Lei Wang

Bio: Lei Wang is an academic researcher from Qingdao University of Science and Technology. The author has contributed to research in topics: Materials science & Medicine. The author has an hindex of 95, co-authored 1486 publications receiving 44636 citations. Previous affiliations of Lei Wang include Northwestern Polytechnical University & Chinese Ministry of Education.

Oxygen Vacancy Clusters Promoting Reducibility and Activity of Ceria Nanorods

Abstract: CeO2 is a catalytic material of exceptional technological importance, and the precise role of oxygen vacancies is crucial to the greater understanding of these oxide materials. In this work, two ceria nanorod samples with different types and distributions of oxygen vacancies were synthesized. A direct relationship between the concentration of the larger size oxygen vacancy clusters and the reducibility/reactivity of nanosized ceria was revealed. These results may be an important step in understanding and designing active sites at the surface of metal oxide catalytic materials.

Reversible epitaxial electrodeposition of metals in battery anodes.

Abstract: The propensity of metals to form irregular and nonplanar electrodeposits at liquid-solid interfaces has emerged as a fundamental barrier to high-energy, rechargeable batteries that use metal anodes. We report an epitaxial mechanism to regulate nucleation, growth, and reversibility of metal anodes. The crystallographic, surface texturing, and electrochemical criteria for reversible epitaxial electrodeposition of metals are defined and their effectiveness demonstrated by using zinc (Zn), a safe, low-cost, and energy-dense battery anode material. Graphene, with a low lattice mismatch for Zn, is shown to be effective in driving deposition of Zn with a locked crystallographic orientation relation. The resultant epitaxial Zn anodes achieve exceptional reversibility over thousands of cycles at moderate and high rates. Reversible electrochemical epitaxy of metals provides a general pathway toward energy-dense batteries with high reversibility.

From coconut shell to porous graphene-like nanosheets for high-power supercapacitors

Abstract: Sheet-like graphitic carbon with a porous structure can provide low-resistant pathways and short ion-diffusion channels for energy storage, and thus is expected to be an excellent material for high-power supercapacitors. Herein, porous graphene-like nanosheets (PGNSs) with a large surface area were synthesized for the first time via an easy and cost-effective SAG (simultaneous activation–graphitization) route from renewable biomass waste coconut shell. In the synthesis, the graphitic catalyst precursor (FeCl3) and activating agent (ZnCl2) were introduced simultaneously into the skeleton of the coconut shell through coordination of the metal precursor with the functional groups in the coconut shell, thus making simultaneous realization of activation and graphitization of the carbon source under heat treatment. Notably, the iron catalyst in the framework of the coconut shell can generate a carburized phase which plays a key role in the formation of a graphene-like structure during the pyrolytic process. Our results indicated that PGNSs possess good electrical conductivity due to the high graphitic degree, exceptionally high Brunauer–Emmett–Teller surface area (SBET = 1874 m2 g−1) and large pore volume (1.21 cm3 g−1). While being used as a supercapacitor electrode without the use of any conductive additives, PGNSs exhibit a high specific capacitance of 268 F g−1, much higher than that of activated carbon (210 F g−1) fabricated by only activation and graphitic carbon (117 F g−1) by only graphitization at 1 A g−1. Also, PGNSs show superior cycle durability and Coulombic efficiency over 99.5% after 5000 cycles in KOH. Remarkably, in an organic electrolyte, PGNSs also display an outstanding capacitance of 196 F g−1 at 1 A g−1. An energy density of up to 54.7 W h kg−1 could be achieved at a high power density of 10 kW kg−1. The SAG strategy developed here would provide a novel route for low-cost and large-scale production of PGNS electrode materials for high-power supercapacitors.

