Operando Spectroscopy Research Articles

A Volcano Correlation between Catalytic Activity for Sulfur Reduction Reaction and Fe Atom Count in Metal Center.

Sulfur reduction reaction (SRR) facilitates up to 16 electrons, which endows lithium-sulfur (Li-S) batteries with a high energy density that is twice that of typical Li-ion batteries. However, its sluggish reaction kinetics render batteries with only a low capacity and cycling life, thus remaining the main challenge to practical Li-S batteries, which require efficient electrocatalysts of balanced atom utilization and site-specific requirements toward highly efficient SRR, calling for an in-depth understanding of the atomic structural sensitivity for the catalytic active sites. Herein, we manipulated the number of Fe atoms in iron assemblies, ranging from single Fe atom to diatomic and triatomic Fe atom groupings, all embedded within a carbon matrix. This led to the revelation of a "volcano peak" correlation between SRR catalytic activity and the count of Fe atoms at the active sites. Utilizing operando X-ray absorption and X-ray diffraction spectroscopies, we observed that polysulfide adsorption-desorption and electrochemical conversion kinetics varied up and down with the incremental addition of even a single iron atom to the catalyst's metal center. Our results demonstrate that the metal center with exactly two iron atoms represents the optimal configuration, maximizing atom utility and adeptly handling the conversion of varied intermediate sulfur species, rendering the Li-S battery with a high areal capacity of 23.8 mAh cm-2 at a high sulfur loading of 21.8 mg cm-2. Our results illuminate the pivotal balance between atom utilization and site-specific requirements for optimal electrocatalytic performance in SRR and diverse electrocatalytic reactions.

Rational Design of Local Reaction Environment for Electrocatalytic Conversion of CO2 into Multicarbon Products

AbstractThe electrocatalytic conversion of CO2 into multi‐carbon (C2+) products provides an attractive route for storing intermittent renewable electricity as fuels and feedstocks with high energy densities. Although substantial progress has been made in selective electrosynthesis of C2+ products via engineering the catalyst, rational design of the local reaction environment in the vicinity of catalyst surface also acts as an effective approach for further enhancing the performance. Here, we discuss recent advances and pertinent challenges in the modulation of local reaction environment, encompassing local pH, the choice of the species and concentrations of cations and anions as well as local reactant/intermediate concentrations, for achieving high C2+ selectivity. In addition, mechanistic understanding in the effects of the local reaction environment is also discussed. Particularly, the important progress extracted from in situ and operando spectroscopy techniques provides insights into how local reaction environment affects C−C coupling and key intermediates formation that lead to reaction pathways toward a desired C2+ product. The possible future direction in understanding and engineering the local reaction environment is also provided.

The Role of Zinc Triflate Additive for Improved Electrochemical Performance of Nickel-Rich Layered Oxide Lithium Battery Cathode via Suppression of Interfacial Parasitic Reactions

Nickel-rich layered oxide cathode materials with low cobalt content, such as LiNi0.90Mn0.05Co0.05O2 (NMC90), have the potential to enable cost-effective, high-energy-density lithium-metal batteries. However, NMC90 cathode materials are prone to severe parasitic reactions at higher voltages during prolonged cycling. The addition of small percentages of electrolyte additives to the neat commercial electrolyte can significantly enhance the overall electrochemical performance of lithium-metal batteries. This study investigates the effects of zinc triflate (Zn(Otf)2) as an electrolyte additive on the enhancement of the electrochemical performances of lithium-metal batteries comprising nickel-rich layered oxide cathode materials. X-ray photoelectron spectroscopy analysis revealed that Zn(Otf)2 decomposition leads to enhanced fluorination at the interfacial layers, which contributes to improved chemical stability. Utilizing operando electrochemical mass spectroscopy, we demonstrate that Zn(Otf)2 additives effectively suppress the electrolyte degradation, which is otherwise detrimental to electrochemical performance. Electrochemical studies show that the inclusion of only ∼1% Zn(Otf)2 as additive in neat commercial electrolyte enhances the electrochemical performance indicated by a 10% improvement in discharge capacity after 150 cycles. This study paves the way for researchers to develop novel fluorinated triflate based electrolyte additives aimed at enhancing the stabilization of interfaces for lithium ion, and potentially also Li-metal batteries.

