To enable the efficient storage, retrieval and reuse of data records deposited in data repository systems regarding traditional laboratory Mössbauer spectroscopy measurements, a corresponding comprehensive framework has been developed, which provides a simple yet versatile approach for describing the measured sample, experimental conditions, spectral data, theoretical models, and associated metadata. Experimental details and common data treatment procedures in laboratory Mössbauer spectroscopy were considered to identify the metadata necessary for a thorough characterization of measurements, facilitating the reproducibility and replicability of the results. A grouping of metadata and related information according to their subject is proposed. Based on these groups, a record structure is defined that is divided into several segments, with each segment containing the metadata of a specific group. The precise description of theories used to analyze Mössbauer spectra is proposed to rely on established encoding systems employed by existing Mössbauer spectral analysis software to represent the fit models they are designed to handle. Nevertheless, to define a standardized theoretical baseline, a simplified representation of common special cases of 57Fe and 119Sn Mössbauer spectral fitting models is proposed, ensuring compatibility with a wide range of existing spectral analysis software. Although the developed framework currently focuses on traditional laboratory Mössbauer spectroscopy, it is designed to enable future expansion to closely related methods, such as synchrotron radiation-based Mössbauer spectroscopy.

Iron-nitrogen-carbon (Fe-N-C) catalysts for oxygen reduction reaction (ORR) are promising candidates in fuel cell devices but the poor stability remains a grave challenge. The elimination of demetallation is pivotal for extending the life but still incapable due to the ambiguous mechanism. Herein, we show that the structure of FeN4 site and its structural evolution during ORR has the significant influence. The end-of-test/in-situ Mössbauer spectroscopy and density functional theory study reveal that D1 mainly contributes to the ORR activity but suffers severe demetallation, which is likely due to the instability of FeN4C8. The faster demetallation during ORR, especially at higher potential, can be attributed to the weaker coordination of FeN4 induced by oxygenated intermediate and electric field according to ab initio molecular dynamics simulations. Finally, the binding energy of Fe-N bond is introduced to describe the influence of structure and structural evolution and give guidance to the improvement of stability.

Higher alcohol synthesis (HAS) from syngas through non petroleum carbon resources is quite prospective but still challenging owing to the unsatisfactory selectivity and catalytic stability. Here, we proposed a monodisperse epsilon'-(CoxFe1-x)(2.2)C alloy carbide catalyst derived from CoxFe3-xO4 spinet oxide nanoparticles, which was applied in the HAS reaction. The Co/Fe molar ratio showed a significant impact on the evolution of active sites, and the catalyst with a Co/Fe molar ratio of 1/2 contained the highest epsilon'-(CoxFe1-x)(2.2)C content of 80.2%, which achieved the best selectivity and space time yield toward higher alcohols (HA) as high as 38.5% and 1.932 g g((Fe + Co))(-1) h(-1), outperforming most of the reported modified Fischer-Tropsch synthesis catalysts for HAS. Density functional theory calculations further confirmed that the formation of epsilon'-(CoxFe1-x)(2.2)C alloy carbide became more difficult when the Co/Fe ratio exceeds 1/2. It is demonstrated that the epsilon'-(CoxFe1-x)(2.2)C exhibited moderate bonding with CO, which is crucial for the balance between CO dissociation and CO insertion, thus increasing the HA selectivity. The Co1Fe2 catalyst with a robust CoFe alloy carbide structure exhibited stable catalytic performance for over 300 h because of the inhibition of phase separation and surface carbon deposition. These insights into the formation and properties of CoFe alloy carbide may provide possibilities for the development of bimetallic catalysts for HAS.

Single-atom catalysts have recently attracted considerable attention because of their highly efficient metal utilization and unique properties. Finding a green, facile method to synthesize them is key to their widespread commercialization. Here we show that single-atom catalysts (including iron, cobalt, nickel and copper) can be prepared via a top-down abrasion method, in which the bulk metal is directly atomized onto different supports, such as carbon frameworks, oxides and nitrides. The level of metal loading can be easily tuned by changing the abrasion rate. No synthetic chemicals, solvents or even water were used in the process and no by-products or waste were generated. The underlying reaction mechanism involves the mechanochemical force in situ generating defects on the supports, then trapping and stably sequestering atomized metals.

