Transition metal oxides are being investigated for many energy related applications, such as energy storage and catalysis. Their properties are dictated by various degrees of spin, charge, orbital and lattice degrees of freedom. To help gain a full understanding, give insight and ultimately control of these degrees of freedom, monitoring in situ and operando techniques are a prerequisite, both during the fabrication as well as the usage of these materials. In the preparation and operation of thin films made by physical vapor techniques, the methods are quite developed in recent years, especially in lab based systems. In this presentation I will review optical, electron and X-ray techniques used with and on pulsed laser deposition of oxide thin layers and heterostructures. The measurements, typically give information about the nomical valence of the transition metal element(s), their local and global crystal symmetry. In addition, I will also discuss various options to prepare (quasi) epitaxial oxide thin films and membranes for further operando experiments.

Understanding complex (photo)electrochemical conversion processes at functional interfaces requires in situ and operando characterization. A tool enabling such investigations is near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS). While NAP-XPS has traditionally been performed at synchrotrons, the emergence of lab-based systems now enables flexible access, long-term measurements, and rapid feedback during materials development. In this contribution, we present first case studies using our recently installed, lab-based NAP-XPS (SPECS). It features three different excitation energies and is designed for depth-resolved studies across gas|solid, liquid|solid and solid|solid interfaces. Beyond flexible reaction atmospheres, the instrument includes an illumination port to investigate light-induced processes in photoactive materials. The central focus of the talk will be the implementation of an open liquid cell for (photo)electrochemical measurements. We discuss several practical challenges, including bubble formation and electrolyte evaporation, and outline mitigation strategies. As a photoelectrochemical case study, we examine sputter-deposited copper bismuthate (CuBi₂O₄) thin films in contact with water-based electrolytes. CuBi₂O₄ is a native p-type semiconductor, with suitable band alignment for photocathode applications [1]. Previous NAP-XPS studies have indicated light- and gas-dependent changes in surface chemistry [2]. Here, we extend these studies to the solid|liquid interface, examining CuBi₂O₄ under aqueous conditions and illumination. These investigations demonstrate the capability of our lab-based NAP-XPS to probe functional interfaces of energy materials under working conditions, offering an accessible and flexible alternative to synchrotron-based measurements.

Electrochemistry and spectroelectrochemistry are powerful tools to probe the optoelectronic properties of lead-halide perovskites and understand the working princinples of related hybrid architectures.[1] Spectroelectrochemical measurements enable the determination of reliable band diagrams, identification of trap-state energies and densities and to understand the corrosion pathways and degradation mechanism in these systems. From these insights we propose a set of boundary conditions and recommended protocols to perform electrochemical studies on lead-halide perovskites. Coupling ultrafast transient absorption specroscopy with electrochemical methods allow probing charge transfer processess on the femtosecond to nanosecond timescales.[2] However the intrinsic instability of lead-halide perovskites restricts the choice of compatible solvents and electrolytes to conduct these measurements. When these studies are extended to highly confined 2D systems the presence of a bulky organic cations in the structure (e.g., buthylammonium, phenethylammonium) further complicates the already complex picture.

The overarching goal of my presentation if to define a stability window for electrochemical testing of various lead-halide perovskite systems. In the first part general principles of performing spetroelectrochemical measurements on 3D, 2D lead-halide perovskite based systems will be outlined. The influence of material composition (e.g., nature of organic cations, halide anions) on the electrochemical stability will be discussed. The insights gained through spectroelectrochemistry combined with ultraviolet photoelectron spectroscopy and surface photovoltage spectroscopy, was used to determine precise band positions and reveal the presence of mid-gap states within these materials.

