The electrocatalytic N_(2)reduction reaction(NRR)is expected to supersede the traditional Haber-Bosch technology for NH3 production under ambient conditions.The activity and selectivity of electrochemical NRR are rest...The electrocatalytic N_(2)reduction reaction(NRR)is expected to supersede the traditional Haber-Bosch technology for NH3 production under ambient conditions.The activity and selectivity of electrochemical NRR are restricted to a strong polarized electric field induced by the catalyst,correct electron transfer direction,and electron tunneling distance between bare electrode and active sites.By coupling the chemical vapor deposition method with the poly(methyl methacylate)-transfer method,an ultrathin sandwich catalyst,i.e.,Fe atoms(polarized electric field layer)sandwiched between ultrathin(within electron tunneling distance)BN(catalyst layer)and graphene film(conducting layer),is fabricated for electrocatalytic NRR.The sandwich catalyst not only controls the transfer of electrons to the BN surface in the correct direction under applied voltage but also suppresses hydrogen evolution reaction by constructing a neutral polarization electric field without metal exposure.The sandwich electrocatalyst NRR system achieve NH3 yield of 8.9μg h^(−1)cm^(−2)and Faradaic Efficiency of 21.7%.The N_(2)adsorption,activation,and polarization electric field changes of three sandwich catalysts(BN-Fe-G,BN-Fe-BN,and G-Fe-G)during the electrocatalytic NRR are investigated by experiments and density functional theory simulations.Driven by applied voltage,the neutral polarized electric field induced by BN-Fe-G leads to the high activity of electrocatalytic NRR.展开更多
Pyridinic N is widely regarded as the active center while pyrrolic N has low‐activity in metal‐free N‐doped carbon for electrocatalytic CO_(2) reduction reaction(CO_(2)RR)to CO,but this viewpoint remains open to qu...Pyridinic N is widely regarded as the active center while pyrrolic N has low‐activity in metal‐free N‐doped carbon for electrocatalytic CO_(2) reduction reaction(CO_(2)RR)to CO,but this viewpoint remains open to question.In this study,through density functional theoretical calculations,we first illustrate that the intrinsic activity of pyrrolic N is high enough for effectively catalyzing CO_(2)RR,however,due to the interplay with the neighboring pyridinic N sites,the activity of pyrrolic N is dramatically suppressed.Then,experimentally,metal‐free N‐doped carbon spheres(NCS)electrocatalysts without significant pyridinic N content are prepared for CO_(2)RR.The pyrrolic N in NCS shows a direct‐positive correlation with the performance for CO_(2)RR,representing the active center with high activity.The optimum NCS could produce syngas with a wide range of CO/H_(2) ratio(0.09 to 12)in CO_(2)RR depending on the applied potential,meanwhile,the best selectivity of 71%for CO can be obtained.Intentionally adding a small amount of pyridinic N to the optimum NCS dramatically decreases the activity for CO_(2)RR,further verifying the suppressed activity of pyrrolic N sites by the neighboring pyridinic N sites.This work reveals the interaction between a variety of N species in N‐doped carbon,and the potential of pyrrolic N as the new type of active site for electrocatalysts,which can improve our understanding of the electrocatalysis mechanism and be helpful for the rational design of high‐efficient electrocatalysts.展开更多
Pure Ca-SiAlON:Eu2+ was synthesized by microwave sintering method at a relatively low temperature of 1550℃.Photoluminescence intensity of the resultant phosphor was higher than those of the samples synthesized by con...Pure Ca-SiAlON:Eu2+ was synthesized by microwave sintering method at a relatively low temperature of 1550℃.Photoluminescence intensity of the resultant phosphor was higher than those of the samples synthesized by conventional gas-pressure sintering technique at 1750℃.When it was excited at 450 nm,the as-prepared yellow Ca-SiAlON:Eu2+ sample had an external quantum efficiency of 42%,comparable to the sample synthesized at 1750℃ under 0.5 MPaN2 gas pressure by the GPS method reported in reference.The experimental results demonstrated that the microwave sintering method was also an interesting approach for synthesizing nitride phosphors,which promises lower firing temperature than those by carbothermal reduction and nitridation (CRN) methods,higher heating rate and shorter duration time compared with those by gas-pressure sintering.展开更多
