Zhang Chun
Degree: PhD
Position: Associate Professor
Affiliation: NUS – Department of Physics
Research Type: Theory
Office: S13-04-09
Email: phyzc@nus.edu.sg
Contact: (65) 6516 6755
Website: http://www.physics.nus.edu.sg/staff/zhangchun.html
Research Interests:
Development of first-principles theories for quantum systems under various conditions; Theoretical design of low-dimensional materials; Molecular scale electronic/spintronic devices; Catalysis at nano or atomic scale.
CA2DM Publications:
2023 |
Jiang, Zhuoling; Yam, Kah-Meng; Ang, Yee Sin; Guo, Na; Zhang, Yongjie; Wang, Hao; Zhang, Chun Symmetry-driven half-integer conductance quantization in Cobalt-fulvalene sandwich nanowire Journal Article NPJ COMPUTATIONAL MATERIALS, 9 (1), 2023. @article{ISI:001095847100002, title = {Symmetry-driven half-integer conductance quantization in Cobalt-fulvalene sandwich nanowire}, author = {Zhuoling Jiang and Kah-Meng Yam and Yee Sin Ang and Na Guo and Yongjie Zhang and Hao Wang and Chun Zhang}, doi = {10.1038/s41524-023-01151-z}, times_cited = {0}, year = {2023}, date = {2023-10-21}, journal = {NPJ COMPUTATIONAL MATERIALS}, volume = {9}, number = {1}, publisher = {NATURE PORTFOLIO}, address = {HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY}, abstract = {Precise manipulation and monitoring spin transport in one-dimensional (1D) systems is a long-sought goal in the field of nano-spintronics. Based on first-principles calculations, we report the observation of half-integer conductance quantization in the Cobalt-fulvalene sandwich nanowire. Compared with a pure monatomic Cobalt wire, the introduction of fulvalene molecules leads to three important features: Firstly, the strong coupling between the fulvalene and the Cobalt prevents the contamination of the ambient air, ensuring both chemical and physical stabilities; Secondly, the fulvalene symmetry-selectively filters out most of the d-type orbitals of the Cobalt while leaving a single d-type orbital to form an open spin channel around the Fermi level, which offers a mechanism to achieve the observed half-integer conductance; Thirdly, it maintains a superexchange coupling between adjacent Co atoms to achieve a high Curie temperature. Spin transport calculations show that this half-metallic nanowire can serve as a perfect spin filter or a spin valve device, thus revealing the potential of Cobalt-fulvalene sandwich nanowire as a promising building block of high-performance spintronics technology.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Precise manipulation and monitoring spin transport in one-dimensional (1D) systems is a long-sought goal in the field of nano-spintronics. Based on first-principles calculations, we report the observation of half-integer conductance quantization in the Cobalt-fulvalene sandwich nanowire. Compared with a pure monatomic Cobalt wire, the introduction of fulvalene molecules leads to three important features: Firstly, the strong coupling between the fulvalene and the Cobalt prevents the contamination of the ambient air, ensuring both chemical and physical stabilities; Secondly, the fulvalene symmetry-selectively filters out most of the d-type orbitals of the Cobalt while leaving a single d-type orbital to form an open spin channel around the Fermi level, which offers a mechanism to achieve the observed half-integer conductance; Thirdly, it maintains a superexchange coupling between adjacent Co atoms to achieve a high Curie temperature. Spin transport calculations show that this half-metallic nanowire can serve as a perfect spin filter or a spin valve device, thus revealing the potential of Cobalt-fulvalene sandwich nanowire as a promising building block of high-performance spintronics technology. |
Yang, Huimin; Xi, Shibo; Guo, Na; Wang, Mu; Liu, Lingmei; Lyu, Pin; Yu, Xiaolong; Li, Jing; Xu, Haomin; Hai, Xiao; Li, Zejun; Li, Xinzhe; Sun, Tao; Zhao, Xiaoxu; Han, Yu; Yu, Wei; Wu, Jie; Zhang, Chun; Fei, Honghan; Koh, Ming Joo; Lu, Jiong Catalytically active atomically thin cuprate with periodic Cu single sites Journal Article NATIONAL SCIENCE REVIEW, 10 (1), 2023, ISSN: 2095-5138. @article{ISI:000943284400001, title = {Catalytically active atomically thin cuprate with periodic Cu single sites}, author = {Huimin Yang and Shibo Xi and Na Guo and Mu Wang and Lingmei Liu and Pin Lyu and Xiaolong Yu and Jing Li and Haomin Xu and Xiao Hai and Zejun Li and Xinzhe Li and Tao Sun and Xiaoxu Zhao and Yu Han and Wei Yu and Jie Wu and Chun Zhang and Honghan Fei and Ming Joo Koh and Jiong Lu}, doi = {10.1093/nsr/nwac100}, times_cited = {0}, issn = {2095-5138}, year = {2023}, date = {2023-01-14}, journal = {NATIONAL SCIENCE REVIEW}, volume = {10}, number = {1}, publisher = {OXFORD UNIV PRESS}, address = {GREAT CLARENDON ST, OXFORD OX2 6DP, ENGLAND}, abstract = {A ligand exchange strategy exfoliates bulk cuprate crystals into atomically thin 2D cuprate layers with periodic unsaturated copper single sites, which are found to promote efficient oxidative Chan-Lam coupling.}, keywords = {}, pubstate = {published}, tppubtype = {article} } A ligand exchange strategy exfoliates bulk cuprate crystals into atomically thin 2D cuprate layers with periodic unsaturated copper single sites, which are found to promote efficient oxidative Chan-Lam coupling. |
2022 |
