Using aberration-corrected electron microscopy and spectroscopy, we reveal the atomic scale structure and catalytic function of the A-site-deficient perovskite La0.7Fe0.7Mn0.3O3, uncovering a heterogeneous defect landscape that governs its activity in reducing NO by CO. We identified a layer of La0.7-xFe0.7Mn0.3O3 that is highly A-site-deficient. This layer is just two to three unit cells thick at the surfaces and the interfaces of the perovskite particles and transitions toward the bulk into stoichiometric LaFe0.7Mn0.3O3. These confined defect layers stabilize catalytically active sites, enabling the formation of FeOx inclusions ranging from approximately 1  nm to several nanometers in size at the surfaces. In situ surface characterization and catalytic measurements reveal that these interfacial FeOx nanoparticles serve as active sites during the NO reduction by CO via the Mars-van Krevelen mechanism. Our findings establish a direct relationship between the structure and properties of nanoscale A-site nonstoichiometry and redox-driven catalytic activity. This relationship offers a new design strategy for tailoring reactivity through defect engineering.

This study introduces a new strategy to electrocatalyst synthesis by immobilizing platinum nanoparticles (Pt-NPs) on carbon spherogels-nanoporous, monodisperse carbon hollow spheres with diameters of 170-240 nm and surface areas of up to 800 m2 g-1 with or without incorporated titanium-dioxide (TiO2) sublayers, using supercritical deposition. The resulting materials feature precisely tunable Pt-loadings (2-11 wt%), narrow Pt-NP size distributions, low interparticle distances (4.4-8.2 nm), and high Pt-NP dispersion (Pt-NP mean diameter 2.2-3.5 nm). The presence of TiO2 sublayers enhances both catalytic activity and durability in the hydrogen evolution reaction compared to a commercial Pt/C benchmark with similar Pt content. TiO2 containing electrocatalysts exhibit Pt-NPs in the inner part of spheres and outstanding stability, demonstrated by (a) minimal potential shifts (1-4 mV) after accelerated stability tests, (b) suppression of Pt-NP growth and detachment, and (c) structural integrity retention after 70 h under harsh conditions. These findings highlight the potential of spherogels as advanced catalyst supports and offer a scalable synthesis route without requirement for hazardous templating agents. Thanks to the tunable support morphology, precise Pt-NP deposition, and remarkable long-term performance, this approach emerges as a strong candidate for designing next generation electrocatalysts.

In situ diffuse reflectance IR spectroscopy (DRIFTS) demonstrates that the lack of suitable CO adsorption sites on LaCu0.5Mn0.5O3 (LCM55) perovskites limits the overall NO + CO reaction. Metallic Cu and vacancy sites (or cationic sites near these vacancies) can both act as active sites for CO adsorption. We provide evidence that adsorbed nitrogen atoms facilitate CO adsorption and conversion at vacancy sites formed under strongly reducing conditions. The proposed mechanism involves the reaction of adsorbed CO with surface nitrogen species to surface isocyanate (NCO) species (represented by a peak at 2170 cm(-1) at 600 degrees C). Subsequently, CO spills from N sites to active reduced sites. This channel of localized CO adsorption increases the reactive sticking coefficient of CO at or next to active centers and indirectly supports the presence of atomically dispersed sites. CO adsorption via this mechanism is especially important for the reaction progress at higher temperatures, where the relatively weak CO adsorption on metallic Cu centers is a limiting factor. In due course, the involvement of nitrogen atoms in the CO adsorption pathway suppresses N2O formation and enhances selectivity toward N-2.

Carbon aerogels derived from organic precursors are gaining attention in various applications, especially in energy storage. On one hand, this paper deals with the substitution of phenolic materials by tannin which could be beneficial to both the bioeconomy and the environment due to its low-cost, bio-based, and non-toxic characteristics. On the other hand, the comparative study aims to explore advantages and drawbacks of both aerogels, their electrical conductivity, morphology, performance in an electrochemical cell, and materials costs. The results illustrate that both nitrogen-doped aerogels exhibit pyridinic and pyrrolic functional groups, while doping with melamine leads to higher nitrogen amount about 5 wt.-

The high-temperature co-electrolysis of CO2 and H2O in solid oxide cells is a promising avenue toward renewable energy storage and climate change mitigation. The present study identifies fundamental electrochemical pathways toward methane under syngas-rich electrochemical conditions and differentiates the specific reactivities of the observed carbon deposits. A thin-film electrode comprising Ni on yttria-stabilized zirconia (YSZ) was evaluated by operando near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and mass-spectrometric product detection under strongly cathodic electrolysis conditions with predominantly CO and H2 in the gas phase. Under these conditions, the reduction of CO toward elemental carbon species takes place. A hitherto unknown methane-forming mechanism via polarization-induced carbon spillover from Ni to YSZ was identified, causing ZrC x formation at the electrolyte surface near the Ni/YSZ boundary. Hydrolysis of this ZrC x species by added traces of steam enhances the methane selectivity. Our experimental results, corroborated by density functional theory (DFT) modeling, enable better control of high-temperature CO2-H2O co-electrolysis for product-selective renewable energy storage.

