The Fe-N-C material represents an attractive oxygen reduction reaction electrocatalyst,and the FeN_(4)moiety has been identified as a very competitive catalytic active site.Fine tuning of the coordination structure of...The Fe-N-C material represents an attractive oxygen reduction reaction electrocatalyst,and the FeN_(4)moiety has been identified as a very competitive catalytic active site.Fine tuning of the coordination structure of FeN_(4)has an essential impact on the catalytic performance.Herein,we construct a sulfur-modified Fe-N-C catalyst with controllable local coordination environment,where the Fe is coordinated with four in-plane N and an axial external S.The external S atom affects not only the electron distribution but also the spin state of Fe in the FeN_(4)active site.The appearance of higher valence states and spin states for Fe demonstrates the increase in unpaired electrons.With the above characteristics,the adsorption and desorption of the reactants at FeN_(4)active sites are optimized,thus promoting the oxygen reduction reaction activity.This work explores the key point in electronic configuration and coordination environment tuning of FeN_(4)through S doping and provides new insight into the construction of M-N-C-based oxygen reduction reaction catalysts.展开更多
Fe-N-C electrocatalysts,comprising FeN_(4) single atom sites immobilized on N-doped carbon supports,offer excellent activity in the oxygen reduction reaction(ORR),especially in alkaline solution.Herein,we report a sim...Fe-N-C electrocatalysts,comprising FeN_(4) single atom sites immobilized on N-doped carbon supports,offer excellent activity in the oxygen reduction reaction(ORR),especially in alkaline solution.Herein,we report a simple synthetic strategy for improving the accessibility of FeN_(4) sites during ORR and simultaneously fine-tuning the microenvironment of FeN_(4) sites,thus enhancing the ORR activity.Our approach involved a simple one-step pyrolysis of a Fe-containing zeolitic imidazolate framework in the presence of NaCl,yielding a hierarchically porous Fe-N-C electrocatalyst containing tailored FeN_(4) sites with slightly elongated Fe-N bond distances and reduced Fe charge.The porous carbon structure improved mass transport during ORR,whilst the microenvironment optimized FeN_(4) sites benefitted the adsorption/desorption of ORR intermediates.Accordingly,the developed electrocatalyst,possessing a high FeN_(4) site density(9.9×10^(19) sites g^(-1))and turnover frequency(2.26 s^(-1)),delivered remarkable ORR performance with a low overpotential(a half-wave potential of 0.90 V vs.reversible hydrogen electrode)in 0.1 mol L^(-1) KOH.展开更多
Over recent years,catalytic materials of Fe-N-C species have been recognized being active for oxygen reduction reaction(ORR).However,the identification of active site remains challenging as it generally involves a pyr...Over recent years,catalytic materials of Fe-N-C species have been recognized being active for oxygen reduction reaction(ORR).However,the identification of active site remains challenging as it generally involves a pyrolysis process and mixed components being obtained.Herein Fe_(3)C/C and Fe_(2)N/C samples were synthesized by temperature programmed reduction of Fe precursors in 15%CH_(4)/H_(2)and pure NH_(3),respectively.By acid leaching of Fe_(2)N/C sample,only single sites of FeN_(4)species were presented,providing an ideal model for identification of catalytic functions of the single sites of FeN_(4)in ORR.A correlation was conducted between the concentration of Fe^(Ⅱ)N_(4)in low spin state by Mossbauer spectra and the kinetic current density at 0.8 V in alkaline media,and such a structure-performance correlation assures the catalytic roles of low spin Fe^(Ⅱ)N_(4) species as highly active sites for the ORR.展开更多
The distance effect of the doped heteroatoms away from the catalytic centers has rarely been reported.In this work,we conducted density functional theory calculations to thoroughly investigate the influence of heteroa...The distance effect of the doped heteroatoms away from the catalytic centers has rarely been reported.In this work,we conducted density functional theory calculations to thoroughly investigate the influence of heteroatom(N,P,B,and S atoms)doping distance on the oxygen reduction reaction(ORR)activity of graphene-based FeN_(4)sites.We uncovered a Sabatier-like relationship between heteroatom doping distance and ORR activity of FeN_(4)sites.The nearest doping does not significantly improve and even block the ORR activity of FeN_(4)sites.Optimal ORR activity is achieved when the heteroatoms are 4-5Å(N,P,and S atoms)or 6-7Å(B atoms)away from the Fe atoms.Analysis of electronic structure indicates that distance effect can modulate the local chemical environment of Fe atoms,thereby account for the changes in ORR activity along with the doping distance and doping atoms.This study provides insights into the influence of heteroatom doping on the chemical environment of reaction active centers,and provides the theoretical guidance for controlling the doping distance of heteroatoms to achieve optimal catalytic activity and selectivity.展开更多
基金supported by the National Key Research and Development Program of China(Grant No.2020YFA0715000)the National Natural Science Foundation of China(Grant No.52127816)+2 种基金supported by the U.S.Department of Energy(DOE),Office of Energy Efficiency and Renewable Energy,Vehicle Technologies Officethe DOE Office of Science by UChicago Argonne LLC under contract no.DE-AC02-06CH11357the Advanced Photon Source(APS),a U.S.Department of Energy(DOE)Office of Science User Facility,operated for the DOE Office of Science by Argonne National Laboratory under Contract No.DE-AC02-06CH11357
文摘The Fe-N-C material represents an attractive oxygen reduction reaction electrocatalyst,and the FeN_(4)moiety has been identified as a very competitive catalytic active site.Fine tuning of the coordination structure of FeN_(4)has an essential impact on the catalytic performance.Herein,we construct a sulfur-modified Fe-N-C catalyst with controllable local coordination environment,where the Fe is coordinated with four in-plane N and an axial external S.The external S atom affects not only the electron distribution but also the spin state of Fe in the FeN_(4)active site.The appearance of higher valence states and spin states for Fe demonstrates the increase in unpaired electrons.With the above characteristics,the adsorption and desorption of the reactants at FeN_(4)active sites are optimized,thus promoting the oxygen reduction reaction activity.This work explores the key point in electronic configuration and coordination environment tuning of FeN_(4)through S doping and provides new insight into the construction of M-N-C-based oxygen reduction reaction catalysts.
