant current densities remains challenging, largely due to the complex and dynamic nature of the electrochemical interface. While copper-based catalysts can facilitate multi-carbon product formation via C–C coupling, the intricate interplay between catalyst surfaces, electrolyte ions, interfacial water networks, and surface-bound intermediates complicates mechanistic understanding and device optimization.

Recent studies increasingly recognize the role of interfacial water in governing reaction pathways by mediating proton transfer and stabilizing intermediates. Water’s ability to form complex hydrogen-bond networks creates local solvent structures that dynamically respond to changes in potential, current density, and ionic composition. In parallel, electrolyte ions and adsorbates further perturb water organization and local pH, modifying selectivity. Yet, most in situ studies are restricted to low current densities, limiting their relevance to practical CO₂R systems.

Here, we employed an integrated approach combining operando Raman spectroscopy in membrane-electrode assembly (MEA) type electrolyser and 2D- correlated Raman spectroscopy to investigate how interfacial environments evolve during CO₂R under high current densities (1A cm^-2). Our study reveals that the structure and orientation of interfacial water layers respond dynamically to applied potential, local ion concentrations, and surface-adsorbed species. These transformations play a central role in modulating proton availability, reaction intermediate stabilization, and overall product selectivity. We identify distinct regimes where changes in interfacial organization correlate with shifts in reaction pathways, influencing the balance between desired multi-carbon products and competing side reactions.

By directly capturing the evolving interfacial landscape under realistic operating conditions, our findings underscore the importance of water structuring as critical design parameters in CO₂R systems. This understanding extends beyond traditional catalyst optimization approaches, offering new levers to improve electrochemical performance through targeted control of interfacial dynamics.

The transition toward sustainable and resource-abundant energy-storage systems has intensified research into sodium-ion battery (SIB) [1] and aluminum-ion battery (AlIB) [2] chemistries, where interfacial phenomena critically dictate efficiency, reversibility, and long-term cycling stability to replace the lithium-ion batteries (LIBs). Across these studies, a central theme emerges: controlling the electrode/electrolyte interface is essential for advancing alternative battery technologies.

Hard carbon (HC) is a highly promising negative electrode material for SIBs [1]. Its disordered graphene structure provides substantial porosity for Na-ion storage, whereas the formation of stage-wise intercalation compounds typical of graphite in lithium-ion batteries does not occur in defect-free HC [3]. Despite decades of research on the solid/electrolyte interphase (SEI) in LIBs, significantly less information is available regarding SEI formation on HC in SIBs, particularly concerning the influence of binders, electrolyte composition, and additives [4]. In this invited talk, I will present our recent efforts to characterize interphase formation on HC anodes using a correlative multimodal approach. Spray-coated HC electrodes were examined in 1 M NaPF₆/diglyme to assess how electrolyte formulation, cycling rate, and electrode microstructure influence SEI development. Scanning electrochemical microscopy (SECM) provided spatially resolved information on the electrochemical properties of the SEI layer [5,6], while atomic force microscopy (AFM) was used to probe morphology, roughness, and nanomechanical properties. Complementary X-ray photoelectron spectroscopy (XPS) [7] and time-of-flight secondary ion mass spectrometry (ToF-SIMS) analyses revealed changes in SEI composition as a function of cycling and current rate. Our results show that HC develops a relatively uniform SEI after the first cycle, followed by partial dissolution and increased chemical and mechanical heterogeneity during extended cycling, indicating a delicate balance between stabilization and degradation in ether-based electrolytes.

For AlIBs, we investigate how aluminum foil properties including thickness, surface finish, roughness, and the characteristics of the native Al₂O₃ layer influence corrosion behavior and interfacial stability in the highly acidic AlCl₃:[EMIm]Cl (1.5:1) ionic liquid. AFM studies after prolonged immersion and electrochemical cycling reveal progressive removal of the amorphous oxide layer and the development of a granular corrosion morphology, providing insight into the origins of performance variability between different aluminum sources.

Together, these results demonstrate how correlative microscopies and spectroscopies can uncover nanoscale mechanisms governing interphase formation and degradation in post-lithium battery systems. Such insights are essential for guiding electrolyte design, surface engineering strategies, and the development of durable sodium- and aluminum-based energy-storage technologies.

Key words: SEI, HC, SIBs, AlIBs, SECM/AFM

Understanding how local physicochemical properties govern electrochemical activity remains a central challenge in the development of next-generation energy technologies. Many structure-function relationships at the nano- and microscales, especially those dictating performance and stability, are still unresolved, in part due to the lack of high-throughput techniques with sufficient spatial, temporal, and chemical sensitivity.