Too, Hon Lin; Guo, Na; Zhang, Chun; Wang, Zhisong Importance of Sugar-Phosphate Backbone and Counterions to First-Principles Modeling of Nucleobases Journal Article JOURNAL OF PHYSICAL CHEMISTRY B, 126 (31), pp. 5744-5751, 2022, ISSN: 1520-6106. @article{ISI:000835390200001, title = {Importance of Sugar-Phosphate Backbone and Counterions to First-Principles Modeling of Nucleobases}, author = {Hon Lin Too and Na Guo and Chun Zhang and Zhisong Wang}, doi = {10.1021/acs.jpcb.2c02621}, times_cited = {0}, issn = {1520-6106}, year = {2022}, date = {2022-07-28}, journal = {JOURNAL OF PHYSICAL CHEMISTRY B}, volume = {126}, number = {31}, pages = {5744-5751}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {DFT-based first-principles calculations were carried out to understand the electronic structure difference among a backbone-free nucleobase, a backbone-containing Na counterion nucleotide, and a backbone-containing H counterion nucleotide and their difference in the adsorption on graphene and on graphitic-carbon nitride. The study discovered that the inclusion of a sugar-phosphate backbone changes the electron affinity of most nucleobases from electron acceptors to electron donors. The methyl-terminated backbone-free model cannot replicate the steric effect induced by the sugar-phosphate backbone during the adsorption of nucleobases on 2D materials. Overall, we established that the sugar phosphate backbone should be included in the study of DNA nucleobase adsorption on 2D material. We also showed that when it comes to the adsorption on 2D materials, the backbone-containing H counterion model is superior to the Na counterion model because the Na counterion produces a LUMO near the Fermi energy, which may significantly affect the interaction with the 2D material.}, keywords = {}, pubstate = {published}, tppubtype = {article} } DFT-based first-principles calculations were carried out to understand the electronic structure difference among a backbone-free nucleobase, a backbone-containing Na counterion nucleotide, and a backbone-containing H counterion nucleotide and their difference in the adsorption on graphene and on graphitic-carbon nitride. The study discovered that the inclusion of a sugar-phosphate backbone changes the electron affinity of most nucleobases from electron acceptors to electron donors. The methyl-terminated backbone-free model cannot replicate the steric effect induced by the sugar-phosphate backbone during the adsorption of nucleobases on 2D materials. Overall, we established that the sugar phosphate backbone should be included in the study of DNA nucleobase adsorption on 2D material. We also showed that when it comes to the adsorption on 2D materials, the backbone-containing H counterion model is superior to the Na counterion model because the Na counterion produces a LUMO near the Fermi energy, which may significantly affect the interaction with the 2D material. |
Telychko, Mykola; Edalatmanesh, Shayan; Leng, Kai; Abdelwahab, Ibrahim; Guo, Na; Zhang, Chun; Mendieta-Moreno, Jesus; Nachtigall, Matyas; Li, Jing; Loh, Kian Ping; Jelinek, Pavel; Lu, Jiong Sub-angstrom noninvasive imaging of atomic arrangement in 2D hybrid perovskites Journal Article SCIENCE ADVANCES, 8 (17), 2022, ISSN: 2375-2548. @article{ISI:000790076700005, title = {Sub-angstrom noninvasive imaging of atomic arrangement in 2D hybrid perovskites}, author = {Mykola Telychko and Shayan Edalatmanesh and Kai Leng and Ibrahim Abdelwahab and Na Guo and Chun Zhang and Jesus Mendieta-Moreno and Matyas Nachtigall and Jing Li and Kian Ping Loh and Pavel Jelinek and Jiong Lu}, doi = {10.1126/sciadv.abj0395}, times_cited = {0}, issn = {2375-2548}, year = {2022}, date = {2022-04-01}, journal = {SCIENCE ADVANCES}, volume = {8}, number = {17}, publisher = {AMER ASSOC ADVANCEMENT SCIENCE}, address = {1200 NEW YORK AVE, NW, WASHINGTON, DC 20005 USA}, abstract = {Noninvasive imaging of the atomic arrangement in two-dimensional (2D) Ruddlesden-Popper hybrid perovskites (RPPs) is challenging because of the insulating nature and softness of the organic layers. Here, we demonstrate a sub-angstrom resolution imaging of both soft organic layers and inorganic framework in a prototypical 2D lead-halide RPP crystal via combined tip-functionalized scanning tunneling microscopy (STM) and noncontact atomic force microscopy (ncAFM) corroborated by theoretical simulations. STM measurements unveil the atomic reconstruction of the inorganic lead-halide lattice and overall twin-domain composition of the RPP crystal, while ncAFM measurements with a CO-tip enable nonperturbative visualization of the cooperative reordering of surface organic cations driven by their hydrogen bonding interactions with the inorganic lattice. Moreover, such a joint technique also allows for the atomic-scale imaging of the electrostatic potential variation across the twin-domain walls, revealing alternating quasi-1D electron and hole channels at neighboring twin boundaries, which may influence in-plane exciton transport and dissociation.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Noninvasive imaging of the atomic arrangement in two-dimensional (2D) Ruddlesden-Popper hybrid perovskites (RPPs) is challenging because of the insulating nature and softness of the organic layers. Here, we demonstrate a sub-angstrom resolution imaging of both soft organic layers and inorganic framework in a prototypical 2D lead-halide RPP crystal via combined tip-functionalized scanning tunneling microscopy (STM) and noncontact atomic force microscopy (ncAFM) corroborated by theoretical simulations. STM measurements unveil the atomic reconstruction of the inorganic lead-halide lattice and overall twin-domain composition of the RPP crystal, while ncAFM measurements with a CO-tip enable nonperturbative visualization of the cooperative reordering of surface organic cations driven by their hydrogen bonding interactions with the inorganic lattice. Moreover, such a joint technique also allows for the atomic-scale imaging of the electrostatic potential variation across the twin-domain walls, revealing alternating quasi-1D electron and hole channels at neighboring twin boundaries, which may influence in-plane exciton transport and dissociation. |
2021 |
