Non-precious metal catalysts(NPMCs)are promising low-cost alternatives of Pt/C for oxygen reduction reaction(ORR),which however suffer from serious stability challenge in the devices of proton-exchange-membrane fuel c...Non-precious metal catalysts(NPMCs)are promising low-cost alternatives of Pt/C for oxygen reduction reaction(ORR),which however suffer from serious stability challenge in the devices of proton-exchange-membrane fuel cells(PEMFC).Different from the traditional strategies of increasing the degree of graphitization of carbon substrates and using less Fenton-reactive metals,we prove here that proper regulation of coordination anions is also an effective way to improve the stability of NPMC.N/P cocoordinated Fe-Co dual-atomic-sites are constructed on ZIF-8 derived carbon support using a molecular precursor of C_(34)H_(28)Cl_(2)CoFeP_(2)and a“precursor-preselected”method.A composition of FeCoN_(5)P1 is infered for the dual-atom active site by microscopy and spectroscopy analysis.By comparing with N-coordinated references,we investigate the effect of P-coodination on the ORR catalysis of Fe-Co dual-atom catalysts in PEMFC.The metals in FeCoN_(5)P1 have the lower formation energy than those in the solo N-coordinated active sites of FeCoN6 and FeN_(4),and exhibits a much better fuel cell stability.This anion approach provides a new way to improve the stability of dual-atom catalysts.展开更多
Fe-N-C catalysts represent very promising cathode catalysts for polymer electrolyte fuel cells,owing to their outstanding activity for the oxygen reduction reaction(ORR),especially in alkaline media.In this review,we ...Fe-N-C catalysts represent very promising cathode catalysts for polymer electrolyte fuel cells,owing to their outstanding activity for the oxygen reduction reaction(ORR),especially in alkaline media.In this review,we summarize recent advances in the design and synthesis of Fe-N-C catalysts rich in highly dispersed FeNx active sites.Special emphasis is placed on emerging strategies for tuning the electronic structure of the Fe atoms to enhance the ORR activity,and also maximizing the surface concentration of FeNx sites that are catalytically accessible during ORR.While great progress has been made over the past 5 years in the development of Fe-N-C catalyst for ORR,significant technical obstacles still need to be overcome to enable the large-scale application of Fe-N-C materials as cathode catalysts in real-world fuel cells.展开更多
Contaminants(K,Na,Ca,and Mg)were introduced into Cu-SAPO-18 via incipient wetness impregnation to investigate their effect on the selective catalytic reduction of NOx with NH3(NH3-SCR)over Cu-SAPO-18.After the introdu...Contaminants(K,Na,Ca,and Mg)were introduced into Cu-SAPO-18 via incipient wetness impregnation to investigate their effect on the selective catalytic reduction of NOx with NH3(NH3-SCR)over Cu-SAPO-18.After the introduction of contaminants into Cu-SAPO-18,the quantity of acidic sites and Cu^2+ species in catalyst decreases owing to the replacement of H^+ and Cu^2+ by K^+,Na^+,Ca^2+,and Mg^2+.Furthermore,the loss of isolated Cu^2+ induces the generation of CuO and CuAl2O4-like phases,which causes further loss in the Brunauer-Emmett-Teller surface area of the catalyst.Consequently,the deNOx performance of the contaminated Cu-SAPO-18 catalysts drops.Such decline in NH3-SCR performance becomes more pronounced by increasing the contaminant contents from 0.5 to 1.0 mmol/gcatal.In addition,the deactivation influence of the contaminants on Cu-SAPO-18 is presented in the order of K>Na>Ca>Mg,which is consistent with the order of reduction of acidic sites.To a certain degree,the effect of the acidic sites on the deactivation of Cu-SAPO-18 might be more significant than that of isolated Cu2+ and the catalyst framework.Moreover,kinetic analysis of NH3-SCR was conducted,and the results indicate that there is no influence of contaminants on the NH3-SCR mechanism.展开更多
Nonprecious metal catalysts are known of significance for electrochemical N2 reduction reaction(NRR)of which the mechanism has been illustrated by ongoing investigations of single atom catalysis.However,it remains cha...Nonprecious metal catalysts are known of significance for electrochemical N2 reduction reaction(NRR)of which the mechanism has been illustrated by ongoing investigations of single atom catalysis.However,it remains challenging to fully understand the size-dependent synergistic effect of active sites inherited in substantial nanocatalysts.In this work,four types of small iron clusters Fen(n=1–4)supported on nitrogen-doped graphene sheets are constructed to figure out the size dependence and synergistic effect of active sites for NRR catalytic activities.It is revealed that Fe3 and Fe4 clusters on N4G supports exhibit higher NRR activity than single-iron atom and iron dimer clusters,showing lowered limiting potential and restricted hydrogen evolution reaction(HER)which is a competitive reaction channel.In particular,the Fe4-N4G displays outstanding NRR performance for“side-on”adsorption of N2 with a small limiting potential(−0.45 V).Besides the specific structure and strong interface interaction within the Fe4-N4G itself,the high NRR activity is associated with the unique bonding/antibonding orbital interactions of N-N and N-Fe for the adsorptive N2 and NNH intermediates,as well as relatively large charge transfer between N2 and the cluster Fe4-N4G.展开更多
