Brownmillerite‐type Ca<sub>2</sub>FeCoO<sub>5</sub> as a Practicable Oxygen Evolution Reaction Catalyst

Tsuji, Etsushi; Motohashi, Teruki; Noda, Hiroyuki; Kowalski, Damian; Aoki, Yoshitaka; Tanida, Hajime; Niikura, Junji; Koyama, Yukinori; Mori, Masahiro; Arai, Hajime; Ioroi, Tsutomu; Fujiwara, Naoko; Uchimoto, Yoshiharu; Ogumi, Zempachi; Habazaki, H.

doi:10.1002/cssc.201700499

Cited by 57 publications

(76 citation statements)

References 41 publications

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“…There are other structural systems of transition metal oxides that include different geometric sites. Some of the oxide families (e.g., brownmillerite‐type oxides) show promising OER activity; however, studies on the role of TM geometry is currently very limited. Thus, investigations on the role of TM geometry in OER should be extended to other promising oxide families. iii)Gain comprehensive mechanism understanding.…”

Section: Discussionmentioning

confidence: 99%

Significance of Engineering the Octahedral Units to Promote the Oxygen Evolution Reaction of Spinel Oxides

et al. 2019

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electrolyzer are oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively. The OER at the anode, proceeding through 4e − transfer and generates more than one intermediates, is much more kinetically sluggish than the 2e − transfer HER. [1] Lowering the energy barrier of OER is the key to the enhancement of overall water splitting efficiency. The state-of-the-art OER electrocatalysts, such as iridium-and ruthenium-based materials, are not sustainable choices due to the high cost and element scarcity. Transition metal (TM) oxides, with wide variety of physical and electronic properties, are considered as promising low-cost alternatives. [2] Spinel-type oxides have been extensively investigated as OER electrocatalysts and have presented outstanding catalytic performances. [2b,3] The crystal structure of spinel is made up of oxygen anions arranged in a cubic close-packed lattice with metallic ions filling the tetrahedral and octahedral interstices. Of all the 96 interstices between the oxygen anions in one cubic unit cell, 64 are four oxygencoordinated tetrahedral sites and 32 are six oxygen-coordinated octahedral sites. In the spinel lattice, only half of the octahedral interstices and one-eighth of the tetrahedral interstices are filled with metal cations. The remaining unoccupied interstitial sites make spinel a very open structure to accommodate the migration of cations. [4] For binary spinel AB 2 O 4 , the distribution of The clean energy carrier, hydrogen, if efficiently produced by water electrolysis using renewable energy input, would revolutionize the energy landscape. It is the sluggish oxygen evolution reaction (OER) at the anode of water electrolyzer that limits the overall efficiency. The large spinel oxide family is widely studied due to their low cost and promising OER activity. As the distribution of transition metal (TM) cations in octahedral and tetrahedral site is an important variable controlling the electronic structure of spinel oxides, the TM geometric effect on OER is discussed. The dominant role of octahedral sites is found experimentally and explained by computational studies. The redox-active TM locating at octahedral site guarantees an effective interaction with the oxygen at OER conditions. In addition, the adjacent octahedral centers in spinel act cooperatively in promoting the fast OER kinetics. In remarkable contrast, the isolated tetrahedral TM centers in spinel prohibit the OER mediated by dual-metal sites. Furthermore, various spinel oxides preferentially expose octahedral-occupied cations on the surface, making the octahedral cations easily accessible to the reactants. The future perspectives and challenges in advancing fundamental understanding and developing robust spinel catalysts are discussed.

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Section: Discussionmentioning

confidence: 99%

Significance of Engineering the Octahedral Units to Promote the Oxygen Evolution Reaction of Spinel Oxides

et al. 2019

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“…Brownmillerite SrFeO x (SFO) with similar structure of SCO has been extensively studied due to its promising application in the fields of electrodes of fuel cell, magnetic storage, redox reaction catalyst, etc. In addition, partial substitutions of the B specie of ABO 2.5 produce complex brownmillerite oxides such as Ca 2 FeAlO 5 , Ca 2 FeCoO 5 , etc . with more versatile and controllable properties.…”

Section: Introductionmentioning

confidence: 99%

“…. Moreover, the partial occupancy conditions have important influence on the properties of brownmillerites . However, relevant experimental studies only provided an average statistical proportion of B and B' elements at octahedral and tetrahedral sites without demonstrating specific configurations due to the experimental limitations.…”

Section: Introductionmentioning

confidence: 99%

Atomic occupancy mechanism in brownmillerite Ca₂FeAlO₅ from a thermodynamic perspective