Chen, Cheng; Ou, Wei; Yam, Kah-Meng; Xi, Shibo; Zhao, Xiaoxu; Chen, Si; Li, Jing; Lyu, Pin; Ma, Lu; Du, Yonghua; Yu, Wei; Fang, Hanyan; Yao, Chuanhao; Hai, Xiao; Xu, Haomin; Koh, Ming Joo; Pennycook, Stephen J; Lu, Junling; Lin, Ming; Su, Chenliang; Zhang, Chun; Lu, Jiong Zero-Valent Palladium Single-Atoms Catalysts Confined in Black Phosphorus for Efficient Semi-Hydrogenation Journal Article ADVANCED MATERIALS, 33 (35), 2021, ISSN: 0935-9648. @article{ISI:000676091000001, title = {Zero-Valent Palladium Single-Atoms Catalysts Confined in Black Phosphorus for Efficient Semi-Hydrogenation}, author = {Cheng Chen and Wei Ou and Kah-Meng Yam and Shibo Xi and Xiaoxu Zhao and Si Chen and Jing Li and Pin Lyu and Lu Ma and Yonghua Du and Wei Yu and Hanyan Fang and Chuanhao Yao and Xiao Hai and Haomin Xu and Ming Joo Koh and Stephen J Pennycook and Junling Lu and Ming Lin and Chenliang Su and Chun Zhang and Jiong Lu}, doi = {10.1002/adma.202008471}, times_cited = {0}, issn = {0935-9648}, year = {2021}, date = {2021-07-23}, journal = {ADVANCED MATERIALS}, volume = {33}, number = {35}, publisher = {WILEY-V C H VERLAG GMBH}, address = {POSTFACH 101161, 69451 WEINHEIM, GERMANY}, abstract = {Single-atom catalysts (SACs) represent a new frontier in heterogeneous catalysis due to their remarkable catalytic properties and maximized atomic utilization. However, single atoms often bond to the support with polarized electron density and thus exhibit a high valence state, limiting their catalytic scopes in many chemical transformations. Here, it is demonstrated that 2D black phosphorus (BP) acts as giant phosphorus (P) ligand to confine a high density of single atoms (e.g., Pd-1, Pt-1) via atomic layer deposition. Unlike other 2D materials, BP with relatively low electronegativity and buckled structure favors the strong confinement of robust zero-valent palladium SACs in the vacancy site. Metallic Pd-1/BP SAC shows a highly selective semi-hydrogenation of phenylacetylene toward styrene, distinct from metallic Pd nanoparticles that facilitate the formation of fully hydrogenated products. Density functional theory calculations reveal that Pd atom forms covalent-like bonding with adjacent P atoms, wherein H atoms tend to adsorb, aiding the dissociative adsorption of H-2. Zero-valent Pd in the confined space favors a larger energy gain for the synthesis of partially hydrogenated product over the fully hydrogenated one. This work provides a new route toward the synthesis of zero-valent SACs on BP for organic transformations.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Single-atom catalysts (SACs) represent a new frontier in heterogeneous catalysis due to their remarkable catalytic properties and maximized atomic utilization. However, single atoms often bond to the support with polarized electron density and thus exhibit a high valence state, limiting their catalytic scopes in many chemical transformations. Here, it is demonstrated that 2D black phosphorus (BP) acts as giant phosphorus (P) ligand to confine a high density of single atoms (e.g., Pd-1, Pt-1) via atomic layer deposition. Unlike other 2D materials, BP with relatively low electronegativity and buckled structure favors the strong confinement of robust zero-valent palladium SACs in the vacancy site. Metallic Pd-1/BP SAC shows a highly selective semi-hydrogenation of phenylacetylene toward styrene, distinct from metallic Pd nanoparticles that facilitate the formation of fully hydrogenated products. Density functional theory calculations reveal that Pd atom forms covalent-like bonding with adjacent P atoms, wherein H atoms tend to adsorb, aiding the dissociative adsorption of H-2. Zero-valent Pd in the confined space favors a larger energy gain for the synthesis of partially hydrogenated product over the fully hydrogenated one. This work provides a new route toward the synthesis of zero-valent SACs on BP for organic transformations. |
Li, Shulong; Yam, Kah-Meng; Guo, Na; Zhao, Yong; Zhang, Chun Highly stable two-dimensional metal-carbon monolayer with interpenetrating honeycomb structures Journal Article NPJ 2D MATERIALS AND APPLICATIONS, 5 (1), 2021. @article{WOS:000650635200001, title = {Highly stable two-dimensional metal-carbon monolayer with interpenetrating honeycomb structures}, author = {Shulong Li and Kah-Meng Yam and Na Guo and Yong Zhao and Chun Zhang}, doi = {10.1038/s41699-021-00235-y}, times_cited = {0}, year = {2021}, date = {2021-05-01}, journal = {NPJ 2D MATERIALS AND APPLICATIONS}, volume = {5}, number = {1}, publisher = {NATURE RESEARCH}, address = {HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY}, abstract = {With the ongoing effort in proposing and realizing functional two-dimensional (2D) materials, we predict by first-principles calculations a family of 2D metal-carbon (M-C) crystals consisting of M-C trigonal lattice interpenetrated with the metal buckled honeycomb structure. We suggest by simulations that the 2D M-C crystals can be readily fabricated by a self-organizing lattice reconstruction process after placing metal atoms on hollow sites of gamma-graphyne. In total, we found 12 members of the family and they exhibit a variety of electronic and magnetic properties. In this work, we highlight and focus on the Fe member of the family, 2D-Fe2C12. Each Fe in 2D-Fe2C12 has a magnetic moment of 1 mu(B) due to the spin splitting of Fe E1 bands at Fermi surface, resulting in half metallicity and high catalytic activity with unusually high-density single-atom Fe active sites. Ab initio molecular dynamics simulations revealed that the 2D-Fe2C12 retains its structural integrity up to 700 K of simulated short duration annealing. We expect these results to stimulate experimental research for the 2D M-C crystals we proposed.}, keywords = {}, pubstate = {published}, tppubtype = {article} } With the ongoing effort in proposing and realizing functional two-dimensional (2D) materials, we predict by first-principles calculations a family of 2D metal-carbon (M-C) crystals consisting of M-C trigonal lattice interpenetrated with the metal buckled honeycomb structure. We suggest by simulations that the 2D M-C crystals can be readily fabricated by a self-organizing lattice reconstruction process after placing metal atoms on hollow sites of gamma-graphyne. In total, we found 12 members of the family and they exhibit a variety of electronic and magnetic properties. In this work, we highlight and focus on the Fe member of the family, 2D-Fe2C12. Each Fe in 2D-Fe2C12 has a magnetic moment of 1 mu(B) due to the spin splitting of Fe E1 bands at Fermi surface, resulting in half metallicity and high catalytic activity with unusually high-density single-atom Fe active sites. Ab initio molecular dynamics simulations revealed that the 2D-Fe2C12 retains its structural integrity up to 700 K of simulated short duration annealing. We expect these results to stimulate experimental research for the 2D M-C crystals we proposed. |
2020 |