The development of cost-effective,robust,and durable electrocatalysts to replace the expensive Pt-based catalysts towards oxygen reduction reaction(ORR)is the trending frontier research topic in renewable energy and e...The development of cost-effective,robust,and durable electrocatalysts to replace the expensive Pt-based catalysts towards oxygen reduction reaction(ORR)is the trending frontier research topic in renewable energy and electrocatalysis.Particular attention has been paid to metal-nitrogen-carbon(M-N-C)single atom catalysts(SACs)due to their maximized atom utilization efficiency,biomimetic active site,and distinct electronic structure.More importantly,their catalytic properties can be further tailored by rationally regulating the microenvironment of active sites(i.e.,M-N coordination number,heteroatom doping and substitution.Herein,we present a comprehensive summary of the recent advancement in the microenvironment regulation of MN-C SACs towards improved ORR performance.The coordination environment manipulation regarding central metal and coordinated atoms is first discussed,focusing on the structure-function relationship.Apart from the near-range coordination,longrange substrate modulation including heteroatom doping,defect engineering is discussed as well.Besides,the synergy mechanism of nanoparticles and single atom sites to tune the electron cloud density at the active sites is summarized.Finally,we provide the challenges and outlook of the development of M-N-C SACs.展开更多
Ammonia(NH_(3))is an important raw material for modern agriculture and industry,being widely demanded to sustain the sustainable development of modern society.Currently,the industrial production methods of NH_(3),such...Ammonia(NH_(3))is an important raw material for modern agriculture and industry,being widely demanded to sustain the sustainable development of modern society.Currently,the industrial production methods of NH_(3),such as the traditional Haber-Bosch process,have drawbacks including high energy consumption and significant carbon dioxide emissions.In recent years,the electrocatalytic nitrate reduction reaction(NO_(3)RR)powered by intermittent renewable energy sources has gradually become a multidisciplinary research hotspot,as it allows for the efficient synthesis of NH_(3)under mild conditions.In this review,we focus on the research of electrocatalysts with atomic-level site,which have attracted attention due to their extremely high atomic utilization efficiency and unique structural characteristics in the field of NO_(3)RR.Firstly,we introduce the mechanism of nitrate reduction for ammonia synthesis and discuss the in-situ characterization techniques related to the mechanism study.Secondly,we review the progress of the electrocatalysts with atomic-level site for nitrate reduction and explore the structure-activity relationship to guide the rational design of efficient catalysts.Lastly,the conclusions of this review and the challenges and prospective of this promising field are presented.展开更多
The high-temperature pyrolysis process for preparing M–N–C single-atom catalyst usually results in high heterogeneity in product structure concurrently contains multiscale metal phases from single atoms(SAs),atomic ...The high-temperature pyrolysis process for preparing M–N–C single-atom catalyst usually results in high heterogeneity in product structure concurrently contains multiscale metal phases from single atoms(SAs),atomic clusters to nanoparticles.Therefore,understanding the interactions among these components,especially the synergistic effects between single atomic sites and cluster sites,is crucial for improving the oxygen reduction reaction(ORR)activity of M–N–C catalysts.Accordingly,herein,we constructed a model catalyst composed of both atomically dispersed FeN4 SA sites and adjacent Fe clusters through a site occupation strategy.We found that the Fe clusters can optimize the adsorption strength of oxygen reduction intermediates on FeN4 SA sites by introducing electron-withdrawing–OH ligands and decreasing the d-band center of the Fe center.The as-developed catalyst exhibits encouraging ORR activity with halfwave potentials(E1/2)of 0.831 and 0.905 V in acidic and alkaline media,respectively.Moreover,the catalyst also represents excellent durability exceeding that of Fe–N–C SA catalyst.The practical application of Fe(Cd)–CNx catalyst is further validated by its superior activity and stability in a metalair battery device.Our work exhibits the great potential of synergistic effects between multiphase metal species for improvements of singleatom site catalysts.展开更多
