Characterization of MnO2 positive electrode for Fuel Cell/Battery (FCB)

The use of manganese dioxide (MnO₂) as a positive electrode material in Fuel Cell/Battery (FCB) systems is described. A positive electrode containing MnO₂ was fabricated and its performance was evaluated for charge/discharge behavior in three different systems: (i) secondary battery positive electrode, (ii) positive electrode in an alkaline fuel cell, and (iii) positive electrode performance in an FCB system by performing half cell tests. MnO₂ was observed to possess redox capabilities as the positive electrode of a secondary battery when it was subject to charge/discharge cycles. It was found that Mn₃O₄, which inhibits the discharge reaction, was produced during charge/discharge cycles. The I–V characteristics of MnO₂ material were measured to check the feasibility of the fuel cell system by supplying H₂ into the negative electrode and O₂ into the MnO₂ positive electrode, respectively. The MnO₂ electrode showed similar performance to Ni electrode, which was fabricated by using a similar method to the MnO₂ electrode. The MnO₂ electrode also showed that it functioned as an FCB positive electrode, which was confirmed by continued production of current when the O₂ supply was terminated. These results suggest that MnO₂ is a good candidate for an FCB positive electrode material.     

Preparation methods and progress of manganese dioxide/graphene based composites in supercapacitors

综述了基于MnO₂/石墨烯的二元、三元复合材料在超级电容器方面的最新研究进展。由于范德华力造成的堆叠，石墨烯实际比电容并不高。MnO₂理论比电容高达1370 F/g，但因其赝电容受MnO₂片层厚度的限制，实际比电容远小于理论值。将石墨烯和MnO₂复合，MnO₂纳米结构锚定在石墨烯纳米片之间充当间隔物，可以有效抑制石墨烯的堆叠，增强界面电荷转移，借助二者的协同效应有望实现高比电容、高电导率和良好的循环稳定性。介绍了MnO₂/石墨烯复合材料的制备方法及电化学性能。对比分析了MnO₂/石墨烯三元复合材料的电化学性能，由于金属氧化物或导电聚合物的引入，电化学性能进一步提升。最后总结指出基于MnO₂/石墨烯的多元复合材料和器件还面临着安全可靠、规模化生产以及降成本等一系列问题。随着技术的不断成熟和突破，有望在工业、交通以及日常电子器件中获得应用。     

Thermodynamic calculation on energy densities of multi-electron transfer Mg/Al batteries

镁离子电池和铝离子电池因其高能量密度、地壳储量丰富、安全等优良特性有望成为下一代新型高能量密度储能体系,是未来二次电池研究的热点之一。本文采用热力学方法计算和分析了近300种镁离子和铝离子电池体系的理论质量能量密度、体积能量密度和电压。在所得数据的基础上,以目前商业化锂离子电池正极材料钴酸锂为对比参考,综合考虑质量能量密度、体积能量密度、标准电极电位、毒性、腐蚀性、易燃性、环境友好性等诸多因素,逐步筛选出符合条件的一系列镁离子正极材料（O₂、S、MnO₂、MoO₃、Fe₂O₃、Fe₃O₄、NiO、MoO₂、CuO、Cu₂O）和铝离子的正极材料（O₂、S、MnO₂、MoO₃、NiO、CuO、Cu₂O）。     

Lithium insertion into manganese dioxide electrode in MnO2/Zn aqueous battery: Part I. A preliminary study

The discharge characteristics of manganese dioxide (γ-MnO₂ of electrolytic manganese dioxide (EMD) type) as a cathode material in a Zn–MnO₂ battery containing saturated aqueous LiOH electrolyte have been investigated. The X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) data on the discharged material indicate that lithium is intercalated into the host structure of EMD without the destruction of its core structure. The XPS data show that a layer of insoluble material, possibly Li₂CO₃, is deposited on the cathode, creating a barrier to H₂O, thus preventing the formation of Mn hydroxides, but allowing the migration of Li ions into the MnO₂ structure. The cell could be reversibly charged with 83% of voltaic efficiency at 0.5 mA/cm² current density to a 1.9 V cutoff voltage. The percentage utilization of the cathode material during discharge was 56%.     

