Electrocatalytic nitrate reduction reaction (NO3RR) presents a sustainable paradigm for green NH3 synthesis and NO3 - wastewater valorization. However, overcoming sluggish NO3RR kinetics under industrial-current operation persists as a critical challenge. Herein, robust oxygen vacancy-enriched heterostructures (Ov-Co(OH)2/Cu) are engineered through in situ electrochemical reconstruction. By coupling Cu-mediated NO3 --to-NO2 - conversion with Ov-Co(OH)2-accelerated NO2 --to-NH3 transformation, this heterostructured system delivers an unprecedented NH3 yield rate of 167.8 mg h-1 cm-2 and 97.7% Faradaic efficiency at >2 A cm-2, while maintaining exceptional current tolerance over 25 h. Operando spectroscopic characterizations and theoretical calculations reveal that the introduction of Ov in Co(OH)2 synergistically accelerates water dissociation to ensure continuous hydrogen supply and optimizes *NOOH adsorption, reducing the energy barrier for the rate-limiting step (*NO2 to *NOOH). To demonstrate practical viability, a membrane-electrode-assembly electrolyzer integrating NO3RR with glycerol oxidation reaction achieves highly effective co-production of NH3 and formate alongside wastewater treatment. This work offers new insights into the rational design of electrocatalysts through in situ reconstruction-induced vacancy engineering for scalable and practical NO3RR applications.

Sodium-ion batteries have the potential to meet the growing demand for energy storage due to their low costs stemming from natural resource abundances, but their cathode energy densities must be improved to be comparable to those of lithium-ion batteries. One strategy is accessing high voltage capacity through high-valent redox reactions. Such reactions usually cause instability in cathode materials, but Na2Mn3O7 (NMO) has demonstrated excellent performance and reversibility in the high-valent regime due to its unique lattice structure with ordered Mn vacancies. This work expands the universality of the ordered vacancy as a design principle and increases the material candidates with such exceptional electrochemical behavior. Our approach involves synergizing cationic ordered vacancies with tunable metal-ligand hybridization through partial metal substitution. In particular, we successfully incorporated Fe3+ for Mn4+ in NMO to make Na2.25Mn2.75Fe0.25O7 and achieved improved high-valent redox behavior. Fe substitution leads to larger specific capacities (171 vs. 159 mA h g-1 first cycle), enhanced cycle stability (97 vs. 60 mA h g-1 after 50 cycles), and superior rate performance. This study lays the foundation for developing new cathode materials with stable high-valent redox through substitution of redox-active transition metals by employing cationic ordered vacancies and partial transition metal substitution as design principles in tandem.

Complementary X-ray absorption fine structure (XAFS) and Raman spectroscopy studies were conducted on various UCl3 concentrations in alkali chloride salt compositions. The samples were 5 mol % UCl3 in LiCl (S1), 5 mol % UCl3 in KCl (S2), 5 mol % UCl3 in LiCl-KCl eutectic (S4), 50 mol % UCl3 in KCl (S5), and 20 mol % UCl3 in KCl (S6) molar concentrations. Samples were heated to 800 degrees C and allowed to cool to room temperature with measurements performed at selected temperatures; the highest temperatures showed the most stability and will be primarily referenced for conclusions. The processing and interpretation of the Raman and extended X-ray absorption fine structure (EXAFS) peaks revealed several uranium-oxygen bond lengths and symmetries in the samples before, during, and after heating. Based on published thermodynamic data of similar systems, X-ray absorption fine structure spectroscopy, and identification of Raman peaks, a beta variation of alpha-U3O8, typical at room temperature, is the suspected dominant phase of all samples at high temperatures (800 degrees C). In the existing literature, this beta structure of U3O8 was synthesized by slow cooling of uranium oxides from 1350 degrees C. This paper suggests the rapid formation of the compound due to the decomposition of the uranium chlorides or oxychlorides at increasing temperatures and O2 reaction kinetics.

