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.

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 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 Electronic regulation of Ni single atom by confined Ni nanoparticles for fast and energy-efficient CO2 electroreduction

2021 ◽  
Author(s):  
Wenhao Ren ◽  
Xin Tan ◽  
Chen Jia ◽  
Anna Krammer ◽  
Qian Sun ◽  
...  
Keyword(s):  
Active Sites ◽  
Cell Voltage ◽  
Single Atom ◽  
Ni Nanoparticles ◽  
Precious Metal Catalysts ◽  
Co Conversion ◽  
Co2 Electroreduction ◽  
Enhanced Adsorption ◽  
Direct Solid ◽  
Nanoparticle Catalyst

Abstract Electrocatalytic CO2 to CO conversion is approaching the industrial benchmark. Currently, Au electrodes show the best performance, whereas non-precious metal catalysts exhibit inferior activity. Here we show a densely populated Ni single-atom on nanoparticle catalyst (NiSA/NP) via direct solid-sate pyrolysis, where Ni nanoparticles donate electrons to Ni(i)-N-C sites via carbon nanotubes network, achieves a high CO current of 352 mA cm− 2 at -0.55 V vs RHE in an alkaline flow cell. When coupled with a NiFe-based oxygen evolution anode into a zero-gap membrane electrolyser, it delivers an industrial-relevant CO current of 310 mA cm− 2 at a low cell voltage of -2.3 V, corresponding to an overall energy efficiency of 57%. The superior CO2 electroreduction performance is attributed to the enhanced adsorption of key intermediate COOH* on electron-rich Ni single atom, together with the dense active sites.

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 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 Electronic regulation of Ni single atom by confined Ni nanoparticles for fast and energy-efficient CO2 electroreduction

2021 ◽  
Author(s):  
Wenhao Ren ◽  
Xin Tan ◽  
Chen Jia ◽  
Anna Krammer ◽  
Qian Sun ◽  
...  
Keyword(s):  
Active Sites ◽  
Cell Voltage ◽  
Single Atom ◽  
Ni Nanoparticles ◽  
Precious Metal Catalysts ◽  
Co Conversion ◽  
Co2 Electroreduction ◽  
Enhanced Adsorption ◽  
Direct Solid ◽  
Nanoparticle Catalyst

Abstract Electrocatalytic CO2 to CO conversion is approaching the industrial benchmark. Currently, Au electrodes show the best performance, whereas non-precious metal catalysts exhibit inferior activity. Here we show a densely populated Ni single-atom on nanoparticle catalyst (NiSA/NP) via direct solid-sate pyrolysis, where Ni nanoparticles donate electrons to Ni(i)-N-C sites via carbon nanotubes network, achieves a high CO current of 352 mA cm−2 at -0.55 V vs RHE in an alkaline flow cell. When coupled with a NiFe-based oxygen evolution anode into a zero-gap membrane electrolyser, it delivers an industrial-relevant CO current of 310 mA cm−2 at a low cell voltage of -2.3 V, corresponding to an overall energy efficiency of 57%. The superior CO2 electroreduction performance is attributed to the enhanced adsorption of key intermediate COOH* on electron-rich Ni single atom, together with the dense active sites.

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

2019 ◽  
Author(s):  
Jingkun Li ◽  
Li Jiao ◽  
Evan Wegener ◽  
Lynne K. LaRochelle Richard ◽  
Ershuai Liu ◽  
...  
Keyword(s):  
Gas Phase ◽  
Active Sites ◽  
Active Catalyst ◽  
Reduction Reaction ◽  
Physical Contact ◽  
Single Atom ◽  
Iron Compounds ◽  
X Ray ◽  
Highly Active ◽  
X Ray Absorption

<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>

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

2019 ◽  
Author(s):  
Jingkun Li ◽  
Li Jiao ◽  
Evan Wegener ◽  
Lynne K. LaRochelle Richard ◽  
Ershuai Liu ◽  
...  
Keyword(s):  
Gas Phase ◽  
Active Sites ◽  
Active Catalyst ◽  
Reduction Reaction ◽  
Physical Contact ◽  
Single Atom ◽  
Iron Compounds ◽  
X Ray ◽  
Highly Active ◽  
X Ray Absorption

<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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