Magnetic susceptibility, EPR, NEXAFS and XPS spectra of Fe-doped CaBi2Nb2O9

Жук, Н. А.; Lutoev, V. P.; Макеев, Б. А.; Nekipelov, S. V.; Королева, А. В.; Fedorova, Anna; Yermolina, Maria V.; Beznosikov, D.S.; Karlova, L.O.

doi:10.1016/j.jmrt.2020.02.044

Cited by 16 publications

(5 citation statements)

References 52 publications

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“…[55] The g ≈4.3 value is assigned to high spin Fe 3+ with rhombic zero field splitting (E/D = 1/3), [9,55] while the weak shoulder at g ≈9.6 has been previously assigned to Fe 3+ with lower rhombicity E/D ≤1/3. [55] Finally, a broad axial signal between g = 6 and g = 2 is also observed in TAP 900@Fe, previously characterized as high spin Fe III with large axial zero field splitting owing to a square pyramidal or quasi octahedral coordination environment. [9,56] Low temperature Mössbauer spectra with an external low (60 mT) and high (7 T) magnetic field were recorded to help resolve the Fe sites, with best fit simulations yielding five separate Fe assignments (Figure 5d and Table S5, Supporting Information).…”

Section: Resultsmentioning

confidence: 97%

“…Interestingly, the signal of TAP 900@Fe closely resembles EPR results from a Fe‐doped CaBi 2 Nb 2 O 9 material. [ 55 ] The g ≈4.3 value is assigned to high spin Fe 3+ with rhombic zero field splitting ( E/D = 1/3), [ 9,55 ] while the weak shoulder at g ≈9.6 has been previously assigned to Fe 3+ with lower rhombicity E/D ≤1/3. [ 55 ] Finally, a broad axial signal between g = 6 and g = 2 is also observed in TAP 900@Fe, previously characterized as high spin Fe III with large axial zero field splitting owing to a square pyramidal or quasi octahedral coordination environment.…”

Section: Resultsmentioning

confidence: 99%

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FeNC Oxygen Reduction Electrocatalyst with High Utilization Penta‐Coordinated Sites

et al. 2023

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Atomic Fe in N-doped carbon (FeNC) electrocatalysts for oxygen (O 2 ) reduction at the cathode of proton exchange membrane fuel cells (PEMFCs) are the most promising alternative to platinum-group-metal catalysts. Despite recent progress on atomic FeNC O 2 reduction, their controlled synthesis and stability for practical applications remains challenging. A two-step synthesis approach has recently led to significant advances in terms of Fe-loading and mass activity; however, the Fe utilisation remains low owing to the difficulty of building scaffolds with sufficient porosity that electrochemically exposes the active sites. Herein, we addressed this issue by coordinating Fe in a highly porous nitrogen doped carbon support (~3295 m 2 g -1 ), prepared by pyrolysis of inexpensive 2,4,6triaminopyrimidine and a Mg 2+ salt active site template and porogen. Upon Fe coordination, a high electrochemical active site density of 2.54×10 19 sites g FeNC -1 and a record 52% FeN x electrochemical utilisation based on in situ nitrite stripping was achieved. The Fe single atoms are characterised pre-and post-electrochemical accelerated stress testing by aberration-corrected high-angle annular dark field scanning transmission electron microscopy, showing no Fe clustering. Moreover, ex situ X-ray absorption spectroscopy and low-temperature Mössbauer spectroscopy suggest the presence of penta-coordinated Fe sites, which were further studied by density functional theory calculations. catalysts [7,8] or introducing axial ligands. Different FeN x active site axial ligands have been recently proposed following in situ Mössbauer, x-ray absorption spectroscopy, nuclear inelastic scattering or electron paramagnetic resonance. [9,10] Some of them bearing close resemblance to biological systems, [11] such as N axially coordinated FeN 4 sites resembling heme. [12] However, spectroscopic discernibility is often challenging in these typically heterogeneous FeNC catalysts, [13] therefore experimental structure-activity correlations are hard to conclude. To overcome experimental limitations, the effect of O axial ligands on model FeNC systems has been calculated by density functional theory, [14,15] although the effect of other possible axial ligands on different Fe sites (pyridinic and pyrrolic) has not been fully considered. [16] Alternatively, to improve catalyst performance, the number of active sites can be increased, an approach which has shown significant progress in recent years. [17] To selectively form a high density of atomic Fe sites and avoid undesired Fe-induced carbothermal reduction, Fellinger and coworkers first identified that the high temperature pyrolytic step (800-1000ºC) should be decoupled from the Fe loading, by using a suitable N x site template. [17][18][19][20] The decoupled two-step synthetic approach to prepare FeNC O 2 reduction catalysts has led to remarkable progress; Mehmood et al. recently showed bulk FeN x site density (SD Mössbauer, , Eq. 1-2) up to 7.4×10 20 sites g FeNC -1 . The reported in situ nitrite strippin...