Yao, Chuanhao; Guo, Na; Xi, Shibo; Xu, Cong-Qiao; Liu, Wei; Zhao, Xiaoxu; Li, Jing; Fang, Hanyan; Su, Jie; Chen, Zhongxin; Yan, Huan; Qiu, Zhizhan; Lyu, Pin; Chen, Cheng; Xu, Haomin; Peng, Xinnan; Li, Xinzhe; Liu, Bin; Su, Chenliang; Pennycook, Stephen J; Sun, Cheng-Jun; Li, Jun; Zhang, Chun; Du, Yonghua; Lu, Jiong Atomically-precise dopant-controlled single cluster catalysis for electrochemical nitrogen reduction Journal Article NATURE COMMUNICATIONS, 11 (1), 2020, ISSN: 2041-1723. @article{ISI:000569891500016, title = {Atomically-precise dopant-controlled single cluster catalysis for electrochemical nitrogen reduction}, author = {Chuanhao Yao and Na Guo and Shibo Xi and Cong-Qiao Xu and Wei Liu and Xiaoxu Zhao and Jing Li and Hanyan Fang and Jie Su and Zhongxin Chen and Huan Yan and Zhizhan Qiu and Pin Lyu and Cheng Chen and Haomin Xu and Xinnan Peng and Xinzhe Li and Bin Liu and Chenliang Su and Stephen J Pennycook and Cheng-Jun Sun and Jun Li and Chun Zhang and Yonghua Du and Jiong Lu}, doi = {10.1038/s41467-020-18080-w}, times_cited = {0}, issn = {2041-1723}, year = {2020}, date = {2020-09-01}, journal = {NATURE COMMUNICATIONS}, volume = {11}, number = {1}, publisher = {NATURE PUBLISHING GROUP}, address = {MACMILLAN BUILDING, 4 CRINAN ST, LONDON N1 9XW, ENGLAND}, abstract = {The ability to precisely engineer the doping of sub-nanometer bimetallic clusters offers exciting opportunities for tailoring their catalytic performance with atomic accuracy. However, the fabrication of singly dispersed bimetallic cluster catalysts with atomic-level control of dopants has been a long-standing challenge. Herein, we report a strategy for the controllable synthesis of a precisely doped single cluster catalyst consisting of partially ligand-enveloped Au4Pt2 clusters supported on defective graphene. This creates a bimetal single cluster catalyst (Au4Pt2/G) with exceptional activity for electrochemical nitrogen (N-2) reduction. Our mechanistic study reveals that each N-2 molecule is activated in the confined region between cluster and graphene. The heteroatom dopant plays an indispensable role in the activation of N-2 via an enhanced back donation of electrons to the N-2 LUMO. Moreover, besides the heteroatom Pt, the catalytic performance of single cluster catalyst can be further tuned by using Pd in place of Pt as the dopant. The fabrication of singly dispersed metal cluster catalysts with atomic-level control of dopants is a long-standing challenge. Here, the authors report a strategy for the synthesis of a precisely doped single cluster catalyst which shows exceptional activity for electrochemical dinitrogen reduction.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The ability to precisely engineer the doping of sub-nanometer bimetallic clusters offers exciting opportunities for tailoring their catalytic performance with atomic accuracy. However, the fabrication of singly dispersed bimetallic cluster catalysts with atomic-level control of dopants has been a long-standing challenge. Herein, we report a strategy for the controllable synthesis of a precisely doped single cluster catalyst consisting of partially ligand-enveloped Au4Pt2 clusters supported on defective graphene. This creates a bimetal single cluster catalyst (Au4Pt2/G) with exceptional activity for electrochemical nitrogen (N-2) reduction. Our mechanistic study reveals that each N-2 molecule is activated in the confined region between cluster and graphene. The heteroatom dopant plays an indispensable role in the activation of N-2 via an enhanced back donation of electrons to the N-2 LUMO. Moreover, besides the heteroatom Pt, the catalytic performance of single cluster catalyst can be further tuned by using Pd in place of Pt as the dopant. The fabrication of singly dispersed metal cluster catalysts with atomic-level control of dopants is a long-standing challenge. Here, the authors report a strategy for the synthesis of a precisely doped single cluster catalyst which shows exceptional activity for electrochemical dinitrogen reduction. |
Yam, Kah-Meng; Guo, Na; Jiang, Zhuoling; Li, Shulong; Zhang, Chun Enhancing Reactivity of SiC-Supported Graphene by Engineering Intercalated Metal Atoms at the Interface Journal Article JOURNAL OF PHYSICAL CHEMISTRY C, 124 (33), pp. 18126-18131, 2020, ISSN: 1932-7447. @article{ISI:000563746200029, title = {Enhancing Reactivity of SiC-Supported Graphene by Engineering Intercalated Metal Atoms at the Interface}, author = {Kah-Meng Yam and Na Guo and Zhuoling Jiang and Shulong Li and Chun Zhang}, doi = {10.1021/acs.jpcc.0c05286}, times_cited = {0}, issn = {1932-7447}, year = {2020}, date = {2020-08-20}, journal = {JOURNAL OF PHYSICAL CHEMISTRY C}, volume = {124}, number = {33}, pages = {18126-18131}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Controlling the reactivity of graphene with effective yet practical physical/chemical methods has been known to be the key for many applications of graphene including graphene-based solid-state catalysis. Here, by state-of-art ab initio modeling, we present a new avenue to enhance reactivity and catalytic activity of graphene that is supported on a SiC substrate. We show that intercalated metal atoms (e.g., Ru atoms) at the SiC-graphene interface form a self-assembled two-dimensional monolayer with hexagonal lattice, and by controlling the concentration of the metal atoms, the reactivity of the supported graphene could be greatly enhanced, resulting in the chemisorption of O-2 molecule on graphene. Detailed analysis revealed that the O-2 chemisorption originates from the charge transfer of nearly one electron from the activated graphene to the O-2 2 pi* orbital. We further show that the activated graphene can be an excellent catalyst toward CO oxidation reaction.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Controlling the reactivity of graphene with effective yet practical physical/chemical methods has been known to be the key for many applications of graphene including graphene-based solid-state catalysis. Here, by state-of-art ab initio modeling, we present a new avenue to enhance reactivity and catalytic activity of graphene that is supported on a SiC substrate. We show that intercalated metal atoms (e.g., Ru atoms) at the SiC-graphene interface form a self-assembled two-dimensional monolayer with hexagonal lattice, and by controlling the concentration of the metal atoms, the reactivity of the supported graphene could be greatly enhanced, resulting in the chemisorption of O-2 molecule on graphene. Detailed analysis revealed that the O-2 chemisorption originates from the charge transfer of nearly one electron from the activated graphene to the O-2 2 pi* orbital. We further show that the activated graphene can be an excellent catalyst toward CO oxidation reaction. |
