Interplay of structural and magnetic nanoscale phase separation in layered cobaltites

Allieta, Mattia; Scavini, Marco; Naldoni, Alberto; Coduri, Mauro; Cappelli, S.; Oliva, Cesare; Santangelo, S.; Triolo, Claudia; Patanè, Salvatore; Lascialfari, A.; Scagnoli, V.

doi:10.1103/physrevb.92.054202

Cited by 5 publications

(5 citation statements)

References 31 publications

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“…As the applied potential shifts from 0 to −0.3 V vs RHE, the A 1g peak of Co Oh for both Co 3 O 4 and MgCo 2 O 4 gradual ly becomes weaker and wider (Figure d,e), which may be attributed to the electrochemical reduction for generating O v on Co Oh sites. When the potential negatively shifts to −0.4 V vs RHE, a new subpeak can be observed on the A 1g peak, indicating the generation of a new Co Oh sites, which can be identified as Co Oh with local distorted coordination structure induced by the O v . − Furthermore, with the potential further negatively shifting to −0.9 V vs RHE, the intensity of this subpeak is rapidly enhanced, further verifying that the new subpeak originates from the generation of O v resulted from the electrochemical reduction (Figure e). In sharp contrast, the F 2g 1 peak of Co Td for Co 3 O 4 remains almost unchanged during the whole potential shift process, reflecting the absence of an electrochemical change at Co Td during the NO 3 – RR.…”

Section: Resultsmentioning

confidence: 68%

Designing Efficient Nitrate Reduction Electrocatalysts by Identifying and Optimizing Active Sites of Co-Based Spinels

Hu,

Qi,

Huo

et al. 2023

J. Am. Chem. Soc.

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Cobalt-based spinel oxides (i.e., Co 3 O 4 ) are emerging as low-cost and selective electrocatalysts for the electrochemical nitrate reduction reaction (NO 3 − RR) to ammonia (NH 3 ), although their activity is still unsatisfactory and the genuine active site is unclear. Here, we discover that the NO 3 − RR activity of Co 3 O 4 is highly dependent on the geometric location of the Co site, and the NO 3 − RR prefers to occur at octahedral Co (Co Oh ) rather than tetrahedral Co (Co Td ) sites. Moreover, Co Oh O 6 is electrochemically transformed to Co Oh O 5 along with the formation of O vacancies (O v ) during the process of NO 3 − RR. Both experimental and theoretic results reveal that in situ generated Co Oh O 5 −O v configuration is the genuine active site for the NO 3 − RR. To further enhance the activity of Co Oh sites, we replace inert Co Td with different contents of Cu 2+ cations, and a volcano-shape correlation between NO 3 − RR activity and electronic structures of Co Oh is observed. Impressively, in 1.0 M KOH, (Cu 0.6 Co 0.4 )Co 2 O 4 with optimized Co Oh sites achieves a maximum NH 3 Faradaic efficiency of 96.5% with an ultrahigh NH 3 rate of 1.09 mmol h −1 cm −2 at −0.45 V vs reversible hydrogen electrode, outperforming most of other reported nonprecious metal-based electrocatalysts. Clearly, this work paves new pathways for boosting the NO 3 − RR activity of Co-based spinels by tuning local electronic structures of Co Oh sites.

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Section: Resultsmentioning

confidence: 68%

Designing Efficient Nitrate Reduction Electrocatalysts by Identifying and Optimizing Active Sites of Co-Based Spinels

Hu,

Qi,

Huo

et al. 2023

J. Am. Chem. Soc.

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“…It has been observed that the oxygen vacancies in the lanthanide plane (RO δ ) of RBaCo 2 O 5.5+ δ are ordered for δ = 0 and δ = 0.25 while no vacancy ordering has be detected for δ = 0.37 and δ = 0.5. Moreover, with increasing δ value of RBaCo 2 O 5.5+ δ , metallic Co 4+ sites increase while oxygen vacancies on Co 3+ sites decrease in the lattice (detailed electronic structures and local coordination environments are provided in Figure a and Discussion 2 in the Supporting Information). Herein, motivated by the tunability and controllability of both the oxygen vacancies at pyramidal Co 3+ sites (Co 3+ pyr ) and the metallic Co 4+ ions at octahedral sites (Co 4+ oct ) in this family, we attempt to develop a superior cobalt‐based perovskite‐type oxide toward the alkaline HER.…”

Section: Introductionmentioning

confidence: 99%

“…Moreover, with increasing δ value of RBaCo 2 O 5.5+ δ , metallic Co 4+ sites increase while oxygen vacancies on Co 3+ sites decrease in the lattice (detailed electronic structures and local coordination environments are provided in Figure a and Discussion 2 in the Supporting Information). Herein, motivated by the tunability and controllability of both the oxygen vacancies at pyramidal Co 3+ sites (Co 3+ pyr ) and the metallic Co 4+ ions at octahedral sites (Co 4+ oct ) in this family, we attempt to develop a superior cobalt‐based perovskite‐type oxide toward the alkaline HER. Theoretically, we predict a synergistic effect of two active sites on RBaCo 2 O 5.5+ δ surfaces from our computational studies, namely, the oxygen vacancies at Co 3+ pyr sites and O 2p ligand holes (OLH) of oxygen atoms from the Co 4+ oct clusters can be active sites for H 2 O adsorption and H 2 desorption, respectively.…”