Abstract By in situ electron microscopy we show the intermediate phase formation during decomposition of LaNiO 3 , a model methane dry reforming (DRM) catalyst, under different gas atmospheres. By combining dark- and bright-field imaging with secondary-electron contrast and operando electronic structure characterization, we localize the coupled formation of Ni(O) particles and La 2 NiO 4 as key intermediates under DRM operation preceding full decomposition into metallic Ni and La 2 O 3 . Reduced and bar-level reactant partial pressures enable detailed observation of early decomposition stages. Ni particles formed in vacuum or DRM mixtures undergo transient surface oxidation by lattice oxygen, while highly dynamic Ni particles result from hydrogen reduction. At high temperatures, concurrent Ni formation, LaNiO 3 -to-La 2 NiO 4 transitions, Ostwald ripening, and particle fragmentation/agglomeration govern the dynamics. DRM exposure of reduction-formed Ni leads to rapid oxidation to sintering-resistant NiO with size-dependent dissolution/agglomeration characteristics. As CO 2 cannot directly oxidize Ni here, oxygen migration from the perovskite bulk drives this transient, DRM-detrimental NiO formation.

Bimetallic Ni-Zr layers on top of a Zr metal substrate are oxidatively transformed into an active Ni metal-ZrO2 interfacial state under methane dry reforming (DRM) conditions, which exhibits progressive coking with increasing DRM cycle number and time. Complementing established anticoking catalyst- and process-design strategies, the efficiency, as well as the structural and surface-chemical consequences of the intermediate regeneration of the active state using pure CO2, were studied. By combining repeated catalytic DRM testing, X-ray photoelectron spectroscopy, and chemically resolved scanning electron microscopy, we show that catalyst regeneration using the inverse Boudouard reaction not only depletes the main part of the deposited coke efficiently but also leads to an improved and particularly active catalyst state exhibiting redispersion of Ni toward small particles and optimized Ni/ZrO2 interfacial dimensions.

Temperature-dependent in situ continuous wave (cw) electron spin resonance (ESR) measurements are used for investigating changes in magnetization upon reduction and reoxidation in La-deficient La x Fe0.7Mn0.3O3 (x < 1) samples to advance the understanding of structural and chemical changes in these materials where A-site deficiency was shown to affect catalytic performance. For these defect-rich mixed perovskites with ferromagnetic ordering, the magnetic properties as characterized by in situ cw ESR spectroscopy are sensitive probes for structural changes in these materials. To this end, the ESR spectra observed in a redox cycle in H2- and O2-containing atmospheres not only show structural changes that were not observed by XRD but also provide evidence for heterogeneity in the magnetic phases, which notably depends on the La deficiency of the samples. This not only demonstrates the potential of such investigations for obtaining information complementary to other methods but also emphasizes the sensitivity of magnetic properties as probed by ESR to elucidate structural and chemical changes in such complex perovskite materials. While the XRD results lack indication for the presence of structural heterogeneity, STEM measurements provide evidence for a compositional heterogeneity between the grains but not for the presence of an additional magnetic phase, as observed by ESR for one of the samples. Importantly, the different magnetic phases exhibit distinct responses to reducing and (re)oxidizing atmospheres indicating for the sample with a lower La deficiency a facilitated reaction under reducing conditions at low temperatures but an overall higher structural stability. Both effects are expected to affect the reactivity in the redox reactions. Thus, these results provide new and complementary insights that can enhance the understanding of the effect of A-site deficiency in perovskite materials in redox reactions considered to be important for the catalytic activity of these systems.

