Oxidation of ash-free coal from sub-bituminous and bituminous coals in a direct carbon fuel cell

The present study proposes the production of ash-free coal (AFC) and its oxidation as a primary fuel in direct carbon fuel cells (DCFCs). The AFC was produced by the extraction of Arutmin sub-bituminous coal (AFC1) and Berau bituminous coal (AFC2) using polar solvents such as N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMA), N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO). It was carried out at a temperature of around 202 °C under atmospheric conditions and using a microwave irradiation method. Using NMP as the solvent showed the highest extraction yield, and the values of 23.53% for Arutmin coal and 33.80% for Berau coal were obtained. When NMP was added to DMSO, DMA and DMF, the extraction yield in the solvents was greatly increased. The yield of AFC from a sub-bituminous coal was slightly lower than that from a bituminous coal. The AFC was evaluated in a coin-type DCFC with a mixture of AFC and carbonate electrolyte (3 g/3 g) at 850 °C. The AFC and gaseous H₂ fuels were compared using the electrochemical methods of steady-state polarisation and step chronopotentiometry. The DCFC ran successfully with the AFCs at 850 °C. The open-circuit voltages were about 1.35 V (AFC1) and 1.27 V (AFC2), and the voltages at 150 mA cm^?2 were 0.61 V (AFC1) and 0.74 V (AFC2).     

Experimental results on the direct electrochemical oxidation of methanol in PEM fuel cells

The cell performance of direct methanol fuel cells (DMFC) is 0.5 V at 0.5 A cm^–2 under high pressure oxygen operation (3 bar abs.) at 110 °C. However, high oxygen pressure operation at high temperatures is only useful in special market niches. Therefore, our work has now focused on air operation of a DMFC under low pressure (up to 1.5 bar abs.). At present, a power density of more than 100 mW cm^–2 can be achieved at 0.5 V on air operation at 110 °C. These measurements were carried out in single cells with an electrode area of 3 cm² and the air stoichiometry only amounted to 10. The effects of methanol concentration and temperature on the anode performance were studied by pseudo half cell measurements and the results are presented together with their impact on the cell voltage. A cell design with an electrode area of 550 cm², which is appropriate for assembling a DMFC stack, was tested. A three-celled stack based on this design revealed nearly the same power densities as in the small experimental cells at low air excess pressure and the voltage–current curves for the three cells were almost identical. At 110 °C a power output of 165 W at a stack voltage of 1.5 V can be obtained in the air mode.     

配煤对煤灰熔点的影响及灰熔点预测模型研究

针对皖北刘桥二矿煤（A）属于高灰熔点煤,无法满足Shell气化炉液态排渣的需要。考察了采用配煤技术降低煤A的灰熔点的效果,结果表明,配煤可以显著的降低煤A的高灰熔融性。使其能够满足Shell气化炉液态排渣工艺的要求。并采用最小二乘法对灰熔点与煤灰灰成分之间建立并回归了预测模型,预测模型方程表明,若能增加配煤煤灰中MgO的含量可显著降低煤灰熔点,增加配煤煤灰中CaO的含量可使煤灰熔点降低,在煤灰中SiO2和Al2O3总含量一定的条件下,高硅低铝的配煤煤灰可进一步降低煤灰熔点。同时该模型能较好地预测三种原煤配煤的灰熔点。     

A carbon in molten carbonate anode model for a direct carbon fuel cell

The electrochemical oxidation of carbon at the anode of a direct carbon fuel cell (DCFC) includes charge transfer steps and chemical steps. A microstructural model of carbon particle is built, in which perfect graphene stacks are taken as the basic building blocks of carbon. A modified mechanism taking account of the irreversibility of the process and supposing that the electrochemical oxidation of carbon takes place only at the edges of the graphene sheets is proposed. A Tafel type overall rate equation is deduced along with expressions of exchange current density (j₀) and activation polarization (η_act). The performance of carbon black and graphite as the fuel of DCFC is examined. It has been found that j₀ is in the range of 0.10-6.12 mA cm⁻² at 923-1123 K and η_act is in the range of 0.024-0.28 V at 923-1123 K with current density in 10-120 mA cm⁻². Analysis of the j₀, η_act values and the product composition reveals that the charge transfer steps as well as the oxygen ion absorption steps are both important for the reaction rate. The activity of the carbon material with respect to atom location is introduced to the open circuit potential difference (OCP) calculation with Nernst equation.     

