Co-reporter:Jingyuan Liu;Wei Kong Pang;Tong Zhou;Long Chen;Yonggang Wang;Vanessa K. Peterson;Zaiping Guo;Yongyao Xia
Energy & Environmental Science (2008-Present) 2017 vol. 10(Issue 6) pp:1456-1464
Publication Date(Web):2017/06/14
DOI:10.1039/C7EE00763A
To date, anode materials for lithium-ion batteries (LIBs) have been dominated by carbonaceous materials, which have a low intercalation potential but easily allow lithium dendrites to form under high current density, leading to a safety risk. The other anode material, the “zero-strain” spinel-structured Li4Ti5O12, with a ∼1.5 V vs. Li+/Li intercalation potential, exhibits excellent cycling stability and avoids the issues of dendrite growth and Li plating. The low capacity and high voltage of Li4Ti5O12, however, result in low energy density. Herein, we report a new and environmentally friendly anode material, Li2TiSiO5, which delivers a capacity as high as 308 mA h g−1, with a working potential of 0.28 V vs. Li+/Li, and excellent cycling stability. The lithium-storage mechanism of this material is also proposed based on the combination of in situ synchrotron X-ray diffraction, neutron powder diffraction with Fourier density mapping, ex situ X-ray absorption near edge structure analysis, ex situ transmission electron microscopy, and density-functional theory calculations with the projector-augmented-wave formalism. The lithium-storage mechanism of this material is shown to involve a two-electron (Ti4+/Ti2+ redox) conversion reaction between TiO and Li4SiO4.
Co-reporter:Yongcheng Wang;Tong Zhou;Kun Jiang;Peimei Da;Zheng Peng;Jing Tang;Biao Kong;Wen-Bin Cai;Gengfeng Zheng
Advanced Energy Materials 2014 Volume 4( Issue 16) pp:
Publication Date(Web):
DOI:10.1002/aenm.201400696
While electrochemical water splitting is one of the most promising methods to store light/electrical energy in chemical bonds, a key challenge remains in the realization of an efficient oxygen evolution reaction catalyst with large surface area, good electrical conductivity, high catalytic properties, and low fabrication cost. Here, a facile solution reduction method is demonstrated for mesoporous Co3O4 nanowires treated with NaBH4. The high-surface-area mesopore feature leads to efficient surface reduction in solution at room temperature, which allows for retention of the nanowire morphology and 1D charge transport behavior, while at the same time substantially increasing the oxygen vacancies on the nanowire surface. Compared to pristine Co3O4 nanowires, the reduced Co3O4 nanowires exhibit a much larger current of 13.1 mA cm-2 at 1.65 V vs reversible hydrogen electrode (RHE) and a much lower onset potential of 1.52 V vs RHE. Electrochemical supercapacitors based on the reduced Co3O4 nanowires also show a much improved capacitance of 978 F g-1 and reduced charge transfer resistance. Density-functional theory calculations reveal that the existence of oxygen vacancies leads to the formation of new gap states in which the electrons previously associated with the Co-O bonds tend to be delocalized, resulting in the much higher electrical conductivity and electrocatalytic activity.
Co-reporter:Dongwei Ma, Zhongyao Li, Zhongqin Yang
Carbon 2012 Volume 50(Issue 1) pp:297-305
Publication Date(Web):January 2012
DOI:10.1016/j.carbon.2011.08.055
Spin–orbit (SO) splitting in graphene with adsorbed Au atoms is investigated by using a first-principles method. Considerable (∼200 meV) Rashba-type SO splitting can be achieved in the graphene π bands. When a Au atom is adsorbed above a C–C bond, Dresselhaus-type SO splitting is found to be present due to the absence of inversion symmetry and the substantial contribution of Au 5dxz components. The influence of strains in graphene on SO splitting is also explored. A slight strain with the strength of −5% to 5% usually does not change much the SO splitting. The variation of SO splitting versus strain strength is rationalized through structural relaxation and effective hybridization between C 2pz and certain Au 5d states. Our study predicts a new way to increase the SO splitting in graphene and provides useful understanding of the mechanism.
Co-reporter:Yipeng An, Xinyuan Wei and Zhongqin Yang
Physical Chemistry Chemical Physics 2012 vol. 14(Issue 45) pp:15802-15806
Publication Date(Web):26 Sep 2012
DOI:10.1039/C2CP42123B
Using an ab initio method, we explored electronic structures and transport properties of zigzag graphene nanoribbons (ZGNRs) with ordered doping of B or N atoms. We find B or N atoms doping can increase significantly the conductance of the ZGNRs with an even number of zigzag chains due to additional conducting channels being induced and the breakdown of parity limitation. The higher the doping concentration, the larger the current amplification factor obtained. For the nanojunctions with one row B (or N) atoms, the current amplification factor can be larger when the doping position is near to the center, while for the junction with two rows, the trend is subtle due to the interactions between the two rows of B (or N) atoms. Negative differential resistive phenomena are found for the case of B doping at low concentrations and the case for N doping. The conductance of the ZGNR with odd numbers of zigzag chains can also be increased by doping of B or N atoms. More interestingly, the B or N doping can almost completely remove the even–odd effect on electronic transport of the ZGNRs. Our studies provide avenues to drastically improve the electronic transport of ZGNRs, helpful for graphene applications.