Iron-nitrogen-carbon(Fe-N-C)catalysts for the oxygen reduction reaction(ORR)in proton exchange membrane fuel cells(PEMFCs)have seriously been hindered by their poor ORR performance of Fe-N-C due to the low active site...Iron-nitrogen-carbon(Fe-N-C)catalysts for the oxygen reduction reaction(ORR)in proton exchange membrane fuel cells(PEMFCs)have seriously been hindered by their poor ORR performance of Fe-N-C due to the low active site density(SD)and site utilization.Herein,we reported a melamine-assisted vapor deposition approach to overcome these hindrances.The melamine not only compensates for the loss of nitrogen caused by high-temperature pyrolysis but also effectively etches the carbon substrate,increasing the external surface area and mesoporous porosity of the carbon substrate.These can provide more useful area for subsequent vapor deposition on active sites.The prepared 0.20Mela-FeNC catalyst shows a fourfold higher SD value and site utilization than the FeNC without the treatment of melamine.As a result,0.20Mela-FeNC catalyst exhibits a high ORR activity with a half-wave potential(E_(1/2))of 0.861 V and 12-fold higher ORR mass activity than the FeNC in acidic media.As the cathode in a H_(2)-O_(2)PEMFCs,0.20Mela-FeNC catalyst demonstrates a high peak power density of 1.30 W cm^(-2),outstripping most of the reported Fe-N-C catalysts.The developed melamine-assisted vapor deposition approach for boosting the SD and utilization of Fe-N-C catalysts offers a new insight into high-performance ORR electrocatalysts.展开更多
Fe-N-C catalysts are widely considered as promising non-precious-metal candidates for electrocatalytic oxygen reduction reaction(ORR),Yet despite their high catalytic activity through rational modulation,challenges re...Fe-N-C catalysts are widely considered as promising non-precious-metal candidates for electrocatalytic oxygen reduction reaction(ORR),Yet despite their high catalytic activity through rational modulation,challenges remain in their low site density and unsatisfactory mass transfer structure.Herein,we present a structural engineering approach employing a soft-template coating strategy to fabricate a hollow and hierarchically porous N-doped carbon framework anchored with atomically dispersed Fe sites(FeNCh) as an efficient ORR catalyst.The combination of hierarchical porosity and high exterior surface area is proven crucial for exposing more active sites,which gives rise to a remarkable ORR performance with a half-wave potential of 0.902 V in 0.1 m KOH and 0.814 V in 0.1 m HClO_(4),significantly outperforming its counterpart with solid structure and dominance of micropores(FeNC-s).The mass transfer property is revealed by in-situ electrochemical impedance spectroscopy(EIS) measurement.The distribution of relaxation time(DRT) analysis is further introduced to deconvolve the kinetic and mass transport processes,which demonstrates an alleviated mass transport resistance for FeNC-h,validating the effectiveness of structural engineering.This work not only provides an effective structural engineering approach but also contributes to the comprehensive mass transfer evaluation on advanced electrocatalyst for energy conversion applications.展开更多
The development of nitrogen-rich biomass- derived carbon catalysts provides an attractive perspective to substitute for Pt-based electrocatalysts for oxygen reduction reaction （ORR）. We here report a facile strategy...The development of nitrogen-rich biomass- derived carbon catalysts provides an attractive perspective to substitute for Pt-based electrocatalysts for oxygen reduction reaction （ORR）. We here report a facile strategy for synthesis of a nitrogen-doped biocarbon/graphene-like composite electrocatalyst by pyrolyzing a solid-state mixture of coprinus comatus biomass and melamine under nitrogen protection. The graphtic carbon nitride formed by polycondensation of melamine at 600 ℃ acts as a self-sacrificing template to generate the nitrogen-doped graphene-like sheet, which can function as an inserting agent and self-generating support. The composite catalyst exhibits the most promising catalytic activity towards the four-electron ORR with a half-wave potential of around 0.83 V （vs. RHE）, and more excellent stability and tolerance to methanol/ethanol compared to the commercial Pt/C catalyst. It is interestingly found that both a higher content of nitrogen and a larger ratio of graphitic-nitrogen species, which may derive from self-addition of graphene-like support into the catalyst, can effectively improve theelectrocatalytic activity. The planar N group may be the nitrogen functionality that is most responsible for main-taining the ORR activity in alkaline medium. This study can largely encourage the exploration of high-performance carbon-based catalysts from economical and sustainable fungus biomass.展开更多
Fe-N-doped carbon materials(Fe-N-C)are promising candidates for oxygen reduction reaction(ORR)relative to Pt-based catalysts in proton exchange membrane fuel cells(PEMFCs).However,the intrinsic contributions of Fe-N_(...Fe-N-doped carbon materials(Fe-N-C)are promising candidates for oxygen reduction reaction(ORR)relative to Pt-based catalysts in proton exchange membrane fuel cells(PEMFCs).However,the intrinsic contributions of Fe-N_(4)moiety with different chemical/spin states(e.g.D1,D2,D3)to ORR are unclear since various states coexist inevitably.In the present work,Fe-N-C core-shell nanocatalyst with single lowspin Fe(Ⅱ)-N_(4)species(D1)is synthesized and identified with ex-situ ultralow temperature Mossbauer spectroscopy(T=1.6 K)that could essentially differentiate various Fe-N_(4)states and invisible Fe-O species.By quantifying with CO-pulse chemisorption,site density and turnover frequency of Fe-N-C catalysts reach 2.4×10^(-9)site g^(-1)and 23 e site~(-1)s^(-1)during the ORR,respectively.Half-wave potential(0.915V_(RHE))of the Fe-N-C catalyst is more positive(approximately 54 mV)than that of Pt/C.Moreover,we observe that the performance of PEMFCs on Fe-N-C almost achieves the 2025 target of the US Department of Energy by demonstrating a current density of 1.037 A cm^(-2)combined with the peak power density of 0,685 W cm^(-2),suggesting the critical role of Fe(Ⅱ)-N_(4)site(D1).After 500 h of running,PEMFCs still deliver a power density of 1.26 W cm^(-2)at 1.0 bar H_(2)-O_(2),An unexpected rate-determining step is figured out by isotopic labelling experiment and theoretical calculation.This work not only offers valuable insights regarding the intrinsic contribution of Fe-N_(4)with a single spin state to alkaline/acidic ORR,but also provides great opportunities for developing high-performance stable PEMFCs.展开更多