CO2 electrolysis converts the greenhouse gas CO2 into valuable fuels and chemicals, such as carbon monoxide, ethylene, ethanol, etc. Currently, Cu is the only known monometallic catalyst capable of producing multicarbon products from electrochemical CO2 reduction reaction (eCO2RR), while the poor selectivity limits its further use. It has been found that introducing Ag atoms into the Cu lattice can modulate product preference. However, the synergistic effects between Cu and Ag, and thus, the catalytic performance, are strongly influenced by catalyst morphology, electrolyzer configuration, reaction conditions, etc. Operando measurements can provide explicit information on the catalyst dynamic variation during the reaction, but their operation and analysis are challenging. Herein, we prepared CuAg multiphase alloy catalysts by magnetron sputtering, which allowed for investigating the intrinsic interaction between Cu and Ag. eCO2RR performance exhibited an improved selectivity toward carbonyls at the expense of hydrogen and hydrocarbons. The partially alloyed Cu and Ag phases were confirmed by operando X-ray diffraction. By means of combining operando X-ray measurements and density functional theory (DFT) calculations, the preferred carbonyl production is attributed to the reduced electron density and compressive strain of Cu due to Ag incorporation, which leads to a deeper d-band center and therefore weakened intermediate adsorption and oxophilicity. This work provides evidence of the intrinsic structural and electronic interaction between Cu and Ag during eCO2RR. The obtained information will facilitate the design of bi/multi-phase metallic or alloy electrocatalysts.

Aqueous Na-ion batteries using Prussian blue materials have inherent advantages in safety, material sustainability, and economic cost. However, it is challenging to obtain long-term cycling stability because many redox reactions have poor intrinsic stability in water. Here, we demonstrate reversible Fe2.4+ to Fe3+ redox reaction of Prussian blue electrodes cycled in a 17 m NaClO4 water-in-salt electrolyte. The cubic phase c-Na1.17Fe[Fe(CN)6]·0.35H2O) derived from monoclinic Prussian blue (m-Na1.88Fe[Fe(CN)6]·0.7H2O) through ball milling delivers excellent cycling stability of >18,000 cycles with >90% capacity retention at the 10C rate. The specific capacity is ∼75 and ∼67 mAh/g at 1C and 10C rates, respectively. Systematic characterizations including electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy have verified the phase transition and iron oxidation state evolution, revealing the mechanism that enables the material's high rate and long durability as the battery cathode.

We highlight a paradigm for studying complex reaction mechanisms that guide the synthesis of materials. Thin films of FeCl2 and Na2S2 were deposited to study the metathesis reaction to form FeS2 and NaCl. In situ X-ray reflectivity was used to monitor the interface between materials, which revealed a slow, impeded reaction at high temperatures as compared to previous studies using powder samples. AC impedance and X-ray photoelectron spectroscopy provided insight into distribution of elements and conductivity of the phases present during the reaction, and phase-field modeling was used to elucidate the diffusion of ions throughout the thin-film bilayers. The use of thin-film bilayers provides a simplified system to study solid-state metathesis reactions and highlights the complexity of diffusion at solid-state interfaces.

Introduction: The in vivo generator Ce-134/La-134 has the potential to serve as a PET imaging surrogate for both alpha-emitting Ac-225 and Th-227 radionuclides due to the unique Ce-III/Ce-IV redox couple and the relatively long half-life of Ce-134. The purpose of this study was to demonstrate the compatibility of Ce-134 with DOTA-based antibody drug conjugates, which would act as therapeutic agents when incorporating Ac-225. Methods: The in vivo biodistributions of [Ce-134]Ce-DOTA and [Ce-134]Ce-citrate were assayed by microPET imaging over 25 h in Swiss Webster mice to determine the in vivo stability of the [Ce-134]Ce-DOTA complex. L-3-edge X-ray absorption spectroscopy measurements were used to confirm the Ce oxidation state and the formation of a fully coordinated Ce-DOTA complex. The in vivo biodistribution of [Ce-134]Ce-DOTA-Trastuzumab was assayed over 147 h by microPET imaging in SK-OV-3 tumor-bearing NOD SCID mice to evaluate tumor uptake and in vivo stability. Mice were euthanized at 214 h after administration of the radiolabeled antibody conjugate, and imaged 1 h later. An ex vivo biodistribution experiment was then performed in order to corroborate the PET images. Results: [Ce-134]Ce-DOTA displayed rapid renal elimination and high in vivo stability over 25 h, with negligible bone and liver uptake, in comparison to [Ce-134]Ce-citrate. L-3-edge X-ray absorption spectroscopy experiments confirmed the 3+ oxidation state within the stable Ce-DOTA complex. MicroPET images of [Ce-134]Ce-DOTA-Trastuzumab displayed elevated tumor uptake over 214 h, with minimal bone and liver uptake analogous to previously reported [Ac-225]Ac-DOTA-Trastuzumab biodistribution results, and the ex vivo biodistribution of [Ce-134]Ce-DOTA-Trastuzumab corroborated the final PET images. Conclusion: These results demonstrate that Ce-134 allows for long-term tumor targeting with DOTA-based antibody drug conjugates and may therefore be used to trace antibody drug conjugates incorporating Ac- 225.