Tao

Zhang

et al. 2019

J Am Ceram Soc

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Brownmillerite‐type oxides are a large family of structural and functional materials that are of great concern. In this study, the occupancy mechanism of Fe and Al ions in brownmillerite Ca2FeAlO5 is revealed and the specific configuration of Ca2FeAlO5 is proposed for the first time. Through the energy analysis of a series of conjectured models based on well‐defined ab initio calculations, we find that the distribution of Al and Fe in Ca2FeAlO5 follows the “homogeneous layer principle”, namely, Al and Fe tend to form homogeneous octahedral layers or tetrahedral chains rather than mixed layers or chains of two elements along the b axis. The theoretical Ca2FeAlO5 structure with specific atomic occupancy is proposed based on energy analysis and previous experiments, which is of fundamental significance for further study of its physical and chemical properties. Moreover, the influence of entropy increment on the stability of Ca2FeAlO5 crystal is clarified, which paves the way to investigate the structures and properties of Ca2FeAlO5 and other brownmillerite members.

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“…[1][2][3][4][5] Electrochemical splitting of water,a s widely accepted, is one of the most expedient and environmentally friendly techniques for the possible clean production of hydrogen energy. [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] However,t he efficiencyo ft his methodi sm ainly restricted by the sluggish anodic oxygen evolution reaction (OER), the rate-limitings tep for overall water splitting, which involves four sequential proton-coupled electron-transfer steps and the formation of an oxygenoxygen bond. [26][27][28][29] Generally,p recious-metal oxidess uch as IrO 2 and RuO 2 are seen as benchmark OER catalysts owing to low overpotentials, especially on the anode side.…”

Section: Introductionmentioning

confidence: 99%

Free‐Sustaining Three‐Dimensional S235 Steel‐Based Porous Electrocatalyst for Highly Efficient and Durable Oxygen Evolution

et al. 2018

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A novel oxygen evolution reaction (OER) catalyst (3 D S235-P steel) based on a steel S235 substrate was successfully prepared by facile one-step surface modification. The standard carbon-manganese steel was phosphorized superficially, which led to the formation of a unique 3 D interconnected nanoporous surface with a high specific area that facilitated the electrocatalytically initiated oxygen evolution reaction. The prepared 3 D S235-P steel exhibited enhanced electrocatalytic OER activities in the alkaline regime, as confirmed by a low overpotential (326 mV at a 10 mA cm ) and a small Tafel slope of 68.7 mV dec . Moreover, the catalyst was found to be stable under long-term usage conditions, functioning as an oxygen-evolving electrode at pH 13, as evidenced by the sufficient charge-to-oxygen conversion rate (faradaic efficiency: 82.11 and 88.34 % at 10 and 5 mA cm , respectively). In addition, it turned out that the chosen surface modification delivered steel S235 as an OER electrocatalyst that was stable under neutral pH conditions. Our investigation revealed that the high catalytic activities likely stemmed from the generated Fe/(Mn) hydroxide/oxohydroxides generated during the OER process. Phosphorization treatment therefore not only is an efficient way to optimize the electrocatalytic performance of standard carbon-manganese steel but also enables for the development of low-costing and abundant steels in the field of energy conversion.

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Brownmillerite‐type Ca₂FeCoO₅ as a Practicable Oxygen Evolution Reaction Catalyst

Cited by 57 publications

References 41 publications

Significance of Engineering the Octahedral Units to Promote the Oxygen Evolution Reaction of Spinel Oxides

Significance of Engineering the Octahedral Units to Promote the Oxygen Evolution Reaction of Spinel Oxides

Atomic occupancy mechanism in brownmillerite Ca₂FeAlO₅ from a thermodynamic perspective

Free‐Sustaining Three‐Dimensional S235 Steel‐Based Porous Electrocatalyst for Highly Efficient and Durable Oxygen Evolution

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Brownmillerite‐type Ca2FeCoO5 as a Practicable Oxygen Evolution Reaction Catalyst

Cited by 57 publications

References 41 publications

Significance of Engineering the Octahedral Units to Promote the Oxygen Evolution Reaction of Spinel Oxides

Significance of Engineering the Octahedral Units to Promote the Oxygen Evolution Reaction of Spinel Oxides

Atomic occupancy mechanism in brownmillerite Ca2FeAlO5 from a thermodynamic perspective

Free‐Sustaining Three‐Dimensional S235 Steel‐Based Porous Electrocatalyst for Highly Efficient and Durable Oxygen Evolution

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Brownmillerite‐type Ca₂FeCoO₅ as a Practicable Oxygen Evolution Reaction Catalyst

Atomic occupancy mechanism in brownmillerite Ca₂FeAlO₅ from a thermodynamic perspective