In this talk, I will demonstrate how correlative scanning electrochemical cell microscopy (SECCM) provides a powerful route to uncover these hidden relationships. SECCM delivers high-throughput, spatially resolved electrochemical measurements that can be directly correlated with structural and compositional information from co-located high-resolution microscopy and spectroscopy. This multi-microscopy approach enables identification of nanoscale heterogeneities, visualization of dynamic interfacial transformations, and quantitative mapping of local electrochemical reactivity. By leveraging automated and combinatorial SECCM workflows, we can accelerate mechanistic insights and guide the rational design of functional electrode materials. I will illustrate the versatility of this approach through three case studies: (i) electrocatalytic structure-activity mapping,[1] (ii) nanoscale investigation of solid-electrolyte interphase formation in Li-ion battery materials,[2-3] and (iii) probing Li metal plating and stripping processes.[4] Together, these examples highlight how correlative SECCM establishes new paradigms for probing, visualizing, and understanding electrochemical interfaces, and how it can drive faster development of optimized materials.

Gas-diffusion electrodes (GDEs) enable high current densities in CO₂ electroreduction (CO₂RR), yet they often degrade via flooding, salt precipitation or catalyst detachment[1]. Despite extensive ex-situ analyses on pre-catalysts and post-mortem samples, a direct, time-resolved picture of how these processes unfold from the nanometer to millimeter scale under relevant operating conditions remains elusive. This is notoriously challenging due to the continuous bubble nucleation that disturbs the probe-sample interface[2]. Herein, we combine in-situ electrochemical atomic force microscopy (EC-AFM) with large-area, high-throughput optical profilometry (OP), to quantify GDE reconstruction across scales during CO₂RR and correlate it with catalyst efficiency. We designed an open flow cell that preserves gas transport and diffusion, minimizing bubble formation and allowing the investigation of our catalyst’s surface. EC-AFM mapping of the GDE (nm²) resolves nanoscale roughness evolution, phase restructuring, and particle nucleation, which is more prominent at the grain boundaries. Correlative OP maps of stitched areas (mm²) reveal mesoscale buckling and phase migration which constitute large scale electrode imperfections that can impact stability and performance. By synchronizing electrochemical readouts with both imaging streams, we can link morphological descriptors to performance decay, distinguishing reversible wetting from irreversible structural damage. Ways to stabilize or suppress reconstruction are also investigated by coating the GDEs with polymers (Nafion), which also promote selectivity and reactivity[3]. Complementary to these findings, nanoscale spectroscopic characterization with Tip-Enhanced Raman Scattering (TERS) allows us to evaluate the catalyst chemical structure before CO₂RR. Correlative and multi-scale in-situ methodology is shown to provide mechanistic guidance for GDE architecture by pinpointing the active sites and translating this information to efficient and sustainable catalyst design, ultimately prolonging stable CO₂RR at industrially relevant current densities.

In recent years, more and more evidence has emerged on the intertwining of electrode inhomogeneities, local electrolyte structure and ion distribution, which all affect the nanoscopic electrochemical processes. All these are difficult to infer from macroscopic measurables. In-situ and operando Atomic force microscopy (AFM) is a powerful tool that has demonstrated with atomic resolution, that water structures itself at the interface with solids under equilibrium.

In this work, we use adhesion to probe the interfacial energy of the (biased) electrode/electrolyte under different electrochemical conditions. We track changes at the interface as a function of bias, and investigate the effect of different anions and cations. From adhesion imaging, we reveal that the water structure on even a simple Au film is highly inhomogeneous and dynamic. By disabling the vertical scan, we push the temporal resolution and track adhesion while running standard cyclic voltammograms. Understanding and controlling these nanoscale phenomena provide us with many fascinating challenges, of direct relevance not only in energy storage but also other fields like nanomaterial fabrication.

Contact-mode high-speed atomic force microscopy (HS-AFM) is capable of mapping surface topography in air, liquid, and controlled gas environments with nanometre lateral resolution and sub-second temporal resolution (exceeding 20 frames per second). Video rate imaging speeds enable in-situ observations of dynamic nanoscale phenomena, as well as nanometre-scale mapping across millimetre-scale areas for measurements of rare features, feature distribution analysis, and large-area composite maps. HS-AFM is also able to map surface properties such as stiffness, thermal conductivity, or electrical conductivity with correlated topography.

