scholarly journals Double-Atom Catalysts Provide a Molecular Platform for Oxygen Evolution

2019 ◽  
Author(s):  
Lichen Bai ◽  
Chia-Shuo Hsu ◽  
Duncan Alexander ◽  
Hao Ming Chen ◽  
Xile Hu
Keyword(s):  
Oxygen Evolution ◽  
Active Sites ◽  
Supported Catalysts ◽  
Single Atom ◽  
Bond Forming ◽  
Co2 Electroreduction ◽  
Anode Reaction ◽  
X Ray Absorption ◽  
General Synthesis

The oxygen evolution reaction (OER) is an essential anode reaction for the generation of solar and electric fuels through water splitting or CO2 electroreduction. Mixed metal oxides containing Co, Fe, or Ni prove to be the most promising OER electrocatalysts in alkaline medium. However, the active sites and reaction mechanisms of these catalysts are difficult to study due to their heterogeneous nature. Here we describe a general synthesis of Co, Fe, and Ni-containing double-atom catalysts from their single-atom precursors via in-situ electrochemical transformation. Atomic-resolution microscopy and operando X-ray absorption spectroscopy (XAS) reveal molecule-like bimetallic active sites for these supported catalysts. Based on electrokinetic and XAS data, we propose a complete catalytic cycle for each catalyst. These mechanisms follow a similar O-O bond forming step and all exhibit bimetallic cooperation. However, the mechanisms diverge in the site and source of OH- for O-O bond formation as well as the order of proton and electron transfer. Our work demonstrates double-atom catalysts as an attractive platform for fundamental studies of heterogeneous OER electrocatalysts.

scholarly journals Double-Atom Catalysts Provide a Molecular Platform for Oxygen Evolution

2019 ◽  
Author(s):  
Lichen Bai ◽  
Chia-Shuo Hsu ◽  
Duncan Alexander ◽  
Hao Ming Chen ◽  
Xile Hu
Keyword(s):  
Oxygen Evolution ◽  
Active Sites ◽  
Supported Catalysts ◽  
Single Atom ◽  
Bond Forming ◽  
Co2 Electroreduction ◽  
Anode Reaction ◽  
X Ray Absorption ◽  
General Synthesis

The oxygen evolution reaction (OER) is an essential anode reaction for the generation of solar and electric fuels through water splitting or CO2 electroreduction. Mixed metal oxides containing Co, Fe, or Ni prove to be the most promising OER electrocatalysts in alkaline medium. However, the active sites and reaction mechanisms of these catalysts are difficult to study due to their heterogeneous nature. Here we describe a general synthesis of Co, Fe, and Ni-containing double-atom catalysts from their single-atom precursors via in-situ electrochemical transformation. Atomic-resolution microscopy and operando X-ray absorption spectroscopy (XAS) reveal molecule-like bimetallic active sites for these supported catalysts. Based on electrokinetic and XAS data, we propose a complete catalytic cycle for each catalyst. These mechanisms follow a similar O-O bond forming step and all exhibit bimetallic cooperation. However, the mechanisms diverge in the site and source of OH- for O-O bond formation as well as the order of proton and electron transfer. Our work demonstrates double-atom catalysts as an attractive platform for fundamental studies of heterogeneous OER electrocatalysts.

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 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 Atomically dispersed Fe3+ sites catalyze efficient CO2 electroreduction to CO

Science ◽  
2019 ◽  
Vol 364 (6445) ◽  
pp. 1091-1094 ◽  
Author(s):  
Jun Gu ◽  
Chia-Shuo Hsu ◽  
Lichen Bai ◽  
Hao Ming Chen ◽  
Xile Hu
Keyword(s):  
Active Sites ◽  
Carbon Support ◽  
Single Atom ◽  
Electronic Coupling ◽  
X Ray ◽  
Precious Metal Catalysts ◽  
Co2 Electroreduction ◽  
X Ray Absorption ◽  
Partial Current ◽  
Modest Activity

Currently, the most active electrocatalysts for the conversion of CO2 to CO are gold-based nanomaterials, whereas non–precious metal catalysts have shown low to modest activity. Here, we report a catalyst of dispersed single-atom iron sites that produces CO at an overpotential as low as 80 millivolts. Partial current density reaches 94 milliamperes per square centimeter at an overpotential of 340 millivolts. Operando x-ray absorption spectroscopy revealed the active sites to be discrete Fe3+ ions, coordinated to pyrrolic nitrogen (N) atoms of the N-doped carbon support, that maintain their +3 oxidation state during electrocatalysis, probably through electronic coupling to the conductive carbon support. Electrochemical data suggest that the Fe3+ sites derive their superior activity from faster CO2 adsorption and weaker CO absorption than that of conventional Fe2+ sites.