In the electrochemical process,Pt nanoparticles(NPs)in Pt-based catalysts usually agglomerate due to Oswald ripening or lack of restraint,ultimately resulting in reduction of the active sites and catalytic efficiency....In the electrochemical process,Pt nanoparticles(NPs)in Pt-based catalysts usually agglomerate due to Oswald ripening or lack of restraint,ultimately resulting in reduction of the active sites and catalytic efficiency.How to uniformly disperse and firmly fix Pt NPs on carbon matrix with suitable particle size for catalysis is still a big challenge.Herein,to prevent the agglomeration and shedding of Pt NPs,Ni species is introduced and are evenly dispersed in the surface of carbon matrix in the form of Ni-N-C active sites(Ni ZIF-NC).The Ni sites can be used to anchor Pt NPs,and then effectively limit the further growth and agglomeration of Pt NPs during the reaction process.Compared with commercial Pt/C catalyst,Pt@Ni ZIF-NC,with ultralow Pt loading(7 wt%)and ideal particle size(2.3 nm),not only increases the active center,but also promotes the catalysis kinetics,greatly improving the ORR and HER catalytic activity.Under acidic conditions,its half-wave potential(0.902 V)is superior to commercial Pt/C(0.861 V),and the mass activity(0.38 A per mg Pt)at 0.9 V is 4.7 times that of Pt/C(0.08 A per mg Pt).Besides,it also shows outstanding HER performance.At 20 and 30 mV,its mass activity is even 2 and 6 times that of Pt/C,respectively.Whether it is under ORR or HER conditions,it still shows excellent durability.These undoubtedly indicate the realization of dual-functional catalysts with low-Pt and high-efficiency properties.展开更多
The photocatalytic production of syngas using a noble-metal-free catalytic system is a promising approach for renewable energy and environmental sustainability.In this study,we demonstrate an efficient catalytic syste...The photocatalytic production of syngas using a noble-metal-free catalytic system is a promising approach for renewable energy and environmental sustainability.In this study,we demonstrate an efficient catalytic system formed by integrating Co single sites,which act as the active sites,in covalent triazine frameworks(CTFs),which act as the photoabsorber,for the photocatalytic production of syngas from CO2 in aqueous solution.The enhanced light absorption of the CTFs,which contain intramolecular heterojunctions,in conjunction with 0.8 mmol L^‒1 of the Co complex enables excellent syngas production with a yield of 3303μmol g‒1(CO:H2=1.4:1)in 10 h,which is about three times greater than that achieved using CTF without a heterojunction.In the photocatalytic reaction,the coordinated single Co centers accept the photogenerated electrons from the CTF,and serve as active sites for CO2 conversion through an adsorption-activation-reaction mechanism.Theoretical calculations further reveal that the intramolecular heterojunctions highly promote photogenerated charge separation,thus boosting photocatalytic syngas production.This work reveals the promising potential of CTFs for single-metal-site-based photocatalysis.展开更多
Recently,nitrogen-doped porous carbon supported single atom catalysts(SACs)have become one of the most promising alternatives to precious metal catalysts in oxygen reduction reaction(ORR)due to their outstanding perfo...Recently,nitrogen-doped porous carbon supported single atom catalysts(SACs)have become one of the most promising alternatives to precious metal catalysts in oxygen reduction reaction(ORR)due to their outstanding performance,especially those derived from porphyrin-based materials.However,most of them involve other metal residuals,which would cause the tedious pre-and/or post-treatment,even mislead the mechanistic investigations and active-site identification.Herein,we report a precursor-dilution strategy to synthesize Fe SACs through the Schiff-based reaction via co-polycondensation of amino-metalloporphyrin,followed by pyrolysis at high temperature.Systematic characterization results provide the compelling evidence of the dominant presence of atomically dispersed Fe-Nxspecies.Our catalyst shows superior ORR performance with positive half-wave potential(E1/2=0.85 V vs.RHE)in alkaline condition and moderate activity(E1/2=0.68 V vs.RHE)under the acidic condition,excellent methanol tolerance and good long-term stability.All the results indicate Fe SACs would be a promising candidate for replacing the precious Pt in metal-air batteries and fuel cells.展开更多
基金This work was supported by Natural Science Foundation of Beijing Municipality(No.Z200012)the National Natural Science Foundation of China(No.21975010).
