Dong Wang

Bio: Dong Wang is an academic researcher from Chinese Academy of Sciences. The author has contributed to research in topic(s): Scanning tunneling microscope & Chirality (chemistry). The author has an hindex of 49, co-authored 491 publication(s) receiving 9970 citation(s). Previous affiliations of Dong Wang include University of Science and Technology of China & Shanghai University.

Space-confinement-induced synthesis of pyridinic- and pyrrolic-nitrogen-doped graphene for the catalysis of oxygen reduction

Abstract: The development of high-performance and low-cost catalytic materials for the oxygen reduction reaction (ORR) has been a major challenge for the large-scale application of fuel cells. Currently, platinum and platinum-based alloys are the most efficient ORR catalysts in fuel-cell cathodes; however, they cannot meet the demand for the widespread commercialization of fuel cells because of the scarcity of platinum. Thus, the ongoing search for platinum-free catalysts for the ORR has attracted much attention. Graphene, single-layer sheets of sp-hybridized carbon atoms, has attracted tremendous attention and research interest. The abundance of free-flowing p electrons in carbon materials composed of sp-hybridized carbon atoms makes these materials potential catalysts for reactions that require electrons, such as the ORR. However, these p electrons are too inert to be used directly in the ORR. In N-doped electron-rich carbon nanostructures, carbon p electrons have been shown to be activated through conjugation with lone-pair electrons from N dopants; thus, O2 molecules are reduced on the positively charged C atoms that neighbor N atoms. Recently, Hu and co-workers found that as long as the electroneutrality of the sp-hybridized carbon atoms is broken and charged sites that favor O2 adsorption are created, these materials will be transformed into active metal-free ORR electrocatalysts regardless of whether the dopants are electron-rich (e.g., N) or electrondeficient (e.g., B). Nitrogen-doped carbon (NC) materials are considered to be promising catalysts because of their acceptable ORR activity, low cost, good durability, and environmental friendliness. However, their ORR activity is less competitive, especially in acidic media. Relative to commercial Pt/C, the difference in the half-wave potential for ORR is within 25 mV in alkaline electrolytes but is greater than 200 mV in acidic electrolytes. The activity of NC materials can be enhanced through efficient N doping with sufficient active species that favor ORR and through an increase in electrical conductivity. The annealing of graphitized carbon materials, such as carbon nanotubes and microporous carbon black, in NH3 leads to insufficient substitution of nitrogen because of the well-ordered structure of the host materials. Alternatively, the direct pyrolysis of nitrogen-containing hydrocarbons or polymers produces NC materials with good incorporation of nitrogen. However, suitable pyrolysis temperatures are difficult to pinpoint; without optimization, temperatures that are excessively low or excessively high lead to low electronic conductivity or a remarkable loss of active N species, respectively. Recently, mesoporous-alumina-assisted and silica-template-assisted nitrogen incorporation, which can preserve a high content of N in synthesized NC materials, have been reported. However the activities of the resulting NC materials in the ORR were still significantly lower than that of Pt/C, even when the N content was as high as 10.7 atm%. Among three types of N atoms, that is, pyridinic, pyrrolic, and quaternary N, only the pyridinic and pyrrolic forms, which have planar structures, have been proven to be active in the ORR. In contrast, quaternary N atoms, which possess a 3D structure, are not active in the ORR. The low electrical conductivity of NC materials with quaternary N atoms results from the interruption of their p–p conjugation by the 3D structure and is thought to be predominantly responsible for the poor catalysis. Therefore, the synthesis of NC materials with more planar pyridinic and pyrrolic N atoms and fewer quaternary N atoms is important for the preparation of ORR-active catalysts. Herein, we present a novel strategy for the selective synthesis of pyridinicand pyrrolic-nitrogen-doped graphene (NG) by the use of layered montmorillonite (MMT) as a quasi-closed flat nanoreactor, which is open only along the perimeter to enable the entrance of aniline (AN) monomer molecules. The flat MMT nanoreactor, which is less than 1 nm thick, extensively constrains the formation of quaternary N because of its 3D structure but facilitates the formation of pyridinic and pyrrolic N. Nitrogen is well-known to be incorporated into quaternary N in tetrahedral sp hybridization but incorporated into pyridinic and pyrrolic N in planar sp hybridization. The confinement effect of MMT ensures that N is incorporated into the structure and that the graphitization is successful without significant loss of N species. Furthermore, planar pyridinic and pyrrolic N can be [*] Dr. W. Ding, Prof. Z.-D. Wei, Dr. S.-G. Chen, Dr. X.-Q. Qi, Dr. T. Yang, Dr. S. F. Alvi, Dr. L. Li The State Key Laboratory of Power Transmission Equipment and System Security and New Technology, College of Chemistry and Chemical Engineering, Chongqing University Shapingba 174, Chongqing (China) E-mail: zdwei@cqu.edu.cn

On-surface synthesis of single-layered two-dimensional covalent organic frameworks via solid-vapor interface reactions.

