The nitrogen-coordinated metal single-atom catalysts(M−N−C SACs)with an ultra-high metal loading synthetized by direct high-temperature pyrolysis have been widely reported.However,most of metal single atoms in these c...The nitrogen-coordinated metal single-atom catalysts(M−N−C SACs)with an ultra-high metal loading synthetized by direct high-temperature pyrolysis have been widely reported.However,most of metal single atoms in these catalysts were buried in the carbon matrix,resulting in a low metal utilization and inaccessibility for adsorption of reactants during the catalytic process.Herein,we reported a facile synthesis based on the hard-soft acid-base(HSAB)theory to fabricate Co single-atom catalysts with highly exposed metal atoms ligated to the external pyridinic-N sites of a nitrogen-doped carbon support.Benefiting from the highly accessible Co active sites,the prepared Co−N−C SAC exhibited a superior oxygen reduction reactivity comparable to that of the commercial Pt/C catalyst,showing a high turnover frequency(TOF)of 0.93 e^(−)·s^(-1)·site^(-1)at 0.85 V vs.RHE,far exceeding those of some representative SACs with a ultra-high metal content.This work provides a rational strategy to design and prepare M−N−C single-atom catalysts featured with high site-accessibility and site-density.展开更多
The weak adsorption energy of oxygen-containing intermediates on Co center leads to a considerable performance dis-parity between Co-N-C and costly Pt benchmark in catalyzing oxygen reduction reaction(ORR).In this wor...The weak adsorption energy of oxygen-containing intermediates on Co center leads to a considerable performance dis-parity between Co-N-C and costly Pt benchmark in catalyzing oxygen reduction reaction(ORR).In this work,we strategi-cally engineer the active site structure of Co-N-C via B substitution,which is accomplished by the pyrolysis of ammonium borate.During this process,the in-situ generated NH_(3)gas plays a critical role in creating surface defects and boron atoms substituting nitrogen atoms in the carbon structure.The well-designed CoB_(1)N_(3)active site endows Co with higher charge density and stronger adsorption energy toward oxygen species,potentially accelerating ORR kinetics.As expected,the resulting Co-B/N-C catalyst exhibited superior ORR performance over Co-N-C counterpart,with 40 mV,and fivefold en-hancement in half-wave potential and turnover frequency(TOF).More importantly,the excellent ORR performance could be translated into membrane electrode assembly(MEA)in a fuel cell test,delivering an impressive peak power density of 824 mW·cm^(-2),which is currently the best among Co-based catalysts under the same conditions.This work not only demon-strates an effective method for designing advanced catalysts,but also affords a highly promising non-precious metal ORR electrocatalyst for fuel cell applications.展开更多
Pot grown alfalfa (Medicago sativa L.) were experimented in the open top chambers in which natural air(350×10 -6 ,1×CO 2) and doubled CO 2 air(700×10 -6 ,2×CO 2) were continuous blown through botto...Pot grown alfalfa (Medicago sativa L.) were experimented in the open top chambers in which natural air(350×10 -6 ,1×CO 2) and doubled CO 2 air(700×10 -6 ,2×CO 2) were continuous blown through bottom respectively.Results showed that the biomass in both shoot and root was increased by the 2×CO 2 treatment.The root/shoot ratio was nearly unchange in the short term treatment and slightly decreased in the longer term treatment.The results differed from those reported in literatures that was attributed to the pot grown condition in this experiment.The nitrogen fixation activities(acetylene reduction) per plant were obviously promoted under the 2×CO 2 condition but the difference of the specific nitrogen fixing activities between 1×CO 2 and 2×CO 2 treatment was small.It implied that supplement of ATP,NADP or carbon skeleton under the 2×CO 2 condition was not more than that under the 1×CO 2 condition. C/N ratio in the shoot increased in the doubled CO 2 treatment group,similar to the reports from other authors;but the ratio increased in the root in the 2×CO 2 treatment group was ascribed to the higher nitrogen absorption from the soil and(or) N fixing activity of the nodules as compared with that in the 1×CO 2 treatment.The results demonstrated that assimilation and allocation of carbon and nitrogen in legume plant were deeply influenced by the elevated CO 2.展开更多
基金supported by Shanxi Province Science Foundation for Youths(202203021212300)Taiyuan University of Science and Technology Scientific Research Initial Funding(20212064)Outstanding Doctoral Award Fund in Shanxi Province(20222060).