Novel single step electrochemical route to γ-MnO2 nanoparticle-coated polyaniline nanofibers: Thermal stability and formic acid oxidation on the resulting nanocomposites

γ-MnO₂ nanoparticles-coated polyaniline (PANI) nanofibers on carbon electrode were prepared by potentiodynamic electrochemical deposition of PANI and MnO₂ from a single pot. Higher thermal stability of the resulting nanocomposites and their activity for formic acid oxidation permits the realization of a platinum-free anode for formic acid fuel cells.     

紫外光下Ag掺杂TiO2薄膜基底对VO2相转变温度的影响

利用溶胶−凝胶法和浸渍提拉技术制备了不同结构银掺杂二氧化钛薄膜为基底材料的VO₂薄膜,考察了Ag分级配置的二氧化钛薄膜基底材料对VO₂薄膜相变温度的影响。在紫外灯照射下测试面内电阻随温度,电压随时间的变化,结果表明基底材料为Ag分级配置的VO₂/TiO₂薄膜相变温度点明显降低。这可能是由于光照条件下空穴载流子从基底材料注入到VO₂薄膜导致相变温度点偏移。因此,不同结构银掺杂二氧化钛薄膜为基底材料的VO2薄膜能够根据环境温度和太阳光线变化而应用于光热致变色智能窗。     

Energy-efficient conversion of propane to propylene and ethylene over a V2O5/CeO2/SA5205 catalyst in the presence of limited oxygen

Oxidative conversion of propane to propylene and ethylene over a V₂O₅/CeO₂/SA5205 (V:Ce=1:1) catalyst, with or without steam and limited O₂, has been studied at different temperatures (700–850 °C), C₃H₈/O₂ ratio (4.0), H₂O/C₃H₈ ratio (0.5) and space velocity (3000 cm³ g⁻¹ h⁻¹). The propane conversion, selectivity for propylene and net heat of reaction (ΔHr) are strongly influenced by the reaction temperature and presence of steam in the reactant feed. In the presence of steam and limited O₂, the process involves a coupling of endothermic thermal cracking and exothermic oxidative conversion reactions of propane which occur simultaneously. Because of the coupling of exothermic and endothermic reactions, the process operates in an energy-efficient and safe manner. The net heat of reaction can be controlled by the reaction temperature and concentration of O₂. The process exothermicity is found to be reduced drastically with increasing temperature. Due to the addition of steam in the feed, no coke formation was observed in the process.     

Electrolytic manganese dioxides for battery applications: studies using electron paramagnetic resonance

Electron paramagnetic resonance (EPR) date are presented for four different samples of electrolytic manganese dioxide (EMD) that are intended for use in battery applications. The effects of graphite addition and discharge of active material are examined. Amongst the samples, wide differences in both the intercrystalline parameters and the number of available electrons in the conduction band are observed. The g factor is found to exhibit sensitive variations from sample to sample. In some samples, several types of manganese electrons can be detected. The extent of the γ phase — an essential aspect for aqueous electrochemical activity — can be assessed in samples. MnO₂-graphite agglomerates and reduction products of MnO₂ are identified. The magnetism of active materials is explained from analysis of the EPR spectra.     

Characterisation of oils from the fluidised bed pyrolysis of biomass with zeolite catalyst upgrading

Biomass in the form of pine wood was pyrolysed in an externally heated 7.5 cm diameter, 100 cm high fluidised bed pyrolysis reactor with nitrogen as the fluidising gas. A section of the freeboard of the reactor was packed with zeolite ZSM-5 catalyst. The pyrolysis oils before and after catalysis were collected in a series of condensers and cold traps. In addition, gases were analysed off-line by packed column gas chromatography. The compositions of the oils and gases were determined in relation to the primary fluidised bed and after catalysis at increasing catalyst bed temperatures from 400° to 550°C. The oils were analysed by a number of techniques to determine composition, including liquid chromatography, gas chromatography/mass spectrometry. Fourier transform infrared spectroscopy and size exclusion chromatography. The results showed that the oils before catalysis were highly oxygenated; after catalysis the oils were markedly reduced in oxygenated species with an increase in aromatic and polycyclic aromatic species.