The presented work explores new advances in the adaptations of this imaging technique to enable electrochemical mapping. Various experimental set-ups have been deployed in previous works to measure surface topography with parallel potentiostatic control, the proposed advances aim to spatially resolve these electrochemical signals and correlate them with simultaneous measurements of topography. This additional functionality aims to provide new insight into the nanoscale origins of electrochemical phenomena.

The efficiency and stability of photoelectrochemical (PEC) materials are governed by processes that occur at interfaces and surfaces, where atomic structure, electronic states, and chemical reactions meet. Disorder, local defects, and dynamic surface transformations strongly influence charge dynamics and transfer, often limiting performance under realistic operating conditions. At the same time, material stability is highly sensitive to nanoscale imperfections, which frequently initiate and accelerate degradation processes.

To reveal the impact and dominant role of nanoscale behavior on the macroscopic properties of PEC systems, operando techniques capable of probing interfacial structure and dynamics with nano- to micrometer resolution under realistic conditions are required. In this work, we employ nanoscale in-situ scanning probe microscopy to investigate the interfacial stability of TiO₂/Pt photocathodes by directly monitoring localized surface transformations and detachment processes during operation. To tailor interfacial morphology, Pt catalysts were deposited onto conformal TiO₂ coatings using sputtering and atomic layer deposition (ALD). Whereas sputtering produces a continuous Pt film, ALD forms discrete Pt nano-islands, enabling atom-efficient utilization of precious metals.

Under photoelectrochemical operation, both systems exhibit comparable onset potentials and saturation current densities; however, chronoamperometry reveals markedly improved long-term stability for the nanostructured ALD-Pt films. Specifically, we show that continuous Pt layers undergo delamination from the substrate, while ALD-Pt structures maintain their integrity. This contrasting behavior is attributed to distinct bubble formation and detachment processes at the catalyst–semiconductor interface.

These nanoscale insights highlight the importance of interfacial and morphological engineering, as well as the need to control dynamic conversion processes, to achieve durable and efficient PEC material systems.

Efficient photosystems for solar-to-chemical energy conversion are often based on  nanostructured semiconductor architectures. In these material systems, the nanoscale  
properties frequently dominate the performance at the macroscale. Therefore, local  understanding of their charge transfer and transport properties is decisive for optimizing  
their efficiency and stability.

To this end, we correlate Kelvin probe force microscopy (KPFM) and (photo)conductive  atomic force microscopy (AFM) to study the local band bending, charge accumulation,  
as well as variations in the generated surface photovoltage and (photo)conductivity. However, analyzing nanostructured materials with complex morphologies is not trivial,  as effects such as topographic crosstalk or surface potential averaging can significantly  influence the results obtained with different techniques. To overcome these issues, we  leverage 2nd eigenmode and heterodyne KPFM measurements with improved resolution  and sensitivity compared to conventional frequency- and amplitude-modulated  techniques. For (photo)conductive AFM, a special tapping mode with simultaneous  current measurements is used to reduce sample and probe damage, enabling  measurements on polycrystalline films. For BiVO4, one of the most extensively studied  metal oxide photoanode materials, we compare different KPFM modes and correlate the  results with local conductivity measurements to gain insights into local semiconductor  properties at grain boundaries or different crystal facets. Overall, the gained nanoscale  insights will put forward the development of rational design strategies to enhance the  macroscale durability and efficiency of solar energy conversion systems.

Efficient and cost-effective energy storage systems (ESSs) are require to balance demand and supply of energy generated from intermittent and unpredictable renewable energy sources. Among the available ESS technologies, redox flow batteries (RFBs) have attracted considerable attention due to their ability to decouple power and energy. However, storing energy exclusively in dissolved redox species imposes limitations, such as low energy density and narrow operating temperature ranges.

To overcome these constraints, redox-mediated flow batteries (RMFBs) have recently emerged as a promising alternative. This approach integrates solid electroactive materials to boost energy density. The core mechanism involves a spontaneous and reversible charge transfer between the solid “booster” material and dissolved redox mediators. Despite their potential, RMFBs remain at an early stage of development, and fundamental understanding of the thermodynamics and kinetics governing solid–solution charge transfer is still limited. Progress in this field therefore depends on operando analytical techniques capable of probing these interactions under realistic flow conditions.

