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Synthesis of novel ordered carbon nanorods and its application in electrochemical double layer capacitor

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Science China(Technological Sciences) 2006年第4期49卷 425-433页

作者： XING Wei LIU Xinmei BAI Peng YAN Zifeng LU Gaoqing State Key Laboratory for Heavy Oil Processing CNPC Key Laboratory of Catalysis China University of Petroleum Dongying 257061 China State Key Laboratory for Heavy Oil Processing CNPC Key Laboratory of Catalysis China University of Petroleum Dongying 257061 China State Key Laboratory for Heavy Oil Processing CNPC Key Laboratory of Catalysis China University of Petroleum Dongying 257061 China State Key Laboratory for Heavy Oil Processing CNPC Key Laboratory of Catalysis China University of Petroleum Dongying 257061 China State Key Laboratory for Heavy Oil Processing CNPC Key Laboratory of Catalysis China University of Petroleum Dongying 257061 China

The ordered carbon nanorods (OCNR) was successfully synthesized using the mesoporous silica as hard template. XRD tests and TEM observations showed that OCNR was composed of arrayed carbon nanorods in the p6mm symmetry. N2 sorption analysis demonstrated that OCNR possessed the typically mesoporous structure and centralized mesopore distribution. Compared with Maxsorb, an active carbon with super high surface area, OCNR has superior capacitive behavior, power output and high fre- quency performance due to its ordered pore-structure, which favors the fast diffusion of hydrated ions. As evidenced by cyclic voltammetry measurements, OCNR shows superior capacitive behaviors (exhibiting a high capacitance of 166 F/g even at very high sweep rate of 50 mV/s, as compared to much reduced capacitance of 73 F/g for Maxsorb at the same sweep rate). OCNR can provide much higher power density while still maintaining good energy density, which offers a great potential in electrochemical double layer ca- pacitor (EDLC), particularly for applications where both high power output and energy density are required.

关键词： nanomaterials, porous carbon, electrochemistry, capacitor, cyclic voltammetry.

Land use effects on terrestrial carbon sources and sinks

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Science China(Life Sciences) 2002年第Z1期45卷 1-9页

作者： Josep G. Canadell Global carbon Project GCTE CSIRO Land and Water PO Box 1666 Australia

Current and past land use practices are critical in determining the distribution and size of global terrestrial carbon (C) sources and sinks. Althoughfossil fuel emissions dominate the anthropogenic perturbation of the global C cycle, land use still drives the largest portion of anthropogenic emissions in a number of tropical regions of Asia. The size of the emission flux owing to land use change is still the biggest uncertainty in the global C budget. The Intergovernmental Panel on Climate Change (IPCC) reported a flux term of 1.7 PgC@a-1 for 1990-1995 but more recent estimates suggest the magnitude of this source may be only of 0.96 PgC@a-1 for the 1990s. In addition, current and past land use practices are now thought to contribute to a large degree to the northern hemisphere terrestrial sink, and are the dominant driver for some regional sinks. However, mechanisms other than land use change need to be invoked in order to explain the inferred C sink in the tropics. Potential candidates are the carbon dioxide (CO2) fertilization and climate change; fertilization due to nitrogen (N) deposition is believed to be small or nil. Although the potential for managing C sinks is limited, improved land use management and new land uses such as reforestation and biomass fuel cropping, can further enhance current terrestrial C sinks. Best management practices in agriculture alone could sequester 0.4-0.8 PgC per year in soils if implemented globally. New methodologies to ensure verification and permanency of C sequestration need to be developed.

关键词： land use, terrestrial carbon, carbon emissions, sink mechanisms.

carbon stock assessment for a forest-to-coffee conversion landscape in Sumber-Jaya (Lampung, Indonesia): from allometric equations to land use change analysis

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Science China(Life Sciences) 2002年第Z1期45卷 75-86页

作者： Meine van Noordwijk Subekti Rahayu Kurniatun Hairiah Y. C. Wulan A. Farida Bruno Verbist International Centre for Research in Agroforestry (ICRAF) SE Asia P.O.Box 161 Bogor 16001 Indonesia Brawijaya University Malang Indonesia Bogor Agricultural University Bogor Indonesia International Centre for Research in Agrotorestry (ICRAF) SE Asia P.O.Box 161 Bogor 16001 Indonesia