Improving the Performance of LiNi0.9Co0.05Mn0.05O2 via Atomic Layer Deposition of ZnxOy Coating

AbstractNickel‐rich cathode materials such as LiNi0.9Co0.05Mn0.05O2 (NMC90) have gained attention due to their ability to deliver high energy densities while being cost‐effective for Lithium‐ion battery manufacturing. However, NMC90 cathodes suffer irreversible parasitic reactions such as electrolyte decomposition, severe capacity fading and impedance build‐up upon prolonged cycling. Herein, we synthesize a conformal ultrathin, surface protection layer on NMC90 powder using ZnxOy via atomic layer deposition technique (ZnxOy@NMC90). Prolonged electrochemical investigation of full cells at high discharge rates of 2 C shows that ZnxOy@NMC90 cells yielded ~31 % improvement in discharge capacity compared to pristine NMC90. Furthermore, operando electrochemical mass spectroscopy studies show that the ZnxOy@NMC90 cells have significantly suppressed electrolyte decomposition as compared to pristine NMC90 cells. Post‐cycling electrochemical impedance spectroscopy studies show that the ZnxOy@NMC90 full cells have significantly reduced impedance compared with pristine NMC90 cells. Additionally, post cycling manganese dissolution studies show that ZnxOy@NMC90 cells have greatly enhanced chemo‐mechanical integrity thereby contributing to improved electrochemical performances. Our results underscore the potential of tailored ZnxOy surface coatings on nickel‐rich cathode materials to address critical challenges in advanced energy storage systems, offering promising prospects for the development of high‐energy‐density lithium‐ion batteries.

Time-resolved spectroscopic investigation for the practical application of a photocatalytic air purifier

The photocatalytic efficiency for removing volatile organic compounds (VOCs) is significantly influenced by operational parameters like humidity and flow velocity, exhibiting notable and inconsistent fluctuations in both lab-scale and large-scale demonstrations. In this study, operando spectroscopy and isotope analysis were employed to investigate the correlation between humidity levels and degradation of gaseous acetaldehyde using TiO2 photocatalysts, aiming to demonstrate the scaling-up of photocatalytic air purifier. It was observed that rate constants for the mineralization of acetaldehyde rapidly decreased by 30% as relative humidity increased from 25% to 80% in the flow system (with an air velocity, v = 0.78 m/s). However, batch system showed smaller change with only a 10% reduction of the rate constant. Humidity fluctuations were more pronounced under high-speed conditions and were amplified in air purifier (v = 3.8 m/s). Time-resolved operando spectroscopy using an 13C isotope of acetaldehyde revealed that humidity’s distinct role in dark adsorption and photocatalytic reactions. Water was found to inhibit the formation of crotonaldehyde during aldol condensation reaction in dark condition. Moreover, water suppressed photocatalytic mineralization by inhibiting acetate oxidation to formate. These findings provide valuable insights for improving realistic air purification processes, underscoring the importance of identifying key intermediates and controlling humidity to enhance the selectivity of gaseous pollutant oxidation reactions.

Solar Gas-Phase CO2 Hydrogenation by Multifunctional UiO-66 Photocatalysts.

Solar-assisted CO2 conversion into fuels and chemical products involves a range of technologies aimed at driving industrial decarbonization methods. In this work, we report on the development of a series of multifunctional metal-organic frameworks (MOFs) based on nitro- or amino-functionalized UiO-66(M) (M: Zr or Zr/Ti) supported RuOx NPs as photocatalysts, having different energy band level diagrams, for CO2 hydrogenation under simulated concentrated sunlight irradiation. RuOx(1 wt %; 2.2 ± 0.9 nm)@UiO-66(Zr/Ti)-NO2 was found to be a reusable photocatalyst, to be selective for CO2 methanation (5.03 mmol g-1 after 22 h;, apparent quantum yield at 350, 400, and 600 nm of 1.67, 0.25, and 0.01%, respectively), and to show about 3-6 times activity compared with previous investigations. The photocatalysts were characterized by advanced spectroscopic techniques like femto- and nanosecond transient absorption, spin electron resonance, and photoluminescence spectroscopies together with (photo)electrochemical measurements. The photocatalytic CO2 methanation mechanism was assessed by operando FTIR spectroscopy. The results indicate that the most active photocatalyst operates under a dual photochemical and photothermal mechanism. This investigation shows the potential of multifunctional MOFs as photocatalysts for solar-driven CO2 recycling.