文摘The electrocatalytic N_(2)reduction reaction(NRR)is expected to supersede the traditional Haber-Bosch technology for NH3 production under ambient conditions.The activity and selectivity of electrochemical NRR are restricted to a strong polarized electric field induced by the catalyst,correct electron transfer direction,and electron tunneling distance between bare electrode and active sites.By coupling the chemical vapor deposition method with the poly(methyl methacylate)-transfer method,an ultrathin sandwich catalyst,i.e.,Fe atoms(polarized electric field layer)sandwiched between ultrathin(within electron tunneling distance)BN(catalyst layer)and graphene film(conducting layer),is fabricated for electrocatalytic NRR.The sandwich catalyst not only controls the transfer of electrons to the BN surface in the correct direction under applied voltage but also suppresses hydrogen evolution reaction by constructing a neutral polarization electric field without metal exposure.The sandwich electrocatalyst NRR system achieve NH3 yield of 8.9μg h^(−1)cm^(−2)and Faradaic Efficiency of 21.7%.The N_(2)adsorption,activation,and polarization electric field changes of three sandwich catalysts(BN-Fe-G,BN-Fe-BN,and G-Fe-G)during the electrocatalytic NRR are investigated by experiments and density functional theory simulations.Driven by applied voltage,the neutral polarized electric field induced by BN-Fe-G leads to the high activity of electrocatalytic NRR.
文摘Pyridinic N is widely regarded as the active center while pyrrolic N has low‐activity in metal‐free N‐doped carbon for electrocatalytic CO_(2) reduction reaction(CO_(2)RR)to CO,but this viewpoint remains open to question.In this study,through density functional theoretical calculations,we first illustrate that the intrinsic activity of pyrrolic N is high enough for effectively catalyzing CO_(2)RR,however,due to the interplay with the neighboring pyridinic N sites,the activity of pyrrolic N is dramatically suppressed.Then,experimentally,metal‐free N‐doped carbon spheres(NCS)electrocatalysts without significant pyridinic N content are prepared for CO_(2)RR.The pyrrolic N in NCS shows a direct‐positive correlation with the performance for CO_(2)RR,representing the active center with high activity.The optimum NCS could produce syngas with a wide range of CO/H_(2) ratio(0.09 to 12)in CO_(2)RR depending on the applied potential,meanwhile,the best selectivity of 71%for CO can be obtained.Intentionally adding a small amount of pyridinic N to the optimum NCS dramatically decreases the activity for CO_(2)RR,further verifying the suppressed activity of pyrrolic N sites by the neighboring pyridinic N sites.This work reveals the interaction between a variety of N species in N‐doped carbon,and the potential of pyrrolic N as the new type of active site for electrocatalysts,which can improve our understanding of the electrocatalysis mechanism and be helpful for the rational design of high‐efficient electrocatalysts.
基金supported by the National Natural Science Foundation of China(51102252 and 51272259)the Special Foundation for Young Scientists of Zhejiang Province(R12E020005)
文摘Pure Ca-SiAlON:Eu2+ was synthesized by microwave sintering method at a relatively low temperature of 1550℃.Photoluminescence intensity of the resultant phosphor was higher than those of the samples synthesized by conventional gas-pressure sintering technique at 1750℃.When it was excited at 450 nm,the as-prepared yellow Ca-SiAlON:Eu2+ sample had an external quantum efficiency of 42%,comparable to the sample synthesized at 1750℃ under 0.5 MPaN2 gas pressure by the GPS method reported in reference.The experimental results demonstrated that the microwave sintering method was also an interesting approach for synthesizing nitride phosphors,which promises lower firing temperature than those by carbothermal reduction and nitridation (CRN) methods,higher heating rate and shorter duration time compared with those by gas-pressure sintering.