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 Methanol conversion on borocarbonitride catalysts: Identification and quantification of active sites

2020 ◽  
Vol 6 (26) ◽  
pp. eaba5778 ◽  
Author(s):  
Xuefei Zhang ◽  
Pengqiang Yan ◽  
Junkang Xu ◽  
Fan Li ◽  
Felix Herold ◽  
...  
Keyword(s):  
Active Sites ◽  
Density Functional ◽  
Catalytic Mechanism ◽  
Reaction Pathway ◽  
Methanol Conversion ◽  
Kinetic Measurements ◽  
Catalytic Systems ◽  
X Ray Absorption ◽  
Further Development

Borocarbonitrides (BCNs) have emerged as highly selective catalysts for the oxidative dehydrogenation (ODH) reaction. However, there is a lack of in-depth understanding of the catalytic mechanism over BCN catalysts due to the complexity of the surface oxygen functional groups. Here, BCN nanotubes with multiple active sites are synthesized for oxygen-assisted methanol conversion reaction. The catalyst shows a notable activity improvement for methanol conversion (29%) with excellent selectivity to formaldehyde (54%). Kinetic measurements indicate that carboxylic acid groups on BCN are responsible for the formation of dimethyl ether, while the redox catalysis to formaldehyde occurs on both ketonic carbonyl and boron hydroxyl (B─OH) sites. The ODH reaction pathway on the B─OH site is further revealed by in situ infrared, x-ray absorption spectra, and density functional theory. The present work provides physical-chemical insights into the functional mechanism of BCN catalysts, paving the way for further development of the underexplored nonmetallic catalytic systems.

Discovery of main group single Sb–N4 active sites for CO2 electroreduction to formate with high efficiency

2020 ◽  
Vol 13 (9) ◽  
pp. 2856-2863 ◽  
Author(s):  
Zhuoli Jiang ◽  
Tao Wang ◽  
Jiajing Pei ◽  
Huishan Shang ◽  
Danni Zhou ◽  
...  
Keyword(s):  
Active Sites ◽  
High Efficiency ◽  
Main Group ◽  
Single Atom ◽  
Carbon Nanosheets ◽  
Co2 Electroreduction

We discover that an Sb single atom material consisting of Sb–N4 moieties anchored on N-doped carbon nanosheets can serve as a CO2RR catalyst to produce formate with high efficiency.

scholarly journals Redox Processes of Manganese Oxide in Catalyzing Oxygen Evolution and Reduction: An in Situ Soft X-ray Absorption Spectroscopy Study

2017 ◽  
Vol 121 (33) ◽  
pp. 17682-17692 ◽  
Author(s):  
Marcel Risch ◽  
Kelsey A. Stoerzinger ◽  
Binghong Han ◽  
Tom Z. Regier ◽  
Derek Peak ◽  
...  
Keyword(s):  
Manganese Oxide ◽  
Oxygen Evolution ◽  
Absorption Spectroscopy ◽  
Redox Processes ◽  
Spectroscopy Study ◽  
X Ray ◽  
X Ray Absorption

scholarly journals Photocatalytic degradation of trace CHCl3 in drinking water by nano TiO2

2020 ◽  
Author(s):  
T.-L. Hsiung ◽  
L.-W. Wei ◽  
H.-L. Huang ◽  
H. Paul Wang
Keyword(s):  
Drinking Water ◽  
Photocatalytic Degradation ◽  
Active Sites ◽  
Disinfection Byproducts ◽  
Active Species ◽  
Nano Tio2 ◽  
Edge Structure ◽  
Tio2 Photocatalysts ◽  
X Ray Absorption

Abstract Toxic disinfection byproducts such as trihalomethanes (CHCl3) are frequently found after chlorination for drinking water. Nano TiO2 which has been widely used for photocatalytic degradation of organic pollutants in wastewater, however, has relatively low effectiveness in the treatments of trace CHCl3. To engineer capable TiO2 photocatalysts, an understanding of their photoactive sites is of great importance and interest. By in situ X-ray absorption near edge structure (XANES) spectroscopy, photoactive sites such as A1 (4969 eV), A2 (4971 eV) and A3 (4972 eV) can be distinguished asfour-, five-, and six- coordinated Ti species, respectively in the nano-TiO2 (8.5 and 4.6 nm for TiO2 on SBA-15), TiO2 clusters (TiO2-SiO2), and highly atomic dispersed Ti (Ti-MCM-41) photocatalysts. It appears that the reactivity for the photocatalytic degradation of trace CHCl3 in drinking water lacks an expected relationship with the crystalline phase, band gap absorption edge, nor the particle size of the TiO2-based photocatalysts. Notably, the A2 sites being the main photocatalytic active species of the TiO2 may be accountable for the main (about 95%) photocatalytic degradation of trace CHCl3 in drinking water (7.2 ppm CHCl3/gTiO2∙hr). This work reveals that the A2 active sites of a TiO2-based photocatalyst are responsible for the photocatalytic reactivity, especially in photocatalytic degradation of CHCl3 in drinking water.

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