Liang Ji    Li Feng    成会明    

Energy Storage Materials

2016

Giant, positive, and near-temperature-independent linear magnetoresistance (LMR), as large as 340%, was observed in graphene foam with a three-dimensional flexible network. Careful analysis of the magnetoresistance revealed that Shubnikov-de Haas (SdH) oscillations occurred at low temperatures and decayed with increasing temperature. The average classical mobility ranged from 300 (2 K) to 150 (300 K) cm2V-1s-1, which is much smaller than that required by the observed SdH oscillations. To understand the mechanism behind the observation, we performed the same measurements on the microsized graphene sheets that constitute the graphene foam. Much more pronounced SdH oscillations superimposed on the LMR background were observed in these microscaled samples, which correspond to a quantum mobility as high as 26,500cm2V-1s-1. Moreover, the spatial mobility fluctuated significantly from 64,200cm2V-1s-1 to 1370cm2V-1s-1, accompanied by a variation of magnetoresistance from near 20,000% to less than 20%. The presence of SdH oscillations actually excludes the possibility that the observed LMR originated from the extreme quantum limit, because this would demand all electrons to be in the first Landau level. Instead, we ascribe the large LMR to the second case of the classical Parish and Littlewood model, in which spatial mobility fluctuation dominates electrical transport. This is an experimental confirmation of the Parish and Littlewood model by measuring the local mobility randomly (by measuring the microsized graphene sheets) and finding the spatial mobility fluctuation.

Li Peng    Zhang Qiang    He Xin    任文才    成会明     Zhang Xi-Xiang   

Physical Review B - Condensed Matter and Materials Physics

2016

The properties of two-dimensional (2D) materials such as graphene and monolayer transition metal dichalcogenides are strongly influenced by domain boundaries. Ultrathin transition metal carbides are a class of newly emerging 2D materials that are superconducting and have many potential applications such as in electrochemical energy storage, catalysis, and thermoelectric energy conversion. However, little is known about their domain structure and the influence of domain boundaries on their properties. Here we use atomic-resolution scanning transmission electron microscopy combined with large-scale diffraction-filtered imaging to study the microstructure of chemical vapor deposited high-quality 2D α-MoC superconducting crystals of different regular shapes including triangles, rectangles, hexagons, octagons, nonagons, and dodecagons. The Mo atom sublattice in all these crystals has a uniform hexagonal closely packed arrangement without any boundaries. However, except for rectangular and octagonal crystals, the C atom sublattices are composed of three or six domains with rotational-symmetry and well-defined line-shaped domain boundaries because of the presence of three equivalent off-center directions of interstitial carbon atoms in Mo octahedra. We found that there is very small lattice shear strain across the domain boundary. In contrast to the single sharp transition observed in single-domain crystals, transport studies across domain boundaries show a broad resistive superconducting transition with two distinct transition processes due to the formation of localized phase slip events within the boundaries, indicating a significant influence of the boundary on 2D superconductivity. These findings provide new understandings on not only the microstructure of 2D transition metal carbides but also the intrinsic influence of domain boundaries on 2D superconductivity.

Zhibo Liu    Xu Chuan    Ning Kang    Wang    Jiang Yixiao    Du Jiao    Liu Ying    Xiuliang Ma    成会明     任文才   

Nano Letters

2016

Yang Yongqiang    Gang Liu    Irvine John T. S.    成会明    

Advanced Materials

2016

A hierarchically meso/micro-porous Fe-N-doped carbon nanotube electrocatalyst (meso/micro-Fe-N-CNT), for the first time, was synthesized. Anodic aluminum oxide (AAO) was used as a template to cast the CNT framework and Fe(NO) was filled in the AAO nanochannels as both a mesopore template in CNT walls and the iron source to form Fe-N-C active sites. Subsequent NH activation was carried out to create abundant micropores and active sites to produce the meso/micro-Fe-N-CNT. This hybrid material has a unique characteristic of a high-conductivity CNT framework, an ultrahigh surface area of 2137 m g, a high density of Fe-N-C catalytic active sites, and abundant meso- and micropores for efficient mass transport channels. As a consequence, excellent oxygen reduction reaction performance under acidic conditions and even better performance under alkaline conditions were demonstrated that are comparable to that of Pt/C.