Role of Electrolyte pH on Water Oxidation for Iridium Oxides.

Understanding the effect of noncovalent interactions of intermediates at the polarized catalyst-electrolyte interface on water oxidation kinetics is key for designing more active and stable electrocatalysts. Here, we combine operando optical spectroscopy, X-ray absorption spectroscopy (XAS), and surface-enhanced infrared absorption spectroscopy (SEIRAS) to probe the effect of noncovalent interactions on the oxygen evolution reaction (OER) activity of IrOx in acidic and alkaline electrolytes. Our results suggest that the active species for the OER (Ir4.x+-*O) binds much stronger in alkaline compared with acid at low coverage, while the repulsive interactions between these species are higher in alkaline electrolytes. These differences are attributed to the larger fraction of water within the cation hydration shell at the interface in alkaline electrolytes compared to acidic electrolytes, which can stabilize oxygenated intermediates and facilitate long-range interactions between them. Quantitative analysis of the state energetics shows that although the *O intermediates bind more strongly than optimal in alkaline electrolytes, the larger repulsive interaction between them results in a significant weakening of *O binding with increasing coverage, leading to similar energetics of active states in acid and alkaline at OER-relevant potentials. By directly probing the electrochemical interface with complementary spectroscopic techniques, our work goes beyond conventional computational descriptors of the OER activity to explain the experimentally observed OER kinetics of IrOx in acidic and alkaline electrolytes.

CO Cofeeding Affects Product Distribution in CH3Cl Coupling over ZSM‐5 Zeolite: Pressure Twists the Plot

AbstractC1 coupling reactions over zeolite catalysts are central to sustainable chemical production strategies. However, questions persist regarding the involvement of CO in ketene formation, and the impact of this elusive oxygenate intermediate on reactivity patterns. Using operando photoelectron photoion coincidence spectroscopy (PEPICO), we investigate the role of CO in methyl chloride conversion to hydrocarbons (MCTH), a prospective process for methane valorization with a reaction network akin to methanol to hydrocarbons (MTH) but without oxygenate intermediates. Our findings reveal the transformative role of CO in MCTH at the low pressures, inducing ketene formation in MCTH and boosting olefin production, confirming the Koch carbonylation step in the initial stages of C1 coupling. We uncover pressure‐dependent product distributions driven by CO‐induced ketene formation, and its subsequent desorption from the zeolite surface, which is enhanced at low pressure. Inspired by the above results, extension of the co‐feeding approach to CH3OH as another simple oxygenate showcases the additional potential for improved catalyst stability in MCTH at ambient pressure.

Monitoring Redox Processes in Lithium-Ion Batteries by Laboratory-Scale Operando X-ray Emission Spectroscopy.

Tracking changes in the chemical state of transition metals in alkali-ion batteries is crucial to understanding the redox chemistry during operation. X-ray absorption spectroscopy (XAS) is often used to follow the chemistry through observed changes in the chemical state and local atomic structure as a function of the state-of-charge (SoC) in batteries. In this study, we utilize an operando X-ray emission spectroscopy (XES) method to observe changes in the chemical state of active elements in batteries during operation. Operando XES and XAS were compared by using a laboratory-scale setup for four different battery systems: LiCoO2 (LCO), Li[Ni1/3Co1/3Mn1/3]O2 (NMC111), Li[Ni0.8Co0.1Mn0.1]O2 (NMC811), and LiFePO4 (LFP) under a constant current charging the battery in 10 h (C/10 charge rate). We show that XES, despite narrower chemical shifts in comparison to XAS, allows us to fingerprint the battery SOC in real time. We further demonstrate that XES can be used to track the change in net spin of the probed atoms by analyzing changes in the emission peak shape. As a test case, the connection between net spin and the local chemical and structural environment was investigated by using XES and XAS in the case of electrochemically delithiated LCO in the range of 2-10% lithium removal.