In the second part of the use of in situ transient spectroelectrochemistry will be demonstrated, where the role of thermodynamic band offsets in hole transfer will be evaluated using FA_0.83Cs_0.17Pb(I_xBr_1-x)₃ films on mesoporous NiO. Systematic tuning of the valence band revealed that larger valence band offsets enhance hole extraction. In situ transient spectroelectrochemistry further showed that applying negative bias accelerates hole transfer, with stronger effects observed for compositions exhibiting larger offsets. These findings clarify how band alignment governs hole extraction at NiO/perovskite interfaces and provide design principles for more efficient optoelectronic devices.[3]

Electrochemical technologies for converting and storing energy, including fuel cells and electrolysers, depend critically on electrocatalysts that can operate efficiently, selectively, and stably under demanding conditions, ideally while relying on earth-abundant and affordable materials. To find and evaluate such catalysts, initial screening of their performance is typically carried out in aqueous model systems, for example using rotating disk electrode (RDE) half-cell setups. However, such configurations fail to accurately reproduce the conditions of real devices. Conversely, catalyst testing in full fuel cells or electrolyser stacks is prohibitively expensive, labor-intensive, and often too complex to enable detailed mechanistic insights.

In recent years, gas diffusion electrode (GDE) half-cell setups have emerged as a powerful intermediate platform that bridges the gap between model systems and operating devices. GDEs allow the evaluation of catalyst layers under realistic conditions, including high current densities and device-relevant mass transport, while maintaining experimental flexibility and mechanistic accessibility [1].

Drawing on representative examples from our own research and the broader literature, this talk will illustrate how GDE setups can offer critical insights into catalyst performance and degradation under practical conditions. It will be shown, for instance, that Pt dissolution in fuel cells is strongly suppressed due to the low diffusion coefficient of dissolved species in Nafion compared to aqueous electrolytes [2]. For Fe–N–C catalysts, the detrimental impact of the oxygen reduction reaction on catalyst stability and pH change-related effects in the catalyst layer will be discussed [3, 4]. Furthermore, the application of GDE methodology to water electrolysis research will be highlighted through recent studies of Ir dissolution, with comparisons to aqueous model systems and full PEM electrolyser cells [5]. The talk will conclude with perspectives on future developments, including advanced and spatially resolved approaches such as scanning GDE setups [6].

Hybrid metal‑halide perovskites (MHPs) promise low‑cost, high‑efficiency solar cells, yet their macroscopic performance is limited by loss pathways that originate in nano‑ and microscale structures. Thus, to understand MHP materials requires the characterization of the many nano- and microscale structures; from sub-granular twin domains, over grain boundaries and interfaces to lateral variations in crystal grains orientations and facets. Electrical SPM operation modes like Kelvin probe force microscopy (KPFM) or conductive atomic force microscopy are ideally suited to decipher these structure-function relationships. In this presentation, I will present some of our recent activities in the development of specialized scanning probe microscopy methods to study hybrid perovskite materials.

As one single measurement technique cannot capture the full picture, we develop a combined optical‑scanning‑probe platform that integrates spatially resolved photoluminescence (PL), time‑resolved PL (TRPL) and electrical scanning probe microscopy (Kelvin‑probe force microscopy, conductive AFM and nanoscale surface‑photovoltage spectroscopy). This multimodal microscope allows simultaneous measurements of the same region with diffraction‑limited confocal PL spectroscopy (≈300 nm lateral resolution), time-resolved photoluminescence (TRPL, time-resolution ~ps) and quantitative electrical AFM (10-20 nm lateral resolution).  This nanoscale photovoltaics lab on a tip therefore bridges the long‑standing divide between optical spectroscopy and nanoscale electrical probing. By delivering a correlative view of band‑gap emission, carrier dynamics and electrostatic landscape, it enables quantitative identification of the dominant nanoscale loss mechanisms that limit MHP solar‑cell performance. The approach can be extended to other emerging photovoltaic materials and offers a powerful tool for rational engineering of grain boundaries, transport layers and compositional stability. 

