Transition metal oxides for water oxidation: All about oxyhydroxides?

Xu, Zhichuan J.

doi:10.1007/s40843-019-9588-5

Cited by 88 publications

(74 citation statements)

References 27 publications

(32 reference statements)

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“…It is generally recognized that some Co-based perovskites and spinels undergo operando surface reconstruction to form active Co (oxy) hydroxides in alkaline conditions to promote OER. 44 – 46 In our case, there are no changes in OER performance of CoFe 2 O 4 during CA tests in 1 M KOH for 1 h shown in Supplementary Fig. 4 , indicating CoFe 2 O 4 is stable without noticed surface reconstruction during the OER process.…”

Section: Resultsmentioning

confidence: 48%

Spin-polarized oxygen evolution reaction under magnetic field

et al. 2021

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The oxygen evolution reaction (OER) is the bottleneck that limits the energy efficiency of water-splitting. The process involves four electrons’ transfer and the generation of triplet state O2 from singlet state species (OH- or H2O). Recently, explicit spin selection was described as a possible way to promote OER in alkaline conditions, but the specific spin-polarized kinetics remains unclear. Here, we report that by using ferromagnetic ordered catalysts as the spin polarizer for spin selection under a constant magnetic field, the OER can be enhanced. However, it does not applicable to non-ferromagnetic catalysts. We found that the spin polarization occurs at the first electron transfer step in OER, where coherent spin exchange happens between the ferromagnetic catalyst and the adsorbed oxygen species with fast kinetics, under the principle of spin angular momentum conservation. In the next three electron transfer steps, as the adsorbed O species adopt fixed spin direction, the OER electrons need to follow the Hund rule and Pauling exclusion principle, thus to carry out spin polarization spontaneously and finally lead to the generation of triplet state O2. Here, we showcase spin-polarized kinetics of oxygen evolution reaction, which gives references in the understanding and design of spin-dependent catalysts.

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Section: Resultsmentioning

confidence: 48%

Spin-polarized oxygen evolution reaction under magnetic field

et al. 2021

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“…However,e fforts aiming at the design of catalysts with controllable cation leaching and surface reconstruction towards ah ighly active surface for OER remain limited. [37] Here,w er eport controllable leaching of Cr from CoCr 2 O 4 spinel oxide to promote surface reconstruction for boosting its OER activity.B ya ctivating CoCr 2 O 4 at high potential, Cr leaching occurs and leads to the reconstruction of Co species into oxyhydroxide.T he leaching increases with the applied anodic potential and is facilitated by the activation of lattice oxygen redox which gives rise to favorable surface condition for vigorous reorganization and activity enhancement. CoCr 2 O 4 activated at 1.7 Vf or 1.5 hours (Act-CoCr 2 O 4 )e xhibits one magnitude higher performance than pristine CoCr 2 O 4 (Pri-CoCr 2 O 4 ), which outperforms CoOOH thin film.…”

Section: Introductionmentioning

confidence: 99%

Anodic Oxidation Enabled Cation Leaching for Promoting Surface Reconstruction in Water Oxidation

et al. 2021

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Ar ational design for oxygen evolution reaction (OER) catalysts is pivotal to the overall efficiency of water electrolysis.M uchw ork has been devoted to understanding cation leaching and surface reconstruction of very active electrocatalysts,b ut little on intentionally promoting the surface in acontrolled fashion. We now report controllable anodic leaching of Cr in CoCr 2 O 4 by activating the pristine material at high potential, which enables the transformation of inactive spinel CoCr 2 O 4 into ah ighly active catalyst. The depletion of Cr and consumption of lattice oxygen facilitate surface defects and oxygen vacancies,exposing Co species to reconstruct into active Co oxyhydroxides differ from CoOOH. An ovel mechanism with the evolution of tetrahedrally coordinated surface cation into octahedral configuration via non-concerted proton-electron transfer is proposed. This work shows the importance of controlled anodic potential in modifying the surface chemistry of electrocatalysts.

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“…The intermittent nature of such energy sources necessitates the development of suitable methods for energy conversion and storage. Electrochemical water splitting is one such storage and conversion technique that is becoming more prominent . The electrochemical water splitting process involves two half‐cell reactions: the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER).…”

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confidence: 99%

Antiferromagnetic Inverse Spinel Oxide LiCoVO₄ with Spin‐Polarized Channels for Water Oxidation

et al. 2020

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Exploring highly efficient catalysts for the oxygen evolution reaction (OER) is essential for water electrolysis. Cost‐effective transition‐metal oxides with reasonable activity are raising attention. Recently, OER reactants' and products' differing spin configurations have been thought to cause slow reaction kinetics. Catalysts with magnetically polarized channels could selectively remove electrons with opposite magnetic moment and conserve overall spin during OER, enhancing triplet state oxygen molecule evolution. Herein, antiferromagnetic inverse spinel oxide LiCoVO4 is found to contain d7 Co2+ ions that can be stabilized under active octahedral sites, possessing high spin states S = 3/2 (t2g5eg2). With high spin configuration, each Co2+ ion has an ideal magnetic moment of 3 µB, allowing the edge‐shared Co2+ octahedra in spinel to be magnetically polarized. Density functional theory simulation results show that the layered antiferromagnetic LiCoVO4 studied contains magnetically polarized channels. The average magnetic moment (µave) per transition‐metal atom in the spin conduction channel is around 2.66 µB. Such channels are able to enhance the selective removal of spin‐oriented electrons from the reactants during the OER, which facilitates the accumulation of appropriate magnetic moments for triplet oxygen molecule evolution. In addition, the LiCoVO4 reported has been identified as an oxide catalyst with excellent OER activity.

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Transition metal oxides for water oxidation: All about oxyhydroxides?

Cited by 88 publications

References 27 publications

Spin-polarized oxygen evolution reaction under magnetic field

Spin-polarized oxygen evolution reaction under magnetic field

Anodic Oxidation Enabled Cation Leaching for Promoting Surface Reconstruction in Water Oxidation

Antiferromagnetic Inverse Spinel Oxide LiCoVO₄ with Spin‐Polarized Channels for Water Oxidation

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Transition metal oxides for water oxidation: All about oxyhydroxides?

Cited by 88 publications

References 27 publications

Spin-polarized oxygen evolution reaction under magnetic field

Spin-polarized oxygen evolution reaction under magnetic field

Anodic Oxidation Enabled Cation Leaching for Promoting Surface Reconstruction in Water Oxidation

Antiferromagnetic Inverse Spinel Oxide LiCoVO4 with Spin‐Polarized Channels for Water Oxidation

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Antiferromagnetic Inverse Spinel Oxide LiCoVO₄ with Spin‐Polarized Channels for Water Oxidation