We studied the effect of Ti substitution on nickel B-sites in LaNiO3 to unravel the influence of Ti doping on structural stability, Ni exsolution, and methane dry reforming (DRM) properties. Ni can be substituted by Ti down to compositions of xNi = 0.25 without compromising both phase and structure purity. At even higher Ti doping levels, formation of the pyrochlore-type La2Ti2O7 phase occurs. Ti substitution has a significant influence on the stability under reducing conditions and the appearance of specific intermediate structures relevant for DRM operation. Full decomposition is only observed for LaNiO3 and the xNi = 0.75 sample, which yield the La2O3 phase relevant for DRM activity at low Ti doping levels. A common impurity phase between xNi = 0.75 and 0.25 is La2TiO5, which acts as a Ti and La sink and hinders the formation of La2O3. For higher Ti doping levels, hydrogen reduction increases the amount of La2Ti2O7. A common denominator of all samples after hydrogen reduction is the full leaching of all nominally available Ni from the perovskite. The self-activation properties during DRM operation strongly depend on the Ti substitution level. Self-activation with either full or partial decomposition is only possible for LaNiO3 and xNi = 0.75, where intermediate lanthanum oxycarbonate formation occurs. For xNi = 0.50, the remaining perovskite structure is stable, but Ni exsolution nevertheless occurs, triggering DRM activity. Successive Ti doping invokes a change in the DRM mechanism from oxycarbonate-based at low Ti amounts (LaNiO3 and xNi = 0.75) to a more reactive-oxygendominated one for samples xNi ≤ 0.50, as indicated by X-ray photoelectron spectra. Ti doping also allows to economize the amount of Ni for DRM applications it can be lowered to a quarter of the initial amount referenced to pure LaNiO3 without compromising DRM activity.

We explore the fundamental pathways of carbon formation and regeneration in a model Pd/Zr catalyst during dry reforming of methane (DRM) and under related reaction conditions. Using a combination of XPS, SEM, and EDX, we track the structural and chemical changes of the catalyst throughout the reaction, deactivation, and regeneration cycles. By systematically adjusting feed composition, CO2 conversion, and regeneration atmospheres, the study identifies how different gas-phase species contribute to carbon formation and clean-off. It also determines the conditions that influence the accessibility of the reactive metal-oxide interfaces. A comparison with the analogous Ni/Zr system highlights how the choice of the metal affects regeneration chemistry and the importance of accessible metal oxide phase boundaries in CO2 activation. The experimental setup combines temperature-resolved reaction profiling with micro- and spectroscopic surface characterization at key intermediate stages, enabling direct links among catalytic activity, surface morphology, and regeneration results. This approach offers insights into how catalyst design, operational conditions, and regeneration methods can be optimized to achieve high DRM activity and effective carbon management in noble metal-oxide systems.

We demonstrate that in situ impedance spectroscopy is a marker method to follow LaNiO3 decomposition upon hydrogen reduction and is highly potent for the in situ detection of bulk- and surface-located chemical and structural transitions. Combined with in situ X-ray diffraction (XRD), it simultaneously proved the possibility to assess the electrochemical properties of oxygen-deficient phases and the full decomposition products La2O3 and Ni. In situ correlation of impedance and differential thermoanalytic data allows quantitatively pinpointing distinct exothermic peaks to LaNiO2.5 and La2O3 + Ni formation. The initial impedance increase at low temperatures is related by in situ near-ambient pressure X-ray photoelectron spectroscopy to near-surface redox transformations. Equilibrium impedance investigations revealed a pronounced kinetic delay in the structural transformations at low temperatures. In situ impedance spectroscopy upon redox cycling between reductive (H2) and oxidative (O2) conditions allowed us to clearly discriminate between reversible and irreversible transformations and demonstrated exceptional sensitivity to surface reorganization, including the reoccupation of oxygen vacancies and recompensation of structural defects. Frequency-dependent investigations demonstrate that LaNiO3 exhibits an inductive reactance in O2. Formation of oxygen-deficient LaNiO2.5 and irreversible decomposition into La2O3 + Ni are reflected in the frequency-dependent investigations and expressed via increasing capacitance. p-type semiconduction profoundly influences the impedance behavior of NiO in oxidative and reductive atmospheres and was found to be the key conduction contribution of LaNiO3 decomposition at 600 °C. Our work highlights the strength of in situ impedance spectroscopy as a noninvasive, highly responsive marker for surface chemistry, defect dynamics, and bulk structural transformations during redox experiments in perovskites, as evidenced for LaNiO3.