文摘Non-precious metal catalysts(NPMCs)are promising low-cost alternatives of Pt/C for oxygen reduction reaction(ORR),which however suffer from serious stability challenge in the devices of proton-exchange-membrane fuel cells(PEMFC).Different from the traditional strategies of increasing the degree of graphitization of carbon substrates and using less Fenton-reactive metals,we prove here that proper regulation of coordination anions is also an effective way to improve the stability of NPMC.N/P cocoordinated Fe-Co dual-atomic-sites are constructed on ZIF-8 derived carbon support using a molecular precursor of C_(34)H_(28)Cl_(2)CoFeP_(2)and a“precursor-preselected”method.A composition of FeCoN_(5)P1 is infered for the dual-atom active site by microscopy and spectroscopy analysis.By comparing with N-coordinated references,we investigate the effect of P-coodination on the ORR catalysis of Fe-Co dual-atom catalysts in PEMFC.The metals in FeCoN_(5)P1 have the lower formation energy than those in the solo N-coordinated active sites of FeCoN6 and FeN_(4),and exhibits a much better fuel cell stability.This anion approach provides a new way to improve the stability of dual-atom catalysts.
基金support from the Ministry of Business,Innovation and Employment for a Catalyst Fund grant(MAUX 1609)the University of Auckland Faculty Research Development Fund,the MacDiarmid Institute for Advanced Materials and Nanotechnology,and a generous Philanthropic donation from Greg and Kathryn Trounson.The authors are also grateful for financial support from the National Key Projects for Fundamental Research and Development of China(2017YFA0206904,2017YFA0206900)+1 种基金the National Natural Science Foundation of China(51825205,51772305,21871279)the Beijing Natural Science Foundation(2191002).
文摘Fe-N-C catalysts represent very promising cathode catalysts for polymer electrolyte fuel cells,owing to their outstanding activity for the oxygen reduction reaction(ORR),especially in alkaline media.In this review,we summarize recent advances in the design and synthesis of Fe-N-C catalysts rich in highly dispersed FeNx active sites.Special emphasis is placed on emerging strategies for tuning the electronic structure of the Fe atoms to enhance the ORR activity,and also maximizing the surface concentration of FeNx sites that are catalytically accessible during ORR.While great progress has been made over the past 5 years in the development of Fe-N-C catalyst for ORR,significant technical obstacles still need to be overcome to enable the large-scale application of Fe-N-C materials as cathode catalysts in real-world fuel cells.
基金supported by the National Natural Science Foundation of China(21473064)~~
文摘Contaminants(K,Na,Ca,and Mg)were introduced into Cu-SAPO-18 via incipient wetness impregnation to investigate their effect on the selective catalytic reduction of NOx with NH3(NH3-SCR)over Cu-SAPO-18.After the introduction of contaminants into Cu-SAPO-18,the quantity of acidic sites and Cu^2+ species in catalyst decreases owing to the replacement of H^+ and Cu^2+ by K^+,Na^+,Ca^2+,and Mg^2+.Furthermore,the loss of isolated Cu^2+ induces the generation of CuO and CuAl2O4-like phases,which causes further loss in the Brunauer-Emmett-Teller surface area of the catalyst.Consequently,the deNOx performance of the contaminated Cu-SAPO-18 catalysts drops.Such decline in NH3-SCR performance becomes more pronounced by increasing the contaminant contents from 0.5 to 1.0 mmol/gcatal.In addition,the deactivation influence of the contaminants on Cu-SAPO-18 is presented in the order of K>Na>Ca>Mg,which is consistent with the order of reduction of acidic sites.To a certain degree,the effect of the acidic sites on the deactivation of Cu-SAPO-18 might be more significant than that of isolated Cu2+ and the catalyst framework.Moreover,kinetic analysis of NH3-SCR was conducted,and the results indicate that there is no influence of contaminants on the NH3-SCR mechanism.
基金This work was financially supported by the National Natural Science Foundation of China(Nos.21802146 and 21722308)CAS Key Research Project of Frontier Science(No.QYZDB-SSW-SLH024)Frontier Cross Project of National Laboratory for Molecular Sciences(No.051Z011BZ3).
文摘Nonprecious metal catalysts are known of significance for electrochemical N2 reduction reaction(NRR)of which the mechanism has been illustrated by ongoing investigations of single atom catalysis.However,it remains challenging to fully understand the size-dependent synergistic effect of active sites inherited in substantial nanocatalysts.In this work,four types of small iron clusters Fen(n=1–4)supported on nitrogen-doped graphene sheets are constructed to figure out the size dependence and synergistic effect of active sites for NRR catalytic activities.It is revealed that Fe3 and Fe4 clusters on N4G supports exhibit higher NRR activity than single-iron atom and iron dimer clusters,showing lowered limiting potential and restricted hydrogen evolution reaction(HER)which is a competitive reaction channel.In particular,the Fe4-N4G displays outstanding NRR performance for“side-on”adsorption of N2 with a small limiting potential(−0.45 V).Besides the specific structure and strong interface interaction within the Fe4-N4G itself,the high NRR activity is associated with the unique bonding/antibonding orbital interactions of N-N and N-Fe for the adsorptive N2 and NNH intermediates,as well as relatively large charge transfer between N2 and the cluster Fe4-N4G.
基金supported by the National Natural Science Foundation of China(No.22272161).