In this presentation, the development and validation of two in-situ X-ray-based techniques for Redox-Mediated Flow Batteries will be discussed: X-ray diffraction and X-ray absorption spectroscopy (synchrotron source). These techniques enable real-time monitoring of the structural evolution of the solid booster during electrochemical charge and discharge processes mediated by redox species. Additionally, they will be applied to investigate the influence of electrolyte cations on the mediation mechanism. Overall, our findings demonstrate the potential of these in-situ techniques to uncover fundamental processes in RMFBs, providing insights essential for advancing next-generation flow battery technologies.

Diatom microalgae naturally produce intricately patterned SiO₂ (SiO₃) frustules with hierarchical porosity and species-specific morphologies that cannot be replicated by conventional synthesis routes. These biogenic silica architectures offer a unique and sustainable template for producing advanced silicon-based materials for Li-ion battery anodes. In this work, frustules obtained from industrially cultured diatoms were converted into nanostructured SiOₓ through a controlled magnesiothermic reduction (MgTR) reaction, preserving their characteristic 3D morphology while generating interconnected porous SiOₓ frameworks. TEM and TEM-EDS analyses confirm uniform Si/O distributions and nanoscale porosity, which together provide mechanically adaptive structures ideal for mitigating volume changes of Si-based negative electrodes during cycling.

The MgTR-derived SiOₓ was subsequently incorporated into upscaled SiOₓ–graphite blended electrodes processed under industrially relevant slurry preparation and coating conditions. To directly link the bio-derived architecture to electrode behaviour, the composite electrodes were investigated operando using synchrotron X-ray computed microtomography (X-ray CT) at the FaXToR beamline (ALBA Synchrotron). The operando measurements reveal the evolution of porosity, particle rearrangement, and mechanical deformation during lithiation and delithiation, highlighting the distinct mesoscale response of diatom-derived SiOₓ within the graphite matrix.

These results demonstrate that diatom-templated silica, when converted via MgTR, provides a structurally resilient and scalable pathway to SiOₓ for blended anodes, and they underscore the importance of operando 3D characterization to guide the rational design of sustainable, high-capacity silicon-based electrodes for Li-ion battery technology.

Developing next-generation electrochemical storage and conversion devices with superior performance and longevity requires a fundamental understanding of electrochemical processes at the nanoscale. Our group employs a multimodal approach utilizing in-situ electron microscopy to unravel the dynamic processes governing energy materials, including batteries, solid oxide cells [1]. This presentation highlights our capabilities in characterizing dynamics at solid-solid, solid-gas, and solid-liquid interfaces.

Regarding solid-solid interfaces, we examined lithiation/delithiation dynamics in coated and uncoated silicon particles [2], [3]. These insights are critical for understanding failure mechanisms in all-solid-state batteries and establishing protocols to evaluate coating material architectures.

We investigated gas-solid interactions to decipher catalyst and fuel electrode behavior under operational conditions [4]. These studies reveal catalyst exsolution mechanisms in solid oxide cells and catalyst behavior during CO₂ conversion. When coupled with FIB-SEM tomography, these findings link long-term microstructural evolution to electrode design.

Finally, I will present pioneering in-situ liquid phase TEM studies of solid-liquid interactions [5],[6]. We have developed a novel liquid purging method that dynamically controls liquid thickness, enabling high-resolution imaging and analytical studies under realistic flow conditions. We utilize this method to investigate zinc battery dynamics, aiming to optimize charge-discharge routines and electrolyte additives.

By directly visualizing these processes, we gain crucial insights that guide the development of next-generation energy technologies.

Zinc-based alloys are promising candidates for alkaline electrochemical systems, yet their hydrogen evolution reactivity, microstructural stability, and degradation pathways remain strongly dependent on alloy composition. In particular, Sn additions to Zn can simultaneously modify the hydrogen evolution reaction (HER) kinetics and the mechanical integrity of the electrode during cycling, but a systematic correlation between Sn content, microstructure, and electrochemical behavior is still lacking. In this work, we comparatively investigate three Zn-Sn alloys with different Sn contents and bare Zn to elucidate how alloying level governs surface activation, gas evolution, and long-term stability under alkaline operation.

Electrochemical characterization is carried out using HER polarization measurements, Tafel analysis, symmetric Zn-Zn cell testing, and cyclic (charge-discharge) cell protocols in concentrated alkaline electrolyte. From these measurements, we extract key kinetic parameters such as HER overpotential, Tafel slope, and exchange current density, as well as galvanostatic cycling stability, polarization hysteresis, and interfacial resistance evolution. In parallel, operando optical microscopy is employed to directly monitor bubble nucleation, surface roughening, and morphological changes of the Zn-Sn electrodes under bias, providing real-time visualization of degradation and gas evolution behavior as a function of alloy composition.