Enhanced Methanol Synthesis from CO2 Hydrogenation Achieved by Tuning the Cu-ZnO Interaction in ZnO/Cu2O Nanocube Catalysts Supported on ZrO2 and SiO2.

The nature of the Cu-Zn interaction and especially the role of Zn in Cu/ZnO catalysts used for methanol synthesis from CO2 hydrogenation are still debated. Migration of Zn onto the Cu surface during reaction results in a Cu-ZnO interface, which is crucial for the catalytic activity. However, whether a Cu-Zn alloy or a Cu-ZnO structure is formed and the transformation of this interface under working conditions demand further investigation. Here, ZnO/Cu2O core-shell cubic nanoparticles with various ZnO shell thicknesses, supported on SiO2 or ZrO2 were prepared to create an intimate contact between Cu and ZnO. The evolution of the catalyst's structure and composition during and after the CO2 hydrogenation reaction were investigated by means of operando spectroscopy, diffraction, and ex situ microscopy methods. The Zn loading has a direct effect on the oxidation state of Zn, which, in turn, affects the catalytic performance. High Zn loadings, resulting in a stable ZnO catalyst shell, lead to increased methanol production when compared to Zn-free particles. Low Zn loadings, in contrast, leading to the presence of metallic Zn species during reaction, showed no significant improvement over the bare Cu particles. Therefore, our work highlights that there is a minimum content of Zn (or optimum ZnO shell thickness) needed to activate the Cu catalyst. Furthermore, in order to minimize catalyst deactivation, the Zn species must be present as ZnOx and not metallic Zn or Cu-Zn alloy, which is undesirably formed during the reaction when the precatalyst ZnO overlayer is too thin.

Rational Design of Multinary Metal Chalcogenide Bi0.4 Sb1.6 Te3 Nanocrystals for Efficient Potassium Storage.

Multinary metal chalcogenides hold considerable promise for high-energy potassium storage due to their numerous redox reactions. However, challenges arise from issues such as volume expansion and sluggish kinetics. Here, a design featuring a layered ternary Bi0.4 Sb1.6 Te3 anchored on graphene layers as a composite anode, where Bi atoms act as a lattice softening agent on Sb, is presented. Benefiting from the lattice arrangement in Bi0.4 Sb1.6 Te3 and structure, Bi0.4 Sb1.6 Te3 /graphene exhibits a mitigated expansion of 28% during the potassiation/depotassiation process and demonstrates facile K+ ion transfer kinetics, enabling long-term durability of 500 cycles at various high rates. Operando synchrotron diffraction patterns and spectroscopies including in situ Raman, ex situ adsorption, and X-ray photoelectron reveal multiple conversion and alloying/dealloying reactions for potassium storage at the atomic level. In addition, both theoretical calculations and electrochemical examinations elucidate the K+ migration pathways and indicate a reduction in energy barriers within Bi0.4 Sb1.6 Te3 /graphene, thereby suggesting enhanced diffusion kinetics for K+ . These findings provide insight in the design of durable high-energy multinary tellurides for potassium storage.

Efficacy of Ca/ZSM-5 zeolites derived from precipitated calcium carbonate in the methanol-to-olefin process