Section: Introductionmentioning

confidence: 99%

Searching General Sufficient‐and‐Necessary Conditions for Ultrafast Hydrogen‐Evolving Electrocatalysis

Guan

Zhou

et al. 2019

Adv Funct Materials

106

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The development of cost-effective and high-performance electrocatalysts for the hydrogen evolution reaction (HER) is one critical step toward successful transition into a sustainable green energy era. Different from previous design strategies based on single parameter, here the necessary and sufficient conditions are proposed to develop bulk non-noble metal oxides which are generally considered inactive toward HER in alkaline solutions: i) multiple active sites for different reaction intermediates and ii) a short reaction path created by ordered distribution and appropriate numbers of these active sites. Computational studies predict that a synergistic interplay between the ordered oxygen vacancies (at pyramidal high-spin Co 3+ sites) and the O 2p ligand holes (OLH; at metallic octahedral intermediate-spin Co 4+ sites) in RBaCo 2 O 5.5+δ (δ = 1/4; R = lanthanides) can produce a near-ideal HER reaction path to adsorb H 2 O and release H 2 , respectively. Experimentally, the as-synthesized (Gd 0.5 La 0.5 )BaCo 2 O 5.75 outperforms the state-of-the-art Pt/C catalyst in many aspects. The proof-of-concept results reveal that the simultaneous possession of ordered oxygen vacancies and an appropriate number of OLH can realize a near-optimal synergistic catalytic effect, which is pivotal for rational design of oxygen-containing materials.

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“…To validate this hypothesis, we studied the evolution of the ESR signal as a function of doping at room temperature. ESR allows direct access to the spinenvironment interactions of Fe ions in different valence states [29], [30].…”

Section: Resultsmentioning

confidence: 99%

“…In the case of a strong isotropic exchange interaction, like SE, the Gaussian ESR line, which depends on the magnetic dipole interaction ( H d ), is narrowed into a Lorentzian line by fast dynamics resulting from the exchange coupling ( J ) according to ΔH pp ≈ H d 2 /ω ex where ω ex ≈ J / ℏ , i.e., exchange narrowing . , Conversely, the DE heterospin dipolar interaction gives rise to an effective alternating FM internal magnetic field that relaxes the Fe 3+ spins . Upon doping, one could expect an increase of the spin relaxation rate of Fe 3+ that produces the broadening of the ESR signal, i.e., exchange broadening .…”

Section: Resultsmentioning

confidence: 99%

Electron Small Polaron and Magnetic Interactions Direct Anisotropic Growth of Silicon-Doped Hematite Nanocrystals

Allieta

Beranová

Marelli³

et al. 2020

Crystal Growth & Design

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Understanding the interplay between the structural, chemical and physical properties of nanomaterials is crucial for designing new devices with enhanced performance. In this regards, doping of metal oxides is a general strategy to tune size, morphology, charge, lattice, orbital and spin degrees of freedoms and has been shown to affect nanomaterials properties for photoelectrochemical water splitting, batteries, catalysis, magnetic applications and optics. Here we report the role of lattice small polaron in driving the morphological transition from nearly isotropic to nanowire crystals in Si doped hematite (α-Fe 2 O 3 ). Lattice small polaron formation is well evidenced by the increase of hexagonal strain and degree of distortion of FeO 6 showing a hyperbolic trend with increasing Si content. Local analysis via pair distribution function highlights an unreported crossover from small to large polarons, which affects the correlation length of the polaronic distortion from short to average scales. Ferromagnetic double exchange interactions between Fe 2+/ Fe 3+ species is found to be the driving force of the crossover, constraining the chaining of chemical bonds along the [110] crystallographic direction. This promotes the increase in the reticular density of Fe atoms along the hematite basal plane only, which boosts the anisotropic growth of nanocrystals with more extended [110] facets. Our results show that magnetic and electronic interactions drive preferential crystallographic growth in doped metal oxides, thus providing a new route to design their functional properties.

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Interplay of structural and magnetic nanoscale phase separation in layered cobaltites

Cited by 5 publications

References 31 publications

Designing Efficient Nitrate Reduction Electrocatalysts by Identifying and Optimizing Active Sites of Co-Based Spinels

Designing Efficient Nitrate Reduction Electrocatalysts by Identifying and Optimizing Active Sites of Co-Based Spinels

Searching General Sufficient‐and‐Necessary Conditions for Ultrafast Hydrogen‐Evolving Electrocatalysis

Electron Small Polaron and Magnetic Interactions Direct Anisotropic Growth of Silicon-Doped Hematite Nanocrystals

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