Mixed Valent, Distorted Cobalt Ludwigite (Co3BO5/Co3O2BO3) and Its Composite with Reduced Multiwalled Carbon Nanotubes (R‐MWCNT) in Enhancing the Domain Edge‐Sharing Oxygen as Superior Water Oxidation Electrocatalysts

Kundu, Sumana; Malik, Bibhudatta; Pattanayak, Deepak K.; Pillai, Vijayamohanan K.

doi:10.1002/celc.201800389

Cited by 14 publications

(10 citation statements)

References 59 publications

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“…However, the efficiency of H 2 production is affected by the sluggish kinetics of anodic oxygen evolution reaction (OER), a half cell reaction of overall water splitting. The enormous potential loss for OER, owing to the complex four electron transfer process (4e − ), is a main barrier to the grid scale production of hydrogen [9–13] . Hence, efficient catalysts are desired which can lower the overpotential and boost the production rate of molecular hydrogen.…”

Section: Introductionmentioning

confidence: 99%

Promising Electrocatalytic Water and Methanol Oxidation Reaction Activity by Nickel Doped Hematite/Surface Oxidized Carbon Nanotubes Composite Structures

et al. 2022

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Tailoring the precise construction of non-precious metals and carbon-based heterogeneous catalysts for electrochemical oxygen evolution reaction (OER) and methanol oxidation reaction (MOR) is crucial for energy conversion applications. Herein, this work reports the composite of Ni doped Fe 2 O 3 (NiÀ Fe 2 O 3 ) with mildly oxidized multi-walled CNT (OÀ CNT) as an outstanding Mott-Schottky catalyst for OER and MOR. OÀ CNT acts as a cocatalyst which effectively regulates the charge transfer in NiÀ Fe 2 O 3 and thus enhances the electrocatalytic performance.NiÀ Fe 2 O 3 /OÀ CNT exhibits a low onset potential of 260 mV and overpotential 310 mV @ 10 mA cm À 2 for oxygen evolution. Being a Mott-Schottky catalyst, it achieves the higher flat band potential of À 1.15 V with the carrier density of 0.173 × 10 24 cm À 3 . Further, in presence of 1 M CH 3 OH, it delivers the MOR current density of 10 mA cm À 2 at 1.46 V vs. RHE. The excellent electrocatalytic OER and MOR activity of NiÀ Fe 2 O 3 / OÀ CNT could be attributed to the synergistic interaction between Ni-doped Fe 2 O 3 and OÀ CNT.

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Section: Introductionmentioning

confidence: 99%

Promising Electrocatalytic Water and Methanol Oxidation Reaction Activity by Nickel Doped Hematite/Surface Oxidized Carbon Nanotubes Composite Structures

et al. 2022

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“…Indeed, the combination of low dimensional units and mixed valence states leads to a number interesting physical phenomena in ludwigites [16,17], such as dimerized states [9], structural and charge-ordering transitions [9,10,14,18,19], spin-glass states [20][21][22][23][24][25][26][27][28], and multiferroicity [29]. Also, these oxyborates have been tested as high-performance electrodes for lithium-ion and sodium-ion batteries [30][31][32][33], low frequency oscillators [34,35], and as oxygen evolution reaction (OER) electrocatalyst [36].…”

Section: Introductionmentioning

confidence: 99%

Structural and spectroscopic investigation of the charge-ordered, short-range ordered, and disordered phases of the Co3O2BO3 ludwigite

et al. 2021

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Charge ordering is prone to occur in crystalline materials with mixed-valence ions. It is presumably accompanied by a structural phase transition, with possible exceptions in compounds that already present more than one inequivalent site for the mixed-valence ions in the charge-disordered phase. In this work, we investigate the representative case of the homometallic Co ludwigite Co 2+ 2 Co 3+ O 2 BO 3 (Pbam space group) with four distinct Co crystallographic sites [M1-M4] surrounded by oxygen octahedra. The mixed-valent character of the Co ions up to at least T = 873 K is verified through x-ray absorption near-edge structure (XANES) experiments. Single crystal x-ray diffraction (XRD) and neutron powder diffraction (NPD) confirm that the Co ions at the M4 site are much smaller than the others at low temperatures, consistent with a Co 3+ oxidation state at M4 and Co 2+ at the remaining sites. The size difference between the Co ions in the M4 and M2 sites is continuously reduced upon warming above ≈370 K, indicating a gradual charge redistribution within the M4-M2-M4 (424) ladder in the average structure. Minor structural anomalies with no space group modification are observed near 475 and 495 K, where sharp phase transitions were previously revealed by calorimetry and electrical resistivity data. An increasing structural disorder, beyond a conventional thermal effect, is noted above ≈370 K, manifested by an anomalous increment of XRD Debye-Waller factors and broadened vibrational modes observed by Raman scattering. The local Co-O distance distribution, revealed by Co K-edge extended x-ray absorption fine structure (EXAFS) data and analyzed with an evolutionary algorithm method, is similar to that inferred from the XRD crystal structure below ≈370 K. At higher temperatures, the local Co-O distance distribution remains similar to that found at low temperatures, at variance with the average crystal structure obtained with XRD. We conclude that the oxidation states Co 2+ and Co 3+ are instantaneously well defined in a local atomic level at all temperatures, however the thermal energy promotes local defects in the charge-ordered configuration of the 424 ladders upon warming. These defects coalesce into a phase-segregated state within a narrow temperature interval (475 < T < 495 K). Finally, a transition at ≈500 K revealed by differential scanning calorimetry (DSC) in the iron ludwigite Fe 3 O 2 BO 3 is discussed.