Understanding hydrogen intercalation and deintercalation in palladium is the key to utilizing palladium-based materials for hydrogen storage, hydrogen separations, and electrochemical hydrogen evolution and CO2 reduction catalysis. Here, we combine in situ synchrotron X-ray diffraction and coulometry measurements with density functional theory calculations to provide complementary insights on the dynamics of hydrogen intercalation and deintercalation under electrochemical conditions. By employing multimodal in situ characterization, we demonstrate that the interplanar d-spacing and the hydrogen/palladium ratio are decorrelated under certain conditions. Additionally, there is a clear hysteresis in the electrode potentials where the beta-phase of palladium hydride forms and disappears. Computed energetics of hydrogen intercalation and deintercalation predict this hysteresis. These calculations indicate that the potential-driven absorption of subsurface hydrogen during intercalation and oxidation of surface hydrogen during deintercalation could contribute to the observed hysteresis. These results suggest that surface processes during hydrogen intercalation and deintercalation are important, providing additional mechanistic understanding that is complementary to bulk phase transition theory. This multimodal in situ characterization and computational study provides new insights into hydrogen intercalation and deintercalation in palladium electrodes, which could lead to improvements in palladium-based materials needed in a sustainable energy economy.

The efficiency of the synthesis of renewable fuels and feedstocks from electrical sources is limited at present by the sluggish water oxidation reaction. Single atom catalysts (SACs) with a controllable coordination environment and exceptional atom utilization efficiency open new paradigms towards designing high performance water oxidation catalysts. Here, using operando X-ray absorption spectroscopy measurements with calculations of spectra and electrochemical activity, we demonstrate that the origin of water oxidation activity of IrNiFe SACs is the presence of highly oxidized Ir single atom (Ir5.3+) in the NiFe oxyhydroxide under operating conditions. We show that the optimal water oxidation catalyst could be achieved by systematically increasing the oxidation state and modulating the coordination environments of the Ir active sites anchored atop the NiFe oxyhydroxide layers. Based on the proposed mechanism, we have successfully anchored Ir single-atom sites on NiFe oxyhydroxides (Ir0.1/Ni9Fe SAC) via a unique in situ cryogenic photochemical reduction (in situ Cryo-PCR) method which delivers an overpotential of 183 millivolts at 10 milliamperes per square centimeter and retains its performance following 20 hours of operation in 1 M KOH electrolyte, outperforming the reported catalysts and the commercial IrO2 catalysts. These findings open the avenue towards atomic-level understanding of oxygen evolution of catalytic centers under in operando condition.

Designing acid‐stable oxygen evolution reaction electrocatalysts is key to developing sustainable energy technologies such as polymer electrolyte membrane electrolyzers but has proven challenging due to the high applied anodic potentials and corrosive electrolyte. This work showcases advanced nanoscale microscopy techniques supported by complementary structural and chemical characterization to develop a fundamental understanding of stability in promising SrIrO 3 thin film electrocatalyst materials. Cross‐sectional high‐resolution transmission electron microscopy illustrates atomic‐scale bulk and surface structure, while secondary ion mass spectrometry imaging using a helium ion microscope provides the nanoscale lateral elemental distribution at the surface. After accelerated degradation tests under anodic potential, the SrIrO 3 film thins and roughens, but the lateral distribution of Sr and Ir remains homogeneous. A layer‐wise dissolution mechanism is hypothesized, wherein anodic potential causes the IrO x ‐rich surface to dissolve and be regenerated by Sr leaching. The characterization approaches utilized herein and mechanistic insights into SrIrO 3 are translatable to a wide range of catalyst systems.

Layered NaxCoO2 provides multiple degrees of freedom for manipulating its structure and physical properties by tuning the Na concentration, leading to specific functionalities including thermoelectricity, superconductivity, and potentiality in Li-/Na-ion batteries. However, the contribution of varied Na to charge transfer, electrocatalytic kinetics, and energetics in terms of the electrochemical interface reaction for the oxygen evolution reaction (OER) in water splitting and the oxygen reduction reaction (ORR) in fuel cells is not yet fully understood. This work reveals that varied Na concentrations indirectly affect the electrochemical OER or ORR activity by changing the Co-O bond in the constituent CoO6 octahedron of NaxCoO2. Tuning the Na concentration gives rise to the unique evolution of the electronic configuration and subsequently further enhances the Co-O bond's covalency, which results in promoting the catalytic kinetics of OER and ORR. As the Fermi level descends deeper into the O 2p orbitals with increasing Na extraction, the lattice oxygen becomes active in the proton-electron transfer process, which is reflected in the pH and oxygen-concentration dependence of the OER activity. Based on the characterization of its electrochemical properties, the high electrocatalytic activity of Na0.75CoO2, which exhibits competent OER activity superior to that of IrO2, is rationalized. Meanwhile, intrinsic Na0.75CoO2 reveals a half-wave potential of 0.74VRHE for ORR. The evolution of the structure and the electronic configuration of NaxCoO2 related to its electrochemical properties enables further improved NaxCoO2-based catalysts for efficient electrochemical OER and ORR.