Nitrogen-doped graphene with high nitrogen level via a one-step hydrothermal reaction of graphene oxide with urea for superior capacitive energy storage

Abstract: Nitrogen-doped graphene nanosheets (NGS) with the nitrogen level as high as 10.13 atom% were synthesized via a simple hydrothermal reaction of graphene oxide (GO) and urea. N-doping and reduction of GO were achieved simultaneously under the hydrothermal reaction. In the fabrication, the nitrogen-enriched urea plays a pivotal role in forming the NGS with a high nitrogen level. During the hydrothermal process, the N-dopant of urea could release NH3 in a sustained manner, accompanied by the released NH3 reacting with the oxygen functional groups of the GO and then the nitrogen atoms doped into graphene skeleton, leading to the formation of NGS. The nitrogen level and species could be conveniently controlled by easily tuning the experimental parameters, including the mass ratio between urea and GO and the hydrothermal temperature. Remarkably, in 6 M KOH electrolyte, the synthesized NGS with both high nitrogen (10.13 atom%) and large surface area (593 m2 g−1) exhibits excellent capacitive behaviors (326 F g−1, 0.2 A g−1), superior cycling stability (maintaining initial capacity even) and coulombic efficiency (99.58%) after 2000 cycles. The energy density of 25.02 Wh kg−1 could be achieved at power density of 7980 W kg−1 by a two-electrode symmetric capacitor test. A series of experiments results demonstrated that not only the N-content but also the N-type are very significant for the capacitive behaviors. In more detail, the pyridinic-N and pyrrolic-N play mainly roles for improving pseudo-capacitance by the redox reaction, while quaternary-N could enhance the conductivity of the materials which is favorable to the transport of electrons during the charge/discharge process. Hence, the approach in this work could provide a new way for preparing NGS materials which could be used as advanced electrodes in high performance supercapacitors.

Phosphorus‐Modified Tungsten Nitride/Reduced Graphene Oxide as a High‐Performance, Non‐Noble‐Metal Electrocatalyst for the Hydrogen Evolution Reaction

Abstract: Phosphorus-modified tungsten nitride/reduced graphene oxide (P-WN/rGO) is designed as a high-efficient, low-cost electrocatalyst for the hydrogen evolution reaction (HER). WN (ca. 3 nm in size) on rGO is first synthesized by using the H3[PO4(W3O9)4] cluster as a W source. Followed by phosphorization, the particle size increase slightly to about 4 nm with a P content of 2.52 at %. The interaction of P with rGO and WN results in an obvious increase of work function, being close to Pt metal. The P-WN/rGO exhibits low onset overpotential of 46 mV, Tafel slope of 54 mV dec−1, and a large exchange current density of 0.35 mA cm−2 in acid media. It requires overpotential of only 85 mV at current density of 10 mA cm−2, while remaining good stability in accelerated durability testing. This work shows that the modification with a second anion is powerful way to design new catalysts for HER.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Numerical study of convection observed during the Winter Monsoon Experiment using a mesoscale two-dimensional model [presentation]

Abstract: Abstract A two-dimensional version of the Pennsylvania State University mesoscale model has been applied to Winter Monsoon Experiment data in order to simulate the diurnally occurring convection observed over the South China Sea. The domain includes a representation of part of Borneo as well as the sea so that the model can simulate the initiation of convection. Also included in the model are parameterizations of mesoscale ice phase and moisture processes and longwave and shortwave radiation with a diurnal cycle. This allows use of the model to test the relative importance of various heating mechanisms to the stratiform cloud deck, which typically occupies several hundred kilometers of the domain. Frank and Cohen's cumulus parameterization scheme is employed to represent vital unresolved vertical transports in the convective area. The major conclusions are: Ice phase processes are important in determining the level of maximum large-scale heating and vertical motion because there is a strong anvil componen...

Economic growth and income inequality

Abstract: We investigate whether income inequality affects subsequent growth in a cross-country sample for 1965-90, using the models of Barro (1997), Bleaney and Nishiyama (2002) and Sachs and Warner (1997), with negative results. We then investigate the evolution of income inequality over the same period and its correlation with growth. The dominating feature is inequality convergence across countries. This convergence has been significantly faster amongst developed countries. Growth does not appear to influence the evolution of inequality over time. Outline