In the context of heightened environmental consciousness and the growing demand for light olefins, this study explores the promising future prospects for their sustainable production from renewable resources. Light olefins (especially propylene) are a pivotal constituent of the petrochemical industry, and their demand is poised for steady growth driven by various sectors (e.g., electric mobility, consumer goods and packaging industries), which should not rely solely on traditional petroleum-led routes. Therefore, sustainable pathways, such as the methanol-to-olefin (MTO) process catalyzed by zeolites, are gaining attention. Intending to couple the future olefin demands with the concept of a “methanol economy”, this study investigates the synthesis of hierarchical Ca/ZSM-5 zeolites using a cost-effective approach involving Precipitated Calcium Carbonate (PCC) as a hard template, leading to superior catalytic performance. Comprehensive characterization techniques are employed to elucidate the catalyst's properties, highlighting the dual importance of mesoporosity and calcium species in optimizing its performance. Operando spectroscopy provides in-depth insights into its enhanced anti-coking characteristics. This research contributes to expanding the catalyst toolkit for zeolite-catalyzed MTO processes, focusing on propylene production, thereby addressing the increasing demand for light olefins while promoting sustainability and circular economy principles.

Spatially and Temporally Resolved Dynamic Response of Co-Based Composite Interface during the Oxygen Evolution Reaction.

Interfacial interaction dictates the overall catalytic performance and catalytic behavior rules of the composite catalyst. However, understanding of interfacial active sites at the microscopic scale is still limited. Importantly, identifying the dynamic action mechanism of the "real" active site at the interface necessitates nanoscale, high spatial-time-resolved complementary-operando techniques. In this work, a Co3O4 homojunction with a well-defined interface effect is developed as a model system to explore the spatial-correlation dynamic response of the interface toward oxygen evolution reaction. Quasi in situ scanning transmission electron microscopy-electron energy-loss spectroscopy with high spatial resolution visually confirms the size characteristics of the interface effect in the spatial dimension, showing that the activation of active sites originates from strong interfacial electron interactions at a scale of 3 nm. Multiple time-resolved operando spectroscopy techniques explicitly capture dynamic changes in the adsorption behavior for key reaction intermediates. Combined with density functional theory calculations, we reveal that the dynamic adjustment of multiple adsorption configurations of intermediates by highly activated active sites at the interface facilitates the O-O coupling and *OOH deprotonation processes. The dual dynamic regulation mechanism accelerates the kinetics of oxygen evolution and serves as a pivotal factor in promoting the oxygen evolution activity of the composite structure. The resulting composite catalyst (Co-B@Co3O4/Co3O4 NSs) exhibits an approximately 70-fold turnover frequency and 20-fold mass activity than the monomer structure (Co3O4 NSs) and leads to significant activity (η10 ∼257 mV). The visual complementary analysis of multimodal operando/in situ techniques provides us with a powerful platform to advance our fundamental understanding of interfacial structure-activity relationships in composite structured catalysts.

Mechanistic Insights of Ethylene Polymerization on Phillips Chromium Catalysts.

Silica-supported chromium oxide catalysts, also named Phillips chromium catalysts (PCCs), provide more than half of the world's production of high- and medium-density polyethylenes. PCCs are usually prepared in the Cr(VI)/SiO2 form, which is subjected to reductive activation. It has been explicitly proven that CO reduces Cr(VI) to Cr(II) species that initiate ethylene polymerization; ethylene activates Cr(VI) sites as well, but the nature of the catalytic species is complicated by the presence of the ethylene oxidation products. It is widely accepted that the catalytic species are of a Cr(III)-alkyl nature, but this common assumption faces the challenge of "extra" hydrogen: the formation of similar species under the action of even-electron reducing agents requires an additional H atom. Relatively recently, it was found that saturated hydrocarbons can also activate CrOx/SiO2, and alkyl fragments turn out to be bonded with a polyethylene chain. In recent years, there have been numerous experimental and theoretical studies of the structure and chemistry of PCCs at the different stages of preparation and activation. The use of modern spectral methods (such as extended X-ray absorption fine structure (EXAFS), X-ray absorption near-edge structure (XANES), and others); operando IR, UV-vis, EPR, and XAS spectroscopies; and theoretical approaches (DFT modeling, machine learning) clarified many essential aspects of the mechanisms of CrOx/SiO2 activation and catalytic behavior. Overall, the Cosse-Arlman mechanism of polymerization on Cr(III)-alkyl centers is confirmed in many works, but its theoretical support required the development of nontrivial and contentious mechanistic concepts of Cr(VI)/SiO2 or Cr(II)/SiO2 activation. On the other hand, conflicting experimental data continue to be obtained, and certain mechanistic concepts are being developed with the use of outdated models. Strictly speaking, the main question of what type of catalytic species, Cr(II), Cr(III), or Cr(IV), comes into polymerization still has not received an unambiguous answer. The role of the chemical nature of the support-through the prism of the nature, geometry, and distribution of the active sites-is also not clear in depth. In the present review, we endeavored to summarize and discuss the recent studies in the field of the preparation, activation, and action of PCCs, with a focus on existing contradictions in the interpretation of the experimental and theoretical results.

