Atomically ordered Pt-based intermetallic alloys have gained interest as promising cathode materials catalyzing the oxygen reduction reaction (ORR) in hydrogen-fueled proton exchange membrane fuel cells (PEMFCs) with special durability requirements. This is the case because ordered Pt intermetallic alloys are believed to display superior chemical durability over their disordered counterparts. However, achieving the atomic-disorder-to-order phase transition typically necessitates prolonged high-temperature annealing, which often induces nanoparticle sintering and reduces Pt utilization. These challenges are particularly pronounced in acid-stable early transition metal Pt-M alloy systems (e.g., Pt-V), where alloy formation is hindered by the large disparity in reduction potentials. Here we present a lattice-vacancy-mediated synthesis strategy using evaporating Zn atoms as a cataloreactant to trigger the formation of the L12 intermetallic phase in the Pt-V system. This approach enabled the synthesis of highly ordered Pt-V alloy nanocatalysts with significantly suppressed non-noble transition metal leaching, thereby delivering enhanced PEMFC performance and durability. Online spectrometric and in situ spectroscopic analyses suggest distinct degradation mechanisms, characterized by isotropic V leaching in the ordered structure versus anisotropic segregation in the disordered structure. These findings underscore the efficacy of vacancy-mediated ordering as a synthetic paradigm for designing durable, high-performance intermetallic catalysts for PEMFC applications.

Abstract A strong societal and political drive is motivating the development and optimization of novel energy conversion and storage systems for decarbonization. The successful implementation of solid state devices such as fuel cells and secondary batteries depends, however, on achieving ambitious targets in terms of performance, reliability and cost competitiveness. Research and technology are addressing these needs through a holistic approach including exploration of new materials and nanoarchitectures, as well as system engineering. These significant efforts require the support of appropriate characterization tools capable of assessing nanometer-scale phenomena such as concentration profiles of ionic and electronic charges, local chemical compositions and their evolution over time across interfaces. This roadmap provides an overview of selected advanced characterization techniques for energy materials and devices. Specific focus is put on in situ/operando methods for probing electrochemical phenomena in real-time under realistic working conditions. Experts in the field provide an extensive review of the current state of the art in 2025 and the current and future challenges for the characterization of local chemistry and kinetics in the bulk of the material, in nanoarchitectures (e.g. thin films) and at the interfaces (e.g. grain boundaries, phase contacts, solid/liquid and solid/gas interfaces) . The aim is to provide a detailed guide to the techniques, describing opportunities and bottlenecks for their practical deployment and examples of successful applications. This roadmap provides an overview of selected advanced characterization techniques for energy materials and devices. Specific focus is put on in situ/operando methods for probing electrochemical phenomena in real time under realistic working conditions. Experts in the field provide an extensive review of the current state of the art in 2024 and the current and future challenges for the characterization of local chemistry and kinetics in the bulk of the material, in nanoarchitectures (e.g. thin films) and at the interfaces (e.g. grain boundaries, phase contacts, solid/liquid and solid/gas interfaces) . The aim is to provide a detailed guide to the techniques, describing opportunities and bottlenecks for their practical deployment and examples of successful applications.

Graphite electrodes face fast charging limitations in Li-ion batteries. Using operando X-ray diffraction and ex situ holotomography, we assess ionic transport restrictions and recalculate the actual C-rate within the electrode.

The transition to net-zero emissions hinges on circular economy strategies that valorize waste and enhance resource efficiency. Among X-to-liquid (XTL) technologies, the Fischer-Tropsch (FT) process stands out for converting biomass, waste, and CO2 into hydrocarbons and chemicals, especially when powered by renewable hydrogen. Cobalt-based catalysts are preferred in FT synthesis due to their efficiency and CO2 tolerance, yet their catalytic performance is closely tied to their polymorphic structuresface-centered cubic (FCC), hexagonal close-packed (HCP), and stacking-faulted intergrowths thereof. HCP cobalt has been shown to exhibit high activity and selectivity for higher hydrocarbons and oxygenates, particularly when transformed into cobalt carbide (Co2C), which forms more readily at low H2/CO ratios. This study presents a quantitative analysis of cobalt polymorphs and stacking faults in Mn-promoted Co/TiO2 FT catalysts from in situ powder X-ray diffraction (XRD) data and X-ray Diffraction Computed Tomography (XRD-CT) data from spent catalysts in order to obtain a more complete correlation of structural features with catalytic performance. By modeling stacking fault probabilities using supercell simulations, the proportion of faulted FCC and HCP domains was determined across varying Mn loadings (0-5%). Increased Mn loading was found to decrease stacking faults in the FCC phase while increasing them in HCP, promoting the formation of HCP domains and ultimately Co2C under reaction conditions. Notably, the 3% Mn-loaded sample showed a marked rise in HCP content and Co2C formation, correlating with the highest observed alcohol and olefin selectivity. These findings highlight a critical structure-function relationship: Mn facilitates a transformation from FCC to HCP and then to Co2C, this final transition driven by similar stacking sequences and metal-support interactions. The findings show that Mn promotion not only stabilizes smaller Co particles and enhances its dispersion, but also modulates the distribution of Co polymorphs and stacking faults, leading to altered catalytic behavior. This highlights the importance of stacking fault characterization for optimizing FT catalyst design and performance, and suggests pathways to more efficient and selective carbon-neutral fuel production through engineered polymorphic and interfacial structures.

