High temperature carbon–carbon supercapacitor using ionic liquid as electrolyte

This paper presents results about the electrochemical and cycling characterizations of a supercapacitor cell using a microporous activated carbon as the active material and N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR₁₄TFSI) ionic liquid as the electrolyte. The microporous activated carbon exhibited a specific capacitance of 60 F g⁻¹ measured from the three-electrode cyclic voltammetry experiments at 20 mV s⁻¹ scan rate, with a maximum operating potential range of 4.5 V at 60 °C. A coin cell assembled with this microporous activated carbon and PYR₁₄TFSI as the electrolyte was cycled for 40,000 cycles without any change of cell resistance (9 Ω cm²), at a voltage up to 3.5 V at 60 °C, demonstrating a high cycling stability as well as a high stable specific capacitance in this ionic liquid electrolyte. These high performances make now this type of supercapacitor suitable for high temperature applications (≥60 °C).     

县级市碳达峰碳中和规划案例分析

温室气体排放的持续增加已成为制约经济社会可持续发展的重要因素。为实现温室气体减排，我国提出了“碳达峰碳中和”发展战略。以西北地区某县级市为对象，采用联合国政府间气候变化专门委员会(IPCC)制定的IPCC清单指南核算了该县CO₂和温室气体排放现状。基于不同情景和假设，对CO₂和温室气体排放趋势进行分析，发现在GDP高速增长和正常增长情景下，该县分别于2029年和2027年实现碳达峰，达峰时CO₂年排放量分别为2 181.33万t和1 931.48万t；分别于2046年和2044年实现碳中和。分析了影响碳排放的因素，并对该县实现“双碳”目标的重点工作和保障措施提出了建议，以期助力该县“双碳”目标的顺利实现。     

Effect of hydrogen additive on methane decomposition to hydrogen and carbon over activated carbon catalyst

The effect of H₂ addition on CH₄ decomposition over activated carbon (AC) catalyst was investigated. The results show that the addition of H₂ to CH₄ changes both methane conversion over AC and the properties of carbon deposits produced from methane decomposition. The initial methane conversion declines from 6.6% to 3.3% with the increasing H₂ flowrate from 0 to 25 mL/min, while the methane conversion in steady stage increases first and then decreases with the flowrate of H₂, and when the H₂ flowrate is 10 mL/min, i.e. quarter flowrate of methane, the methane conversion over AC in steady stage is four times more than that without hydrogen addition. It seems that the activity and stability of catalyst are improved by the introduction of H₂ to CH₄ and the catalyst deactivation is restrained. Filamentous carbon is obtained when H₂ is introduced into CH₄ reaction gas compared with the agglomerate carbon without H₂ addition. The formation of filamentous carbon on the surface of AC and slower decrease rate of surface area and pores volume may cause the stable activity of AC during methane decomposition.     

Analysis of the carbon anode in carbon conversion cells

We examine further the electrochemical oxidation of carbon in molten carbonate, based on analysis of published research. Ascending and descending branches of voltage hysteresis found in current sweeps of atomically-ordered graphite and of disordered carbon (coal char) are separated by about 0.20–0.25 V and by 0.10–0.15 V for ordered and disordered forms, respectively, over a wide band of current density, 0.03–0.10 A/cm². The higher voltage of the descending branch is in rough agreement with prediction of the Y. Li model for the carbon/carbonate electrode in the same current range, for ordered graphite (L_a = 70–100 nm) and for disordered structures (L_a = 3–5 nm), respectively. We suggest that the amplitude of the hysteresis represents the difference between the overvoltage requirements for 2- and 4 electron net transfer processes, respectively. The 2 e− reaction (C + CO₃²⁻ = CO + CO₂ + 2e⁻) dominates the low current segment (LCS) of our previous analysis, and the more hindered 4e− transfer reaction (C + 2CO₃²⁻ = 3CO₂ + 4e⁻) dominates the high current segment (HCS). The voltage increase separating LCS from HCS is effected by accumulation of CO₂ within small, melt-filled pores to form highly supersaturated solutions of CO₂, which enhance anode voltage by a concentration overpotential of 0.10–0.25 V. Overpotential increases with reaction extent until (1) overall polarization inhibits the interior reaction and shifts CO₂ production to the more accessible exterior surface, or, (2) at a critical concentration (dependent on surface tension and pore diameter) bubbles nucleate and block current flow in the pores. Further support for this picture comes from the often-reported deviation of the gas composition from the CO/CO₂ ratio of the Boudouard equilibrium at atmospheric pressure, as open circuit conditions are approached in an electrochemical cell. Our interpretation accounts for the mole fraction of CO₂ at open circuit being greater than predicted from the Boudouard equilibrium.     