The development of highly efficient and cost-effective electrocatalysts for the sluggish oxygen evolution reaction (OER) remains a significant barrier to establish effective utilization of renewable energy storage systems and water splitting to produce clean fuel. The current status of the research in developing OER catalysts shows that NiFe-based oxygen evolution catalysts (OECs) have been proven as excellent and remarkable candidates for this purpose. But it is critically important to understand the factors that influence their activity and underlying mechanism for the development of state-of-the-art OER catalysts. Therefore, the development of in-situ/operando characterizations is urgently required to detect key intermediates along with active sites and phases responsible for OER. 57Fe Mössbauer spectroscopy is one of the appropriate and suitable techniques for determining the phase structure of catalysts under their electrochemical working conditions, identifying the active sites, clarifying the catalytic mechanisms, and determining the relationship between catalytic activity and the coordination structure of catalysts. In this tutorial review, we have discussed the current status of research on NiFe-based catalysts with particular attention to introduce in detail the knowhow about the development and utilization of in-situ/operando 57Fe Mössbauer-electrochemical spectroscopy for the study of OER mechanism. A brief overview using NiFe-(oxy)hydroxide catalysts, derived from ordered porous metal-organic framework (MOF) material NiFe-PBAs (Prussian blue analogues), as a typical model study case for the OER electrocatalyst and self-designed in-situ/operando 57Fe Mössbauer-electrochemical instrument, has been provided for the better understanding of readers. Moreover, using in-situ/operando 57Fe Mössbauer spectroscopy, the crucial role of Fe species during OER reaction has been explained very well.

Magnetic field enhanced electrocatalysis has recently emerged as a promising strategy for the development of a viable and sustainable hydrogen economy via water oxidation. Generally, the effects of magnetic field enhanced electrocatalysis are complex including magnetothermal, magnetohydrodynamic and spin selectivity effects. However, the exploration of magnetic field effect on the structure regulation of electrocatalyst is still unclear whereas is also essential for underpinning the mechanism of magnetic enhancement on the electrocatalytic oxygen evolution reaction (OER) process. Here, it is identified that in a mixed NiFe2 O4 (NFO), a large magnetic field can force the Ni2+ cations to migrate from the octahedral (Oh ) sites to tetrahedral (Td ) sites. As a result, the magnetized NFO electrocatalyst (NFO-M) shows a two-fold higher current density than that of the pristine NFO in alkaline electrolytes. The OER enhancement of NFO is also observed at 1 T (NFO@1T) under an operando magnetic field. Our first-principles calculations further confirm the mechanism of magnetic field driven structure regulation and resultant OER enhancement. These findings provide a strategy of manipulating tetrahedral units of spinel oxides by a magnetic field on boosting OER performance.

The web-accessible online database (WAD) of the Mössbauer Effect Data Center (MEDC) is one of the worldwide available information services provided by MEDC to the scientific community. It is based on the uniquely wide scope Mössbauer spectroscopy database that has been compiled and maintained by MEDC since the 1960’s. Following enhancements applied to the capabilities of the MEDC core database in connection with the development of a new database management software named “MEDC DBM”, the development of a new web-accessible online database (MEDC WAD) was started in 2019. Here we introduce the current state and the main features of the newly developed MEDC WAD system with emphasis put on its novel and rather unique attributes that can effectively aid the scientific research process in the field of Mössbauer spectroscopy.

