scholarly journals Achieving delafossite analog by in situ electrochemical self-reconstruction as an oxygen-evolving catalyst

2020 ◽  
Vol 117 (36) ◽  
pp. 21906-21913
Author(s):  
Juzhe Liu ◽  
Qi Hu ◽  
Yu Wang ◽  
Zhao Yang ◽  
Xiaoyu Fan ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Electron Conductivity ◽  
Intrinsic Activity ◽  
Cobalt Iron ◽  
Alkaline Conditions ◽  
Oxygen Evolving ◽  
X Ray Absorption ◽  
Original Crystal ◽  
Excellent Stability

Development of novel and robust oxygen evolution reaction (OER) catalysts with well-modulated atomic and electronic structure remains a challenge. Compared to the well-known metal hydroxides or (oxyhydr)oxides with lamellar structure, delafossites (ABO2) are characterized by alternating layers of A cations and edge-sharing BO2octahedra, but are rarely used in OER due to their poor electron conductivity and intrinsic activity. Here, we propose a delafossite analog by mutation of metal oxyhydroxide and delafossite based on first-principles calculations. Modulation on the electronic structure due to distortion of the original crystal field of the BO2layers is calculated to enhance electron conductivity and catalytic activity. Inspired by the theoretical design, we have experimentally realized the delafossite analog by electrochemical self-reconstruction (ECSR).OperandoX-ray absorption spectroscopy and other experimental techniques reveal the formation of delafossite analog with Ag intercalated into bimetallic cobalt–iron (oxyhydr)oxide layers from a metastable precursor through amorphization. Benefitting from the featured local electronic and geometric structures, the delafossite analog shows superior OER activity, affording a current density of 10 mA⋅cm−2at an overpotential of 187 mV and an excellent stability (300 h) in alkaline conditions.

Revealing the structural transformation of rutile RuO2via in situ X-ray absorption spectroscopy during the oxygen evolution reaction

2019 ◽  
Vol 48 (21) ◽  
pp. 7122-7129 ◽  
Author(s):  
Chia-Jui Chang ◽  
You-Chiuan Chu ◽  
Hao-Yu Yan ◽  
Yen-Fa Liao ◽  
Hao Ming Chen
Keyword(s):  
Oxygen Evolution ◽  
Structural Transformation ◽  
Absorption Spectroscopy ◽  
Oxygen Evolution Reaction ◽  
The State ◽  
X Ray ◽  
Alkaline Conditions ◽  
X Ray Absorption ◽  
State Of Art

The state-of-art RuO2 catalyst for the oxygen evolution reaction (OER) is measured by using in situ X-ray absorption spectroscopy (XAS) to elucidate the structural transformation during catalyzing the reaction in acidic and alkaline conditions.

scholarly journals Stoichiometry and disorder influence over electronic structure in nanostructured VOx films

2021 ◽  
Vol 23 (1) ◽  
Author(s):  
A. D’Elia ◽  
S. J. Rezvani ◽  
N. Zema ◽  
F. Zuccaro ◽  
M. Fanetti ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Distorted Octahedral Geometry ◽  
Edge Structure ◽  
Distorted Octahedral ◽  
X Ray Absorption ◽  
Complex Matter ◽  
Nanometric Size

AbstractWe present and discuss the role of nanoparticles size and stoichiometry over the local atomic environment of nanostructured VOx films. The samples have been characterized in situ using X-ray absorption near-edge structure (XANES) spectroscopy identifying the stoichiometry-dependent fingerprints of disordered atomic arrangement. In vanadium oxides, the ligand atoms arrange according to a distorted octahedral geometry depending on the oxidation state, e.g. trigonal distortion in V2O3 and tetragonal distortion in bulk VO2. We demonstrate, taking VO2 as a case study, that as a consequence of the nanometric size of the nanoparticles, the original ligands symmetry of the bulk is broken resulting in the coexistence of a continuum of distorted atomic conformations. The resulting modulation of the electronic structure of the nanostructured VOx as a function of the oxygen content reveals a stoichiometry-dependent increase of disorder in the ligands matrix. This work shows the possibility to produce VOx nanostructured films accessing new disordered phases and provides a unique tool to investigate the complex matter.

scholarly journals A Cobalt-Iron Double-Atom Catalyst for the Oxygen Evolution Reaction

2019 ◽  
Author(s):  
Lichen Bai ◽  
Chia-Shuo Hsu ◽  
Duncan Alexander ◽  
Hao Ming Chen ◽  
Xile Hu
Keyword(s):  
Oxygen Evolution ◽  
Active Site ◽  
Oxygen Evolution Reaction ◽  
Active Sites ◽  
Single Atom ◽  
X Ray ◽  
Highly Active ◽  
Cobalt Iron ◽  
X Ray Absorption

Single atom catalysts exhibit well-defined active sites and potentially maximum atomic efficiency. However, they are unsuitable for reactions that benefit from bimetallic promotion such as the oxygen evolution reaction (OER) in alkaline medium. Here we show that a single atom Co precatalyst can be in-situ transformed into a Co-Fe double atom catalyst for OER. This catalyst exhibits one of the highest turnover frequencies among metal oxides. Electrochemical, microscopic, and spectroscopic data including those from operando X-ray absorption spectroscopy, reveal a dimeric Co-Fe moiety as the active site of the catalyst. This work demonstrates double-atom catalysis as a promising approach for the developed of defined and highly active OER catalysts.