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Section: Resultsmentioning

confidence: 97%

Section: Resultsmentioning

confidence: 99%

FeNC Oxygen Reduction Electrocatalyst with High Utilization Penta‐Coordinated Sites

et al. 2023

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“…The observation of hydrogen in the outlet stream during the TPR measurements supports hydroxyl formation and hydrogen removal. This observation is supported further as barium cerate-based proton conductors retain hydroxyl groups at higher temperatures even at 800 °C under high steam operation conditions. , Niobium in a coexisting environment with Fe is known to assume the higher oxidation state, that stabilizes the crystal lattice. , Fe has been reported to exsolve to the Fe 0 state in reducing conditions but in the presence of B site cations with higher oxidation states, Fe has been shown to remain trivalent as confirmed by XPS and NEXAFS analysis of the Fe-doped double perovskite CaBi 2 Nb 2 O 9 . , Figure S14 indicates a lack of satellite features or shouldering around a binding energy of 715 and 718 eV which have been previously shown to account for mixed Fe 2+/3+ oxidation states in La 0.6 Sr 0.4 FeO 3−δ (LSF), and SrTi 0.7 Fe 0.3 O 3−δ (STF) electrodes . Thus, Fe 3d XPS scans for all of the samples before and after TPR measurements showed the presence of Fe 3+ with no peak or satellite features observed corresponding to Fe 2+ or Fe 0 (Figure S14).…”

Section: Resultsmentioning

confidence: 64%

“…61,62 FigureS14indicates a lack of satellite features or shouldering around a binding energy of 715 and 718 eV which have been previously shown to account for mixed Fe 2+/3+ oxidation states in La 0.6 Sr 0.4 FeO 3−δ (LSF), and SrTi 0.7 Fe 0.3 O 3−δ (STF) electrodes 63. Thus, Fe 3d XPS scans for all of the samples before and after TPR measurements showed the presence of Fe 3+ with no peak or satellite features observed corresponding to Fe 2+ or Fe 0 (FigureS14).…”

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confidence: 99%

Electrochemical Oxidative Coupling of Methane: Deciphering the Exceptional Properties of BaMg_0.33Nb_0.67–xFe_xO_3−δ for Enhanced Electrocatalysis and Durable Operation