Song, Shaotang; Guo, Na; Li, Xinzhe; Li, Guangwu; Haketa, Yohei; Telychko, Mykola; Su, Jie; Lyu, Pin; Qiu, Zhizhan; Fang, Hanyan; Peng, Xinnan; Li, Jing; Wu, Xinbang; Li, Ying; Su, Chenliang; Koh, Ming Joo; Wu, Jishan; Maeda, Hiromitsu; Zhang, Chun; Lu, Jiong Real-Space Imaging of a Single-Molecule Monoradical Reaction Journal Article JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 142 (31), pp. 13550-13557, 2020, ISSN: 0002-7863. @article{ISI:000558793400039, title = {Real-Space Imaging of a Single-Molecule Monoradical Reaction}, author = {Shaotang Song and Na Guo and Xinzhe Li and Guangwu Li and Yohei Haketa and Mykola Telychko and Jie Su and Pin Lyu and Zhizhan Qiu and Hanyan Fang and Xinnan Peng and Jing Li and Xinbang Wu and Ying Li and Chenliang Su and Ming Joo Koh and Jishan Wu and Hiromitsu Maeda and Chun Zhang and Jiong Lu}, doi = {10.1021/jacs.0c05337}, times_cited = {1}, issn = {0002-7863}, year = {2020}, date = {2020-08-05}, journal = {JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, volume = {142}, number = {31}, pages = {13550-13557}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Organic radicals consisting of light elements exhibit a low spin- orbit coupling and weak hyperfine interactions with a long spin coherence length, which are crucial for future applications in molecular spintronics. However, the synthesis and characterization of these organic radicals have been a formidable challenge due to their chemical instability arising from unpaired electrons. Her; we report a direct imaging of the surface chemical transformation of an organic monoradical synthesized via the monodehydrogenation of a chemically designed precursor. Bond-resolved scanning tunneling microscopy unambiguously resolves various products formed through a complex structural dissociation and rearrangement of organic monoradicals. Density functional theory calculations reveal detailed reaction pathways from the monoradical to different cyclized products. Our study provides unprecedented insights into complex surface reaction mechanisms of organic radical reactions at the single molecule level, which may guide the design of stable organic radicals for future quantum technology applications.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Organic radicals consisting of light elements exhibit a low spin- orbit coupling and weak hyperfine interactions with a long spin coherence length, which are crucial for future applications in molecular spintronics. However, the synthesis and characterization of these organic radicals have been a formidable challenge due to their chemical instability arising from unpaired electrons. Her; we report a direct imaging of the surface chemical transformation of an organic monoradical synthesized via the monodehydrogenation of a chemically designed precursor. Bond-resolved scanning tunneling microscopy unambiguously resolves various products formed through a complex structural dissociation and rearrangement of organic monoradicals. Density functional theory calculations reveal detailed reaction pathways from the monoradical to different cyclized products. Our study provides unprecedented insights into complex surface reaction mechanisms of organic radical reactions at the single molecule level, which may guide the design of stable organic radicals for future quantum technology applications. |
Hai, Xiao; Zhao, Xiaoxu; Guo, Na; Yao, Chuanhao; Chen, Cheng; Liu, Wei; Du, Yonghua; Yan, Huan; Li, Jing; Chen, Zhongxin; Li, Xing; Li, Zejun; Xu, Haomin; Lyu, Pin; Zhang, Jia; Lin, Ming; Su, Chenliang; Pennycook, Stephen J; Zhang, Chun; Xi, Shibo; Lu, Jiong Engineering Local and Global Structures of Single Co Atoms for a Superior Oxygen Reduction Reaction Journal Article 16 ACS CATALYSIS, 10 (10), pp. 5862-5870, 2020, ISSN: 2155-5435. @article{ISI:000535291500050, title = {Engineering Local and Global Structures of Single Co Atoms for a Superior Oxygen Reduction Reaction}, author = {Xiao Hai and Xiaoxu Zhao and Na Guo and Chuanhao Yao and Cheng Chen and Wei Liu and Yonghua Du and Huan Yan and Jing Li and Zhongxin Chen and Xing Li and Zejun Li and Haomin Xu and Pin Lyu and Jia Zhang and Ming Lin and Chenliang Su and Stephen J Pennycook and Chun Zhang and Shibo Xi and Jiong Lu}, doi = {10.1021/acscatal.0c00936}, times_cited = {16}, issn = {2155-5435}, year = {2020}, date = {2020-05-15}, journal = {ACS CATALYSIS}, volume = {10}, number = {10}, pages = {5862-5870}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {The ability to tune both local and global environments of a single metal active center on a support is crucial for the development of highly robust and efficient single-atom electrocatalysts (SAECs) that can surmount both thermodynamic and kinetic constraints in electrocatalysis. Here, we designed a core-shell-structured SAEC (Co-1-SAC) with superior oxygen reduction reaction (ORR) performance. Co-1-SAC consists of a locally engineered single Co-N3C1 site on a N-doped microporous amorphous carbon support enveloped by a globally engineered highly conductive mesoporous graphitic carbon shell. Theoretical calculations reveal that Co-N3C1 exhibits near-Fermi electronic states distinct from those of Co-N2C2 and Co-N-4, which facilitate both the electronic hybridization with O-2 and the subsequent protonation of adsorbed O-2* toward the formation of OOH*. Engineering Co-N3C1-SAC into a micro/mesoporous structure dramatically enhances the mass transport and electron transfer, which further boosts the ORR and Zn-air battery performance (slightly outperforming Pt/C). Our findings open an avenue toward engineering of the local and global environment of SACs for a wide range of efficient electrochemical conversions.