Improving the intrinsic activity and utilization of iridium (Ir)-based catalysts for the oxygen evolution reaction (OER) is essential to the market penetration of proton exchange membrane water electrolyzers (PEMWEs). However, conventional electronic structure modulation strategies relying on the introduction of transition metals through alloying and doping face serious stability issues. In this study, we examine the structure-activity-stability relationships toward the OER of an IrCu aerogel in comparison to dispersed IrCu nanoparticles and a commercial IrO x benchmark. Using a combination of ex situ, in situ, and post mortem techniques, we show that the high OER activity of the IrCu aerogel originates primarily from the presence of lattice distortions, i.e., through a structural effect rather than an alloying effect. Moreover, beyond decisively influencing the electrocatalytic activity, the structure is shown to inhibit the formation of stable Ir oxide species during operation unlike for isolated nanoparticles, which is detrimental to the aerogel stability during accelerated stress tests in PEMWE.

Manganese-based Prussian White (PW) Na2-xMn[Fe(CN)6]y & centerdot;square 1-y & centerdot;zH2O (0 <= x <= 2, 0 <= y <= 1) is a promising cathode material for sodium-ion batteries, due to the variety of its composition, its intercalation properties, and its good electrochemical performance. However, water-induced structural transformations limit its practical application and remain poorly understood. To unravel how water content governs structure transformations in relation to electrochemical performance, a rehydration of a heat-treated Na1.67Mn[Fe(CN)6]0.88 & centerdot;square 0.12 compound was monitored by in situ synchrotron X-ray diffraction performed under a controlled atmosphere. At a dew point of -8 degrees C and a flow rate of 30 mL min-1, the original rhombohedral (dehydrated) phase transforms in 20 minutes into a newly formed disordered monoclinic structure. Water uptake induces a significant expansion of the lattice volume and enhanced structural disorder. Regarding the electrochemical performance, a promising first discharge capacity of 145 mAh g-1 is obtained for the dehydrated PW, corresponding to 85% of its theoretical capacity (similar to 170 mAh g-1). Surprisingly, the rehydrated compound demonstrates a rather high capacity retention of 64%, while the hydrated compound retains only 14% of its initial capacity over 100 cycles at a C/10 rate in a voltage range of 2.5-4 V vs. Na+/Na. This study provides new quantitative insights into the impact of humidity exposure on PW and on its structural integrity after a heat treatment. The present work will help implement cost-effective PW cathode materials in practice.

Dissolution of iridium in proton exchange membrane water electrolyzer anodes is a critical challenge on the path towards low-cost and durable water electrolysis. While end-of-test analysis of electrolyzers showed that most of the dissolved catalyst redeposits in the membrane and the cathode catalyst layer, this approach offers only limited insight into the dynamics of iridium dissolution, transport, and redeposition mechanisms. By means of 2D-mapping with synchrotron-based operando X-ray fluorescence (XRF) spectroscopy, we detected dissolved iridium in the membrane electrode assembly (MEA) during electrolysis operation and traced the dynamics of its transport under varied operation conditions with reasonable temporal (20 min per map) and spatial (10 µm) resolution. During electrolysis, we observed an accumulation of dissolved iridium in the cathode catalyst layer. With the toggling flow of dry gas at the cathode, we can distinguish between mobile and redeposited iridium. Though thermodynamically favored, no significant deposition within the cathode was observed after ~1 h of electrolysis. The results obtained are another puzzle piece in the understanding of iridium dissolution in electrolyzers towards its possible mitigation.

Green hydrogen produced by proton exchange membrane water electrolysis (PEM-WE), has gained significant attention as a future energy carrier and as a feedstock for the chemical industry. Reducing the use of scarce iridium in PEM-WE anodes is a critical requirement. In this work, porous iridium-based inverse opal structures (IrOx-IO) of varying pore sizes are introduced as novel unsupported bulk anode catalysts and their superior performance compared to commercial alternatives is demonstrated. The influence of porosity and surface area on the electrochemical performance is systematically investigated and categorized using voltage breakdown analysis and equivalent circuit modeling. Efficient IrOx-IO operation requires balancing surface area and pore size, enabling high performance up to 13 A cm- 2 with iridium utilizations below 0.1 gIr/kW at 70% efficiency. The findings advance our understanding of unsupported bulk catalysts and, more importantly, expand the range of viable anode materials by clarifying how catalyst morphology influences electrode reactivity.