文摘The development of cost-effective,robust,and durable electrocatalysts to replace the expensive Pt-based catalysts towards oxygen reduction reaction(ORR)is the trending frontier research topic in renewable energy and electrocatalysis.Particular attention has been paid to metal-nitrogen-carbon(M-N-C)single atom catalysts(SACs)due to their maximized atom utilization efficiency,biomimetic active site,and distinct electronic structure.More importantly,their catalytic properties can be further tailored by rationally regulating the microenvironment of active sites(i.e.,M-N coordination number,heteroatom doping and substitution.Herein,we present a comprehensive summary of the recent advancement in the microenvironment regulation of MN-C SACs towards improved ORR performance.The coordination environment manipulation regarding central metal and coordinated atoms is first discussed,focusing on the structure-function relationship.Apart from the near-range coordination,longrange substrate modulation including heteroatom doping,defect engineering is discussed as well.Besides,the synergy mechanism of nanoparticles and single atom sites to tune the electron cloud density at the active sites is summarized.Finally,we provide the challenges and outlook of the development of M-N-C SACs.
基金financial support from the Postgraduate Research & Practice Innovation Program of Jiangsu Province (KYCX24_0690)financial support from the National Natural Science Foundation of China (Project No. 22275088, 52101260)+4 种基金the Project of Shuangchuang Scholar of Jiangsu Province (Project No. JSSCBS20210212)the Fundamental Research Funds for the Central Universities (Project No. 30921011203)the Start-Up Grant (Project No. AE89991/340) from Nanjing University of Science and Technologyfinancial support from the Foundation of Jiangsu Educational Committee (22KJB310008)the Senior Talent Program of Jiangsu University (20JDG073)
文摘Ammonia(NH_(3))is an important raw material for modern agriculture and industry,being widely demanded to sustain the sustainable development of modern society.Currently,the industrial production methods of NH_(3),such as the traditional Haber-Bosch process,have drawbacks including high energy consumption and significant carbon dioxide emissions.In recent years,the electrocatalytic nitrate reduction reaction(NO_(3)RR)powered by intermittent renewable energy sources has gradually become a multidisciplinary research hotspot,as it allows for the efficient synthesis of NH_(3)under mild conditions.In this review,we focus on the research of electrocatalysts with atomic-level site,which have attracted attention due to their extremely high atomic utilization efficiency and unique structural characteristics in the field of NO_(3)RR.Firstly,we introduce the mechanism of nitrate reduction for ammonia synthesis and discuss the in-situ characterization techniques related to the mechanism study.Secondly,we review the progress of the electrocatalysts with atomic-level site for nitrate reduction and explore the structure-activity relationship to guide the rational design of efficient catalysts.Lastly,the conclusions of this review and the challenges and prospective of this promising field are presented.
基金supported by the National Natural Science Foundation of China(22109100,22075203)Guangdong Basic and Applied Basic Research Foundation(2022A1515011677)+1 种基金Shenzhen Science and Technology Project Program(JCYJ2021032409420401)Natural Science Foundation of SZU(000002111605).
文摘The high-temperature pyrolysis process for preparing M–N–C single-atom catalyst usually results in high heterogeneity in product structure concurrently contains multiscale metal phases from single atoms(SAs),atomic clusters to nanoparticles.Therefore,understanding the interactions among these components,especially the synergistic effects between single atomic sites and cluster sites,is crucial for improving the oxygen reduction reaction(ORR)activity of M–N–C catalysts.Accordingly,herein,we constructed a model catalyst composed of both atomically dispersed FeN4 SA sites and adjacent Fe clusters through a site occupation strategy.We found that the Fe clusters can optimize the adsorption strength of oxygen reduction intermediates on FeN4 SA sites by introducing electron-withdrawing–OH ligands and decreasing the d-band center of the Fe center.The as-developed catalyst exhibits encouraging ORR activity with halfwave potentials(E1/2)of 0.831 and 0.905 V in acidic and alkaline media,respectively.Moreover,the catalyst also represents excellent durability exceeding that of Fe–N–C SA catalyst.The practical application of Fe(Cd)–CNx catalyst is further validated by its superior activity and stability in a metalair battery device.Our work exhibits the great potential of synergistic effects between multiphase metal species for improvements of singleatom site catalysts.
基金granted by the National Natural Science Foundation of China(22172134,22288102)the National Key Research and Development Program of China(2017YFA0206500)
文摘Iron-nitrogen-carbon(Fe-N-C)catalysts for the oxygen reduction reaction(ORR)in proton exchange membrane fuel cells(PEMFCs)have seriously been hindered by their poor ORR performance of Fe-N-C due to the low active site density(SD)and site utilization.Herein,we reported a melamine-assisted vapor deposition approach to overcome these hindrances.The melamine not only compensates for the loss of nitrogen caused by high-temperature pyrolysis but also effectively etches the carbon substrate,increasing the external surface area and mesoporous porosity of the carbon substrate.These can provide more useful area for subsequent vapor deposition on active sites.The prepared 0.20Mela-FeNC catalyst shows a fourfold higher SD value and site utilization than the FeNC without the treatment of melamine.As a result,0.20Mela-FeNC catalyst exhibits a high ORR activity with a half-wave potential(E_(1/2))of 0.861 V and 12-fold higher ORR mass activity than the FeNC in acidic media.As the cathode in a H_(2)-O_(2)PEMFCs,0.20Mela-FeNC catalyst demonstrates a high peak power density of 1.30 W cm^(-2),outstripping most of the reported Fe-N-C catalysts.The developed melamine-assisted vapor deposition approach for boosting the SD and utilization of Fe-N-C catalysts offers a new insight into high-performance ORR electrocatalysts.