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The ability to tune both local and global environments of a single metal active center on a support is crucial for the development of highly robust and efficient single-atom electrocatalysts (SAECs) that can surmount both thermodynamic and kinetic constraints in electrocatalysis. Here, we designed a core-shell-structured SAEC (Co-1-SAC) with superior oxygen reduction reaction (ORR) performance. Co-1-SAC consists of a locally engineered single Co-N3C1 site on a N-doped microporous amorphous carbon support enveloped by a globally engineered highly conductive mesoporous graphitic carbon shell. Theoretical calculations reveal that Co-N3C1 exhibits near-Fermi electronic states distinct from those of Co-N2C2 and Co-N-4, which facilitate both the electronic hybridization with O-2 and the subsequent protonation of adsorbed O-2* toward the formation of OOH*. Engineering Co-N3C1-SAC into a micro/mesoporous structure dramatically enhances the mass transport and electron transfer, which further boosts the ORR and Zn-air battery performance (slightly outperforming Pt/C). Our findings open an avenue toward engineering of the local and global environment of SACs for a wide range of efficient electrochemical conversions. |
Yam, Kah Meng; Guo, Na; Jiang, Zhuoling; Li, Shulong; Zhang, Chun Graphene-Based Heterogeneous Catalysis: Role of Graphene Journal Article 24 CATALYSTS, 10 (1), 2020. @article{WOS:000516825000053, title = {Graphene-Based Heterogeneous Catalysis: Role of Graphene}, author = {Kah Meng Yam and Na Guo and Zhuoling Jiang and Shulong Li and Chun Zhang}, doi = {10.3390/catal10010053}, times_cited = {24}, year = {2020}, date = {2020-01-01}, journal = {CATALYSTS}, volume = {10}, number = {1}, publisher = {MDPI}, address = {ST ALBAN-ANLAGE 66, CH-4052 BASEL, SWITZERLAND}, abstract = {Graphene, the reincarnation of a surface, offers new opportunities in catalytic applications, not only because of its peculiar electronic structure, but also because of the ease of modulating it. A vast number of proposals have been made to support this point, but there has been a lack of a systematic understanding of the different roles of graphene, as many other reviews published have focused on the synthesis and characterization of the various graphene-based catalysts. In this review, we surveyed the vast literature related to various theoretical proposals and experimental realizations of graphene-based catalysts to first classify and then elucidate the different roles played by graphene in solid-state heterogeneous catalysis. Owing to its one-atom thickness and zero bandgap with low density of states around Fermi level, graphene has great potential in catalysis applications. In general, graphene can function as a support for catalysts, a cover to protect catalysts, or the catalytic center itself. Understanding these functions is important in the design of catalysts in terms of how to optimize the electronic structure of the active sites for particular applications, a few case studies of which will be presented for each role.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Graphene, the reincarnation of a surface, offers new opportunities in catalytic applications, not only because of its peculiar electronic structure, but also because of the ease of modulating it. A vast number of proposals have been made to support this point, but there has been a lack of a systematic understanding of the different roles of graphene, as many other reviews published have focused on the synthesis and characterization of the various graphene-based catalysts. In this review, we surveyed the vast literature related to various theoretical proposals and experimental realizations of graphene-based catalysts to first classify and then elucidate the different roles played by graphene in solid-state heterogeneous catalysis. Owing to its one-atom thickness and zero bandgap with low density of states around Fermi level, graphene has great potential in catalysis applications. In general, graphene can function as a support for catalysts, a cover to protect catalysts, or the catalytic center itself. Understanding these functions is important in the design of catalysts in terms of how to optimize the electronic structure of the active sites for particular applications, a few case studies of which will be presented for each role. |
2019 |
Nandakumar, Dilip Krishna; Zhang, Yaoxin; Ravi, Sai Kishore; Guo, Na; Zhang, Chun; Tan, Swee Ching Solar Energy Triggered Clean Water Harvesting from Humid Air Existing above Sea Surface Enabled by a Hydrogel with Ultrahigh Hygroscopicity Journal Article ADVANCED MATERIALS, 31 (10), 2019, ISSN: 0935-9648. @article{ISI:000460329300019, title = {Solar Energy Triggered Clean Water Harvesting from Humid Air Existing above Sea Surface Enabled by a Hydrogel with Ultrahigh Hygroscopicity}, author = {Dilip Krishna Nandakumar and Yaoxin Zhang and Sai Kishore Ravi and Na Guo and Chun Zhang and Swee Ching Tan}, doi = {10.1002/adma.201806730}, times_cited = {0}, issn = {0935-9648}, year = {2019}, date = {2019-03-08}, journal = {ADVANCED MATERIALS}, volume = {31}, number = {10}, publisher = {WILEY-V C H VERLAG GMBH}, address = {POSTFACH 101161, 69451 WEINHEIM, GERMANY}, abstract = {Water scarcity is a ubiquitous problem with its magnitude expected to rise in the near future, and efforts to seek alternative water sources are on the rise. Harvesting water from air has intrigued enormous research interest among many groups with Scientific American listing this technology as the second most impactful technology that can bring about a massive change in people's lives. Though desalination offers a huge prospect in mitigating water crisis, its practicality is limited by exorbitant energy requirement. Alternatively, the air above sea water is moisture rich, with the quantity of vapor increasing at the rate of 0.41 kg m(-2). Herein, a method to sustainably harvest water from this moisture rich zone is demonstrated by employing a nanoporous superhygroscopic hydrogel, which is capable of absorbing water from highly humid atmospheres by over 420% (highest) of its own weight. The desorption process from the hydrogel, occurring at 55 degrees C (lowest), is triggered by natural sunlight (A.M 1.5) thereby ensuing an external energy-less water harvesting approach. The hydrogel exhibits excellent stability even after 1000 absorption/desorption cycles. Through multiple absorption/desorption cycles, it is possible to harvest over 10 L water per kg of hydrogel daily.