To establish structure-property relationships, we combine X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) with electron backscatter diffraction (EBSD) before and after electrochemical testing. XRD and TEM are used to identify phases, grain size, and possible intermetallic formation, while EBSD maps grain orientation, texture, and local misorientation to reveal microstructural heterogeneity and damage accumulation. Post-mortem SEM/EBSD analysis after cycling enables us to correlate crack formation, grain boundary attack, and phase redistribution with the observed electrochemical performance.

By comparing the three Zn-Sn alloys across this integrated electrochemical and microstructural dataset, we demonstrate how varying Sn content influences HER activity, electrode polarization, and the onset of performance-limiting degradation modes. The results provide design guidelines for optimizing Zn-Sn alloy composition and microstructure for use as robust, hydrogen-tolerant electrodes in alkaline energy storage and conversion technologies, including Zn-based rechargeable systems.

(Electro-)catalytic processes are the pacemakers for energy conversion and storage technologies. A key prerequisite to control catalyst properties and performances in these processes is the detailed understanding of the reaction dynamics at solid-liquid and solid-gas interfaces during the reactions, calling for in-situ and operando studies.

Our approach exploits atomically-defined epitaxy of complex oxide catalysts to precisely tune material properties on the nanoscale and to tailor catalytic systems under controlled conditions. [1],[2] Recently, entirely new opportunities arise from delamination processes established for epitaxial complex oxides [3], yielding nanometer-thick oxide membranes with well-defined, single-crystalline structure. Being essentially transparent for electrons and x-rays, these membranes are prone to enable operando studies of complex oxide catalysts under atomically defined structural conditions.

In this talk, we will highlight implications for in-situ & operando x-rays spectroscopy (XAS/XPS) and electron microscopy, based on membrane transfer processes to SiNx-based (graphene-based) supports, allowing to study transient processes during catalyst activation and reaction conditions. We will explicitly discuss the transient processes during metal exsolution processes, yielding catalytic nanoparticles on complex oxide support.[4],[5] Further, we will discuss the electronic structure of perovskite-based oxygen evolution (OER) catalysts, evolving over time under repeated cycling in alkaline water spitting. As we elaborate, free-standing oxide transfer may offer a wide range of promising sample geometries to facilitate the in-depth understanding of catalyst activation and degradation processes.

Quantitative atomic scale and molecular level insight into structural (geometrical and electronic) and morphological properties on an absolute scale and under reaction conditions is imperative for understanding mechanisms and phenomena across scales in electrochemical systems. Interpreted in the context of device performance, this knowledge can be used for rational design of and new concepts for improved materials and processes. Following a brief introduction, a general overview of (novel) operando-capable X-ray-based methods and a rationalization of their particular usefulness for studying electrochemical systems, and several examples using model systems, four topics will be discussed in detail.

The first topic concerns charge and mass transport in various electrolytes. Here, we used a combination of correlative operando X-ray photon correlation spectroscopy, small and wide-angle X-ray scattering, and X-ray absorption microscopy to measure electrolyte velocity and concentration fields as well as solvent orientation upon cell polarization. The results were combined with macroscopic and microscopic theory to quantify and rationalize transport numbers, and to provide length-scale bridging insight into ion transport.

The second topic covers the surface-electrochemistry in Li-ion batteries, with a specific focus on the origin of LiF in the solid electrolyte interphase. Towards this end, we sought out a multimodal correlative operando experimental and theoretical approach using model electrodes. Our results reveal that LiF nucleates via the electrocatalytic reduction of HF followed by significant PF₆^- anion reduction. We then applied this understanding to develop a methodologically novel electrochemical approach to selectively remove HF from carbonate-based LiPF₆-containing LIB electrolytes.

The third topic covers desalination batteries. Here, we employed (quasi-high-throughput) operando high-energy X-ray diffraction microscopy to spatially resolve ion intercalation processes and mechanisms in realistic flow-by desalination reactors. We focus on atomic- to electrode-level insight into structural changes and ion selectivity in manganese oxides and iron phosphate electrodes.

The fourth topic concerns some recent methodological developments in surface X-ray scattering. These include surface X-ray scattering measurements using nanoscale X-ray beams, increasing accuracy and precision of geometrical corrections in X-ray reflectivity, and approaches for sub-second surface X-ray scattering.