In situ characterization of electrochemical systems can provide deep insights into the structure of electrodes under applied potential. Grazing-incidence X-ray diffraction (GIXRD) is a particularly valuable tool owing to its ability to characterize the near-surface structure of electrodes through a layer of electrolyte, which is of paramount importance in surface-mediated processes such as catalysis and adsorption. Corrections for the refraction that occurs as an X-ray passes through an interface have been derived for a vacuum-material interface. In this work, a more general form of the refraction correction was developed which can be applied to buried interfaces, including liquid-solid interfaces. The correction is largest at incidence angles near the critical angle for the interface and decreases at angles larger and smaller than the critical angle. Effective optical constants are also introduced which can be used to calculate the critical angle for total external reflection at the interface. This correction is applied to GIXRD measurements of an aqueous electrolyte-Pd interface, demonstrating that the correction allows for the comparison of GIXRD measurements at multiple incidence angles. This work improves quantitative analysis of d-spacing values from GIXRD measurements of liquid-solid systems, facilitating the connection between electrochemical behavior and structure under in situ conditions.

The efficiency of the synthesis of renewable fuels and feedstocks from electrical sources is limited at present by the sluggish water oxidation reaction. Single atom catalysts (SACs) with a controllable coordination environment and exceptional atom utilization efficiency open new paradigms towards designing high performance water oxidation catalysts. Here, using operando X-ray absorption spectroscopy measurements with calculations of spectra and electrochemical activity, we demonstrate that the origin of water oxidation activity of IrNiFe SACs is the presence of highly oxidized Ir single atom (Ir 5.3+ ) in the NiFe oxyhydroxide under operating conditions. We show that the optimal water oxidation catalyst could be achieved by systematically increasing the oxidation state and modulating the coordination environments of the Ir active sites anchored atop the NiFe oxyhydroxide layers. Based on the proposed mechanism, we have successfully anchored Ir single-atom sites on NiFe oxyhydroxides (Ir 0.1 /Ni 9 Fe SAC) via a unique in situ cryogenic photochemical reduction ( in situ Cryo-PCR) method which delivers an overpotential of 183 millivolts at 10 milliamperes per square centimeter and retains its performance following 20 hours of operation in 1 M KOH electrolyte, outperforming the reported catalysts and the commercial IrO 2 catalysts. These findings open the avenue towards atomic-level understanding of oxygen evolution of catalytic centers under in operando condition.

The metastable zone width is the region on a phase diagram where a phase transformation is thermodynamically favored but kinetically hindered. Reaction conditions may need to be far beyond the Pourbaix phase diagram boundaries to initiate nucleation.

(Hf,Zr)O 2 ultrathin films are used as ferroelectric layers in emerging digital logic and nonvolatile memory devices. The ferroelectric properties of (Hf,Zr)O 2 can be improved by interface engineering, such as the formation of nanolaminates with distinct HfO 2 and ZrO 2 layers. Herein, the ferroelectric performance of HfO 2 –ZrO 2 ultrathin bilayer devices is shown to depend on the stacking order of HfO 2 and ZrO 2 , which affects the quantity of the noncentrosymmetric orthorhombic Pca 2 1 crystal phase. By combining X‐ray diffraction with a novel extended X‐ray absorption fine structure (EXAFS) analysis procedure, the orthorhombic, tetragonal, and monoclinic phase fractions are quantified for bilayers composed of 3 nm HfO 2 and 3 nm ZrO 2 . A significantly larger orthorhombic ZrO 2 phase fraction is found when ZrO 2 has an unconstrained surface during annealing, whereas the presence of a ZrO 2 interface with the substrate results in a substantial tetragonal ZrO 2 phase fraction and a 2.4× smaller remanent polarization. HfO 2 is found to be less susceptible than ZrO 2 to crystal phase templating. The methods presented herein enable mechanistic studies of ferroelectric wake‐up, fatigue, and processing effects in (Hf,Zr)O 2 films, accelerating the development of electronic devices that rely on ferroelectric oxides.