Abstract: Surface covalent organic frameworks (SCOFs), featured by atomic thick sheet with covalently bonded organic building units, are promised to possess unique properties associated with reduced dimensionality, well-defined in-plane structure, and tunable functionality. Although a great deal of effort has been made to obtain SCOFs with different linkages and building blocks via both “top-down” exfoliation and “bottom-up” surface synthesis approaches, the obtained SCOFs generally suffer a low crystallinity, which impedes the understanding of intrinsic properties of the materials. Herein, we demonstrate a self-limiting solid–vapor interface reaction strategy to fabricate highly ordered SCOFs. The coupling reaction is tailored to take place at the solid–vapor interface by introducing one precursor via vaporization to the surface preloaded with the other precursor. Following this strategy, highly ordered honeycomb SCOFs with imine linkage are obtained. The controlled formation of SCOFs in our study shows the possib...

Oxygen-Aided Synthesis of Polycrystalline Graphene on Silicon Dioxide Substrates

Abstract: We report the metal-catalyst-free synthesis of high-quality polycrystalline graphene on dielectric substrates [silicon dioxide (SiO2) or quartz] using an oxygen-aided chemical vapor deposition (CVD) process The growth was carried out using a CVD system at atmospheric pressure After high-temperature activation of the growth substrates in air, high-quality polycrystalline graphene is subsequently grown on SiO2 by utilizing the oxygen-based nucleation sites The growth mechanism is analogous to that of growth for single-walled carbon nanotubes Graphene-modified SiO2 substrates can be directly used in transparent conducting films and field-effect devices The carrier mobilities are about 531 cm2 V–1 s–1 in air and 472 cm2 V–1 s–1 in N2, which are close to that of metal-catalyzed polycrystalline graphene The method avoids the need for either a metal catalyst or a complicated and skilled postgrowth transfer process and is compatible with current silicon processing techniques

Mesoporous Transition Metal Oxides for Supercapacitors.

Abstract: Recently, transition metal oxides, such as ruthenium oxide (RuO2), manganese dioxide (MnO2), nickel oxides (NiO) and cobalt oxide (Co3O4), have been widely investigated as electrode materials for pseudo-capacitors. In particular, these metal oxides with mesoporous structures have become very hot nanomaterials in the field of supercapacitors owing to their large specific surface areas and suitable pore size distributions. The high specific capacities of these mesoporous metal oxides are resulted from the effective contacts between electrode materials and electrolytes as well as fast transportation of ions and electrons in the bulk of electrode and at the interface of electrode and electrolyte. During the past decade, many achievements on mesoporous transition metal oxides have been made. In this mini-review, we select several typical nanomaterials, such as RuO2, MnO2, NiO, Co3O4 and nickel cobaltite (NiCo2O4), and briefly summarize the recent research progress of these mesoporous transition metal oxides-based electrodes in the field of supercapacitors.

Bio-inspired surface-functionalization of graphene oxide for the adsorption of organic dyes and heavy metal ions with a superhigh capacity

Abstract: By utilizing the synergistic effect of poly-dopamine (PD) with functional groups and graphene oxide (GO) with a high surface area, a series of sub-nano thick PD layer coated GO (PD/GO) composites were fabricated by a well-controlled self-polymerization of dopamine via catechol chemistry and used for effectively decontaminating wastewater. The obtained PD/GO could selectively adsorb the dyes containing an Eschenmoser structure and showed an extremely high adsorption capacity up to 2.1 g g−1, which represents the highest value among dye adsorptions reported so far. The adsorption mechanism was investigated by FTIR analysis, solution pH effect, and some control experiments. It was concluded that the adsorption process was based on the Eschenmoser salt assisted 1,4-Michael addition reaction between the ortho position of the catechol phenolic hydroxyl group of PD and Eschenmoser groups in the dyes. The adsorption isotherms were explored according to the Langmuir and Freundlich models respectively, and matched well with the Langmuir model. The thermodynamic parameters (ΔH, ΔG, ΔS, and E) were also calculated, which suggested an exothermic and spontaneous adsorption process. In addition, PD/GO exhibited an improved adsorption capacity for heavy metal ions (53.6 mg g−1 for Pb2+, 24.4 mg g−1 for Cu2+, 33.3 mg g−1 for Cd2+, and 15.2 mg g−1 for Hg2+, respectively) than pure PD and GO. Our results indicate the effectiveness of the synergistic effect of individual components on designing new functional composites with high performance.