Li Jin-Cheng    Pengxiang Hou    Shi Chao    Zhao Shi-Yong    Daiming Tang    Cheng Min    Chang Liu    成会明    

Carbon

2016

We report the temperature-dependent evolution of Raman spectra of monolayer WS directly CVD-grown on a gold foil and then transferred onto quartz substrates over a wide temperature range from 84 to 543 K. The nonlinear temperature dependence of Raman shifts for both E and A modes has been observed. The first-order temperature coefficients of Raman shifts are obtained to be -0.0093 (cm/K) and -0.0122 (cm/K) for E and A peaks, respectively. A physical model, including thermal expansion and three- and four-phonon anharmonic effects, is used quantitatively to analyze the observed nonlinear temperature dependence. Thermal expansion coefficient (TEC) of monolayer WS is extracted from the experimental data for the first time. It is found that thermal expansion coefficient of out-plane mode is larger than one of in-plane mode, and TECs of E and A modes are temperature-dependent weakly and strongly, respectively. It is also found that the nonlinear temperature dependence of Raman shift of E mode mainly originates from the anharmonic effect of three-phonon process, whereas one of A mode is mainly contributed by thermal expansion effect in high temperature region, revealing that thermal expansion effect cannot be ignored.

Huang Xiaoting    Yang Gao    Yang Tianqi    任文才    成会明     Lai Tianshu   

Scientific Reports

2016

Lithium-sulfur (Li-S) batteries are attracting increasing interest due to their high theoretical specific energy density, low cost, and eco-friendliness. However, most reports of the high gravimetric specific capacity and long cyclic life are not practically reliable because of their low areal specific capacity derived from the low areal sulfur loading and low sulfur content. Here, we fabricated a highly porous graphene with high pore volume of 3.51 cm g as the sulfur host, enabling a high sulfur content of 80 wt %, and based on this, we further proposed an all-graphene structure for the sulfur cathode with highly conductive graphene as the current collector and partially oxygenated graphene as a polysulfide-adsorption layer. This cathode structural design enables a 5 mg cm sulfur-loaded cathode showing both high initial gravimetric specific capacity (1500 mAh g) and areal specific capacity (7.5 mAh cm), together with excellent cycling stability for 400 cycles, indicating great promise for more reliable lithium-sulfur batteries.

Ruopian Fang    Zhao Shi-Yong    Songfeng Pei    Qian Xitang    Pengxiang Hou    成会明     Chang Liu    Feng Li   

ACS Nano

2016

The kinetics and stability of the redox of lithium polysulfides (LiPSs) fundamentally determine the overall performance of lithium-sulfur (Li-S) batteries. Inspired by theoretical predictions, we herein validated the existence of a strong electrostatic affinity between polymeric carbon nitride (p-CN) and LiPSs, that can not only stabilize the redox cycling of LiPSs, but also enhance their redox kinetics. As a result, utilization of p-CN in a Li-S battery has brought much improved performance in the aspects of high capacity and low capacity fading over prolonged cycling. Especially upon the application of p-CN, the kinetic barrier of the LiPS redox reactions has been significantly reduced, which has thus resulted in a better rate performance. Further density functional theory simulations have revealed that the origin of such kinetic enhancement was from the distortion of molecular configurations of the LiPSs anchored on p-CN. Therefore, this proof-of-concept study opens up a promising avenue to improve the performance of Li-S batteries by accelerating their fundamental electrochemical redox processes, which also has the potential to be applied in other electrochemical energy storage/conversion systems.

Ji Liang    Lichang Yin    Tang Xiaonan    Yang Huicong    Wensheng Yan    Song Li    成会明     Feng Li   

ACS Applied Materials and Interfaces

2016

Compact energy storage with high volumetric performance is highly important. However, the state-of-the-art electrodes and devices remain far from the requirements due to the lack of consideration from a device perspective, which not only demands a high specific gravimetric capacity, but also needs to take into account operation voltage, material density and electrode thickness. We develop a novel approach to fabricate a monolithic ultra-thick and dense carbon electrode for symmetric supercapacitors, starting with graphene assembly and taking all the above factors into consideration. We found that zinc chloride is an ideal sacrificial pore former, and taken together with capillary drying can tune the specific surface area of the monolithic graphene from 370 to over 1000 m g while the monoliths maintain a high density from 1.6 to 0.6 g cm. Having a good balance of porosity and density, the directly sliced graphene pellet electrode with a thickness up to 400 μm delivers a capacitance of 150 F cm in an ionic liquid electrolyte, corresponding to a volumetric energy density of ∼65 W h L for a symmetrical supercapacitor device, the highest value reported to date for supercapacitors. This study presents a design principle for electrode materials towards next-generation energy storage devices, not limited to supercapacitors, which are becoming smaller, lighter but more energetic.

Li Huan    陶莹    Xiaoyu Zheng    Luo Jiayan    康飞宇    成会明     Quanhong Yang   

Energy and Environmental Science

2016

Ji Liang    Li Feng    成会明    

Energy Storage Materials

2016