scholarly journals In situ characterization of cofacial Co(IV) centers in Co4O4 cubane: Modeling the high-valent active site in oxygen-evolving catalysts

2017 ◽  
Vol 114 (15) ◽  
pp. 3855-3860 ◽  
Author(s):  
Casey N. Brodsky ◽  
Ryan G. Hadt ◽  
Dugan Hayes ◽  
Benjamin J. Reinhart ◽  
Nancy Li ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Active Site ◽  
Resting State ◽  
Structural Model ◽  
Reorganization Energy ◽  
Electrochemical Kinetics ◽  
Absorption Data ◽  
High Valent ◽  
Oxygen Evolving

The Co4O4 cubane is a representative structural model of oxidic cobalt oxygen-evolving catalysts (Co-OECs). The Co-OECs are active when residing at two oxidation levels above an all-Co(III) resting state. This doubly oxidized Co(IV)2 state may be captured in a Co(III)2(IV)2 cubane. We demonstrate that the Co(III)2(IV)2 cubane may be electrochemically generated and the electronic properties of this unique high-valent state may be probed by in situ spectroscopy. Intervalence charge-transfer (IVCT) bands in the near-IR are observed for the Co(III)2(IV)2 cubane, and spectroscopic analysis together with electrochemical kinetics measurements reveal a larger reorganization energy and a smaller electron transfer rate constant for the doubly versus singly oxidized cubane. Spectroelectrochemical X-ray absorption data further reveal systematic spectral changes with successive oxidations from the cubane resting state. Electronic structure calculations correlated to experimental data suggest that this state is best represented as a localized, antiferromagnetically coupled Co(IV)2 dimer. The exchange coupling in the cofacial Co(IV)2 site allows for parallels to be drawn between the electronic structure of the Co4O4 cubane model system and the high-valent active site of the Co-OEC, with specific emphasis on the manifestation of a doubly oxidized Co(IV)2 center on O–O bond formation.

scholarly journals A Cobalt-Iron Double-Atom Catalyst for the Oxygen Evolution Reaction

2019 ◽  
Author(s):  
Lichen Bai ◽  
Chia-Shuo Hsu ◽  
Duncan Alexander ◽  
Hao Ming Chen ◽  
Xile Hu
Keyword(s):  
Oxygen Evolution ◽  
Active Site ◽  
Oxygen Evolution Reaction ◽  
Active Sites ◽  
Single Atom ◽  
X Ray ◽  
Highly Active ◽  
Cobalt Iron ◽  
X Ray Absorption

Single atom catalysts exhibit well-defined active sites and potentially maximum atomic efficiency. However, they are unsuitable for reactions that benefit from bimetallic promotion such as the oxygen evolution reaction (OER) in alkaline medium. Here we show that a single atom Co precatalyst can be in-situ transformed into a Co-Fe double atom catalyst for OER. This catalyst exhibits one of the highest turnover frequencies among metal oxides. Electrochemical, microscopic, and spectroscopic data including those from operando X-ray absorption spectroscopy, reveal a dimeric Co-Fe moiety as the active site of the catalyst. This work demonstrates double-atom catalysis as a promising approach for the developed of defined and highly active OER catalysts.

scholarly journals In situ X-ray emission and high-resolution X-ray absorption spectroscopy applied to Ni-based bimetallic dry methane reforming catalysts

Nanoscale ◽  
2020 ◽  
Vol 12 (28) ◽  
pp. 15185-15192
Author(s):  
Abbas Beheshti Askari ◽  
Mustafa al Samarai ◽  
Nozomu Hiraoka ◽  
Hirofumi Ishii ◽  
Lukas Tillmann ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Catalytic Activity ◽  
High Resolution ◽  
Absorption Spectroscopy ◽  
Methane Reforming ◽  
X Ray ◽  
Reforming Catalyst ◽  
Reforming Catalysts ◽  
X Ray Absorption

The effect of cobalt on the catalytic activity of a NiCoO dry methane reforming catalyst was investigated by in situ XES and HERFD XAS. Co is shown to hamper the reduction of the Ni in the NiCoO catalyst by modulation of its electronic structure.

In situ X-ray absorption spectroscopy of transition metal based water oxidation catalysts

2017 ◽  
Vol 46 (1) ◽  
pp. 102-125 ◽  
Author(s):  
Christina H. M. van Oversteeg ◽  
Hoang Q. Doan ◽  
Frank M. F. de Groot ◽  
Tanja Cuk
Keyword(s):  
Electronic Structure ◽  
Transition Metal ◽  
Absorption Spectroscopy ◽  
Water Oxidation ◽  
Oxidation Catalysts ◽  
X Ray ◽  
Absorption Studies ◽  
X Ray Absorption

X-ray absorption studies of the geometric and electronic structure of primarily heterogeneous Co, Ni, and Mn based water oxidation catalysts are reviewed.

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