As a type of important non-precious catalyst for the oxygen reduction reaction (ORR), the regulating role of a metal centre in metal-macrocycles and other complexes for activity has been extensively studied. However, a common guideline to explain the effect of peripheral coordinated-ligands has not been reached. Herein, a series of organic iron complexes (denoted as FeL, L = TAA, Pc, TPP, Corrole, Tim and Salen) were synthesized as ORR catalysts and an explicit relationship of structure-activity was constructed. The kinetic current density for these compounds was identified to follow the order of FeTAA > FePc > FeTPP > FeCorrole > FeTim > FeSalen. An electron-transfer number close to 4 was derived for all these complexes except for FeTim and FeSalen, implying a near complete reduction of oxygen to water. X-ray absorption near edge structure spectroscopy (XANES) and Mossbauer spectroscopy were used to probe the nature of the distinct activities by investigating the iron-centre electron structures. Density function theory (DFT) calculations were carried out to study the charge redistribution across the iron complexes. Novel activity descriptors including the charge and spin densities on the Fe site were proposed and validated by available experimental data, presenting a strategy to design highly-active nonprecious metal complex catalysts with specific supporting ligands.

The production of high-value chemicals by single-atom catalysis is an attractive proposition for industry owing to its remarkable selectivity. Successful demonstrations to date are mostly based on gas-phase reactions, and reports on liquid-phase catalysis are relatively sparse owing to the insufficient activation of reactants by single-atom catalysts (SACs), as well as, their instability in solution. Here, mechanically strong, hierarchically porous carbon plates are developed for the immobilization of SACs to enhance catalytic activity and stability. The carbon-based SACs exhibit excellent activity and selectivity (≈68%) for the synthesis of substituted quinolines by a three-component oxidative cyclization, affording a wide assortment of quinolines (23 examples) from anilines and acetophenones feedstock in an efficient, atom-economical manner. Particularly, a Cavosonstat derivative can be synthesized through a one-step, Fe1 -catalyzed cyclization instead of traditional Suzuki coupling. The strategy is also applicable to the deuteration of quinolines at the fourth position, which is challenging by conventional methods. The synthetic utility of the carbon-based SAC, together with its reusability and scalability, renders it promising for industrial scale catalysis.

N-doped carbon materials as catalyst supports have shown great superiority because of rich porosity, tunable metal-support interaction and electronic promotion effect. Controllable fabrication of carbon materials with specific morphology and different configurations provides wider possibilities for applications in catalysis. Herein, N-doped carbon nanosheets (CNS) were successfully synthesized by using monoclinic ZIF-8 nanosheets as templates. Compared with commercial active carbon and cubic ZIF-8 particles-derived carbon particles, the derived CNS exhibit superior graphitization degree and electronic effect. Consequently, the promoted Fe carburization improved the intrinsic activity for Fe/CNS catalysts in FTS. Further investigation on pyrolysis temperature achieved tunable configuration and content of N dopant. XPS, Raman, Mössbauer spectroscopy, TEM, H2-TPR etc. were combined to elucidate the promotion effect of CNS on dispersion, electronic properties and formation of Fe carbides. By correlating the composition and structure to catalytic performance in FTS, we illustrated the significance of carbon materials in Fe supported catalysts.

The low efficiency of oxygen evolution reaction (OER) is regarded as one of the major roadblocks for metal-air batteries and water electrolysis. Herein, a high-performance OER catalyst of NiFe0.2 (oxy)hydroxide (NiFe0.2-OxHy) was developed through topotactic transformation of a Prussian blue analogue in an alkaline solution, which exhibits a low overpotential of only 263 mV to reach a current density of 10 mA cm(-2) and a small Tafel slope of 35 mV dec(-1). Ex-situ/operando Raman spectroscopy results indicated that the phase structure of NiFe0.2-OxHy was irreversibly transformed from the type of alpha-Ni(OH)(2) to gamma-NiOOH with applying an anodic potential, while ex-situ/operando Fe-57 Mossbauer spectroscopic studies evidenced the in-situ production of abundant high-valent iron species under OER conditions, which effectively promoted the OER catalysis. Our work elucidates that the amount of high-valent iron species in-situ produced in the NiFe (oxy)hydroxide has a positive correlation with its water oxidation reaction performance, which further deepens the understanding of the mechanism of NiFe-based electrocatalysts. (C) 2020 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. All rights reserved.