基金supported by a James Cook Research Fellowship,administered by the Royal Society Te Apārangifunding support from Greg and Kathryn Trounson,the Energy Education Trust of New Zealand,the Mac Diarmid Institute for Advanced Materials and Nanotechnology,the National Key Projects for Fundamental Research and Development of China(2017YFA0206904 and 2017YFA0206900)+1 种基金the National Natural Science Foundation of China(51825205 and 21871279)the Beijing Natural Science Foundation(2191002)。
文摘Fe-N-C electrocatalysts,comprising FeN_(4) single atom sites immobilized on N-doped carbon supports,offer excellent activity in the oxygen reduction reaction(ORR),especially in alkaline solution.Herein,we report a simple synthetic strategy for improving the accessibility of FeN_(4) sites during ORR and simultaneously fine-tuning the microenvironment of FeN_(4) sites,thus enhancing the ORR activity.Our approach involved a simple one-step pyrolysis of a Fe-containing zeolitic imidazolate framework in the presence of NaCl,yielding a hierarchically porous Fe-N-C electrocatalyst containing tailored FeN_(4) sites with slightly elongated Fe-N bond distances and reduced Fe charge.The porous carbon structure improved mass transport during ORR,whilst the microenvironment optimized FeN_(4) sites benefitted the adsorption/desorption of ORR intermediates.Accordingly,the developed electrocatalyst,possessing a high FeN_(4) site density(9.9×10^(19) sites g^(-1))and turnover frequency(2.26 s^(-1)),delivered remarkable ORR performance with a low overpotential(a half-wave potential of 0.90 V vs.reversible hydrogen electrode)in 0.1 mol L^(-1) KOH.
基金the National Key R&D Program of China(No.2017YFA0700103)the National Natural Science Foundation of China(Nos.21932002,21872014,21707015,21902018,21577013)+1 种基金the Postdoctoral Science Foundation of China(Nos.2019 T 120210,2018M 641687)the Natural Science Foundation of Liaoning Province(No.2019-MS-053).
文摘Over recent years,catalytic materials of Fe-N-C species have been recognized being active for oxygen reduction reaction(ORR).However,the identification of active site remains challenging as it generally involves a pyrolysis process and mixed components being obtained.Herein Fe_(3)C/C and Fe_(2)N/C samples were synthesized by temperature programmed reduction of Fe precursors in 15%CH_(4)/H_(2)and pure NH_(3),respectively.By acid leaching of Fe_(2)N/C sample,only single sites of FeN_(4)species were presented,providing an ideal model for identification of catalytic functions of the single sites of FeN_(4)in ORR.A correlation was conducted between the concentration of Fe^(Ⅱ)N_(4)in low spin state by Mossbauer spectra and the kinetic current density at 0.8 V in alkaline media,and such a structure-performance correlation assures the catalytic roles of low spin Fe^(Ⅱ)N_(4) species as highly active sites for the ORR.
文摘The distance effect of the doped heteroatoms away from the catalytic centers has rarely been reported.In this work,we conducted density functional theory calculations to thoroughly investigate the influence of heteroatom(N,P,B,and S atoms)doping distance on the oxygen reduction reaction(ORR)activity of graphene-based FeN_(4)sites.We uncovered a Sabatier-like relationship between heteroatom doping distance and ORR activity of FeN_(4)sites.The nearest doping does not significantly improve and even block the ORR activity of FeN_(4)sites.Optimal ORR activity is achieved when the heteroatoms are 4-5Å(N,P,and S atoms)or 6-7Å(B atoms)away from the Fe atoms.Analysis of electronic structure indicates that distance effect can modulate the local chemical environment of Fe atoms,thereby account for the changes in ORR activity along with the doping distance and doping atoms.This study provides insights into the influence of heteroatom doping on the chemical environment of reaction active centers,and provides the theoretical guidance for controlling the doping distance of heteroatoms to achieve optimal catalytic activity and selectivity.
