Owing to their high earth-abundance, eco-friendliness, high electrical conductivity, large surface area, structure tunability at the atomic/morphological levels, and excellent stability in harsh conditions, carbon-based metal-free materials have become promising advanced electrode materials for high-performance pseudocapacitors and metal–air batteries. Furthermore, carbon-based nanomaterials with well-defined structures can function as green catalysts because of their efficiency in advanced oxidation processes to remove organics in air or from water, which reduces the cost for air/water purification and avoids cross-contamination by eliminating the release of heavy metals/metal ions. Here, the research and development of carbon-based catalysts in supercapacitors and batteries for clean energy storage as well as in air/water treatments for environmental remediation are reviewed. The related mechanistic understanding and design principles of carbon-based metal-free catalysts are illustrated, along with the challenges and perspectives in this emerging field.

Chuangang Hu;Yi Lin;John W. Connell;会明 成;Yury Gogotsi;Maria Magdalena Titirici;黎明 戴

Advanced Materials

2019-3-27

The development of semiconductor photocatalysts with highly reactive facets exposed has great potential to improve their photocatalytic reactivity. We report the synthesis of mesoporous rutile TiO₂ single crystals with tunable ratios of {110} and {111} facets through the seeded-template hydrothermal method. With increasing the amount of morphology controlling agent NaF, the facet ratio of {111} to {110} increases, and eventually the mesoporous rutile TiO₂ single crystals with wholly exposed {111} reactive facets are obtained. The resultant faceted mesoporous single crystals exhibit a superior photocatalytic performance of hydrogen evolution to mesoporous single crystals with a large percentage of thermodynamically stable {110} facets, as well as the solid rutile single crystals.

Tingting Wu;Xiangdong Kang;Mohammad W. Kadi;Iqbal Ismail;Gang Liu;会明 成

Chinese Journal of Catalysis

2015-12-20

Developing high-capacity anodes is a must to improve the energy density of lithium batteries for electric vehicle applications. Alloy anodes are one promising option, but without pre-stored lithium, the overall energy density is limited by the low-capacity lithium metal oxide cathodes. Recently, lithium metal has been revived as a high-capacity anode, but faces several challenges owing to its high reactivity and uncontrolled dendrite growth. Here, we show a series of Li-containing foils inheriting the desirable properties of alloy anodes and pure metal anodes. They consist of densely packed Li x M (M = Si, Sn, or Al) nanoparticles encapsulated by large graphene sheets. With the protection of graphene sheets, the large and freestanding Li x M/graphene foils are stable in different air conditions. With fully expanded Li x Si confined in the highly conductive and chemically stable graphene matrix, this Li x Si/graphene foil maintains a stable structure and cyclability in half cells (400 cycles with 98% capacity retention). This foil is also paired with high-capacity Li-free V 2 O 5 and sulfur cathodes to achieve stable full-cell cycling.

Jie Zhao;Guangmin Zhou;Kai Yan;Jin Xie;Yuzhang Li;Lei Liao;Yang Jin;Kai Liu;Po Chun Hsu;Jiangyan Wang;会明 成;Yi Cui

Nature Nanotechnology

2017-10-1

Doping NaAlH₄ with Ti-catalyst has produced a promising hydrogen storage system that can be reversibly operated at moderate temperature conditions. Of the various dopant precursors, TiCl₃ was well recognized due to its pronounced catalytic effect on the reversible dehydrogenation processes of sodium aluminium hydrides. Quite recently we experimentally found that TiF₃ was even better than TiCl₃ in terms of the critical hydrogen storage properties of the doped hydrides, in particular the dehydriding performance at Na₃AlH₆/NaH + Al step at moderate temperature. We present here the DFT calculation results of the TiF₃ or TiCl₃ doped Na₃AlH₆. Our computational studies have demonstrated that F^- and Cl^- anions differ substantially from each other with regard to the state and function in the doped sodium aluminium hydride. In great contrast to the case of chloride doping where Cl^- anion constitutes the "dead weight" NaCl, the fluoride doping results in a substitution of H ^- by F^- anion in the hydride lattice and accordingly, a favorable thermodynamics adjustment. These results well explain the observed dehydriding performance associated with TiF₃/TiCl₃-doping. More significantly, the coupled computational and experimental efforts allow us to put forward a "functional anion" concept. This renews the current mechanism understanding in the catalytically enhanced sodium alanate.

Li Chang Yin;Ping Wang;Xiang Dong Kang;Cheng Hua Sun;会明 成

Physical Chemistry Chemical Physics

2007

Purified single-walled carbon nanotubes (SWNTs) with a large mean diameter of ∼1.85 nm, synthesized by a semicontinuous hydrogen are discharge method, were employed for electrochemical hydrogen adsorption experiments. A maximal discharge capacity of 316 mAh/g, corresponding to ∼1.2 wt% hydrogen storage, for the purified SWNTs after high-temperature heat-treatment, was achieved reproducibly at 298 K under normal atmosphere. After 100 charge/discharge cycles, more than 81% of the maximal capacity was maintained. Moreover, the plateau of the discharge potential was observed over -0.6 V (vs. Hg/HgO) at a charge/discharge current density of 400 mA/g. Pretreatments, especially heat-treatment, had significant effects on the improvement in the electrochemical capacity of SWNTs. These results imply that the SWNTs have potential for application as electrode materials in secondary hydrogen batteries.