The gases evolved from the fluidised bed pyrolysis of biomass were CO₂, CO, H₂, CH₄, C₂H₄, C₃H₆ and minor concentrations of other hydrocarbon gases. After catalysis the concentrations of CO₂ and CO were increased. The conversion of oxygenated compounds was mainly to H₂O at lower catalyst temperatures and CO₂ and CO at high catalyst temperatures. Detailed analysis of the oils showed that there were high concentrations of biologically active polycyclic aromatic species in the catalysed oil which increased with increasing catalyst temperature. The oxygenated compounds in the uncatalysed oil were mainly phenols and carboxylic acids. After catalysis these decreased in concentration with increasing catalyst temperature     

Carbothermal reduction of alumina: Thermochemical equilibrium calculations and experimental investigation

The production of aluminum by the electrolytic Hall–Héroult process suffers from high energy requirements, the release of perfluorocarbons, and vast greenhouse gas emissions. The alternative carbothermic reduction of alumina, while significantly less energy-intensive, is complicated by the formation of aluminum carbide and oxycarbides. In the present work, the formation of Al, as well as Al₂OC, Al₄O₄C, and Al₄C₃ was proven by experiments on mixtures of Al₂O₃ and activated carbon in an Ar atmosphere submitted to heat pulses by an induction furnace. Thermochemical equilibrium calculations indicate that the Al₂O₃-reduction using carbon as reducing agent is favored in the presence of limited amounts of oxygen. The temperature threshold for the onset of aluminum production is lowered, the formation of Al₄C₃ is decreased, and the yield of aluminum is improved. Significant further enhancement in the carbothermic reduction of Al₂O₃ is predicted by using CH₄ as the reducing agent, again in the presence of limited amounts of oxygen. In this case, an important by-product is syngas, with a H₂/CO molar ratio of about 2, suitable for methanol or Fischer–Tropsch syntheses. Under appropriate temperature and stoichiometry of reactants, the process can be designed to be thermo-neutral. Using alumina, methane, and oxygen as reagents, the co-production of aluminum with syngas, to be converted to methanol, predicts fuel savings of about 68% and CO₂ emission avoidance of about 91%, vis-à-vis the conventional production of Al by electrolysis and of methanol by steam reforming of CH₄. When using carbon (such as coke or petcoke) as reducing agent, fuel savings of 66% and CO₂ emission avoidance of 15% are predicted. Preliminary evaluation for the proposed process indicates favorable economics, and the required high temperatures process heat is readily attainable using concentrated solar energy.     

Cathodes with MnO2 catalysts for metal fuel battery

A series of cathodes with MnO₂ catalysts of metal fuel battery were prepared. The catalyst slurry was treated by ultrasonic dispersion under the ultrasonic time of 20 min, 40 min and 60 min. The cathodes were also dried with the temperature of 90°C, 120°C and 150°C. Besides, the microstructures of the cathodes and discharging performance were investigated. The results indicated that the ultrasonic time and drying temperature had a remarkable influence on the electric current densities, but had little effect on the open-circuit voltage. The effects of oxygen on the current density and voltage of cathode were also studied, and it was found that the method of blowing oxygen to cathode could increase the current density of the metal fuel battery.     

Pilot scale autothermal gasification of coconut shell with CO2-O2 mixture

This paper explored the feasibility and benefit of CO₂ utilization as gasifying agent in the autothermal gasification process. The effects of CO₂ injection on reaction temperature and producer gas composition were examined in a pilot scale downdraft gasifier by varying the CO₂/C ratio from 0.6 to 1.6. O₂ was injected at an equivalence ratio of approximately 0.33–0.38 for supplying heat through partial combustion. The results were also compared with those of air gasification. In general, the increase in CO₂ injection resulted in the shift of combustion zone to the downstream of the gasifier. However, compared with that of air gasification, the long and distributed high temperature zones were obtained in CO₂-O₂ gasification with a CO₂/C ratio of 0.6–1.2. The progress of the expected CO₂ to CO conversion can be implied from the relatively insignificant decrease in CO fraction as the CO₂/C ratio increased. The producer gas heating value of CO₂-O₂ gasification was consistently higher than that of air gasification. These results show the potential of CO₂-O₂ gasification for producing high quality producer gas in an efficient manner, and the necessity for more work to deeply imply the observation.     