Mesoporous carbon/graphitic carbon nitride spheres for photocatalytic H2 evolution under solar light irradiation

Herein, two different photocatalytic composites based on ordered (OCS) and disordered (DCS) mesoporous hollow carbon spheres and graphitic carbon nitride (gCN) have been successfully fabricated through facile acid treatment. The influence of carbon shell morphology of the spheres on gCN loading and photocatalytic H₂ production under simulated solar light irradiation has been revealed. The amount of evolved H₂ was ~6.2 (OCS/gCN) and ~5.3 (DCS/gCN) times higher in comparison to pristine gCN. It was found that graphitic carbon nitride was much more homogenously supported onto ordered mesoporous carbon spheres than disordered ones. The deposition of gCN onto ordered carbon spheres was found to be more efficient to increase carrier concentration, enhance photogenerated charge carrier transport and separation. It is assigned to the formation of the graphitic carbon nitride/carbon heterojunction facilitating the contact surface between the two phases of hybrid. Therefore, via tuning of the morphology of carbon shell being a host for gCN it was possible to find more promising candidate as a photocatalyst in H₂ production under solar light irradiation.     

Analysis of the carbon anode in direct carbon conversion fuel cells

The total electrochemical efficiency of a direct carbon fuel cell with molten carbonate electrolyte is dominated by the product of coulombic efficiency (electron yield (n) per carbon atom, divided by 4) and voltaic efficiency (ratio of cell voltage to theoretical voltage). The voltaic efficiency is acceptably high (70–80%) for many atomically-disordered carbon materials. High coulombic efficiency is more difficult to achieve but ranges from below 50% at low current densities in porous material to 100% in certain monolithic and particulate carbon anodes at high current densities where substantially pure CO₂ is the product gas. We find evidence for two competing anode reactions associated with distinct low- and high polarization segments, respectively: (1) a charge-transfer controlled, linear–polarization reaction occurring predominately within pores, proportional to specific area, and tending toward low efficiency by co-production of CO and CO₂; and (2) a flow-dependent reaction occurring on the exterior surface of the anode, requiring > 100 mV polarization and tending to produce CO₂. Based on this interpretation, high electrochemical efficiency of a carbon fuel cell is expected with anodes made of atomically disordered ("turbostratic") carbon that have negligible porosity, or with anodes of disordered carbon for which interior pores are intentionally blocked with an impervious solid material, such as an inert salt or readily carbonized pitch.     

Study of methane and carbon dioxide adsorption capacity by synthetic nanoporous carbon based on pyrogallol-formaldehyde

Nanoporous carbons were synthesized at certain conditions by sol–gel method combined with furnace firing in inert atmosphere from pyrogallol-formaldehyde (PF) mixtures in water using perchloric acid as catalyst. Their morphology was studied experimentally to examine their adsorption capacity for greenhouse gases. The preparation conditions of the nanoporous carbons were explored by changing the pyrolysis temperature. The effect of this factor on determining the pore structures and the adsorption capacities were evaluated. The synthesized xerogels were characterized by X-ray diffraction, nitrogen adsorption–desorption isotherms, thermogravimetric analysis (TGA), differential thermal analysis (DTA), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that surface areas and nitrogen adsorption capacity are dependent completely on the pyrolysis temperature. Equilibrium and enthalpies studies for the CO₂ and CH₄ adsorption on PF were measured at room temperature and up to 25 bar. The adsorption capacity on PF was highest for CO₂ and then CH₄. The best sample shows maximal adsorption capacities as follows 5.50 mmol g^?1 of CH₄ and 7.62 mmol g^?1 of CO₂ at 25 bar and 30 °C.     