Gui Ping Dai;Min Liu;Min De Chen;Peng Xiang Hou;Yu Tong;会明 成

Electrochemical and Solid-State Letters

2002-4

In the present study, a selectively exposed (101)-crystal facet engineered TiO₂ photoanode is investigated for the higher efficiency of the hydrogen evolution reaction. To date, even though the photoelectrochemical performance (PEC) dependent on exposed crystal facets has been calculated and demonstrated in semiconducting microcrystals, selectively exposed crystal facets of photocatalyst thin films have not been reported yet. Herein, we demonstrate a TiO₂ thin film photoanode with 100%-exclusively exposed crystal facets and suggest a methodology to obtain metal oxide thin film photoanodes with selectively exposed crystal facets. A selectively exposed crystal facet-manipulated metal oxide thin film photoanode is fabricated over pre-synthesized microcrystals through a three-step strategy: (1) hydrothermal synthesis of microcrystals, (2) positioning of microcrystals via polymer-induced manual assembly, and (3) fabrication of selectively exposed crystal facets of a TiO₂ thin film through a secondary growth hydrothermal reaction. Based on the synthesis of representative TiO₂ microcrystals with dominantly exposed (101), (100) and (001) crystal facets, the selectively exposed crystal faceted TiO₂ thin film photoanode is comparatively investigated for practical PEC performance. The photocurrent density of the selectively exposed (101) crystal faceted TiO₂ thin film photoanode is determined as 0.13 mA cm^-2 and has an 18% conversion efficiency of incident photon-to-current at a 0.65 V Ag/AgCl potential under AM 1.5G illumination. Its photoelectrochemical hydrogen production reached 0.07 mmol cm^-2 for 12 h, which is higher than those of (100) and (001) faceted photoelectrodes.

Chang Woo Kim;So Jin Yeob;会明 成;Young Soo Kang

Energy and Environmental Science

2015-12

A sandwich-structured composite, which contains an inner layer of C_f/SiC between two outer layers of C_f/SiC-ZrB₂-ZrC, was fabricated by a technique that involved rapid chemical vapor infiltration and precursor infiltration and pyrolysis. In both cyclic and single ablation conditions for one thousand seconds by an oxyacetylene flame, the composites exhibited good ablation-resistant properties and low strength reductions after ablation because of the introduction of a great amount of UHTCs into the outer layers and the small thickness of the ablation-affected area, respectively. The ablation rate and strength reduction in cyclic ablation were lower than those in single ablation.

Chenglong Hu;Shengyang Pang;Sufang Tang;Shijun Wang;Hongtao Huang;会明 成

Corrosion Science

2014-3

LiBH₄ possesses a high hydrogen content, and though it is highly stable, its restoration from LiH+B+H₂ can only be accomplished under unacceptable high temperature and pressure conditions (650 °C and 15 MPa). Recently, it has been reported that destabilizing LiBH₄ by, i.e., MgH₂, transition metal oxides and chlorides presents a promising approach to exert its potential for hydrogen storage. In the present study, we find that simple mechanical milling with Al in a mole ratio of 2:1, markedly improves the reversible dehydrogenation performance of LiBH₄. The system possesses a theoretical capacity of 8.5 wt.∈% and could be reversibly operated at 400-450 °C. The combined property and phase examinations suggest that the observed property improvement should be associated with the formation of AlB₂ in the dehydriding process. Further cyclic examination found that the system suffered from a serious capacity loss in the dehydriding/rehydriding cycles. A better understanding of the degradation mechanism may provide a means for further material property improvement.

Xiang Dong Kang;Ping Wang;Lai Peng Ma;会明 成

Applied Physics A: Materials Science and Processing

2007-12

Masses of single-walled carbon nanotubes (SWNTs) with a large mean diameter of about 1.85 nanometers, synthesized by a semicontinuous hydrogen arc discharge method, were employed for hydrogen adsorption experiments in their as-prepared and pretreated states. A hydrogen storage capacity of 4.2 weight percent, or a hydrogen to carbon atom ratio of 0.52, was achieved reproducibly at room temperature under a modestly high pressure (about 10 megapascal) for a SWNT sample of about 500 milligram weight that was soaked in hydrochloric acid and then heat-treated in vacuum. Moreover, 78.3 percent of the adsorbed hydrogen (3.3 weight percent) could be released under ambient pressure at room temperature, while the release of the residual stored hydrogen (0.9 weight percent) required some heating of the sample. Because the SWNTs can be easily produced and show reproducible and modestly high hydrogen uptake at room temperature, they show promise as an effective hydrogen storage material.

畅 刘;Y. Y. Fan;M. Liu;H. T. Cong;会明 成;M. S. Dresselhaus

Science

1999-11-5

A systematic investigation was performed on the hydrogen-storage performance of TiF₃ doped NaAlH₄ that was prepared under varied conditions. It was found that the starting material, milling atmosphere (inert or reactive) and milling time all exerted substantial influence on the hydrogen-storage performance of the materials. In particular, the variation of milling time or milling atmosphere was observed to influence only the NaAlH₄/Na₃AlH₆ + Al step, but not the following decomposition/reconstruction of Na₃AlH₆. Moreover, it was observed that the specific hydrogen-storage performance of the doped hydrides arising from the variation of the preparation conditions persisted through the following dehydriding/rehydriding cycles. These results elucidate the optimized preparation conditions of the NaAlH₄-TiF₃ system. More significantly, they provide valuable hint in exploring the nature of active Ti-species in the doped NaAlH₄.

P. Wang;X. D. Kang;会明 成

Journal of Alloys and Compounds

2006-9-14