Preparation and characterization of KF-KCl/SiO2 composite materials

采用混合烧结工艺将相变材料KF-KCl和陶瓷材料SiO₂进行复合,并添加聚乙烯醇作为黏结剂、B₂O₃作为烧结助剂,成功制备出一种陶瓷基复合结构储热材料。通过试验,确定了复合材料的烧结程序以及最佳的烧结温度。XRD分析表明,由KF-KCl/SiO₂构成的复合结构储热材料各物质之间具有良好的化学相容性;TG-DSC分析表明,复合材料在591.7 ℃时出现吸热峰,相变潜热是157.4 J/g。该复合材料具有储热密度高、无需容器盛装等特点,可以实现高温储热。     

A study of cathode catalysis for the aluminium/hydrogen peroxide semi-fuel cell

The characterization and use of a Pd and Ir catalyst combination on a C substrate in an Al/H₂O₂ semi-fuel cell is described. The Pd–Ir combination outperforms Pd alone or Ir alone on the same substrate. Scanning electron microscopy (SEM) and energy dispersive spectrophotometry (EDS) were used to establish the location of Pd, Ir and O in clusters on the cathode substrate surface. X-ray photoelectron spectroscopy (XPS) binding energy measurements indicate that Pd is in the metallic state and the Ir is in the +3 state. A configuration consisting of an Ir(III) oxide (Ir₂O₃) core and a Pd shell is proposed. The electrochemical, corrosion, direct and decomposition reactions which take place during cell discharge were evaluated. Improved initial and long term performance, at low current densities, of the Al/H₂O₂ semi-fuel cell incorporating a Pd–Ir on C cathode relative to a similarly catalyzed Ni substrate and a baseline silver foil catalyst is demonstrated.     

Fast pyrolysis of cellulose in a single pulse shock tube

A shock tube technique was employed to study the thermal decomposition of cellulose in an inert argon gas under the conditions of high temperature, high heating rate, and short reaction times. The influence of temperature and reaction times on product yields and their distribution were investigated. A clean, tar and char free gas consisting mainly of CO, CO₂, C₂H₂, C₂H₄ and CH₄ were produced throughout the course of this investigation. A mass conversion of cellulose to gas exceeding 90 wt% has been realized between the temperatures 700 and 2200°C for the reaction times examined. Carbon monoxide is the major product and attains a yield in excess of 65 wt% for temperatures above 1300°C. Global kinetic parameters for the decomposition of cellulose and its principal gas products were obtained by fitting the experimental data to a single, first order kinetic model. The energy of activation for the decomposition of cellulose was found to be 130.5 kJ/mol. The material balances made for the total mass, carbon and oxygen are good.     

Effect of Bi2O3 content on characteristics of Bi2O3–GDC systems for direct methane oxidation

Ceramic systems of Bi₂O₃ and gadolinia-doped ceria (GDC) solid mixture were prepared as catalysts for direct methane oxidation. These systems were characterized by temperature-programmed reduction using hydrogen and carbon monoxide, temperature-programmed reaction of methane, fixed-temperature direct methane oxidation, and X-ray diffraction analysis. Adding Bi₂O₃ to GDC promotes both hydrogen and CO oxidation activities, because of the presence of surface Bi₂O₃ and the high content of mobile oxygen in Bi₂O₃. The reactivity of CO with surface lattice oxygen is enhanced to a higher extent than that of H₂, and this enhanced extent shows a maximum in Bi₂O₃ content. Such a maximum also exists for the catalytic activity of direct methane oxidation. A synergistic effect occurs due to a combination of the high methane reactivity of GDC and the high content of mobile oxygen in Bi₂O₃. The CO₂ selectivity of direct methane oxidation can be modulated by varying the Bi₂O₃ content. The mixing of Bi₂O₃ with GDC also increases the self-de-coking capability of the catalyst during direct methane oxidation, which stabilizes the activity.     