Halide solid electrolytes are promising candidates for all-solid-state batteries owing to their high ionic conductivity at room temperature and excellent oxidative stability, yet they are chemically unstable against Li metal, forming a mixed ionic/electronic conductor that necessitates a protective interlayer. Here, we evaluate the use of β-Li3N as an interlayer for Li3YBr2Cl4. We found that introducing a thick β-Li3N interlayer into the full cell reduced early polarization and delayed failure, though it did not prevent it. By combining porosity measurement and electrochemical testing, we demonstrate that the β-Li3N interlayer has high porosity, allowing Li to penetrate under stack pressure and during electrodeposition. Moreover, through synchrotron X-ray nano-holo-tomography and scanning microdiffraction, we provide direct visualization of Li penetration into the layers of β-Li3N and LYBC, explaining the significant voltage spikes and the cell polarization observed during electrochemical cycling. This work highlights the need to develop thinner and denser interlayers to overcome the key limitation of the porous microstructure in β-Li3N, which hinders the development of durable halide-based all-solid-state Li-metal batteries.

LiNi0.8Mn0.1Co0.1O2 (NMC811) is a promising cathode material for high-energy-density Li-ion batteries (LiBs). However, its practical application is limited by capacity fading during electrochemical cycling, mainly associated with cation mixing, structural degradation, and lattice collapse at high voltages. In this work, zirconium (Zr) doping was introduced during the co-precipitation step to improve the structural stability of NMC811 and mitigate its degradation mechanisms. X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) measurements confirmed the incorporation of Zr into the NMC811 host structure at low doping concentrations, whereas concentrations above 0.1 mol% promoted the formation of an additional Li2ZrO3 (LZO) phase. The excess Zr was found to segregate locally on the surface of NMC811 particles rather than forming a homogeneous protective coating. Although higher Zr concentrations improved the rate capability, combined electrochemical and morphological analyses revealed that this enhancement primarily originates from the formation of smaller secondary particles induced by Zr addition during co-precipitation. However, the increased fraction of smaller particles negatively affects long-term cycling stability by promoting a larger electrode–electrolyte interfacial area and enhanced parasitic reactions. These results highlight that controlling the Zr concentration is essential to maximize lattice incorporation while minimizing secondary-phase formation and undesired morphological changes.

Reducing the iridium content while preserving the activity and robustness of anode catalysts remains a central challenge for Proton Exchange Membrane Water Electrolysis (PEM-WE). In this work, we demonstrate that controlled lattice distortion – introduced during magnetron co-sputtering – can serve as a powerful materials-design parameter for Ir–Co catalysts. By adjusting the conditions of the plasma deposition process, we prepare a series of thin-film Ir–Co layers exhibiting systematically varied strain states and defect densities. The catalysts are evaluated through single-cell PEM-WE testing, complemented by ex-situ and operando characterization including X-ray photoelectron spectroscopy (XPS), wide-angle X-ray diffraction, and Scanning Photoelectron Microscopy (SPRES). The combined dataset reveals that increased lattice distortion changes the process of subsurface oxidation of Ir into IrOx, which leads to improved activity and stability both in the PEM-WE and half-cell measurements. Our results highlight strain modulation during magnetron sputtering as a scalable and tunable strategy for designing high-performance, low-Iridium catalysts. This approach provides a clear structure–property link and opens new opportunities for engineering thin-film PEM-WE anodes beyond composition alone.

Electrochemical direct Li extraction (eDLE) enables the utilization of unconventional new Li sources such as geothermal brines. Methods based on ion intercalation, which operate similarly to Liion batteries, are particularly promising. To rationally design respective materials and processes, a phenomenological and mechanistic understanding of the physics and chemistry underlying (de-)intercalation and degradation is needed. Ideally, this knowledge is quantitative, bridges the atomic and mesoscopic scales, and can be interpreted in the context of material and device performance under various operating conditions. Given the complexity of electrochemical Li-capturing system (ELiCS) reactors, this task is challenging, and innovative approaches using advanced operando methods are necessary. Towards this end, we devised an operando high-energy X-ray diffraction (HEXRD) microscopy study of spinel manganese oxide Li extraction electrodes under realistic conditions. For this purpose, we designed a realistic flow-by reactor, integrated into a quasi-high-throughput system, allowing us to investigate the atomic scale structural evolution across the electrodes during operation. Our results suggest a peculiar phase evolution exhibiting a three-phase coexistence of variously lithiated phases and a complex combination of solid solution reactions and bi-/tri-phasic phase transitions with significant heterogeneity across the electrode. Intriguingly, we observe a markedly asymmetric behavior in the phase evolution during lithiation and delithiation, indicating significant differences in intercalation and deintercalation mechanism. We rationalise our results, interpret their implications for ELiCS performance, and discuss how they inform ELiCS process design.