热力学碳泵：角色、模型与案例分析

制约碳捕集技术发展的瓶颈之一在于能耗过高,而现有碳捕集能效分析的方法论与适用模型并未从能源转换的共性机制层面揭示碳捕集理论能耗的"天花板"。因此,也较难像热力学经典概念热机、热泵及其衍生研究框架一样,从"理想与现实之间的不可逆性"这一思考原点出发,探索节能降耗的新机制与新途径。从碳捕集中能源转换的普遍特性出发,提出了热力学碳泵这一概念,首先对其在既有碳捕集研究体系中的辅助角色进行了论述,其后建立了基于热力学观点的模型并展开案例分析,最后与既有混合气体分离模型进行了异同讨论,阐述了两者的互补性。对热力学在面向新型工业应用情景下的能效分析进行了可供参考的尝试。     

Deliberating on low carbon development

Low carbon development (LCD) is a much used word in development circles today. As such, governments are actively exploring how to achieve their growth targets through a low carbon trajectory or even through a ‘carbon neutral’ pathway. This is a new area that challenges how development has been done so far, calling for not only a serious rethink of old practices but also contesting entrenched value systems. In this viewpoint, we explore some of the underlying issues that are driving the process of mainstreaming climate change in development. Recognising that there are variations in LCD, we map out the diversity of understandings and interpretations with a view to lay out the range of possibilities that countries can consider. We argue that whilst countries should certainly draw lessons from the experiences of others on mainstreaming climate change in their policies and practices, the version of LCD that each country follows needs to emerge from within its own national reality, anchored in its development prospects, aspirations and capacities.     

Enhanced capacitance in partially exfoliated multi-walled carbon nanotubes

We report for the first time the enhanced capacitance of multi-walled carbon nanotubes (MWCNTs) after exfoliation. Transmission electron microscopy studies confirmed that the MWCNTs were partially exfoliated with improved effective surface area. Carbon cloth electrode deposited with partially exfoliated carbon nanotubes (Ex-CNTs) yielded specific capacitances in a range of 130-165 F g⁻¹ at charging/discharging current densities from 5 to 0.5 A g⁻¹, with coulombic efficiencies of ∼98%. The specific capacitance of Ex-CNTs was an order of magnitude higher than untreated MWCNTs, and comparable to graphene at all charging/discharging current densities we studied. The enhanced capacitance can be attributed to improved effective surface area and increased defect density of the exfoliated tubular structure. The results declared that Ex-CNTs are promising electrode materials for high-capacitance supercapacitors.     

Studies on the carbon reactions in the anode of deposited carbon fuel cells

The carbon reactions in the anode of deposited carbon fuel cells were studied experimentally and theoretically. Deposition experiments were conducted by decomposing methane in a thermogravimetric analyzer at 800 °C, with both NiO or YSZ powders and small chips of an unused anode-supported SOFC button cell used separately as bed materials. The carbon tended to deposit on the Ni surfaces with the NiO or YSZ powders, while with the anode chips, the deposited carbon formed particles comparable in size to the Ni or YSZ particles with little carbon deposited near the electrolyte where the electrochemical reactions occur. Thus, the results infer that the deposited carbon has little opportunity to participate in the electrochemical reactions. A two-dimensional isothermal model was then developed to examine the influence of the deposited carbon on the cell performance. The results show the diffusion coefficient of CO has the largest influence, followed by the gasifying reactivity and the electrochemical reactivity of the carbon. Finally, a short deposition time and a high methane concentration are favored to improve the performance of deposited carbon fuel cells.     