Unique CoP Microflower Decorated with Phosphorous‐Enriched PtP2 onto Nickel Foam with Interfacial Electronic Interactions to Boost Alkaline Water‐Splitting

AbstractThe development of stable and efficient electrocatalysts for overall freshwater/seawater water‐splitting has received significant attention. In this study, the fabrication and electrocatalytic properties of phosphorus‐enriched PtP2 dispersed on CoP (PtP2/CoP) for HER and OER in both alkaline fresh/seawater media are described. Physical characterization and density functional theory calculations reveal that strong electronic interfacial interactions between PtP2 and CoP optimized the reaction kinetics by regulating the adsorption/desorption of intermediates and the cleavage of reactants. Additionally, operando electrochemical impedance spectroscopy reveals that PtP2/CoP significantly decreased phase angle with increasing applied potential compared with CoP, demonstrating that the construction of heterostructure provides a faster charge transfer on the surface and in the inner layer. Notably, the catalyst only requires overpotentials of 101 and 298 mV to achieve a benchmark of 100 mA cm−2 in alkaline freshwater for HER and OER. Moreover, the prepared catalyst featured overpotentials of 108 and 330 mV in an alkaline seawater electrolyte. Furthermore, a stable and high‐efficiency water electrolysis operation can be achieved using PtP2/CoP as both the anode and cathode (1.63 V@100 mA cm−2) coupled with satisfactory durability. This finding provides a deeper comprehension of the interaction of Pt‐less compounds and matrix in electrocatalysis for bifunctional electrocatalysts.

Self-Assembly Intermetallic PtCu3 Core with High-Index Faceted Pt Shell for High-Efficiency Oxygen Reduction.

Rational design of well-defined active sites is crucial for promoting sluggish oxygen reduction reactions. Herein, leveraging the surfactant-oriented and solvent-ligand effects, we develop a facile self-assembly strategy to construct a core-shell catalyst comprising a high-index Pt shell encapsulating a PtCu3 intermetallic core with efficient oxygen-reduction performance. Without undergoing a high-temperature route, the ordered PtCu3 is directly fabricated through the accelerated reduction of Cu2+, followed by the deposition of the remaining Pt precursor onto its surface, forming high-index steps oriented by the steric hindrance of surfactant. This approach results in a high half-wave potential of 0.911 V versus reversible hydrogen electrode, with negligible deactivation even after 15000-cycle operation. Operando spectroscopies identify that this core-shell catalyst facilitates the conversion of oxygen-involving intermediates and ensures antidissolution ability. Theoretical investigations rationalize that this improvement is attributed to reinforced electronic interactions around high-index Pt, stabilizing the binding strength of rate-determining OHads species.

Operando study of HfO2 atomic layer deposition on partially hydroxylated Si(111)