Higher alcohols synthesis (HAS) from syngas is quite attractive but still challenging due to the unsatisfied product selectivity and stability. Here, we prepared a series of CoFe bimetallic carbide catalysts and investigated the evolution of active species. The catalysts reduced above 300 degrees C could ensure an adequate interdiffusion between Co and Fe species to form CoFe alloy and then achieved a high fraction of epsilon-(CoxFe1-x)(2.2)C species during HAS reaction, which exhibited excellent catalytic performance and stability over 200 h. The epsilon-(CoxFe1-x)(2.2)C, acting as uniformly atomic neighboring CoxC-FexC dual sites, facilitated the synergy between CO nondissociative adsorption and CO dissociation, thus boosting the selective production of higher alcohols. It is also demonstrated that adding proper content of Na (0.25 wt%) can enhance the formation of epsilon-(CoxFe1-x)(2.2)C as well as modulate the surface concentration of intermediates. These results may provide new idea for the design of high-performance catalysts for HAS. (C) 2021 Elsevier Inc. All rights reserved.

Grain size has obvious influence on the transport kinetics of oxygen species for mixed ionic-electronic conducting materials. Electrical conductivity relaxation and oxygen isotopic exchange with secondary ion mass spectrometry measurements cannot be used to determine the kinetic parameters at a steady state, while the permeation model study can give the kinetic parameters under real experimental steady states. Cobalt-free BaCe0.1Fe0.9O3-δ (BCF) membranes selected as an example with different grain sizes are studied by Zhu's model to disclose the influence of grain size on oxygen transport kinetics. The model is available for analyzing data of BCF membranes to obtain reasonable and exclusive oxygen diffusion and oxygen exchange kinetic parameters. The permeation flux of BCF membranes decreases with the increase of grain size. Model studies reveal that interfacial oxygen exchange resistances on both sides increase with the increase of grain size, while the bulk diffusion resistance changes slightly. It indicates that grain boundaries are active sites for oxygen exchange reactions and have little effect on the bulk diffusion.

The Mössbauer spectroscopy database compiled and maintained by the Mössbauer Effect Data Center (MEDC) is a unique, wide-scope Mössbauer-spectroscopy related information resource, which forms the basis of information services provided by the Mössbauer Effect Data Center to the worldwide scientific community. The Mössbauer Effect Reference and Data Journal (MERDJ) and the Mössbauer Web Access Database (MWAD), both published by MEDC, are widely known examples of the services that rely on the MEDC database. In recent years a further improvement of these services, especially that of MWAD, has been envisaged, and as a first step of the corresponding process the further development of the MEDC database was started. In the present work we introduce the main features of the MEDC database and the steps that have been already taken in the frame of its further development. Implications of the work regarding the associated services are also presented.

The lack of model single-atom catalysts (SACs) and atomic-resolution operando spectroscopic techniques greatly limits our comprehension of the nature of catalysis. Herein, based on the designed model single-Fe-atom catalysts with well-controlled microenvironments, we have explored the exact structure of catalytic centers and provided insights into a spin-crossover-involved mechanism for oxygen reduction reaction (ORR) using operando Raman, X-ray absorption spectroscopies, and the developed operando Fe-57 Mossbauer spectroscopy. In combination with theoretical studies, the N-FeN4C10 moiety is evidenced as a more active site for ORR. Moreover, the potential-relevant dynamic cycles of both geometric structure and electronic configuration of reactive single-Fe-atom moieties are evidenced via capturing the peroxido (*0(2)(-)) and hydroxyl (*OH-) intermediates under in situ ORR conditions. We anticipate that the integration of operando techniques and SACs in this work shall shed some light on the electronic-level insight into the catalytic centers and underlying reaction mechanism.

Abstract3D well‐crystallized metal–organic frameworks (MOFs), M‐THBQ (M=Fe, Co, Mn, THBQ=tetrahydroxybenzoquinone), are synthesized and characterized. Their structures are determined as cubic cell in the group of Pm from powder X‐ray diffraction data, and their properties of electronic, magnetic and spectroscopic are also investigated. They are all semiconductors, and Fe‐THBQ exhibits the air‐stable n‐type thermoelectric characteristic as its Seebeck coefficient reaches −130 μV K−1, and the electrical conductivity is 2.7×10−4 S cm−1 at 300 K. Additional, M‐THBQ are paramagnetic, and the value of Weiss constant of Fe‐THBQ is −219.37 K, indicating the existence of robust intramolecular antiferromagnetic exchanges. Meanwhile, they display strong absorption bands in the range of 220 to 1000 nm, suggest M‐THBQ could have the potential to become photoabsorbers, and Fe‐THBQ exhibits a narrow band gap of 0.63 eV according to the ultraviolet absorption edge spectrum.