活性炭纤维(ACF)在环境保护中的应用

活性炭纤维作为第三代活性炭产品，与传统的活性炭相比，具有高效的吸附性、独特的化学结构、物理结构和吸附性能。文中系统地介绍了活性炭纤维在国内外的发展概况、生产方法以及其在环境保护中的应用，并展望了活性炭纤维的发展前景。     

Lowering risk of methanation of carbon support in Ru/carbon catalysts for CO methanation by adding lanthanum

Two series of Ru/C catalysts doped with lanthanum ions are prepared and studied in CO methanation in the H₂-rich gas. The samples are characterized by N₂ physisorption, TG-MS studies, XRD, XPS, TEM/STEM and CO chemisorption. Two graphitized carbons differing in surface area (115 and 80.6 m²/g) are used as supports. The average sizes of ruthenium crystallites deposited on their surfaces are 4.33 and 5.95 nm, respectively. The addition of the proper amount of La to the Ru/carbon catalysts leads to an above 20% increase in the catalytic activity along with stable CH₄ selectivity higher than 99% at all temperatures. Simultaneously, lanthanum acts as the inhibitor of methanation of the carbon support under conditions of high temperature and hydrogen atmosphere. Such positive effects are achieved at a very low concentration of La in the prepared samples, a maximum 0.04 La/Ru (molar ratio). 0.01 mmol La introduced to the Ru/C system leads to 98% CO conversion at 270 °C.     

Structure and electrochemical properties of activated polyacrylonitrile based carbon fibers containing carbon nanotubes

Solution spun polyacrylonitrile (PAN), PAN/multi-wall carbon nanotube (MWCNT), and PAN/single-wall carbon nanotube (SWCNT) fibers containing 5 wt.% carbon nanotubes were stabilized in air and activated using CO₂ and KOH. The surface area as determined by nitrogen gas adsorption was an order of magnitude higher for KOH activated fibers as compared to the CO₂ activated fibers. The specific capacitance of KOH activated PAN/SWCNT samples was as high as 250 F g⁻¹ in 6 M KOH electrolyte. Under the comparable KOH activation conditions, PAN and PAN/SWCNT fibers had comparable surface areas (BET surface area about 2200 m² g⁻¹) with pore size predominantly in the range of 1–5 nm, while surface area of PAN/MWCNT samples was significantly lower (BET surface area 970 m² g⁻¹). The highest capacitance and energy density was obtained for PAN/SWCNT samples, suggesting SWCNT advantage in charge storage. The capacitance behavior of these electrodes has also been tested in ionic liquids, and the energy density in ionic liquid is about twice the value obtained using KOH electrolyte.     

中碳强度指数与中国低碳发展

中碳强度指数是为全国节能减排行业提供一个以单位国内生产总值(GDP)二氧化碳排放量为载体的指数系统,可有效反映时间序列上地区或行业碳排放强度的变化.2005—2011年中碳强度指数总体呈下降趋势.按中碳强度指数将我国各省级行政区分为五类,其中:大部分地区的指数均集中在0~100之间;指数高于100的四类和五类地区主要是煤炭生产大省和西部欠发达地区;而指数低于0的一类地区主要是经济发达地区.采用对数均值迪氏分解(LMDI)法分析陕西、贵州两省碳强度的影响因素时发现,能源强度下降是其碳强度指数下降的主要原因.结合"十二五"各地区的减排目标,预测了各省级行政区在剩余年份达成目标的压力,结果显示,我国的碳减排任务艰巨,其中内蒙古、宁夏等省份面临巨大的减排压力.     