Strain engineering in single-crystalline oxide membranes offers a versatile platform to tailor functional properties beyond thin films or bulk materials. However, accurately determining strain transfer and distribution within these membranes remains challenging, limiting direct correlations between structural distortion and functional response and hindering the rational design of flexible devices. Here, high-resolution synchrotron x-ray diffraction is used for in situ monitoring of strain in (001)-oriented La 0.7 Sr 0.3 MnO 3 membranes on flexible polymer substrates under stretching and bending. This approach enables quantitative determination of in-plane strain as both macroscopic averages and spatially resolved maps. Macroscopic analysis shows that strain transfer is most efficient in thinner films and leads to distinct strain symmetries under stretching and bending. Spatially resolved measurements reveal local strain heterogeneity that increases with applied stress beyond macroscopic averages. Correlating strain distribution with estimated Curie temperature shifts illustrates how such heterogeneity could translate into spatially non-uniform functional behavior. Additionally, the setup's sensitivity to crystallographic orientation enables analysis of stacked and twisted architectures, where interlayer strain transfer is effective yet attenuated with distance from the substrate. Altogether, this framework establishes a robust approach for probing oxide membranes, opening pathways toward strain-engineered flexible devices, multilayer heterostructures, and operando investigations.

Without activation, no power. The start-up of anion-exchange-membrane fuel cells with nickel-based anodes requires specific activation protocols due to the initial surface oxidation of metallic nickel.

The development of advanced iridium oxide (IrO x ≤ 2) electrocatalysts for the oxygen evolution reaction (OER) remains limited by insufficiently defined structure-property relationships. Here, using operando X-ray diffraction and in-house synthesized unsupported mesoporous IrO x nanoparticles with controlled crystallinity, size, and oxidation state, alongside a commercial benchmark material, we show reversible IrO 2 lattice structure and Ir oxidation state changes across cell voltages ranging from 0.05 V to 2.00 V. At low potentials (E < 0.25 V), the IrO 2 surface partially amorphizes, linked to formation of a poorly conductive iridium oxyhydroxide (IrO (1-δ) (OH) (1+δ) ) phase. Under OER conditions, the IrO 2 lattice contracts and Ir-O bond distances shorten. Density functional theory calculations support these reversible structural and chemical transformations and explain their mechanistic origin, while on-line inductively coupled plasma mass spectrometry measurements directly correlate these changes with Ir dissolution dynamics. Extending to practical conditions, a proton exchange membrane water electrolyzer (PEMWE) operated for 500 h at 2 V shows that an initially amorphous IrO x catalyst crystallizes, ultimately degrading to performance and Tafel slopes comparable to those of rutile IrO 2 . These findings highlight the redox-driven structural flexibility of IrO x materials and link IrO 2 structure, chemistry, OER activity, and Ir dissolution during start–stop operation in PEMWEs.

Proton exchange membrane fuel cells (PEMFC) for heavy-duty transport require cathode catalysts that combine high platinum utilization with exceptional resistance to electrochemical degradation, yet the failure mechanisms of intermetallic alloys under realistic operating conditions remain poorly resolved. In heavy-duty applications, high Pt loadings are further required to maintain thin catalyst layers, thereby enhancing mass transport and overall cell performance. Here we report a high-loaded (> 50 wt% Pt) L10-PtCo nanocatalyst on sulfurdoped carbon that couples strong metal-support interactions with an ordered intermetallic lattice to deliver both high oxygen reduction activity and outstanding stability under fuel-cellrelevant conditions. The catalyst reaches a mass activity of 1.28 A/mgPt at 0.9 V and, after 30,000 accelerated stress-test cycles, retains nearly its full electrochemically active surface area with only 2% loss, while substantially outperforming commercial PtCo/C and Pt/C benchmarks. In a 50 cm2 membrane electrode assembly, the catalyst translates this intrinsic reactivity into practical device performance. The sulfur-doped carbon-support also markedly suppresses carbon corrosion under start-up/shut-down-relevant conditions, limiting carbon mass loss to about 11%, versus 30% for PtCo/C. Operando small- and wide-angle X-ray scattering measurements in a working PEMFC, combined with online inductively coupled plasma mass spectroscopy, reveals the structural origin of this durability: suppressed Pt dissolution, delayed Co leaching, and mitigation of agglomeration. These measurements further uncover a coalescence-induced dealloying pathway and identify an anisotropic lattice evolution in the L10-core during potential cycling. These results provide mechanistic insight into degradation processes in intermetallic catalysts under operating conditions and establish design rules for durable PEMFC cathodes by stabilizing lattice structure and mitigating transition metal dissolution.