By exploiting the lanthanum - nickel - titanate model system for methane dry reforming (DRM), we show how different (double) perovskite precursor structures can be used to tailor the structure and phase composition of specific Ni - (double) perovskite interfaces by activation in different reducing atmospheres. The key parameter for successful steering of the interface structure is the stability of the parent perovskite material in the respective hydrogen or CO2-CH4 mixture. Rietveld refinements of both the precursor perovskite and the interfacial structures verify the sole presence of exsolved Ni and the respective perovskite. Hydrogen reduction of the double perovskite La2NiTiO6 leads to exsolution of nm-sized Ni particles and the formation of a Ni-La2NiTiO6 interface. Structure refinements based on X-ray and neutron powder diffraction, combined with temperature-programmed hydrogen adsorption, reveal that the prevailing La2NiTiO6 is mostly unaffected by the hydrogen treatment and formation of reduced sites is largely suppressed. Treatment of the Ti-doped single perovskite LaNi0.5Ti0.5O3 in a CO2-CH4 mixture equally yields Ni exsolution and consequently, a Ni-LaNi0.5Ti0.5O3 interface. Similarly, LaNi0.5Ti0.5O3 is essentially unaffected by the treatment, with interfacial structure and phase composition remaining stable over several DRM cycles. Only hydrogen reduction of LaNi0.5Ti0.5O3 causes complete transformation of the parent perovskite into a Ni-La2TiO5/LaTiO3 mixture. All interfaces, including Ni particles impregnated on La2TiO5 with outstanding anti-coking behavior, exhibit inherent DRM activity, rivaling or even outperforming undoped LaNiO3. Differences in the stability of (transient) structures during exsolution along the decomposition pathway are mainly due to the Ti dopant, which stabilizes the perovskite structures in reducing atmospheres. This enhanced stability allows us to approach specific Ni-perovskite interfaces and assess their inherent DRM activity.

As the combination of Co with other non-noble metals is a viable way to improve the catalytic properties of Co in methane dry reforming (DRM), we studied Co 3 O 4 /β-Ga 2 O 3 to understand the influence of Ga and the Co–Ga 2 O 3 interface in DRM.

ZrO2 is a versatile material with diverse applications, including structural ceramics, sensors, and catalysts. The properties of ZrO2 are largely determined by its crystal structure, which is temperature- and atmosphere dependent. Thus, this work focuses on a quantitative analysis of the temperature- and gas atmosphere-dependent phase transformation of tetragonal t-ZrO2 into monoclinic m-ZrO2 during heating-cooling cycles from room temperature to 1273 K. Synchrotron-based in situ X-ray diffraction (XRD) studies in gas atmospheres of different reduction strengths, namely, 5 vol% H-2/Ar, He, CO2, and air, revealed a stabilizing effect of inert and reductive environments, directly yielding different temperature onsets in the phase transformation during cooling (i.e., 435, 510, 710, and 793 K for 5 vol% H-2/Ar, He, CO2, and air, respectively). Rietveld refinement shows a direct influence of the atmosphere on grain size, unit cell, and weight fraction of both polymorphs in the product composite matrix. The tetragonal-to-monoclinic (t-m) phase transformation is suppressed in the sample heated only up to similar to 850 K, independent of the gas atmosphere. The results of ex situ XRD, transmission electron microscopic, electron paramagnetic resonance, and oxygen titration experiments confirmed that the phase transformation is accompanied by a change in the crystallite/particle size and the amount of lattice defects (i.e., oxygen vacancy). Due to the different onset temperatures, a complex interplay between kinetic limitations of phase transformation and grain sintering yields different pathways of the phase transformation and, eventually, very different final crystallite sizes of both t-ZrO2 and m-ZrO2.

Solid oxide cell technologies play a pivotal role in the realm of renewable energy storage, guiding us through the journey toward decarbonization. Understanding how electrocatalytic materials behave under high‐temperature conditions is an absolute necessity to push these technologies forward. Operando spectroscopic investigations, such as near‐ambient pressure X‐ray photoelectron spectroscopy (NAP–XPS), offer insights into the chemical nature of active working electrodes, including the dynamic response of redox states and adsorbate chemistry to changing electrochemical conditions. Mixed ceramic–metallic electrodes exhibit a limited region with electrochemically active triple‐phase‐boundary (TPB) sites, which are located close to the electrolyte/electrode interface. To monitor this specific region spectroscopically, metallic (Ni) and bimetallic (NiCu) network‐like structures are synthesized on a yttria‐stabilized zirconia electrolyte and the electrochemical state and performance are studied by using operando NAP–XPS. In the experiments, the surface oxidation states under different polarizations are revealed, the gas composition dependent Nernst shift is confirmed, electrocatalytic activities are unraveled, and hydrogen evolution is correlated with the applied potential. The findings demonstrate, the effectiveness of thin‐film model cells with spectroscopically accessible TPB regions for probing interfacial states and electrochemical processes. The obtained fundamental knowledge can provide valuable insights for the advancement of renewable energy storage technologies.