Heterostructure based on exfoliated graphitic carbon nitride coated by porous carbon for photocatalytic H2 evolution

In this contribution, the heterostructure based on exfoliated graphitic carbon nitride (ex-gCN) coated by a porous carbon layer was fabricated by a simple approach and tested as a photocatalyst for hydrogen evolution under simulated solar light illumination. Bulk-gCN was firstly exfoliated and annealed under a hydrogen atmosphere in carefully selected conditions. The catalyst with the highest photoactivity was fabricated at 400 °C for 4 h. This material exhibited about a 23-fold higher amount of photogenerated hydrogen (18.2 μmol/g) compared to reference ex-gCN (0.8 μmol/g). Boosted photoactivity could be attributed to the (i) highly developed Specific Surface Area leading to more active sites on the surface due to the porous carbon layer, (ii) better transfer, and separation of photogenerated carriers, and (iii) sufficient suppression of the recombination process. Moreover, the mechanism of photocatalytic H₂ evolution from water splitting based on a full physicochemical characterization of the studied materials was proposed.     

Influence of different carbon materials on performance of lead carbon negative electrode

在铅炭负极中添加不同比例的造粒炭黑（CB）和活性炭（AC）,在部分荷电状态下,采用恒流充放电对比测试其循环性能,利用SEM、XRD对碳材料和铅炭负极活性物质进行表征分析。结果表明,造粒炭黑（CB）与活性炭（AC）添加到负极后,均能与铅结合形成铅炭结构,并明显提升部分荷电态下的循环性能。     

Investigation of hydrogen storage capacity of various carbon materials

Hydrogen storage capacity of various carbon materials, including activated carbon (AC), single-walled carbon nanohorn, single-walled carbon nanotubes, and graphitic carbon nanofibers, was investigated at 303 and 77 K, respectively. The results showed that hydrogen storage capacity of carbon materials was less than 1 wt% at 303 K, and a super activated carbon, Maxsorb, had the highest capacity (0.67 wt%). By lowering adsorption temperature to 77 K, hydrogen storage capacity of carbon materials increased significantly and Maxsorb could store a large amount of hydrogen (5.7 wt%) at a relatively low pressure of 3 MPa. Hydrogen storage capacity of carbon materials was proportional to their specific surface area and the volume of micropores, and the narrow micropores was preferred to adsorption of hydrogen, indicating that all carbon materials adsorbed hydrogen gas through physical adsorption on the surface.     

Cryo- and xerogel carbon supported PtRu for DMFC anodes

The specific catalytic activity of DMFC anodes based on PtRu may be improved using conducting carbon supports of high surface area and mesoporosity with pore size >20 nm for a high accessible surface area. To this purpose we pursued the strategy of developing PtRu catalysts deposited by chemical and electrochemical route on mesoporous cryo- and xerogel carbons. Here, we report the preparation and characterization data of different mesoporous cryo- and xerogel carbons as well as we present and discuss the results of the structural and morphological study and the catalytic activity data of PtRu catalysts chemically and electrochemically prepared, also by pulse techniques, on such carbons. The results are also compared to those obtained with PtRu supported on the generally used Vulcan carbon support.     

Modification of single wall carbon nanotubes (SWNT) for hydrogen storage

Due to unique structural, mechanical and electrical properties of single wall carbon nanotubes, SWNTs, they have been proposed as promising hydrogen storage materials especially in automotive industries. This research deals with investing of CNT’s and some activated carbons hydrogen storage capacity. The CNT’s were prepared through natural gas decomposition at a temperature of 900?C over cobalt-molybdenum nanoparticles supported by nanoporous magnesium oxide (Co–Mo/MgO) during a chemical vapor deposition (CVD) process. The effects of purity of CNT (80–95%wt.) on hydrogen storage were investigated here. The results showed an improvement in the hydrogen adsorption capacity with increasing the purity of CNT’s. Maximum adsorption capacity was 0.8%wt. in case of CNT’s with 95% purity and it may be raised up with some purification to 1%wt. which was far less than the target specified by DOE (6.5%wt.). Also some activated carbons were manufactured and the results compared to CNTs. There were no considerable H₂-storage for carbon nanotubes and activated carbons at room-temperature due to insufficient binding between H₂ molecules carbon nanostructures. Therefore, hydrogen must be adsorbed via interaction of atomic hydrogen with the storage environment in order to achieve DOE target, because the H atoms have a very stronger interaction with carbon nanostructures.