Recent Advances in Ultrathin Two-Dimensional Nanomaterials

Abstract: Since the discovery of mechanically exfoliated graphene in 2004, research on ultrathin two-dimensional (2D) nanomaterials has grown exponentially in the fields of condensed matter physics, material science, chemistry, and nanotechnology. Highlighting their compelling physical, chemical, electronic, and optical properties, as well as their various potential applications, in this Review, we summarize the state-of-art progress on the ultrathin 2D nanomaterials with a particular emphasis on their recent advances. First, we introduce the unique advances on ultrathin 2D nanomaterials, followed by the description of their composition and crystal structures. The assortments of their synthetic methods are then summarized, including insights on their advantages and limitations, alongside some recommendations on suitable characterization techniques. We also discuss in detail the utilization of these ultrathin 2D nanomaterials for wide ranges of potential applications among the electronics/optoelectronics, electrocat...

Molecular self-assembly and nanochemistry: A chemical strategy for the synthesis of nanostructures

Abstract: Molecular self-assembly is the spontaneous association of molecules under equilibrium conditions into stable, structurally well-defined aggregates joined by noncovalent bonds. Molecular self-assembly is ubiquitous in biological systems and underlies the formation of a wide variety of complex biological structures. Understanding self-assembly and the associated noncovalent interactions that connect complementary interacting molecular surfaces in biological aggregates is a central concern in structural biochemistry. Self-assembly is also emerging as a new strategy in chemical synthesis, with the potential of generating nonbiological structures with dimensions of 1 to 10(2) nanometers (with molecular weights of 10(4) to 10(10) daltons). Structures in the upper part of this range of sizes are presently inaccessible through chemical synthesis, and the ability to prepare them would open a route to structures comparable in size (and perhaps complementary in function) to those that can be prepared by microlithography and other techniques of microfabrication.

Active sites of nitrogen-doped carbon materials for oxygen reduction reaction clarified using model catalysts

Abstract: Nitrogen (N)-doped carbon materials exhibit high electrocatalytic activity for the oxygen reduction reaction (ORR), which is essential for several renewable energy systems. However, the ORR active site (or sites) is unclear, which retards further developments of high-performance catalysts. Here, we characterized the ORR active site by using newly designed graphite (highly oriented pyrolitic graphite) model catalysts with well-defined π conjugation and well-controlled doping of N species. The ORR active site is created by pyridinic N. Carbon dioxide adsorption experiments indicated that pyridinic N also creates Lewis basic sites. The specific activities per pyridinic N in the HOPG model catalysts are comparable with those of N-doped graphene powder catalysts. Thus, the ORR active sites in N-doped carbon materials are carbon atoms with Lewis basicity next to pyridinic N.

Toward Safe Lithium Metal Anode in Rechargeable Batteries: A Review.

Abstract: The lithium metal battery is strongly considered to be one of the most promising candidates for high-energy-density energy storage devices in our modern and technology-based society. However, uncontrollable lithium dendrite growth induces poor cycling efficiency and severe safety concerns, dragging lithium metal batteries out of practical applications. This review presents a comprehensive overview of the lithium metal anode and its dendritic lithium growth. First, the working principles and technical challenges of a lithium metal anode are underscored. Specific attention is paid to the mechanistic understandings and quantitative models for solid electrolyte interphase (SEI) formation, lithium dendrite nucleation, and growth. On the basis of previous theoretical understanding and analysis, recently proposed strategies to suppress dendrite growth of lithium metal anode and some other metal anodes are reviewed. A section dedicated to the potential of full-cell lithium metal batteries for practical applicatio...

Recent Advances in Electrocatalysts for Oxygen Reduction Reaction

Abstract: The recent advances in electrocatalysis for oxygen reduction reaction (ORR) for proton exchange membrane fuel cells (PEMFCs) are thoroughly reviewed. This comprehensive Review focuses on the low- and non-platinum electrocatalysts including advanced platinum alloys, core–shell structures, palladium-based catalysts, metal oxides and chalcogenides, carbon-based non-noble metal catalysts, and metal-free catalysts. The recent development of ORR electrocatalysts with novel structures and compositions is highlighted. The understandings of the correlation between the activity and the shape, size, composition, and synthesis method are summarized. For the carbon-based materials, their performance and stability in fuel cells and comparisons with those of platinum are documented. The research directions as well as perspectives on the further development of more active and less expensive electrocatalysts are provided.