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Water scarcity is a ubiquitous problem with its magnitude expected to rise in the near future, and efforts to seek alternative water sources are on the rise. Harvesting water from air has intrigued enormous research interest among many groups with Scientific American listing this technology as the second most impactful technology that can bring about a massive change in people's lives. Though desalination offers a huge prospect in mitigating water crisis, its practicality is limited by exorbitant energy requirement. Alternatively, the air above sea water is moisture rich, with the quantity of vapor increasing at the rate of 0.41 kg m(-2). Herein, a method to sustainably harvest water from this moisture rich zone is demonstrated by employing a nanoporous superhygroscopic hydrogel, which is capable of absorbing water from highly humid atmospheres by over 420% (highest) of its own weight. The desorption process from the hydrogel, occurring at 55 degrees C (lowest), is triggered by natural sunlight (A.M 1.5) thereby ensuing an external energy-less water harvesting approach. The hydrogel exhibits excellent stability even after 1000 absorption/desorption cycles. Through multiple absorption/desorption cycles, it is possible to harvest over 10 L water per kg of hydrogel daily. |
2018 |
Leng, Kai; Abdelwahab, Ibrahim; Verzhbitskiy, Ivan; Telychko, Mykola; Chu, Leiqiang; Fu, Wei; Chi, Xiao; Guo, Na; Chen, Zhihui; Chen, Zhongxin; Zhang, Chun; Xu, Qing-Hua; Lu, Jiong; Chhowalla, Manish; Eda, Goki; Loh, Kian Ping Molecularly thin two-dimensional hybrid perovskites with tunable optoelectronic properties due to reversible surface relaxation Journal Article NATURE MATERIALS, 17 (10), pp. 908-+, 2018, ISSN: 1476-1122. @article{ISI:000445410900016, title = {Molecularly thin two-dimensional hybrid perovskites with tunable optoelectronic properties due to reversible surface relaxation}, author = {Kai Leng and Ibrahim Abdelwahab and Ivan Verzhbitskiy and Mykola Telychko and Leiqiang Chu and Wei Fu and Xiao Chi and Na Guo and Zhihui Chen and Zhongxin Chen and Chun Zhang and Qing-Hua Xu and Jiong Lu and Manish Chhowalla and Goki Eda and Kian Ping Loh}, doi = {10.1038/s41563-018-0164-8}, times_cited = {0}, issn = {1476-1122}, year = {2018}, date = {2018-10-01}, journal = {NATURE MATERIALS}, volume = {17}, number = {10}, pages = {908-+}, publisher = {NATURE PUBLISHING GROUP}, address = {MACMILLAN BUILDING, 4 CRINAN ST, LONDON N1 9XW, ENGLAND}, abstract = {Due to their layered structure, two-dimensional Ruddlesden-Popper perovskites (RPPs), composed of multiple organic/inorganic quantum wells, can in principle be exfoliated down to few and single layers. These molecularly thin layers are expected to present unique properties with respect to the bulk counterpart, due to increased lattice deformations caused by interface strain. Here, we have synthesized centimetre-sized, pure-phase single-crystal RPP perovskites (CH3(CH2)(3)NH3)(2)(CH3NH3)n(-1)Pb(n)I(3n+1) (n = 1-4) from which single quantum well layers have been exfoliated. We observed a reversible shift in excitonic energies induced by laser annealing on exfoliated layers encapsulated by hexagonal boron nitride. Moreover, a highly efficient photodetector was fabricated using a molecularly thin n = 4 RPP crystal, showing a photogain of 10(5) and an internal quantum efficiency of similar to 34%. Our results suggest that, thanks to their dynamic structure, atomically thin perovskites enable an additional degree of control for the bandgap engineering of these materials}, keywords = {}, pubstate = {published}, tppubtype = {article} } Due to their layered structure, two-dimensional Ruddlesden-Popper perovskites (RPPs), composed of multiple organic/inorganic quantum wells, can in principle be exfoliated down to few and single layers. These molecularly thin layers are expected to present unique properties with respect to the bulk counterpart, due to increased lattice deformations caused by interface strain. Here, we have synthesized centimetre-sized, pure-phase single-crystal RPP perovskites (CH3(CH2)(3)NH3)(2)(CH3NH3)n(-1)Pb(n)I(3n+1) (n = 1-4) from which single quantum well layers have been exfoliated. We observed a reversible shift in excitonic energies induced by laser annealing on exfoliated layers encapsulated by hexagonal boron nitride. Moreover, a highly efficient photodetector was fabricated using a molecularly thin n = 4 RPP crystal, showing a photogain of 10(5) and an internal quantum efficiency of similar to 34%. Our results suggest that, thanks to their dynamic structure, atomically thin perovskites enable an additional degree of control for the bandgap engineering of these materials |
Bogaert, Kevin; Liu, Song; Liu, Tao; Guo, Na; Zhang, Chun; Gradecak, Silvija; Garaj, Slaven Two-Dimensional MoxW1-xS2 Graded Alloys: Growth and Optical Properties Journal Article SCIENTIFIC REPORTS, 8 , 2018, ISSN: 2045-2322. @article{ISI:000442870300067, title = {Two-Dimensional Mo\textit{_{x}}W_{1-\textit{x}}S_{2} Graded Alloys: Growth and Optical Properties}, author = {Kevin Bogaert and Song Liu and Tao Liu and Na Guo and Chun Zhang and Silvija Gradecak and Slaven Garaj}, doi = {10.1038/s41598-018-31220-z}, times_cited = {0}, issn = {2045-2322}, year = {2018}, date = {2018-08-27}, journal = {SCIENTIFIC REPORTS}, volume = {8}, publisher = {NATURE PORTFOLIO}, address = {HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY}, abstract = {Two-dimensional (2D) transition metal dichalcogenides can be alloyed by substitution at the metal atom site with negligible effect on lattice strain, but with significant influence on optical and electrical properties. In this work, we establish the relationship between composition and optical properties of the MoxW1-xS2 alloy by investigating the effect of continuously-varying