The change in stored carbon (C) stocks was assessed for a 700 km2 areawhere forest cover decreased from 60% to 10% in the last 30 years. At the same time, the area under coffee increased from 7% to 70% with a gradual evolution from open "sun coffee" systems to multi-strata "shade coffee" systems that providea partial compensation for C loss. The use of a generic tropical forest rather than tree-specific allometric equation can lead to substantial (up to 100%) overestimates of aboveground biomass depending on wood density and tree shape. The shoot:root ratio (biomass) of coffee shifted with age, from the 4:1 value often assumed for tropical trees to 2:1. Annual aboveground C stock accumulation rates during the establishment stage after slash-and- burn land clearing were 1, closeto 2 or 3.5 Mg C ha-1a-1 for sun coffee, shade coffee and fallow regrowth, respectively. Forest remnants, shade coffee and sun coffee had soil C stocks in the upper 30 cm of the soil that were 79%, 60% or 45%, respectively, of the values expected for primary forest in Sumatra. Total C stock (time averaged, above - 0.3m in the soil) for forest, shade and sun coffee was 262, 82 and 52 Mg C ha-1, respectively. In the 1970-1984 period, while forest cover was reduced from 59.5%to 19.7%, the landscape lost on average 6.8 Mg C ha-1 a-1. In the 1984-2000 period forest cover was further reduced to 12.6%, but the landscape lost only 0.39Mg C ha-1 a-1, as forest loss was partially compensated by an increase in shadecoffee systems. Conversion of all current sun coffee to shade coffee systems while protecting the remaining forest, could increase average landscape level C stocks by 10 Mg ha-1 over a time frame of say 20 years, or 0.5 Mg C ha-1 a-1.

关键词： allometrics, carbon stock, coffee, soil carbon, wood density.

Temporal patterns of land-use change and carbon storage in China and tropical Asia

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Science China(Life Sciences) 2002年第Z1期45卷 10-17页

作者： R. A. Houghton Woods Hole Research Center P.O. Box 296 Woods Hole MA 02543

Evaluating the annual sources and sinks of carbon from land-use changehelps constrain other terms in the global carbon cycle and may help countries choose how to comply with commitments for reduced emissions. This paper presents the results of recent analyses of land-use change in China and tropical Asia. The original forest areas are estimated to have covered 546×106 ha in tropical Asia and 425×106 ha in China. By 1850, 44% of China's forests had been cleared, and another 27% was lost between 1850 and 1980, leaving China with 13% forest cover (29% of the initial forest area). Tropical Asia is estimated to have lost 26%of its initial forest cover before 1850 and another 33% after 1850. The annual emissions of carbon from the two regions reflect the different histories over the last 150 years, with China's emissions peaking in the late 1950s (at 0.2-0.5 Pg C@a-1) and tropical Asia's emissions peaking in 1990s (at 1.0 Pg C@a-1). Despite the fact that most deforestation has been for new agricultural land, the majority of the lands cleared from forests in China are no longer croplands, but fallow or degraded shrublands. Unlike croplands, the origins of these other lands are poorly documented, and thus add considerable uncertainty to estimates of flux before the 1980s. Nevertheless, carbon emissions from China seem to have decreased since the 1960s to nearly zero at present. In contrast, emissions of carbon from tropical Asia were higher in the 1990s than that at any time in the past.

关键词： carbon, China, deforestation, land-use change, tropical Asia.

Environmental records of carbon in recent lake sediments

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Science China Earth Sciences 2002年第10期45卷 875-884页

作者：陈敬安万国江汪福顺张峰黄荣贵 D.D.Zhang R.Schmidt State Key Laboratory of Environmental Geochemistry Institute of Geochemistry Chinese Academy of Sciences Guiyang 550002 China Department of Geography and Geology University of Hong Kong Pokfulam Road Hong Kong China Institute of Limnology Austrian Academy of Sciences A-5310 Mondsee Austria

Based on careful sampling and accurate analysis of recent sediments in Lake Chenghai, this paper discusses the staggered positive/negative correlation between organic carbon (OC) concentration and inorganic carbon (IC) concentration. The result indicates that temperature change, and its induced relative changes are the main factors affecting the relationship between IC concentration, δ13C of carbonate and OC concentration. When temperature and its induced photosynthesis strength change control autochthonous calcite precipitation, OC concentration is positively correlated with IC concentration and δ13C of carbonate. When temperature and its induced physical/chemical changes dominate, OC concentration displays negative correlation with IC concentration and δ13C of carbonate. IC concentration and δ13C of carbonate in sediments of Lake Chenghai are good proxies for climatic warm/cold changes.