基金National Natural Science Foundation of China (Nos. 22078242 and U20A20153)Applied Basic Research Program of Yunnan Province (Nos. 202101BE070001-032 and 202101BH070002)。
文摘Fe-N-C catalysts are widely considered as promising non-precious-metal candidates for electrocatalytic oxygen reduction reaction(ORR),Yet despite their high catalytic activity through rational modulation,challenges remain in their low site density and unsatisfactory mass transfer structure.Herein,we present a structural engineering approach employing a soft-template coating strategy to fabricate a hollow and hierarchically porous N-doped carbon framework anchored with atomically dispersed Fe sites(FeNCh) as an efficient ORR catalyst.The combination of hierarchical porosity and high exterior surface area is proven crucial for exposing more active sites,which gives rise to a remarkable ORR performance with a half-wave potential of 0.902 V in 0.1 m KOH and 0.814 V in 0.1 m HClO_(4),significantly outperforming its counterpart with solid structure and dominance of micropores(FeNC-s).The mass transfer property is revealed by in-situ electrochemical impedance spectroscopy(EIS) measurement.The distribution of relaxation time(DRT) analysis is further introduced to deconvolve the kinetic and mass transport processes,which demonstrates an alleviated mass transport resistance for FeNC-h,validating the effectiveness of structural engineering.This work not only provides an effective structural engineering approach but also contributes to the comprehensive mass transfer evaluation on advanced electrocatalyst for energy conversion applications.
基金supported by the Basic and Frontier Research Program of Chongqing Municipality (cstc2015jcyj A50032, cstc2014jcyj A50038)the Scientific and Technological Research Program of Chongqing Municipal Education Commission (KJ1501118)+1 种基金the Talent Introduction Project of Chongqing University of Arts and Sciences (R2014CJ02)the National Natural Science Foundation of China (21273292)
文摘The development of nitrogen-rich biomass- derived carbon catalysts provides an attractive perspective to substitute for Pt-based electrocatalysts for oxygen reduction reaction （ORR）. We here report a facile strategy for synthesis of a nitrogen-doped biocarbon/graphene-like composite electrocatalyst by pyrolyzing a solid-state mixture of coprinus comatus biomass and melamine under nitrogen protection. The graphtic carbon nitride formed by polycondensation of melamine at 600 ℃ acts as a self-sacrificing template to generate the nitrogen-doped graphene-like sheet, which can function as an inserting agent and self-generating support. The composite catalyst exhibits the most promising catalytic activity towards the four-electron ORR with a half-wave potential of around 0.83 V （vs. RHE）, and more excellent stability and tolerance to methanol/ethanol compared to the commercial Pt/C catalyst. It is interestingly found that both a higher content of nitrogen and a larger ratio of graphitic-nitrogen species, which may derive from self-addition of graphene-like support into the catalyst, can effectively improve theelectrocatalytic activity. The planar N group may be the nitrogen functionality that is most responsible for main-taining the ORR activity in alkaline medium. This study can largely encourage the exploration of high-performance carbon-based catalysts from economical and sustainable fungus biomass.
基金financial support from the“Hundred Talents Program”of the Chinese Academy of Sciencesthe“Young Talents Training Program”of the Shanghai Branch of the Chinese Academy of Sciences+3 种基金the financial support from the Xiamen City Natural Science Foundation of China(3502Z20227085,3502Z20227256)the National Science Youth Foundation of China(22202205)the Fujian Provincial Natural Science Foundation of China(2022J01502)Open Source Foundation of State Key Laboratory of Structural Chemistry。
文摘Fe-N-doped carbon materials(Fe-N-C)are promising candidates for oxygen reduction reaction(ORR)relative to Pt-based catalysts in proton exchange membrane fuel cells(PEMFCs).However,the intrinsic contributions of Fe-N_(4)moiety with different chemical/spin states(e.g.D1,D2,D3)to ORR are unclear since various states coexist inevitably.In the present work,Fe-N-C core-shell nanocatalyst with single lowspin Fe(Ⅱ)-N_(4)species(D1)is synthesized and identified with ex-situ ultralow temperature Mossbauer spectroscopy(T=1.6 K)that could essentially differentiate various Fe-N_(4)states and invisible Fe-O species.By quantifying with CO-pulse chemisorption,site density and turnover frequency of Fe-N-C catalysts reach 2.4×10^(-9)site g^(-1)and 23 e site~(-1)s^(-1)during the ORR,respectively.Half-wave potential(0.915V_(RHE))of the Fe-N-C catalyst is more positive(approximately 54 mV)than that of Pt/C.Moreover,we observe that the performance of PEMFCs on Fe-N-C almost achieves the 2025 target of the US Department of Energy by demonstrating a current density of 1.037 A cm^(-2)combined with the peak power density of 0,685 W cm^(-2),suggesting the critical role of Fe(Ⅱ)-N_(4)site(D1).After 500 h of running,PEMFCs still deliver a power density of 1.26 W cm^(-2)at 1.0 bar H_(2)-O_(2),An unexpected rate-determining step is figured out by isotopic labelling experiment and theoretical calculation.This work not only offers valuable insights regarding the intrinsic contribution of Fe-N_(4)with a single spin state to alkaline/acidic ORR,but also provides great opportunities for developing high-performance stable PEMFCs.