composition on photoluminescence intensity. We developed a new process for growth of two-dimensional MoxW1-xS2 alloys that span nearly the full composition range along a single crystal, thus avoiding any sample-related heterogeneities. The graded alloy crystals were grown using a diffusion-based chemical vapor deposition (CVD) method that starts by synthesizing a WS2 crystal with a graded point defect distribution, followed by Mo alloying in the second stage. We show that point defects promote the diffusion and alloying, as confirmed by Raman and photoluminescence measurements, density functional theory calculations of the reaction path, and observation that no alloying occurs in CVD-treated exfoliated crystals with low defect density. We observe a significant dependence of the optical quantum yield as a function of the alloy composition reaching the maximum intensity for the equicompositional Mo0.5W0.5S2 alloy. Furthermore, we map the growth-induced strain distribution within the alloyed crystals to decouple composition and strain effects on optical properties: at the same composition, we observe significant decrease in quantum yield with induced strain. Our approach is generally applicable to other 2D materials as well as the optimization of other composition-dependent properties within a single crystal.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Two-dimensional (2D) transition metal dichalcogenides can be alloyed by substitution at the metal atom site with negligible effect on lattice strain, but with significant influence on optical and electrical properties. In this work, we establish the relationship between composition and optical properties of the MoxW1-xS2 alloy by investigating the effect of continuously-varying composition on photoluminescence intensity. We developed a new process for growth of two-dimensional MoxW1-xS2 alloys that span nearly the full composition range along a single crystal, thus avoiding any sample-related heterogeneities. The graded alloy crystals were grown using a diffusion-based chemical vapor deposition (CVD) method that starts by synthesizing a WS2 crystal with a graded point defect distribution, followed by Mo alloying in the second stage. We show that point defects promote the diffusion and alloying, as confirmed by Raman and photoluminescence measurements, density functional theory calculations of the reaction path, and observation that no alloying occurs in CVD-treated exfoliated crystals with low defect density. We observe a significant dependence of the optical quantum yield as a function of the alloy composition reaching the maximum intensity for the equicompositional Mo0.5W0.5S2 alloy. Furthermore, we map the growth-induced strain distribution within the alloyed crystals to decouple composition and strain effects on optical properties: at the same composition, we observe significant decrease in quantum yield with induced strain. Our approach is generally applicable to other 2D materials as well as the optimization of other composition-dependent properties within a single crystal. |
Yan, Huan; Zhao, Xiaoxu; Guo, Na; Lyu, Zhiyang; Du, Yonghua; Xi, Shibo; Guo, Rui; Chen, Cheng; Chen, Zhongxin; Liu, Wei; Yao, Chuanhao; Li, Jing; Pennycook, Stephen J; Chen, Wei; Su, Chenliang; Zhang, Chun; Lu, Jiong Atomic engineering of high-density isolated Co atoms on graphene with proximal-atom controlled reaction selectivity Journal Article NATURE COMMUNICATIONS, 9 , 2018, ISSN: 2041-1723. @article{ISI:000442381600001, title = {Atomic engineering of high-density isolated Co atoms on graphene with proximal-atom controlled reaction selectivity}, author = {Huan Yan and Xiaoxu Zhao and Na Guo and Zhiyang Lyu and Yonghua Du and Shibo Xi and Rui Guo and Cheng Chen and Zhongxin Chen and Wei Liu and Chuanhao Yao and Jing Li and Stephen J Pennycook and Wei Chen and Chenliang Su and Chun Zhang and Jiong Lu}, doi = {10.1038/s41467-018-05754-9}, times_cited = {0}, issn = {2041-1723}, year = {2018}, date = {2018-08-23}, journal = {NATURE COMMUNICATIONS}, volume = {9}, publisher = {NATURE PUBLISHING GROUP}, address = {MACMILLAN BUILDING, 4 CRINAN ST, LONDON N1 9XW, ENGLAND}, abstract = {Controllable synthesis of single atom catalysts (SACs) with high loading remains challenging due to the aggregation tendency of metal atoms as the surface coverage increases. Here we report the synthesis of graphene supported cobalt SACs (Co-1/G) with a tuneable high loading by atomic layer deposition. Ozone treatment of the graphene support not only eliminates the undesirable ligands of the pre-deposited metal precursors, but also regenerates active sites for the precise tuning of the density of Co atoms. The Co-1/G SACs also demonstrate exceptional activity and high selectivity for the hydrogenation of nitroarenes to produce azoxy aromatic compounds, attributable to the formation of a coordinatively unsaturated and positively charged catalytically active center (Co-O-C) arising from the proximal-atom induced partial depletion of the 3d Co orbitals. Our findings pave the way for the precise engineering of the metal loading in a variety of SACs for superior catalytic activities.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Controllable synthesis of single atom catalysts (SACs) with high loading remains challenging due to the aggregation tendency of metal atoms as the surface coverage increases. Here we report the synthesis of graphene supported cobalt SACs (Co-1/G) with a tuneable high loading by atomic layer deposition. Ozone treatment of the graphene support not only eliminates the undesirable ligands of the pre-deposited metal precursors, but also regenerates active sites for the precise tuning of the density of Co atoms. The Co-1/G SACs also demonstrate exceptional activity and high selectivity for the hydrogenation of nitroarenes to produce azoxy aromatic compounds, attributable to the formation of a coordinatively unsaturated and positively charged catalytically active center (Co-O-C) arising from the proximal-atom induced partial depletion of the 3d Co orbitals. Our findings pave the way for the precise engineering of the metal loading in a variety of SACs for superior catalytic activities. |