Presented herein is an investigation of a promising ternary metal sulfide catalyst that is capable of electrochemically converting CO2 to liquid and gas fuels such as methanol and hydrogen.

The electrochemical CO2 reduction reaction (CO2RR) using Cu-based catalysts holds great potential for producing valuable multi-carbon products from renewable energy. However, the chemical and structural state of Cu catalyst surfaces during the CO2RR remains a matter of debate. Here, we show the structural evolution of the near-surface region of polycrystalline Cu electrodes under in situ conditions through a combination of grazing incidence X-ray absorption spectroscopy (GIXAS) and X-ray diffraction (GIXRD). The in situ GIXAS reveals that the surface oxide layer is fully reduced to metallic Cu before the onset potential for CO2RR, and the catalyst maintains the metallic state across the potentials relevant to the CO2RR. We also find a preferential surface reconstruction of the polycrystalline Cu surface toward (100) facets in the presence of CO2. Quantitative analysis of the reconstruction profiles reveals that the degree of reconstruction increases with increasingly negative applied potentials, and it persists when the applied potential returns to more positive values. These findings show that the surface of Cu electrocatalysts is dynamic during the CO2RR, and emphasize the importance of in situ characterization to understand the surface structure and its role in electrocatalysis.

Molybdenum nitride (Mo–N) catalysts have shown promising activity and stability for the oxygen reduction reaction (ORR) in acid. However, the effect of oxygen (O) incorporation (from synthesis, cat...

Rigorous in situ studies of electrocatalysts are required to enable the design of higher performing materials. Nonplatinum group metals for oxygen reduction reaction (ORR) catalysis containing light elements such as O, N, and C are known to be susceptible to both ex situ and in situ oxidation, leading to challenges associated with ex situ characterization methods. We have previously shown that the bulk O content plays an important role in the activity and selectivity of Mo-N catalysts, but further understanding of the role of composition and morphological changes at the surface is needed. Here, we report the measurement of in situ surface changes to a molybdenum nitride (MoN) thin film under ORR conditions using grazing incidence X-ray absorption and reflectivity. We show that the half-wave potential of MoN can be improved by similar to 90 mV by potential conditioning up to 0.8 V versus RHE. Utilizing electrochemical analysis, dissolution monitoring, and surface-sensitive X-ray techniques, we show that under moderate polarization (0.3-0.7 V vs RHE) there is local ligand distortion, O incorporation, and amorphization of the MoN surface, without changes in roughness. Furthermore, with a controlled potential hold procedure, we show that the surface changes concurrent with potential conditioning are stable under ORR relevant potentials. Conversely, at higher potentials (>= 0.8 V vs RHE), the film incorporates O, dissolves, and roughens, suggesting that in this higher potential regime, the performance enhancements are due to increased access to active sites. Density functional theory calculations and Pourbaix analysis provide insights into film stability and O incorporation as a function of potential. These findings coupled with in situ electrochemical surface-sensitive X-ray techniques demonstrate an approach to studying nontraditional surfaces in which we can leverage our understanding of surface dynamics to improve performance with the rational, in situ tuning of active sites.

Silver-based bimetallic catalysts for the oxygen reduction reaction (ORR) are promising for a wide variety of renewable energy technologies, including alkaline fuel cells and metal-air batteries. The activity of bimetallic catalysts can sometimes surpass that of either constituent element, but the origin of the enhanced performance is still debated. At a given active site, two complementary mechanisms are proposed to explain the performance improvements: the binding energy of intermediate adsorbates can be tuned by direct electronic contributions from the alloying element or by changes in the bond lengths from lattice distortion. To distinguish between these effects and elucidate the respective roles of each element in the bimetallic, it is critical to study catalysts at the molecular scale under reaction conditions. In this work, we use in situ X-ray absorption spectroscopy (XAS) alongside density functional theory (DFT) to show that direct electronic rather than geometric effects are the primary cause of improved ORR activity in a bimetallic CuAg catalyst. Our results indicate that the local bonding as well as the electronic structure of Ag are virtually unchanged by the presence of Cu, whereas the electronic states of Cu in CuAg are significantly altered. DFT calculations support these experimental findings. We show strong evidence that the activity of the bimetallic CuAg catalyst exceeds the sum of the activities of Cu and Ag, not by incremental improvement of the active Ag sites, but by creating highly active Cu-centered catalytic sites. The insight that the main role of Ag in bimetallic catalysts may be to promote its fellow element through local electronic interactions provides a new design principle for engineering the next generation of bimetallic catalysts for the ORR and beyond.