Adjusting the defect level during synthesis of A- and B-site deficient lanthanum iron manganite (LFM) perovskites shows that non-stoichiometry can beneficially influence the catalytic reactivity to N2 in the reduction of NO by CO on noble metal-free LFM-based perovskites. Optimal steering of La deficiency and the associated redox chemistry to reduce the near-surface regions during catalytic operation at low temperatures is the key factor. Surface enrichment by reducible B site cations and a proper design of structural defects resulting from the optimum introduction of La defects exclusively cause in-situ reduction of surface-near regions by CO oxidation, as well as formation of oxygen vacancies for enhanced NO and N2O reactivity. Excess doping with defects causes structural instability and continuous supply of oxygen from the catalyst bulk to the surface at elevated temperatures. Introduction of B site vacancies leads to surface enrichment by non-reducible lanthanum cations, causing suppressed catalyst activity undercutting even stoichiometric LFM.

Inadequate removal of micropollutants in wastewater treatment plants (WWTPs) contributes to environmental contamination, underscoring the need for effective technologies. Mixed-matrix membranes with embedded powdered activated carbon (PAC) show promise, but challenges remain, such as the potential loss of adsorption capacity of embedded PAC particles, limited performance data in different water matrices, and uncertain long-term regenerability. This study comprehensively characterised a specific multi-channel mixed-matrix membrane (MCMMM) and evaluated its micropollutant removal from various water matrices at different pH levels, comparing it to pure PAC and multi-channel membranes. Adsorption isotherms and kinetics were determined for the tested substances, as well as their removal during filtration. Although the BET surface area (563.5 m2/g) and static micropollutant capacity (166.8 mg/g) of PAC embedded in MCMMM were lower than those of pure PAC (884 m2/g, 232.6 mg/g), the capacity increased to 265.8 mg/g during dead-end filtration. Filtration of WWTP effluent demonstrated that the polymeric membrane matrix protected the embedded PAC from competitive adsorption with wastewater DOM and effects from water matrix pH were significant. Overall, this membrane type, with its distinctive characteristics and demonstrated regenerability, is highly influenced by the matrix of the treated water, laying the foundation for further long-term studies.

Cu-doped LaCu x Mn1-x O3 perovskites have been used as a model system for a joint experimental and theoretical assessment of the influence of the Cu doping level on the structural, electronic, and magnetic properties. The different Cu-doped phases LaCu0.3Mn0.7O3 (LCM37), LaCu0.5Mn0.5O3 (LCM55), and LaCu0.7Mn0.3O3 (LCM73) including the respective Cu- and Mn-free benchmark materials La2CuO4 (LC) and LaMnO3 (LM) have been studied by magnetization measurements and electronic paramagnetic resonance. Ferromagnetic behavior was detected for pure LM and all Cu-doped perovskites, whereas antiferromagnetic behavior was revealed for La2CuO4. Generally, an increased antiferromagnetic contribution was shown for higher Cu doping levels. Equally, magnetization was highlighted to decrease with increasing Cu content. Sophisticated hybrid density functional theory calculations of the electronic and magnetic properties using defect-free, idealized Cu-doped model structures agree well with the experimental results. The findings reveal that copper incorporation influences both the electronic conductivity and the magnetic properties. Notably, the materials exhibit a tunable degree of half-metallicity and significant electronic spin polarization, establishing them as promising candidates for advanced technological applications in spintronics and catalysis. The insights gained from this study contribute to a broader understanding of perovskite materials and their versatile applications.

Solid oxide cell technologies play a crucial role in climate change mitigation by enabling the reversible storage of renewable energy. Understanding the electrochemical high-temperature reaction mechanisms and the catalytic role of the electrode and electrolyte materials is essential for advancing power-to-H2 technologies. Despite its significance, limited in situ spectroscopic research focusing on nickel and yttria-stabilized zirconia (Ni/YSZ) is available. We employ near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) to investigate 2D porous Ni/YSZ model electrodes with variable YSZ domain sizes and triple phase boundary (TPB) lengths. Focusing on the hydrogen evolution reaction (HER), we provide a mechanistic explanation for why surface hydroxylation and electrochemical activity are correlated with the YSZ surface area and YSZ domain size and unravel the specific mechanistic role of the YSZ surface. A direct comparison of normalization of the measured total electrolysis current to the purely geometrical length of the TPB vs an electrified "catchment area" next to the TPB, exhibiting strong enough electric fields, is the key to a correct quantitative description of the individual elementary steps of water electrolysis on Ni/YSZ. By combining electrochemical impedance spectroscopy, NAP-XPS, and electric field modeling, the local water reduction process near the TPB can be described, indicating optimized structural parameters for improved HER performance.