Thomas Justus Schmidt

All‐solid‐state batteries (ASSBs) employing sulfide solid electrolytes and lithium metal anodes offer a promising route toward high energy density and improved safety. However, their practical implementation is hindered by coupled electro‐chemo‐mechanical interfacial instabilities, which evolve across multiple length scales and remain poorly understood under operating conditions. Here, we present a multimodal operando characterization approach combining X‐ray computed tomography (XCT), X‐ray diffraction (XRD), and stack pressure monitoring to elucidate degradation mechanisms in LiNi _0.8 Co _0.1 Mn _0.1 O ₂ (NCM811) | Li ₆ PS ₅ Cl (LPSC) | Li cells. By correlating particle‐level morphology with lattice‐scale structural and strain evolution, this approach provides a unified multiscale description of interfacial degradation. Simultaneous operando XCT and XRD measurements reveal reversible ∼6% volume changes in NCM811 particles during (de‐)lithiation, while spatially resolved XRD uncovers heterogeneous lithiation and depth‐dependent electrochemical activity across the cathode. Partial relaxation of interfacial microstrain is linked to oxidative decomposition of LPSC. At the LPSC|Li interface, operando XCT visualizes crack formation, lithium infiltration, and progressive contact loss caused by plating‐induced stress, ultimately leading to mechanical disconnection and short‐circuiting at higher current densities. These mechanically induced degradation processes are partially reversible during lithium stripping. This multimodal operando framework provides critical insights into degradation pathways and design principles for mechanically robust sulfide‐based ASSBs.

Operando visualization of ultrathin lithium is essential for understanding plating and stripping in lithium-metal batteries, but existing neutron imaging techniques lack sufficient sensitivity for ultra-thin lithium layers formed at crucial early stages. Here we introduce neutron capture imaging (NCI), which selectively detects tritons generated by neutron capture in ⁶ Li. Ex situ measurements of electrochemically plated and thermally evaporated ⁶ Li demonstrate sensitivity around 10 nm for a 1.5 h acquisition and two-dimensional imaging with around 100 μm lateral resolution. Simulations indicate that the resolution could approach 25 μm through optical optimization. Operando measurements in an asymmetric Cu|| ⁶ Li cell reveal spatially heterogeneous lithium plating and stripping in agreement with electrochemical data. Our results establish NCI as a high-sensitivity, near-zero-background tool for operando studies of lithium metal batteries, opening new possibilities for resolving early-stage deposition, dead lithium formation, and interfacial dynamics with broad applicability to ultrathin reactive lithium layers in electrochemical systems.

This review highlights recent developments in the characterization of the Pt–ionomer and electrolyte interface using ATR-FTIR techniques.

Thin lithium metal anodes are key to realizing high‐energy‐density and enhanced safety in all‐solid‐state batteries (ASSBs). However, extruded lithium foils below 50 µm suffer from poor structural integrity, rough surfaces, and resistive, native passivation layers, which limit cycling stability. In this study, thermally evaporated, high‐purity lithium with smooth grain‐boundary surface morphology significantly improves interfacial contact and electrochemical performance. Replacing extruded lithium with a 50 µm evaporated lithium anode increases the critical current density (CCD) from 1.6 to 2.1 mA cm ⁻² and enables 161 cycles at 1.5 mA cm ⁻² and 1.6 mAh cm ⁻² . A thickness‐dependence study reveals that maintaining a sufficient lithium reservoir is crucial to mitigate void formation and compensate for solid electrolyte interphase (SEI) growth. To overcome limitations at reduced thickness, an ultra‐thin 65 nm LiF passivation layer was applied to 25 µm evaporated lithium. The LiF coating suppresses chemical degradation during storage, stabilizes lithium/LPSCl interface, limits SEI growth, and mitigates dendrite, increasing the CCD to 2.6 mA cm ⁻² . In full cells, LiF‐coated 25 µm lithium delivers over 500 and 300 cycles at current densities of 1.5 and 3 mA cm ⁻² respectively. These results establish LiF‐passivated thermally evaporated lithium as a high‐performance anode design for next‐generation ASSBs.

In this study, the effect of the ionomer loading on the performance of a nickel single-atom catalyst (Ni-SAC) implemented as the cathode catalyst layer (CL) of a forward-bias bipolar membrane (FB-BPM) zero-gap CO2-electrolyzer was systematically investigated. By varying the ionomer-to-catalyst (I/C) mass ratio at a fixed catalyst loading (1.0 mg·cm–2), we reveal a critical trade-off between ionic conductivity and mass transport within these Ni-SAC catalyst layers. While high ionomer loadings (i.e., I/C values >0.75) improve ionic transport, they simultaneously exacerbate pore blockage and water accumulation within the corresponding CLs, leading to mass transport limitations under full cell operation. As a result, Ni-SAC electrodes with low ionomer loadings (I/C ≤0.75) achieve CO Faradaic efficiencies (FECO) ≥80% at current densities ≤150 mA·cm–2, whereas higher ionomer contents lead to a decrease in FECO accompanied by an increase in cell voltage. Notably, all electrodes exhibit a sharp voltage increase at the latest when reaching a current density of 200 mA·cm–2, highlighting a system-level limitation that we associate with local CO2 depletion. These findings provide initial design guidelines for optimizing Ni-SAC/PiperION cathode CL-microenvironments in FB-BPM CO2-electrolyzers.