文摘The nitrogen-coordinated metal single-atom catalysts(M−N−C SACs)with an ultra-high metal loading synthetized by direct high-temperature pyrolysis have been widely reported.However,most of metal single atoms in these catalysts were buried in the carbon matrix,resulting in a low metal utilization and inaccessibility for adsorption of reactants during the catalytic process.Herein,we reported a facile synthesis based on the hard-soft acid-base(HSAB)theory to fabricate Co single-atom catalysts with highly exposed metal atoms ligated to the external pyridinic-N sites of a nitrogen-doped carbon support.Benefiting from the highly accessible Co active sites,the prepared Co−N−C SAC exhibited a superior oxygen reduction reactivity comparable to that of the commercial Pt/C catalyst,showing a high turnover frequency(TOF)of 0.93 e^(−)·s^(-1)·site^(-1)at 0.85 V vs.RHE,far exceeding those of some representative SACs with a ultra-high metal content.This work provides a rational strategy to design and prepare M−N−C single-atom catalysts featured with high site-accessibility and site-density.
基金the National Key Research and Development Program of China(2022YFB4004100)National Natural Science Foundation of China(22272161,22179126)+1 种基金the Jilin Province Science and Technology Development Program(YDZJ202202CXJD011,20240101019JC)Jilin Province major science and technology project(222648GX0105103875)for financial supports.
文摘The weak adsorption energy of oxygen-containing intermediates on Co center leads to a considerable performance dis-parity between Co-N-C and costly Pt benchmark in catalyzing oxygen reduction reaction(ORR).In this work,we strategi-cally engineer the active site structure of Co-N-C via B substitution,which is accomplished by the pyrolysis of ammonium borate.During this process,the in-situ generated NH_(3)gas plays a critical role in creating surface defects and boron atoms substituting nitrogen atoms in the carbon structure.The well-designed CoB_(1)N_(3)active site endows Co with higher charge density and stronger adsorption energy toward oxygen species,potentially accelerating ORR kinetics.As expected,the resulting Co-B/N-C catalyst exhibited superior ORR performance over Co-N-C counterpart,with 40 mV,and fivefold en-hancement in half-wave potential and turnover frequency(TOF).More importantly,the excellent ORR performance could be translated into membrane electrode assembly(MEA)in a fuel cell test,delivering an impressive peak power density of 824 mW·cm^(-2),which is currently the best among Co-based catalysts under the same conditions.This work not only demon-strates an effective method for designing advanced catalysts,but also affords a highly promising non-precious metal ORR electrocatalyst for fuel cell applications.
文摘Pot grown alfalfa (Medicago sativa L.) were experimented in the open top chambers in which natural air(350×10 -6 ,1×CO 2) and doubled CO 2 air(700×10 -6 ,2×CO 2) were continuous blown through bottom respectively.Results showed that the biomass in both shoot and root was increased by the 2×CO 2 treatment.The root/shoot ratio was nearly unchange in the short term treatment and slightly decreased in the longer term treatment.The results differed from those reported in literatures that was attributed to the pot grown condition in this experiment.The nitrogen fixation activities(acetylene reduction) per plant were obviously promoted under the 2×CO 2 condition but the difference of the specific nitrogen fixing activities between 1×CO 2 and 2×CO 2 treatment was small.It implied that supplement of ATP,NADP or carbon skeleton under the 2×CO 2 condition was not more than that under the 1×CO 2 condition. C/N ratio in the shoot increased in the doubled CO 2 treatment group,similar to the reports from other authors;but the ratio increased in the root in the 2×CO 2 treatment group was ascribed to the higher nitrogen absorption from the soil and(or) N fixing activity of the nodules as compared with that in the 1×CO 2 treatment.The results demonstrated that assimilation and allocation of carbon and nitrogen in legume plant were deeply influenced by the elevated CO 2.
