C2 is a well-known pseudo-oxygen unit with an electron affinity of 3.4 eV. We show that it can exhibit metal-ion like behavior when embedded in a porphyrin sheet and form a metal-free two-dimensional material with sup...C2 is a well-known pseudo-oxygen unit with an electron affinity of 3.4 eV. We show that it can exhibit metal-ion like behavior when embedded in a porphyrin sheet and form a metal-free two-dimensional material with superior oxygen reduction performance. Here, the positively charged C=C units are highly active for oxygen reduction reaction （ORR） via dissociation pathways with a small energy barrier of 0.09 eV, much smaller than that of other non-platinum group metal （non-PGM） ORR catalysts. Using a microkinetics-based model we calculated the partial current density to be 3.0 mA/cm2 at 0.65 V vs. a standard hydrogen electrode （SHE）, which is comparable to that of the state-of-the-art Pt/C catalyst. We further confirm that the C=C embedded porphyrin sheet is dynamically and thermally stable with a quasi-direct band gap of 1.14 eV. The superior catalytic performance and geometric stability make the metal-free C=C porphyrin sheet ideal for fuel cell applications.展开更多
Cr_2Ge_2Te_6is an intrinsic ferromagnetic semiconductor with van der Waals type layered structure,thus represents a promising material for novel electronic and spintronic devices.Here we combine scanning tunneling mic...Cr_2Ge_2Te_6is an intrinsic ferromagnetic semiconductor with van der Waals type layered structure,thus represents a promising material for novel electronic and spintronic devices.Here we combine scanning tunneling microscopy and first-principles calculations to investigate the electronic structure of Cr_2Ge_2Te_6.Tunneling spectroscopy reveals a surprising large energy level shift and change of energy gap size across the ferromagnetic to paramagnetic phase transition,as well as a peculiar double-peak electronic state on the Cr-site defect.These features can be quantitatively explained by density functional theory calculations,which uncover a close relationship between the electronic structure and magnetic order.These findings shed important new lights on the microscopic electronic structure and origin of magnetic order in Cr_2Ge_2Te_6.展开更多
The discovery of ideal spin-1/2 kagome antiferromagnets Herbertsmithite and Zn-doped Barlowite represents a breakthrough in the quest for quantum spin liquids(QSLs),and nuclear magnetic resonance(NMR)spectroscopy play...The discovery of ideal spin-1/2 kagome antiferromagnets Herbertsmithite and Zn-doped Barlowite represents a breakthrough in the quest for quantum spin liquids(QSLs),and nuclear magnetic resonance(NMR)spectroscopy plays a prominent role in revealing the quantum paramagnetism in these compounds.However,interpretation of NMR data that is often masked by defects can be controversial.Here,we show that the most significant interaction strength for NMR,i.e.the hyperfine coupling(HFC)strength,can be reasonably reproduced by first-principles calculations for these proposed QSLs.Applying this method to a supercell containing Cu-Zn defects enables us to map out the variation and distribution of HFC at different nuclear sites.This predictive power is expected to bridge the missing link in the analysis of the low-temperature NMR data.展开更多
基金supported by the Innovation Program for Quantum Science and Technology(2021ZD0302800)the National Natural Science Foundation of China(11904350,12174362)+3 种基金Anhui Provincial Natural Science Foundation(2008085QA30)Shenzhen Science and Technology Program(KQTD20190929173815000)Guangdong Innovative and Entrepreneurial Research Team Program(2019ZT08C044)the National Synchrotron Radiation Laboratory(KY2060000177).
文摘C2 is a well-known pseudo-oxygen unit with an electron affinity of 3.4 eV. We show that it can exhibit metal-ion like behavior when embedded in a porphyrin sheet and form a metal-free two-dimensional material with superior oxygen reduction performance. Here, the positively charged C=C units are highly active for oxygen reduction reaction （ORR） via dissociation pathways with a small energy barrier of 0.09 eV, much smaller than that of other non-platinum group metal （non-PGM） ORR catalysts. Using a microkinetics-based model we calculated the partial current density to be 3.0 mA/cm2 at 0.65 V vs. a standard hydrogen electrode （SHE）, which is comparable to that of the state-of-the-art Pt/C catalyst. We further confirm that the C=C embedded porphyrin sheet is dynamically and thermally stable with a quasi-direct band gap of 1.14 eV. The superior catalytic performance and geometric stability make the metal-free C=C porphyrin sheet ideal for fuel cell applications.
基金supported by the Basic Science Center Project of NSFC(51788104)the MOST of China(2015CB921000)+6 种基金the support from Tsinghua University Initiative Scientific Research Program and NSFC(11774196)S.H.Z.is supported by the National Postdoctoral Program for Innovative Talents of China(BX201600091)the China Postdoctoral Science Foundation(2017M610858)the support of the National Key Research and Development Program(2016YFA0300404)NSFC Grant(11674326)the Joint Funds of NSFC and the Chinese Academy of Sciences’Large-Scale Scientific Facility(U1432139)supported in part by the Beijing Advanced Innovation Center for Future Chip(ICFC)
文摘Cr_2Ge_2Te_6is an intrinsic ferromagnetic semiconductor with van der Waals type layered structure,thus represents a promising material for novel electronic and spintronic devices.Here we combine scanning tunneling microscopy and first-principles calculations to investigate the electronic structure of Cr_2Ge_2Te_6.Tunneling spectroscopy reveals a surprising large energy level shift and change of energy gap size across the ferromagnetic to paramagnetic phase transition,as well as a peculiar double-peak electronic state on the Cr-site defect.These features can be quantitatively explained by density functional theory calculations,which uncover a close relationship between the electronic structure and magnetic order.These findings shed important new lights on the microscopic electronic structure and origin of magnetic order in Cr_2Ge_2Te_6.
基金supported by the National Natural Science Foundation of China(11774196)Tsinghua University Initiative Scientific Research Program+5 种基金supported by the National Postdoctoral Program for Innovative Talents of China(BX201600091)the Funding from China Postdoctoral Science Foundation(2017M610858)the support from US-DOE(DEFG02-04ER46148)supported by National Key Research and Development Program of China(2016YFA0300202)National Natural Science Foundation of China(11774306)the Strategic Priority Research Program of Chinese Academy of Sciences(XDB28000000)
文摘The discovery of ideal spin-1/2 kagome antiferromagnets Herbertsmithite and Zn-doped Barlowite represents a breakthrough in the quest for quantum spin liquids(QSLs),and nuclear magnetic resonance(NMR)spectroscopy plays a prominent role in revealing the quantum paramagnetism in these compounds.However,interpretation of NMR data that is often masked by defects can be controversial.Here,we show that the most significant interaction strength for NMR,i.e.the hyperfine coupling(HFC)strength,can be reasonably reproduced by first-principles calculations for these proposed QSLs.Applying this method to a supercell containing Cu-Zn defects enables us to map out the variation and distribution of HFC at different nuclear sites.This predictive power is expected to bridge the missing link in the analysis of the low-temperature NMR data.