Denoyer,

Benavidez,

Brearley

et al. 2024

Energy Fuels

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Perovskite metal oxides of the form A(B x M 1−x )O 3−δ are of interest to the electrocatalysis and heterogeneous communities due to their tunable electrical and catalytic properties. However, they suffer poor chemical stability under highly reducing and coke-forming conditions. Doped barium niobates show remarkable chemical stability during electrochemical oxidative coupling of methane (E-OCM) measurements. The reason for their chemical stability is not well understood. We i n v e s t i g a t e d t h e h i g h -t e m p e r a t u r e r e d u c t i v e s t a b i l i t y o f BaMg 0.33 Nb 0.67−x Fe x O 3−δ (BMNF), using a variety of methods. BMNF perovskites were exposed to methane-rich conditions in an E-OCM setup and in temperature-programmed reaction (TPR) measurements. X-ray powder diffraction, scanning transmission electron microscopy, and X-ray photoelectron spectroscopy measurements on BMNF before and after methane exposure reveal that BMNF perovskites retain their crystal structure. Iron doping may increase their electronic conductivity, while changes in Nb 4+/5+ oxidation states provide chemical stability in reducing environments. For comparison, Fe nanoparticles supported on BMN perovskites (BMN-01Fe) were synthesized/analyzed. The lattice-doped Fe in BMNF did not show any exsolution while the surface-bound Fe in BMN-01Fe agglomerated to form nanoparticles under reducing conditions. Our research demonstrates that multivalence, transition metal oxide perovskite redox stability results from several complex factors and is not easily predicted from the behavior of the binary oxides.

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“…[39] Nb 5þ 3d 3/2 and Nb 5þ 3d 5/2 binding energy peaks are seen at 207.4 and 210.4 eV, respectively (Figure S1b, Supporting Information). [40][41][42] The main peak of S 2p (S 2p 3/2 and S2p 1/2 ) appeared at 161.5 and 163.4 eV (Figure S1c, Supporting Information), respectively. [43]…”

Section: Characterizationmentioning

confidence: 99%

MnNbS/Polyaniline Composite‐Based Electrode Material for High‐Performance Energy Storage Hybrid Supercapacitor Device

Khan,

Afzal,

Hussain

et al. 2023

Physica Status Solidi (a)

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Supercapacitors (SCs), the most modern energy storage technology, have proven to be a viable solution for high-power applications. [1,2] High-performance SCs might have high specific capacitances, large power capability, and good cycling stability. [3,4] SCs are categorized into different types on the bases of energy storage mechanisms. In the electric double-layer (EDL) SCs, the charges are stored through the electrostatically or non-Faradic mechanism. In pseudocapacitors, the charges are stored chemically. In hybrid (symmetric or asymmetric) SCs, the charges are stored through electrostatically and chemically. [5,6] EDLCs preserve energy via electrostatic charge deposition at electrolyte/electrode interfaces, [7] while the pseudocapacitor is primarily due to the Faradic reactions at electrode surfaces. [8,9] A hybrid SC is an innovative and efficient energy storage device that integrates battery and supercapattery into a single device. [10] Because of

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Magnetic susceptibility, EPR, NEXAFS and XPS spectra of Fe-doped CaBi2Nb2O9

Cited by 16 publications

References 52 publications

FeNC Oxygen Reduction Electrocatalyst with High Utilization Penta‐Coordinated Sites

FeNC Oxygen Reduction Electrocatalyst with High Utilization Penta‐Coordinated Sites

Electrochemical Oxidative Coupling of Methane: Deciphering the Exceptional Properties of BaMg_0.33Nb_0.67–xFe_xO_3−δ for Enhanced Electrocatalysis and Durable Operation

MnNbS/Polyaniline Composite‐Based Electrode Material for High‐Performance Energy Storage Hybrid Supercapacitor Device

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Magnetic susceptibility, EPR, NEXAFS and XPS spectra of Fe-doped CaBi2Nb2O9

Cited by 16 publications

References 52 publications

FeNC Oxygen Reduction Electrocatalyst with High Utilization Penta‐Coordinated Sites

FeNC Oxygen Reduction Electrocatalyst with High Utilization Penta‐Coordinated Sites

Electrochemical Oxidative Coupling of Methane: Deciphering the Exceptional Properties of BaMg0.33Nb0.67–xFexO3−δ for Enhanced Electrocatalysis and Durable Operation

MnNbS/Polyaniline Composite‐Based Electrode Material for High‐Performance Energy Storage Hybrid Supercapacitor Device

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Product

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Electrochemical Oxidative Coupling of Methane: Deciphering the Exceptional Properties of BaMg_0.33Nb_0.67–xFe_xO_3−δ for Enhanced Electrocatalysis and Durable Operation