Catalyst materials play a crucial role in enabling sustainable hydrogen production through water electrolysis. Catalyst materials can be complex in structure, often having various crystal orientations or segregation at the nanoscale. Their effectiveness is usually evaluated based on the performance of catalyst films in devices, which gives an average performance across all structural features. Therefore, it is important to gain a fundamental understanding of what structural features provide enhanced electrocatalytic activity to enable a rational design of catalytic materials with enhanced electrocatalytic activity.

This talk will show examples of how local nano-electrochemical measurements enabled by scanning electrochemical cell microscopy (SECCM) combined with other local characterization techniques such as scanning electron microscopy, RAMAN spectroscopy, atomic force microscopy or Auger spectroscopy can be used to enable composition – structure- activity correlations. I will point out key factors to be considered when testing oxygen and hydrogen evolution reaction catalysts in SECCM, focusing on how the atmosphere used during measurements affects the recorded activity. In the second part, I will provide several examples to highlight the broad use of this approach for different catalyst materials, including oxides, intermetallics, transition metal dichalcogenides, or compositionally complex solid solutions / high entropy alloys.  

The transition from fossile fuels to renewable energy sources requires the efficient conversion of energy. Key for various conversion strategies, such as heterogeneous catalysis or batteries, are reactions at solid-gas, solid-liquid and solid-solid interfaces. The interaction of the solid with the environment leads to the occurence of local chemical dynamics under reaction conditions that can be reversible or irreversible and are decisive for the life and dead of the functional material. Those local chemical dynamics can be visualized and captured by operando electron microscopy enabling a direct way to correlate structure with function.

In this talk I will focus on operando electron microscopy investigation of solid-gas and solid-liquid interfaces under realistic working conditions and show how they can help to deepen our understanding for various energy applications, such as CO₂ hydrogenation, CO₂ reduction reaction, dry reforming of methane or ammonia synthesis. The experimental setup includes scanning electron microscopy and transmission electron microscopy each conducted under reaction conditions using homebuilt systems. These experiments are complemented by near-ambient pressure X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. Using these examples, I will discuss the influence of frustrated phase transitions on the function, the benefit of oscillating reactions, show the importance of conducting long-term experiments and the importance of controlling the interplay of morphology and electronic structure.

In summary, operando electron microscopy experiments are important to support the quest for the ideal energy conversion material by providing more detailed structure-function correlations and allow for capturing metastable states that are important for the lifetime of a functional material, which are often overlooked by ex situ analysis.

This contribution will showcase how lab-based in situ and operando methods can be extended from photoelectrodes to polymer membranes to unravel coupled processes in solar-driven photoelectrochemical (PEC) energy conversion.

On the photoelectrode side, I will present a time-resolved operando Raman spectroscopy (RS) strategy tailored to realistic PEC operation, including broadband-like excitation and complex chemistries such as biomass reforming. In tandem and multi-junction architectures, different absorbers harvest distinct portions of the solar spectrum, so relying on a single monochromatic bias wavelength can be misleading. To address the strong spectral overlap between broadband illumination and Raman probe light, we employ a pulsed-bias approach: the sample is periodically exposed to a controlled light pulse, while Raman spectra are recorded in the subsequent “dark” window. By synchronously triggering the bias light, Raman laser, and detector, we track transient spectral changes relative to a well-defined reference state, resolving reaction intermediates, local pH shifts, and photocorrosion processes over timescales from ∼10 ms to hours [1].

Complementarily, I will discuss a four-terminal electrochemical impedance spectroscopy (EIS) platform for ion-exchange membranes in (photo)electrolyzer-relevant environments. The membrane is mounted between independently addressable flow chambers, and a Kelvin-type configuration enables accurate DC resistance, broadband (1 MHz–1 mHz) impedance spectra, and voltage-loss analysis under galvanostatic operation, free from lead and contact artefacts [2, 3].

Together, these PEC and membrane case studies demonstrate how transient operando spectroscopy and precision impedance diagnostics can be combined to probe dynamic structure–function relationships across interfaces in integrated energy-conversion devices.

