Valence Change Ability and Geometrical Occupation of Substitution Cations Determine the Pseudocapacitance of Spinel Ferrite XFe<sub>2</sub>O<sub>4</sub> (X = Mn, Co, Ni, Fe)

Wei, Chao; Feng, Zhenxing; Baisariyev, Murat; Yu, Linghui; Zeng, Li; Wu, Tianpin; Zhao, Haiyan; Huang, Yaqin; Bedzyk, Michael J.; Sritharan, Thirumany; Xu, Zhichuan J.

doi:10.1021/acs.chemmater.6b00713

Cited by 100 publications

(82 citation statements)

References 37 publications

(76 reference statements)

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“…The mass efficiency of spinel oxides can be improved by reducing particle size. Wet‐chemical synthesis in organic solvents has proven highly efficient in producing various spinel ferrite nanoparticles . However, challenges exist for the synthesis of other spinel oxides which usually crystalize at a high temperatures that exceed the boiling point of the widely used organic solvents (e.g., oleylamine and octadecene).…”

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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“…The site occupancy of each sample was described by one parameter, the number of Mn at tetrahedral sites. The theoretical model was built by referencing landmark studies and had been used in our previous work . Because the fitting range (from 1 to ≈3.5 Å) covers a large number of scattering paths, some constraints and approximations were used.…”

Section: Methodsmentioning

confidence: 99%

Cations in Octahedral Sites: A Descriptor for Oxygen Electrocatalysis on Transition‐Metal Spinels

Wei

Feng

Scherer³

et al. 2017

Advanced Materials

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Exploring efficient and low-cost electrocatalysts for the oxygen-reduction reaction (ORR) and oxygen-evolution reaction (OER) is critical for developing renewable energy technologies such as fuel cells, metal-air batteries, and water electrolyzers. A rational design of a catalyst can be guided by identifying descriptors that determine its activity. Here, a descriptor study on the ORR/OER of spinel oxides is presented. With a series of MnCo O , the Mn in octahedral sites is identified as an active site. This finding is then applied to successfully explain the ORR/OER activities of other transition-metal spinels, including Mn Co O (x = 2, 2.5, 3), Li Mn O (x = 0.7, 1), XCo O (X = Co, Ni, Zn), and XFe O (X = Mn, Co, Ni). A general principle is concluded that the e occupancy of the active cation in the octahedral site is the activity descriptor for the ORR/OER of spinels, consolidating the role of electron orbital filling in metal oxide catalysis.

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“…This indicates a fast‐Faradaic process and superior alkaline OER kinetics, which can be attributed to the mixed valence state of cobalt ions in the porous hexagonal microplates. To be specific, at higher potential Co 2+ species can be transformed to Co 3+ and then Co 4+ species, facilitating the proton‐couple electron transfer process in OER ,. The sequential oxidation was coupled with the transfer of different numbers of protons/hydroxides and the generation of an active Co 4+ =O fragment .…”

Section: Resultsmentioning

confidence: 99%

Self‐Templated Synthesis of Co_1‐xS Porous Hexagonal Microplates for Efficient Electrocatalytic Oxygen Evolution

Liu

Zhang

et al. 2018

ChemElectroChem

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Transition-metal chalcogenides have been widely investigated as a class of promising oxygen evolution reaction (OER) catalysts. But, they are still far from practical use because of moderate catalytic activity. Two-dimensional (2D) materials with porous nanostructures are attractive for the efficient conversion of electrochemical energy. Herein, Co 1-x S novel porous microplates were synthesized through a facile self-templated strategy based on the Kirkendall effect. By taking advantages of porous nanostructure and good catalytic properties of the hexagonal Co(OH) 2 template, the unique Co 1-x S microplates provide higher efficient surface area and more accessible active sites. Moreover, the mass transfer and gas diffusion are also promoted, owing to the pores developed inside the microplates. As expected, the optimized porous Co 1-x S microplates demonstrate remarkable OER performance in alkaline electrolyte with an overpotential of 311 mV at 10 mA cm À2 , a Tafel slope of 55 mV dec À1 and longterm stability, which outperform the commercial IrO 2 catalyst. The facile preparation, high catalytic activity, and excellent durability of the Co 1-x S porous hexagonal microplates show great promise in energy conversion applications.

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Valence Change Ability and Geometrical Occupation of Substitution Cations Determine the Pseudocapacitance of Spinel Ferrite XFe₂O₄ (X = Mn, Co, Ni, Fe)

Cited by 100 publications

References 37 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

Cations in Octahedral Sites: A Descriptor for Oxygen Electrocatalysis on Transition‐Metal Spinels

Self‐Templated Synthesis of Co_1‐xS Porous Hexagonal Microplates for Efficient Electrocatalytic Oxygen Evolution

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Valence Change Ability and Geometrical Occupation of Substitution Cations Determine the Pseudocapacitance of Spinel Ferrite XFe2O4 (X = Mn, Co, Ni, Fe)

Cited by 100 publications

References 37 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

Cations in Octahedral Sites: A Descriptor for Oxygen Electrocatalysis on Transition‐Metal Spinels

Self‐Templated Synthesis of Co1‐xS Porous Hexagonal Microplates for Efficient Electrocatalytic Oxygen Evolution

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Valence Change Ability and Geometrical Occupation of Substitution Cations Determine the Pseudocapacitance of Spinel Ferrite XFe₂O₄ (X = Mn, Co, Ni, Fe)

Self‐Templated Synthesis of Co_1‐xS Porous Hexagonal Microplates for Efficient Electrocatalytic Oxygen Evolution