Thermo-neutral production of metals and hydrogen or methanol by the combined reduction of the oxides of zinc or iron with partial oxidation of hydrocarbons

Stoichiometry and temperature requirements are determined for combining the endothermic reduction of metal oxides (ZnO, Fe₂O₃, and MgO) with the exothermic partial oxidation of hydrocarbons (CH₄, n-butane, n-octane, and n-dodecane) in order to co-produce simultaneously metals and syngas in thermo-neutral reactions. Thermogravimetric and GC measurements on the combined reduction of ZnO and Fe₂O₃ with the partial oxidation of CH₄ were conducted at 1400 K to experimentally verify the products predicted by equilibrium computations, and resulted in the complete reduction to Zn and Fe, respectively, while producing high quality syngas. A preliminary economic assessment that assumes a natural gas price of 11.9 US$/MWh and credit for zinc sale at 750 US$/metric ton, indicates a competitive cost of hydrogen production at 6.0 US$/MWh, based on its high heating value. The proposed combined process offers the possibility of co-producing metals and syngas in autothermal non-catalytic reactors, with significant avoidance of CO₂ emission.     

The influence of noble-metal-containing cathodes on the electrochemical performance of anode-supported SOFCs

In order to enhance the catalytic activity of the cathode for oxygen reduction and thus to increase the electrochemical performance of planar anode-supported solid oxide fuel cells, Pd, Ag, or Pt was added to the cathode. Four routes were used to add these noble metals: infiltration of the cathode with a Pd solution, deposition of Pt on the electrolyte surface, mixing of La_0.65Sr_0.30MnO₃ (LSM) and YSZ cathode powders with different metal precursors (Pt and Pd black, Pd on activated carbon, Ag powder, Ag₂O, Ag acetate, Ag citrate, Ag₂CO₃, colloidal Ag, AgNO₃), and synthesis of LSM powder with the addition of AgNO₃.

Between 750 and 900 °C no electrocatalytic effect occurred with respect to the presence of Pt, either added by deposition on the electrolyte or by mixing with cathode powders. Infiltration of the cathode with a Pd solution or mixing with Pd black did not result in a positive effect either. A catalytic effect was only found with Pd on activated carbon and in particular at lower temperatures.

Cells prepared with Ag powder and Ag₂O showed an improved electrochemical performance compared to Ag-free cells sintered at the same temperature (920 °C). However, in comparison to Ag-free cells sintered at the standard temperature (1100 °C) lower current densities were measured. This can be explained by a weak contact between electrolyte and cathode functional layer and an insufficiently sintered cathode. A detrimental effect was observed regarding the addition of the other Ag precursors. Thermal decomposition of these precursors resulted in the formation of large pores in the cathode.     

Modeling of single coal particle combustion in O2/N2 and O2/CO2 atmospheres under fluidized bed condition

A one-dimensional transient single coal particle combustion model was proposed to investigate the characteristics of single coal particle combustion in both O₂/N₂ and O₂/CO₂ atmospheres under the fluidized bed combustion condition. The model accounted for the fuel devolatilization, moisture evaporation, heterogeneous reaction as well as homogeneous reactions integrated with the heat and mass transfer from the fluidized bed environment to the coal particle. This model was validated by comparing the model prediction with the experimental results in the literature, and a satisfactory agreement between modeling and experiments proved the reliability of the model. The modeling results demonstrated that the carbon conversion rate of a single coal particle (diameter 6 to 8 mm) under fluidized bed conditions (bed temperature 1088 K) in an O₂/CO₂ (30:70) atmosphere was promoted by the gasification reaction, which was considerably greater than that in the O₂/N₂ (30:70) atmosphere. In addition, the surface and center temperatures of the particle evolved similarly, no matter it is under the O₂/N₂ condition or the O₂/CO₂ condition. A further analysis indicated that similar trends of the temperature evolution under different atmospheres were caused by the fact that the strong heat transfer under the fluidized bed condition overwhelmingly dominated the temperature evolution rather than the heat release of the chemical reaction.     

Physical metallurgy of FeTi-hydride and its behaviour in a hydrogen storage container

FeTi-samples have been prepared and characterized by metallography, X-ray diffraction, neutron diffraction and specific heat measurements. The conditions for the presence of the ordered CsCl structure at room temperature have been investigated. This material has been used to study FeTi-hydrides, especially the structure, phase transition and the heat of reaction as a function of the hydrogen concentration. The heat of reaction is 30 kJ/mole H₂ for 0.05 < c < 0.5 (c = atomic ratio: atoms H/atoms metal). The heat of solution (c → 0) is approx. 130 kJ/mole H₂. The FeTi material has been used to build and operate a small hydrogen storage container (1 Nm³H₂) as an alternative to high pressure hydrogen gas containers in the laboratory.