It is of great significance to improve the syngas selectivity of Fe-based oxygen carriers (OCs), because of their sufficient lattice oxygen, low cost, and environmental compatibility in chemical looping partial oxidation of CH4. In this work, it was found that the addition of Y could remarkably increase CO selectivity of Fe2O3/Al2O3 to 98% with a CH4 conversion of , similar to 90%. X-ray diffraction (XRD) and transmission electron microscopy (TEM) characterizations combined with Mossbauer spectroscopy illustrated that the incorporation of Y led to the Fe species gradually transferring from Fe2O3 into the garnet structure (Y3Fe2Al3O12), a newly formed phase, which was found to be highly active for syngas generation. Density functional theory (DFT) calculations demonstrated that such a high CO selectivity of confined Fe species in garnet originated from enhanced oxygen vacancy formation energy (E-ov), compared with Fe2O3, which resulted from the lattice oxygen shared by not only reducible Fe ions but also nonreducible Al and Y ones in a garnet structure. Therefore, our work provides a meaningful guidance of new materials screening for methane partial oxidation in the chemical looping process.

Ni–Fe dual-metal sites on NiFe-codoped polymeric carbon nitride co-participate in the OER process leading to significantly enhanced electrocatalytic activity.

The catalytic hydrodeoxygenation (HDO) of lignin-derived phenolic compounds is a critical step in the upgrading of bio-oil. Here, bimetallic Ni-Fe nanoparticles supported on mesoporous carbon spheres (MCSs) were fabricated and applied in HDO of phenol. In comparison with monometallic Ni and Fe catalysts, the bimetallic Ni-Fe catalyst exhibited better performance for phenol HDO due to the formation of Ni-Fe alloy phase identified by X-ray powder diffraction (XRD) and Mossbauer spectroscopy techniques. Among several explored ratios, the catalysts with Ni/Fe ratio of 3/1 presented the highest cyclohexane yield. The reaction occurred in two consecutive steps: the hydrogenation of phenol to cyclohexanol and the further hydrogenolysis of cyclohexanol to cyclohexane. Kinetic studies showed that the hydrogenolysis of cyclohexanol controlled the overall reaction rate of phenol HDO due to the lower reaction rate of this step. Indeed, the turnover frequency (TOF) values of cyclohexanol normalized by surface metallic Ni sites exhibited a linear correlation with Ni-Fe alloy sites. The alloying of iron in the bimetallic Ni-Fe catalysts significantly enhanced the adsorption strength of cyclohexanol, which is the reason of the high activity of the Ni-Fe alloy particles. Thus, Fe-containing sites adsorb the hydroxyl species while Ni sites perform the H-2 activation, their synergistic effect plays a key role in phenol HDO process.

Methane-to-syngas conversion plays an important role in industrial gas-to-liquid technologies, which is commercially fulfilled by energy-intensive reforming methods. Here we present a highly selective and durable iron-based La 0.6 Sr 0.4 Fe 0.8 Al 0.2 O 3-δ oxygen carrier for syngas production via a solar-driven thermochemical process. It is found that a dynamic structural transformation between the perovskite phase and a Fe 0 @oxides core–shell composite occurs during redox cycling. The oxide shell, acting like a micro-membrane, avoids direct contact between methane and fresh iron(0), and prevents coke deposition. This core–shell intermediate is regenerated to the original perovskite structure either in oxygen or more importantly in H 2 O–CO 2 oxidant with simultaneous generation of another source of syngas. Doping with aluminium cations reduces the surface oxygen species, avoiding overoxidation of methane by decreasing oxygen vacancies in perovskite matrix. As a result, this material exhibits high stability with carbon monoxide selectivity above 95% and yielding an ideal syngas of H 2 /CO ratio of 2/1.