Tai Cao

Bamboo‐Like Nitrogen‐Doped Carbon Nanotubes with Co Nanoparticles Encapsulated at the Tips: Uniform and Large‐Scale Synthesis and High‐Performance Electrocatalysts for Oxygen Reduction

In recent years, various non-precious metal electrocatalysts for the oxygen reduction reaction (ORR) have been extensively investigated. The development of an efficient and simple method to synthesize non-precious metal catalysts with ORR activity superior to that of Pt is extremely significant for large-scale applications of fuel cells. Here, we develop a facile, low-cost, and large-scale synthesis method for uniform nitrogen-doped (N-doped) bamboo-like CNTs (NBCNT) with Co nanoparticles encapsulated at the tips by annealing a mixture of cobalt acetate and melamine. The uniform NBCNT shows better ORR catalytic activity and higher stability in alkaline solutions as compared with commercial Pt/C and comparable catalytic activity to Pt/C in acidic media. NBCNTs exhibit outstanding ORR catalytic activity due to high defect density, uniform bamboo-like structure, and the synergistic effect between the Co nanoparticles and protective graphitic layers. This facile method to synthesize catalysts, which is amenable to the large-scale commercialization of fuel cells, will open a new avenue for the development of low-cost and high-performance ORR catalysts to replace Pt-based catalysts for applications in energy conversion.

Synthesis of novel ZnV2O4 spinel oxide nanosheets and their hydrogen storage properties

We report the synthesis of ZnV2O4 spinel oxide novel nanosheets via a template free route to explore its potential hydrogen storage properties for the first time. 2D layered nanostructures are excellent candidates for storage applications. This attracted our interest to synthesize novel spinel oxide nanosheets (NSNs) of ZnV2O4. The maximum value for hydrogen absorption in ZnV2O4 nanosheets at 473 K is 1.36 wt.% and 1.74 wt.% at 573 K, respectively. Our hydrogen storage measurements along ZnV2O4 reveal its superiority over previous reports on hydrogen absorption values concerning oxides, nitrides and chalcogenides. To understand the rate-limiting mechanism, various kinetics models are applied. The calculations show that kinetics is governed by 3D growth with constant interface velocity. The measurements point to ZnV2O4 spinel oxide as a promising hydrogen storage material. PL measurements demonstrate the potential for violet/blue optoelectronic devices.

A general synthetic strategy to monolayer graphene

The emergence and establishment of new techniques for material fabrication are of fundamental importance in the development of materials science. Thus, we herein report a general synthetic strategy for the preparation of monolayer graphene. This novel synthetic method is based on the direct solid-state pyrolytic conversion of a sodium carboxylate, such as sodium gluconate or sodium citrate, into monolayer graphene in the presence of Na2CO3. In addition, gram-scale quantities of the graphene product can be readily prepared in several minutes. Analysis using Raman spectroscopy and atomic force microscopy clearly demonstrates that the pyrolytic graphene is composed of a monolayer with an average thickness of ∼0.50 nm. Thus, the present pyrolytic conversion can overcome the issue of the low monolayer contents (i.e., 1 wt.%–12 wt.%) obtained using exfoliation methods in addition to the low yields of chemical vapor deposition methods. We expect that this novel technique may be suitable for application in the preparation of monolayer graphene materials for batteries, supercapacitors, catalysts, and sensors.

Two-dimensional SnO 2 /graphene heterostructures for highly reversible electrochemical lithium storage

