The Evolution Pathway from Iron Compounds to Fe1(II)-N4 Sites Through Gas-Phase Iron During Pyrolysis

<div> <div> <div> <p>Pyrolysis is indispensable for synthesizing highly active Fe-N-C catalysts for the oxygen reduction reaction (ORR) in acid, but how Fe, N, and C precursors transform to ORR-active sites during pyrolysis remains unclear. This knowledge gap ob- scures the connections between the input precursors and output products, clouding the pathway toward Fe-N-C catalyst improve- ment. Herein, we unravel the evolution pathway of precursors to ORR-active catalyst comprised exclusively of single atom Fe1(II)- N4 sites via in-temperature X-ray absorption spectroscopy. The Fe precursor transforms to Fe oxides below 300 °C, and then to tetrahedral Fe1(II)-O4 via a crystal-to-melt-like transformation below 600 °C. The Fe1(II)-O4 releases a single Fe atom that flows into the N-doped carbon defect forming Fe1(II)-N4 above 600 °C. This vapor phase single Fe atom transport mechanism is verified by synthesizing Fe1(II)-N4 sites via “non-contact pyrolysis” wherein the Fe precursor is not in physical contact with the N and C precursors during pyrolysis. </p> </div> </div> </div>

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

10.26434/chemrxiv.8131235.v1 ◽

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.

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

10.26434/chemrxiv.8131235 ◽

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.

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Atomically dispersed Fe3+ sites catalyze efficient CO2 electroreduction to CO

Science ◽

10.1126/science.aaw7515 ◽

2019 ◽

Vol 364 (6445) ◽

pp. 1091-1094 ◽

Cited By ~ 284

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.

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Investigation of Highly Active PtCo Nanocatalyts by X-ray Absorption Spectroscopy and its Application towards Oxygen Reduction Reaction

ECS Meeting Abstracts ◽

10.1149/ma2013-01/8/445 ◽

2013 ◽

Keyword(s):

Oxygen Reduction Reaction ◽

Oxygen Reduction ◽

Absorption Spectroscopy ◽

Reduction Reaction ◽

X Ray ◽

Highly Active ◽

X Ray Absorption

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Secondary-Atom-Doping Enables Robust Fe–N–C Single-Atom Catalysts with Enhanced Oxygen Reduction Reaction

Nano-Micro Letters ◽

10.1007/s40820-020-00502-5 ◽

2020 ◽

Vol 12 (1) ◽

Cited By ~ 3

Author(s):

Xin Luo ◽

Xiaoqian Wei ◽

Hengjia Wang ◽

Wenling Gu ◽

Takuma Kaneko ◽

...

Keyword(s):

Active Sites ◽

Reduction Reaction ◽

Single Atom ◽

General Strategy ◽

Carbon Supports ◽

Coordination Environment ◽

Energy Devices ◽

Highly Active ◽

Half Wave ◽

Secondary Doping

AbstractSingle-atom catalysts (SACs) with nitrogen-coordinated nonprecious metal sites have exhibited inimitable advantages in electrocatalysis. However, a large room for improving their activity and durability remains. Herein, we construct atomically dispersed Fe sites in N-doped carbon supports by secondary-atom-doped strategy. Upon the secondary doping, the density and coordination environment of active sites can be efficiently tuned, enabling the simultaneous improvement in the number and reactivity of the active site. Besides, structure optimizations in terms of the enlarged surface area and improved hydrophilicity can be achieved simultaneously. Due to the beneficial microstructure and abundant highly active FeN5 moieties resulting from the secondary doping, the resultant catalyst exhibits an admirable half-wave potential of 0.81 V versus 0.83 V for Pt/C and much better stability than Pt/C in acidic media. This work would offer a general strategy for the design and preparation of highly active SACs for electrochemical energy devices.

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Probe active sites of heterogeneous electrocatalysts by X-ray absorption spectroscopy: From single atom to complex multi-element composites

Current Opinion in Electrochemistry ◽

10.1016/j.coelec.2018.09.011 ◽

2019 ◽

Vol 14 ◽

pp. 7-15 ◽

Cited By ~ 7

Author(s):

Hao Zhang ◽

Xiaopeng Li ◽

Zheng Jiang

Keyword(s):

Absorption Spectroscopy ◽

Active Sites ◽

Single Atom ◽

X Ray ◽

X Ray Absorption

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GAS PHASE X-RAY ABSORPTION SPECTROSCOPY WITH AN ELECTRON YIELD DETECTOR

Le Journal de Physique Colloques ◽

10.1051/jphyscol:1986827 ◽

1986 ◽

Vol 47 (C8) ◽

pp. C8-149-C8-151

Author(s):

F. W. LYTLE ◽

R. B. GREEGOR ◽

G. H. VIA ◽

J. M. BROWN ◽

G. MEITZNER

Keyword(s):

Gas Phase ◽

Absorption Spectroscopy ◽

X Ray ◽

Electron Yield ◽

X Ray Absorption

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Searching novel complex solid solution electrocatalysts in unconventional element combinations

Nano Research ◽

10.1007/s12274-021-3637-z ◽

2021 ◽

Author(s):

Olga A. Krysiak ◽

Simon Schumacher ◽

Alan Savan ◽

Wolfgang Schuhmann ◽

Alfred Ludwig ◽

...

Keyword(s):

High Throughput ◽

High Throughput Screening ◽

Active Sites ◽

Search Space ◽

Reduction Reaction ◽

Film Material ◽

X Ray ◽

High Entropy ◽

Catalyst Composition ◽

Scanning Transmission

AbstractDespite outstanding accomplishments in catalyst discovery, finding new, more efficient, environmentally neutral, and noble metal-free catalysts remains challenging and unsolved. Recently, complex solid solutions consisting of at least five different elements and often named as high-entropy alloys have emerged as a new class of electrocatalysts for a variety of reactions. The multicomponent combinations of elements facilitate tuning of active sites and catalytic properties. Predicting optimal catalyst composition remains difficult, making testing of a very high number of them indispensable. We present the high-throughput screening of the electrochemical activity of thin film material libraries prepared by combinatorial co-sputtering of metals which are commonly used in catalysis (Pd, Cu, Ni) combined with metals which are not commonly used in catalysis (Ti, Hf, Zr). Introducing unusual elements in the search space allows discovery of catalytic activity for hitherto unknown compositions. Material libraries with very similar composition spreads can show different activities vs. composition trends for different reactions. In order to address the inherent challenge of the huge combinatorial material space and the inability to predict active electrocatalyst compositions, we developed a high-throughput process based on co-sputtered material libraries, and performed high-throughput characterization using energy dispersive X-ray spectroscopy (EDS), scanning transmission electron microscopy (SEM), X-ray diffraction (XRD) and conductivity measurements followed by electrochemical screening by means of a scanning droplet cell. The results show surprising material compositions with increased activity for the oxygen reduction reaction and the hydrogen evolution reaction. Such data are important input data for future data-driven materials prediction.

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