Nitrate contamination and the mechanistic complexity of nitrate electroreduction motivate direct, time‑resolved observation of surface intermediates that control selectivity. Nitrate electroreduction (NO₃RR) is the electrochemical conversion of dissolved nitrate into less harmful or value-added nitrogen products (e.g., nitrite, N₂, NH₄⁺/NH₃), offering a remediation route that transforms a persistent pollutant into benign or useful species while enabling integration with renewable electricity.^[1] Understanding NO₃RR is also critical for emerging reactions such as electrochemical urea synthesis, because nitrate‑derived adsorbates and their binding geometries determine opportunities for C–N bond formation.^[2] Silver is an ideal model platform to benchmark nitrogenous adsorbates because it stabilizes key nitrogenous intermediates while providing strong plasmonic enhancement for in-situ surface‑enhanced Raman spectroscopy (SERS).^[3]

In-situ time‑resolved SERS (TR-SERS) was used to follow adsorbate dynamics on roughened Ag during potential sweeps, with spectra synchronized to cyclic voltammetry to directly link spectroscopic events to electrochemical features. TR‑SERS results reveal potential‑dependent Raman bands assigned to interfacial species: Ag–O stretch, aqueous NO₃^– symmetric stretch, NO₃^– antisymmetric stretch ν₃, adsorbed NO₂^–, and two nitrate adsorption bands attributed to bidentate and bridge coordination, respectively.^[4]. Our observations establish a direct, time‑resolved correlation between applied potential, adsorption geometry, and the spectroscopic precursor state for nitrite formation on Ag, demonstrating TR‑SERS as a powerful operando approach for probing dynamic adsorbate behaviour relevant to NO₃RR and C–N coupling chemistry.

Isotope Exchange Raman Spectroscopy (IERS) has emerged as a powerful technique for investigating ion transport dynamics in ionic conductive materials by tracking shifts in their oxygen vibrational Raman modes (see Figure 1).^1,2 In this study, we demonstrate the broader applicability of IERS by introducing a universal methodology that extends beyond materials with Raman-active vibrational features—including those that are Raman-inactive—through the integration of an additional probe layer.³

To validate this approach, we selected four mixed ionic and electronic conductors (MIECs) with perovskite structures: La_1-xSr_xCoO_3₋δ and La_1-xSr_xFeO_3₋δ (x = 0.2 and 0.4). These functional materials were deposited onto a gadolinium-doped ceria (CGO) thin film, which serves as the probe layer. By using CGO, with well-distinguishable Raman modes and fast oxygen diffusivity, as a probe layer, we show that the oxygen gas-solid surface exchange properties of the deposited functional materials can be investigated in situ.

The oxygen surface exchange coefficients obtained via this universal IERS approach are in good agreement with previously reported values, validating the accuracy of the method. This tailored sample configuration effectively overcomes the traditional limitation of IERS as being material-dependent, thereby broadening its applicability to a wider range of materials.

Tailoring the structure of the electrochemical interface is key to elucidating the structure-property relationships and reaction mechanisms in electrocatalysis. Fundamental work on well-defined electrified interfaces is pivotal to understanding the factors controlling the electrocatalytic activity and selectivity in renewable energy conversion reactions. This talk will discuss different strategies to understand the role of the electric double layer structure [1] in electrocatalytic reactions. In situ techniques are key to uncovering the structure of the electrochemical interface, the active sites, and the reaction mechanisms of electrocatalytic reactions for sustainable energy conversion. This talk will illustrate the importance of in situ characterisation combining vibrational spectroscopy and scanning electrochemical microscopy [2] to understand and tune the structure-activity-selectivity relationships for electrocatalytic reactions to produce renewable fuels and chemicals. These reactions include the electrosynthesis of green fuels and value-added chemicals such as sustainable fertilisers using electrochemical carbon dioxide, nitrate, and methane conversion [3-5]. These investigations are key to elucidating interfacial mechanisms and designing active and selective electrocatalytic interfaces.