The ever-growing market demands for lithium ion batteries have stimulated numerous research efforts aiming at the exploration of novel electrode materials with higher capacity and long-term cycling stability. Two-dimensional (2D) nanomaterials and their heterostructures are an intense area of study and promise great potential in electrochemical lithium storage owing to their unique properties that result from structural planar confinement. Here we report a microwave chemistry strategy to integrate ultrathin SnO2 nanosheets into graphene layer to construct surface-to-surface 2D heterostructured architectures, which can provide unique structural planar confinement for highly reversible electrochemical lithium storage. The as-synthesized 2D SnO2/graphene heterostructures can exhibit high reversible capacity of 688.5 mA h g−1 over 500 cycles with excellent long-term cycling stability and good rate capability when used as anode materials for lithium ion batteries. The present work definitely reveals the advantages of 2D heterostructures featured with a surface-to-surface stack between two different nanosheets in energy storage and conversion devices.摘要对锂离子电池日益增长的市场需求已经引起巨大的研究热情来开发具有更高容量和超长循环性的新型电极材料. 而由于具有独特 的平面结构限域性能, 二维材料及其异质结构目前成为材料研究领域的热点, 并有望在电化学能量储存方面发挥巨大的潜力. 因此, 本文 借助于微波化学策略把超薄SnO2纳米片与石墨烯薄层耦合在一起构筑一种面对面型二维异质结构, 利用其独特的平面结构限域性能来获 得高可逆性的电化学储锂性能. 实验结果表明, 所制备的二维SnO2/石墨烯异质结构表现出良好的电化学性能, 连续500次循环之后其可逆 容量仍能保持在688.5 mA h g−1, 同时也具有很好的倍率性能. 本工作揭示了具有面对面型二维异质结构在能量储存与转化设备应用方面 的明显优势, 为新型电极材料的制备提供了更多选择.

A cocoon silk chemistry strategy to ultrathin N-doped carbon nanosheet with metal single-site catalysts

Development of single-site catalysts supported by ultrathin two-dimensional (2D) porous matrix with ultrahigh surface area is highly desired but also challenging. Here we report a cocoon silk chemistry strategy to synthesize isolated metal single-site catalysts embedded in ultrathin 2D porous N-doped carbon nanosheets (M-ISA/CNS, M = Fe, Co, Ni). X-ray absorption fine structure analysis and spherical aberration correction electron microscopy demonstrate an atomic dispersion of metal atoms on N-doped carbon matrix. In particular, the Co-ISA/CNS exhibit ultrahigh specific surface area (2105 m2 g−1) and high activity for C–H bond activation in the direct catalytic oxidation of benzene to phenol with hydrogen peroxide at room temperature, while the Co species in the form of phthalocyanine and metal nanoparticle show a negligible activity. Density functional theory calculations discover that the generated O = Co = O center intermediates on the single Co sites are responsible for the high activity of benzene oxidation to phenol.Single-site catalysts supported by ultrathin two-dimensional (2D) porous matrix are desirable for catalytic reactions, yet their synthesis remains a great challenge. Herein the authors report a cocoon silk chemistry strategy to synthesize isolated metal single-site catalysts embedded in ultrathin 2D porous N-doped carbon nanosheets.

A general strategy for the synthesis of two-dimensional holey nanosheets as cathodes for superior energy storage

Ultrathin and holey two-dimensional (2D) nanosheets are attracting extraordinary attention because of their unprecedented properties. In spite of tremendous progress on the synthesis of the 2D ultrathin nanosheets and research on their energy storage properties, up to now, the utilization of 2D holely nanosheets as cathodes remains clearly limited because of the grain growth and structural destruction. Herein, we rationally designed a general morphology-inheritance strategy to produce 2D ultrathin holey nanosheets as cathodes via a simple and scalable microwave-assisted approach. In this study, the 2D ultrathin nanosheet precursors were facilely synthesized and then, lithium and other sources were implemented to prepare ultrathin and holey 2D nanosheet cathodes (LiCoO2, LiNi0.8Co0.15Al0.05O2, LiNi0.8Co0.1Mn0.1O2, LiNi0.6Co0.2Mn0.2O2, and LiNi0.5Co0.2Mn0.3O2) through a simple solid-state reaction. The as-synthesized holey 2D cathodes present ultrahigh specific capacities, outstanding rate capability, and excellent cycle life, which are attributed to the abundant electrochemical active sites, facile interfacial transfer, and reduced diffusion distance provided by the unique hierarchical ultrathin 2D nanosheet structure with abundant atypical holes.