基金supported by the National Natural Science Foundation of China(22075223,51701146)the State Key Laboratory of Advanced Technology for Materials Synthesis and Processing(Wuhan University of Technology)(2021-ZD-4)。
文摘In the electrochemical process,Pt nanoparticles(NPs)in Pt-based catalysts usually agglomerate due to Oswald ripening or lack of restraint,ultimately resulting in reduction of the active sites and catalytic efficiency.How to uniformly disperse and firmly fix Pt NPs on carbon matrix with suitable particle size for catalysis is still a big challenge.Herein,to prevent the agglomeration and shedding of Pt NPs,Ni species is introduced and are evenly dispersed in the surface of carbon matrix in the form of Ni-N-C active sites(Ni ZIF-NC).The Ni sites can be used to anchor Pt NPs,and then effectively limit the further growth and agglomeration of Pt NPs during the reaction process.Compared with commercial Pt/C catalyst,Pt@Ni ZIF-NC,with ultralow Pt loading(7 wt%)and ideal particle size(2.3 nm),not only increases the active center,but also promotes the catalysis kinetics,greatly improving the ORR and HER catalytic activity.Under acidic conditions,its half-wave potential(0.902 V)is superior to commercial Pt/C(0.861 V),and the mass activity(0.38 A per mg Pt)at 0.9 V is 4.7 times that of Pt/C(0.08 A per mg Pt).Besides,it also shows outstanding HER performance.At 20 and 30 mV,its mass activity is even 2 and 6 times that of Pt/C,respectively.Whether it is under ORR or HER conditions,it still shows excellent durability.These undoubtedly indicate the realization of dual-functional catalysts with low-Pt and high-efficiency properties.
文摘The photocatalytic production of syngas using a noble-metal-free catalytic system is a promising approach for renewable energy and environmental sustainability.In this study,we demonstrate an efficient catalytic system formed by integrating Co single sites,which act as the active sites,in covalent triazine frameworks(CTFs),which act as the photoabsorber,for the photocatalytic production of syngas from CO2 in aqueous solution.The enhanced light absorption of the CTFs,which contain intramolecular heterojunctions,in conjunction with 0.8 mmol L^‒1 of the Co complex enables excellent syngas production with a yield of 3303μmol g‒1(CO:H2=1.4:1)in 10 h,which is about three times greater than that achieved using CTF without a heterojunction.In the photocatalytic reaction,the coordinated single Co centers accept the photogenerated electrons from the CTF,and serve as active sites for CO2 conversion through an adsorption-activation-reaction mechanism.Theoretical calculations further reveal that the intramolecular heterojunctions highly promote photogenerated charge separation,thus boosting photocatalytic syngas production.This work reveals the promising potential of CTFs for single-metal-site-based photocatalysis.
基金supported by the National Natural Science Foundation of China(21938001、21606260、21576302、21376278、21425627、21701199)the National Natural Science Foundation of ChinaSINOPEC Joint Fund(U1663220)+2 种基金the Local Innovative and Research Teams Project of Guangdong Pearl River Talents Program(2017BT01C102)the Natural Science Foundation of Guang-dong Province(2015A030313104)the Fundamental Research Funds for the Central Universities of Sun Yat-sen University(15lgjc33、19lgpy129)。
文摘Recently,nitrogen-doped porous carbon supported single atom catalysts(SACs)have become one of the most promising alternatives to precious metal catalysts in oxygen reduction reaction(ORR)due to their outstanding performance,especially those derived from porphyrin-based materials.However,most of them involve other metal residuals,which would cause the tedious pre-and/or post-treatment,even mislead the mechanistic investigations and active-site identification.Herein,we report a precursor-dilution strategy to synthesize Fe SACs through the Schiff-based reaction via co-polycondensation of amino-metalloporphyrin,followed by pyrolysis at high temperature.Systematic characterization results provide the compelling evidence of the dominant presence of atomically dispersed Fe-Nxspecies.Our catalyst shows superior ORR performance with positive half-wave potential(E1/2=0.85 V vs.RHE)in alkaline condition and moderate activity(E1/2=0.68 V vs.RHE)under the acidic condition,excellent methanol tolerance and good long-term stability.All the results indicate Fe SACs would be a promising candidate for replacing the precious Pt in metal-air batteries and fuel cells.