The introduction of atomic layer deposition (ALD), to the microelectronics industry has introduced a large number of new possible materials able to be deposited in layers with atomic thickness control. One such material is the high-κ oxide HfO2; thermally stable and ultrathin HfO2 films deposited by ALD are a significant contender to replace SiO2 as the gate oxide in capacitor applications. We present a mechanistic study of the first deposition cycle of HfO2 on the Si(111) surface using tetrakis(dimethylamido) hafnium (TDMAHf) and water as precursors using operando ambient pressure x-ray photoelectron spectroscopy. Here, we show that the hydroxylation of the clean Si(111) surface by residual water vapor, resulting in a 0.3 monolayer coverage of hydroxyls, leads to instantaneous full surface coverage of TDMAHf. The change in the atomic ratio of Hf to C/N found during the first deposition half-cycle, however, does not match the assumed immediate ligand loss through reaction with surface hydroxyls. One would expect an immediate loss of ligands, indicated by a Hf:N ratio of approximately 1:3 as TDMAHf deposits onto the surface; however, a Hf:N ratio of 1:3.6 is observed. The partial hydroxylation on the Si(111) surface leads to binding through the TDMAHf ligand N atoms resulting in both N and CH3 being found remaining on the surface post water half-cycle. Although there is evidence of ligand exchange reactions occurring at Si–OH sites, it also seems that N binding can occur on bare Si, highlighting the complexity of the substrate/precursor reaction even when hydroxyls are present. Moreover, the initial low coverage of Si–OH/Si–H appears to severely limit the amount of Hf deposited, which we hypothesize is due to the specific geometry of the initial arrangement of Si–OH/Si–H on the rest- and adatoms.

Bridging length scales in organic mixed ionic-electronic conductors through internal strain and mesoscale dynamics.

Understanding the structural and dynamic properties of disordered systems at the mesoscale is crucial. This is particularly important in organic mixed ionic-electronic conductors (OMIECs), which undergo significant and complex structural changes when operated in an electrolyte. In this study, we investigate the mesoscale strain, reversibility and dynamics of a model OMIEC material under external electrochemical potential using operando X-ray photon correlation spectroscopy. Our results reveal that strain and structural hysteresis depend on the sample's cycling history, establishing a comprehensive kinetic sequence bridging the macroscopic and microscopic behaviours of OMIECs. Furthermore, we uncover the equilibrium and non-equilibrium dynamics of charge carriers and material-doping states, highlighting the unexpected coupling between charge carrier dynamics and mesoscale order. These findings advance our understanding of the structure-dynamics-function relationships in OMIECs, opening pathways for designing and engineering materials with improved performance and functionality in non-equilibrium states during device operation.

Operando film-electrochemical EPR spectroscopy tracks radical intermediates in surface-immobilized catalysts

The development of surface-immobilized molecular redox catalysts is an emerging research field with promising applications in sustainable chemistry. In electrocatalysis, paramagnetic species are often key intermediates in the mechanistic cycle but are inherently difficult to detect and follow by conventional in situ techniques. We report a new method, operando film-electrochemical electron paramagnetic resonance spectroscopy (FE-EPR), which enables mechanistic studies of surface-immobilized electrocatalysts. This technique enables radicals formed during redox reactions to be followed in real time under flow conditions, at room temperature and in aqueous solution. Detailed insight into surface-immobilized catalysts, as exemplified here through alcohol oxidation catalysis by a surface-immobilized nitroxide, is possible by detecting active-site paramagnetic species sensitively and quantitatively operando, thereby enabling resolution of the reaction kinetics. Our finding that the surface electron-transfer rate, which is of the same order of magnitude as the rate of catalysis (accessible from operando FE-EPR), limits catalytic efficiency has implications for the future design of better surface-immobilized catalysts.

The role of the LATP particle size as a cornerstone of the cold sintering process

An innovative sintering technique, the Cold Sintering Process (CSP), has been employed to obtain dense Li1.3Al0.3Ti1.7(PO4)3 (LATP) Solid-State Electrolytes (SSE) by optimising the particle size (d50) of the starting powder. The CSP is carried out at 700 MPa, 150 ºC, and 90 min of sintering time, using acetic acid solution as Transient Liquid Phase (TLP). The CSP lowers the LATP sintering temperatures almost 1000 ºC. To study the electrical properties, an in operando Electrochemical Impedance Spectroscopy (EIS) technique has been used. The optimum d50 is 0.415 µm, yielding to competitive microstructure and electrical properties (ionic conductivity of 6.93·10−5 S cm−1 at 30 ºC, activation energy of 0.363 eV, and a relative density of 81.2 ± 0.8%). Relative density, ionic conductivity and TLP content must be balanced, because at small d50, although relative density is enhanced the ionic conductivity is reduced. A packing model has been used to understand this behaviour and the mass transfer mechanisms.