Co-reporter:Yipeng An ; Wei Ji
The Journal of Physical Chemistry C 2012 Volume 116(Issue 9) pp:5915-5919
Publication Date(Web):February 18, 2012
DOI:10.1021/jp3003646
Electronic transport properties of zigzag graphene nanoribbons (ZGNRs) with one or two triangle protrusions at the edges are studied by using density functional theory combined with nonequilibrium Green’s function method. We find the protrusion generally breaks down the edge state along the same edge, which carries the most current in the junction. For the graphene ribbons having even number of zigzag chains, however, the protrusions can increase or decrease significantly the conductance with different relative position of the two protrusions, accompanied by negative differential resistance characteristics. The abnormal increase of the conductance is ascribed to the forming of a new Z-like conducting pathway as well as the ruining of the mirror symmetry of the ribbons. In terms of odd ZGNRs, the introduction of edge protrusions only suppresses current flow and linear I–V curves are achieved. These edge-modified ways make the graphene-based nanomaterials present more abundant electronic transport phenomena and can be useful for the design of future nanoelectronic devices.
Co-reporter:ZhenHua Zhang;JianHui Yuan;Ming Qiu
Science Bulletin 2007 Volume 52( Issue 21) pp:3016-3019
Publication Date(Web):2007 November
DOI:10.1007/s11434-007-0429-0
Using a spatially symmetric phenyldithiolate molecule sandwiched between two gold electrodes as model system and through shifting one electrode from symmetric contact site to form asymmetric contact, we investigated the properties of electronic transport in such a device by the first-principles. It was found that the I(G)-V characteristics of a device show significant asymmetry and the magnitudes of current and conductance depend remarkably on the variation of molecule-metal distance at one of the two contacts. Namely, an asymmetric contact would lead to the weak rectifying effects on the current-voltage characteristics of a molecular device. The analysis shows that the HOMO is responsible for the resonant tunneling and its shift due to the charging of the device while the bias voltage is the intrinsic origin of asymmetric I(G)-V characteristics.
Co-reporter:Tong Zhou; Jiayong Zhang; Bao Zhao; Huisheng Zhang
Nano Letter () pp:
Publication Date(Web):July 14, 2015
DOI:10.1021/acs.nanolett.5b01373
Electronic and topological behaviors of Sb(111) monolayers decorated with H and certain magnetic atoms are investigated by using ab initio methods. The drastic exchange field induced by the magnetic atoms, together with strong spin–orbit coupling (SOC) of Sb atoms, generates one new category of valley polarized topological insulators, called quantum spin-quantum anomalous Hall (QSQAH) insulators in the monolayer, with a band gap up to 53 meV. The strong SOC is closely related to Sb px and py orbitals, instead of pz orbitals in usual two-dimensional (2D) materials. Topological transitions from quantum anomalous Hall states to QSQAH states and then to time-reversal-symmetry-broken quantum spin Hall states are achieved by tuning the SOC strength. The behind mechanism is revealed. Our work is helpful for future valleytronic and spintronic applications in 2D materials.
Co-reporter:Yipeng An, Xinyuan Wei and Zhongqin Yang
Physical Chemistry Chemical Physics 2012 - vol. 14(Issue 45) pp:NaN15806-15806
Publication Date(Web):2012/09/26
DOI:10.1039/C2CP42123B
Using an ab initio method, we explored electronic structures and transport properties of zigzag graphene nanoribbons (ZGNRs) with ordered doping of B or N atoms. We find B or N atoms doping can increase significantly the conductance of the ZGNRs with an even number of zigzag chains due to additional conducting channels being induced and the breakdown of parity limitation. The higher the doping concentration, the larger the current amplification factor obtained. For the nanojunctions with one row B (or N) atoms, the current amplification factor can be larger when the doping position is near to the center, while for the junction with two rows, the trend is subtle due to the interactions between the two rows of B (or N) atoms. Negative differential resistive phenomena are found for the case of B doping at low concentrations and the case for N doping. The conductance of the ZGNR with odd numbers of zigzag chains can also be increased by doping of B or N atoms. More interestingly, the B or N doping can almost completely remove the even–odd effect on electronic transport of the ZGNRs. Our studies provide avenues to drastically improve the electronic transport of ZGNRs, helpful for graphene applications.
Co-reporter:Tong Zhou, Cheng Zhang, Huisheng Zhang, Faxian Xiu and Zhongqin Yang
Inorganic Chemistry Frontiers 2016 - vol. 3(Issue 12) pp:NaN1643-1643
Publication Date(Web):2016/11/01
DOI:10.1039/C6QI00383D
We report an investigation of temperature- and doping-dependent thermoelectric behavior of the topological semimetal Cd3As2. The electrical conductivity, thermal conductivity, Seebeck coefficient, and figure of merit (ZT) are calculated using the Boltzmann transport theory. The calculated thermoelectric properties of the pristine Cd3As2 match well with the experimental results. Electron or hole doping, especially the latter, is found to much improve the thermoelectric behavior of the material. The optimum figure of merit ZT of Cd3As2 with electron doping is found to be about 0.5 at T = 700 K with n = 1 × 1020 cm−3, which is much larger than the maximum experimental value obtained for pristine Cd3As2 (∼0.15). For p-type Cd3As2, the maximal value of the Seebeck coefficient as a function of temperature increases apparently with the increase of the hole doping concentration and its position shifts drastically towards the lower temperature region, compared to that of n-type Cd3As2. This leads to an optimum figure of merit ZT of about 0.5, obtained at a low temperature of 500 K (p = 1 × 1020 cm−3) in the p-type Cd3As2.