关键词： lake sediment, organic carbon, inorganic carbon, δ13C.

Adsorption performances and refrigeration application of adsorption working pair of CaCl_2-NH_3

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Science China(Technological Sciences) 2004年第2期47卷 173-185页

作者： WANG Liwei WANG Ruzhu WU Jingyi WANG Kai Institute of Refrigeration and Cryogenics Shanghai Jiao Tong University Shanghai 200030 China Institute of Refrigeration and Cryogenics Shanghai Jiao Tong University Shanghai 200030 China Institute of Refrigeration and Cryogenics Shanghai Jiao Tong University Shanghai 200030 China Institute of Refrigeration and Cryogenics Shanghai Jiao Tong University Shanghai 200030 China

The adsorption performance of CaCl2?NH3 is studied under the condition of different expansion spaces for adsorbent, and the relationships between adsorption performance of CaCl2?NH3 and the phenomena of swelling and agglomeration during adsorption are researched. It is found that the performance stability is related to the ratio of expansion space to the volume of adsorbent r as, and the performance attenuation is serious in the case of large r as. Severe adsorption hysteresis exists in the process of adsorption and desorption at the same evaporating and condensing temperatures, which is related to the stability constant of chemical reaction. This phenomenon cannot be explained by the theory of physical adsorption. Moderate agglomeration will be beneficial to the formation of ammoniate complex; the magnitude of expansion space will affect adsorption performance. Analysis shows that the activated energy needed in the process of adsorption for the sample with r as. of 2∶1 is less than that for the sample with r as of 3∶1. The refrigeration performance of CaCl2?NH3 is predicted from experiments. The cooling capacity of one adsorption cycle is about 945.4 kJ/kg for the adsorbent with an r as of 2∶1 at the evaporating temperature of 0°C. Keywords chemical adsorption - attenuation - adsorption hysteresis - ammonia - activated carbon - refrigeration

关键词： chemical adsorption, attenuation, adsorption hysteresis, ammonia, activated carbon, refrigeration.

Impacts of hydrogen dilution on growth and optical properties of a-SiC:H films

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Science China(Technological Sciences) 2004年第3期47卷 327-334页

作者： HU Zhihua LIAO Xianbo DIAO Hongwei KONG Guanglin ZENG Xiangbo XU Yanyue State Key Laboratory for Surface Physics Institute of Semiconductors & Center for Condensed Materials Physics Chinese Academy of Sciences Beijing 100083 China School of Energy and Environmental Sciences Yunnan Normal University Kunming 650092China State Key Laboratory for Surface Physics Institute of Semiconductors & Center for Condensed Materials Physics Chinese Academy of Sciences Beijing 100083 China State Key Laboratory for Surface Physics Institute of Semiconductors & Center for Condensed Materials Physics Chinese Academy of Sciences Beijing 100083 China State Key Laboratory for Surface Physics Institute of Semiconductors & Center for Condensed Materials Physics Chinese Academy of Sciences Beijing 100083 China State Key Laboratory for Surface Physics Institute of Semiconductors & Center for Condensed Materials Physics Chinese Academy of Sciences Beijing 100083 China State Key Laboratory for Surface Physics Institute of Semiconductors & Center for Condensed Materials Physics Chinese Academy of Sciences Beijing 100083 China

Hydrogenated amorphous silicon-carbon (a-SiC:H) films were deposited by plasma enhanced chemical vapor deposition (PECVD) with a fixed methane to silane ratio ([CH4]/[SiH4]) of 1.2 and a wide range of hydrogen dilution (RH=[H2]/[SiH4 + CH4]) values of 12, 22, 33, 102 and 135. The impacts of RH on the structural and optical properties of the films were investigated by using UV-VIS transmission, Fourier transform infrared (FTIR) absorption, Raman scattering and photoluminescence (PL) measur- ements. The effects of high temperature annealing on the films were also probed. It is found that with increasing hydrogen dilution, the optical band gap increases, and the PL peak blueshifts from ～1.43 to 1.62 Ev. In annealed state, the room temperature PL peak for the low RH samples disappears, while the PL peak for the high RH samples appears at ～2.08 Ev, which is attributed to nanocrystalline Si particles confined by Si-C and Si-O bonds.

关键词： amorphous silicon carbon, hydrogen dilution, nanocrystalline silicon.