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Section: Introductionmentioning

confidence: 99%

Structural and spectroscopic investigation of the charge-ordered, short-range ordered, and disordered phases of the Co$_3$O$_2$BO$_3$ ludwigite

Galdino,

Freitas,

Medrano

et al. 2021

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Charge-ordering is prone to occur in crystalline materials with mixed-valence ions. It is presumably accompanied by a structural phase transition, with possible exceptions in compounds that already present more than one inequivalent site for the mixed-valence ions in the chargedisordered phase. In this work, we investigate the representative case of the homometallic Co ludwigite Co 2+ 2 Co 3+ O2BO3 (P bam space group) with four distinct Co crystallographic sites [M 1-M 4] surrounded by oxygen octahedra. The mixed-valent character of the Co ions up to at least T = 873 K is verified through x-ray absorption near-edge structure (XANES) experiments. Single crystal x-ray diffraction (XRD) and neutron powder diffraction (NPD) confirm that the Co ions at the M 4 site are much smaller than the others at low temperatures, consistent with a Co 3+ oxidation state at M 4 and Co 2+ at the remaining sites. The size difference between the Co ions in the M 4 and M 2 sites is continuously reduced upon warming above ≈ 370 K, indicating a gradual charge redistribution within the M 4-M 2-M 4 (424) ladder in the average structure. Minor structural anomalies with no space group modification are observed near 475 and 495 K, where sharp phase transitions were previously revealed by calorimetry and electrical resistivity data. An increasing structural disorder, beyond a conventional thermal effect, is noted above ≈ 370 K, manifested by an anomalous increment of XRD Debye-Waller factors and broadened vibrational modes observed by Raman scattering. The local Co-O distance distribution, revealed by Co K-edge Extended X-Ray Absorption Fine Structure (EXAFS) data and analyzed with an evolutionary algorithm method, is similar to that inferred from the XRD crystal structure below ≈ 370 K. At higher temperatures, the local Co-O distance distribution remains similar to that found at low temperatures, at variance with the average crystal structure obtained with XRD. We conclude that the oxidation states Co 2+ and Co 3+ are instantaneously well defined in a local atomic level at all temperatures, however the thermal energy promotes local defects in the charge-ordered configuration of the 424 ladders upon warming. These defects coalesce into a phase-segregated state within a narrow temperature interval (475 < T < 495 K). Finally, a transition at ≈ 500 K revealed by differential scanning calorimetry (DSC) in the iron ludwigite Fe3O2BO3 is discussed.

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Mixed Valent, Distorted Cobalt Ludwigite (Co₃BO₅/Co₃O₂BO₃) and Its Composite with Reduced Multiwalled Carbon Nanotubes (R‐MWCNT) in Enhancing the Domain Edge‐Sharing Oxygen as Superior Water Oxidation Electrocatalysts

Cited by 14 publications

References 59 publications

Promising Electrocatalytic Water and Methanol Oxidation Reaction Activity by Nickel Doped Hematite/Surface Oxidized Carbon Nanotubes Composite Structures

Promising Electrocatalytic Water and Methanol Oxidation Reaction Activity by Nickel Doped Hematite/Surface Oxidized Carbon Nanotubes Composite Structures

Structural and spectroscopic investigation of the charge-ordered, short-range ordered, and disordered phases of the Co3O2BO3 ludwigite

Structural and spectroscopic investigation of the charge-ordered, short-range ordered, and disordered phases of the Co$_3$O$_2$BO$_3$ ludwigite

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