Fe‐doped transition metal oxides are leading candidates for noble‐metal‐free oxygen evolution reaction (OER) catalysts. However, distinguishing the commingled roles of Fe incorporation pathways and initial structure in governing catalytic activity of Co‐based materials remains incomplete. In this study, we systematically decouple the effects of bulk versus electrolyte Fe incorporation in crystalline, defective crystalline, and amorphous catalysts derived from the same CoSn(OH) ₆ precursor, ensuring identical metal compositions throughout. Electrolyte Fe incorporation equalizes the OER activity across all three structural variants, demonstrating that surface Fe chemistry can dominate initial structural effects on the reconstructed catalyst interface. Notably, amorphous CoSnO _x benefits more from electrolyte Fe than from bulk Fe incorporation, pointing to the amorphization method as a critical design parameter for high‐performance OER catalysts.

Effective water management in polymer electrolyte fuel cells (PEFCs) critically depends on the wettability of gas diffusion layers (GDLs), which controls capillary-driven liquid transport. While hydrophobic coatings (like polytetrafluoroethylene, PTFE) are widely used to tailor wettability, detecting and quantifying their distribution within the complex porous structure remains challenging. Wettability characterization serves as an indirect proxy but is complicated by the coupled effects of pore morphology and surface chemistry, even though effective contact angles remain a required input for capillary transport models. This work summarizes experimental and modeling approaches for GDL wettability assessment. Conventional techniques (sessile drop, Wilhelmy plate) provide surface-level information, whereas bulk methods (Washburn, capillary pressure-saturation (p _c –S) curves, capacitance) capture macroscopic behavior but lack spatial resolution. Advanced imaging-based methods, such as environmental scanning electron microscopy and X-ray tomography with image-based contact angle analysis, enable 3D insight yet remain resource-intensive. Furthermore, the widespread concept of “mixed wettability,” attributed to inhomogeneous PTFE coating, is examined and the influence of pore geometry is highlighted, supported by pore-network modeling approaches. Together, these approaches reveal how pore geometry and surface chemistry jointly define GDL wettability.

Cobalt‐based oxides have been investigated as potential alternatives to Ir/Ru‐based oxides for catalyzing the oxygen evolution reaction (OER) in acidic media. Past research, however, is mainly focused on the spinel oxide structure so far. Exploring alternative crystal structures is essential for expanding the material library and developing highly efficient OER catalysts for acidic environments. As a proof of concept, we demonstrate that Co‐based perovskite oxides can drive acidic OER effectively. Appling hard/soft X‐ray absorption spectroscopy (hXAS/sXAS) characterizations, we show that the La and Ce doped SrCoO ₃ (denoted as LSC and CSC, respectively) have a bulk‐average Co oxidation state close to 3+ and surface‐dominant low‐spin Co ^III species. Electrochemical analysis reveals that they only show one Co redox pair, similar to CoOOH in acidic environments. The recorded Tafel slopes are around ∼65 mV dec ⁻¹ , comparable to the benchmarking Ir/Ru‐based catalysts. The combination of the spectroscopic and electrochemical findings presented here highlights the important role of low‐spin Co ^III species in catalyzing OER in acidic environments and contributes to the rational design of non‐noble metal OER catalysts.

Attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) is becoming a widely-used technique in electrocatalysis thanks to its ability to track surface species during electrochemical reactions, providing valuable insights into the dynamic behavior of reaction intermediates. Here, a new design of a spectroelectrochemical ATR-SEIRAS flow cell is presented, offering a thin (≈ 300 μm) electrolyte layer at the working electrode side to enhance mass transport (e.g., bubble detachment), coupled with a gas chromatograph, mass spectrometer, and a custom-made liquid distribution system for real-time analysis of gaseous and liquid reaction products. To test this setup, we studied the electrochemical CO₂ reduction reaction (CO₂RR) on carbon-supported palladium nanoparticles by performing linear sweep voltammograms in CO₂-saturated 0.1 M KHCO₃. Thereby, we were able to monitor the formation and oxidative stripping of surface-adsorbed CO. Additionally, when performing potential holds in a range favorable for formate production (from -100 to -400 mV vs. the reversible hydrogen electrode), the progressive formation of this CO adsorption layer was found to correlate with the concomitant decrease in formate activity over time. Results emphasize the importance of combining time-resolved monitoring of the formation and depletion of surface intermediates with quantification of reaction products to gain a better understanding of catalytic mechanisms