Trimethoxymethane as an alternative fuel for a direct oxidation PBI polymer electrolyte fuel cell

The oxidation of trimethoxymethane (TMM) (trimethyl orthoformate) in a direct oxidation PBI fuel cell was examined by on-line mass spectroscopy and on-line FTIR spectroscopy. The results show that TMM was almost completely hydrolyzed in a direct oxidation fuel cell which employs an acid doped polymer electrolyte to form a mixture of methylformate, methanol and formic acid. It also found that TMM was hydrolyzed in the presence of water at 120°C even without acidic catalyst. The anode performance improves in the sequence of methanol, TMM, formic acid/methanol, and methylformate solutions. Since formic acid is electrochemically more active than methanol, these results suggest that formic acid is probably a key factor for the improvement of the anode performance by using TMM instead of methanol under these conditions.     

Applications of heterogeneous catalysis in the direct oxidation of hydrocarbons in a solid-oxide fuel cell

This review article provides an overview of our recent studies of the direct oxidation of hydrocarbons in solid-oxide fuel cells. The use of a thermally stable, highly porous, yttria-stabilized zirconia (YSZ) matrix, which allows for the optimization of the anode composition and catalytic properties, is described. Studies of the direct oxidation of hydrocarbons using anodes composed of mixtures of YSZ, copper, ceria and samaria-doped ceria are also presented. The results of these studies demonstrate that copper-ceria based anodes are active for the direct electrocatalytic oxidation of a wide range of hydrocarbons including alkanes, alkenes, and aromatics.     

Effect of temperature, oxidant and catalyst loading on the performance of direct formic acid fuel cell

We investigated the effect of temperature, oxidant and catalyst loading on the performance of direct formic acid fuel cell (DFAFC). When oxidant was changed from air to oxygen, the power density was increased to 17.3 mW/ cm² at 25 ‡C. The power density of DFAFC operated with oxygen showed a maximum value of 40.04 mW/cm² with the temperature rise from room temperature to 70 °C. The highest power density of DFAFC using air was observed for Pt-Ru black catalyst with loading of 8 mgPt/cm² at room temperature. At 70 ‡C; however, the performance of catalyst with the loading of 4 mgPt/cm² was higher than that of 8 mgPt/cm². The DFAFC, operated with oxygen and catalyst of 4 mgPt/cm² loading, showed the best performance at all temperature range. The enhancement of cell performance with an increase of catalyst loading is believed to come from an increase of catalyst active sites. However, operated at higher temperature or with oxygen, the cell with higher catalyst loading showed lower performance than expected. It is speculated that the thick catalyst layer inhibits the proton transport.     

Performance degradation study of a direct methanol fuel cell by electrochemical impedance spectroscopy

A stability test of a direct methanol fuel cell (DMFC) was carried out by keeping at a constant current density of 150 mA cm⁻² for 435 h. After the stability test, maximum power density decreased from 68 mW cm⁻² of the fresh membrane-electrode-assembly (MEA) to 34 mW cm⁻² (50%). Quantitative analysis on the performance decay was carried out by electrochemical impedance spectroscopy (EIS). EIS measurement of the anode electrode showed that the increase in the anode reaction resistance was 0.003 Ω cm². From the EIS measurement results of the single cell, it was found that the increase in the total reaction resistance and IR resistance were 0.02 and 0.05 Ω cm², respectively. Summarizing the EIS measurement results, contribution of each component on the performance degradation was determined as follows: IR resistance (71%) > cathode reaction resistance (24%) > anode reaction resistance (5%). Transmission electron microscopy (TEM) results showed that the average particle size of the Pt catalysts increased by 30% after the stability test, while that of the PtRu catalysts increased by 10%.     

Study on the preparation of activated carbon for direct carbon fuel cell with oak sawdust

Direct carbon fuel cell (DCFC) is a device, which converts chemical energy of carbon into electrical energy through electrochemical oxidisation directly and its performance enormously depends on the characteristics of the fuel used. In this study, oak sawdust is used to prepare the activated carbon for the DCFC, with K₂CO₃ as the activating agent. Nickel catalyst is applied to improve the electrical conductivity, while HNO₃ treatment is used for the purpose of surface modification and ash removal. The performance of the prepared activated carbon in DCFC is evaluated in a self‐built DCFC anode apparatus. The results show that the BET surface area of activated carbon reaches 1240 m²/g under the following conditions: activation temperature, 1173 K; activation time, 2 h; and impregnation ratio, 1. Electrical conductivity is well improved through the nickel catalyst while the amount of surface oxygen functional groups is increased and ash content is decreased through the HNO₃ treatment. When used as the fuel in the DCFC anode, the self‐made activated carbon exhibits predominant performance among all tested carbon fuels, including graphite, activated carbon fibre, etc. © 2011 Canadian Society for Chemical Engineering     

Effect of anode backing layer on the cell performance of a direct methanol fuel cell

We investigated experimentally the effect of the anode backing layers consisting of carbon papers with different thicknesses and different polytetrafluoroethylene (PTFE) contents on the cell performance of a direct methanol fuel cell (DMFC). The membrane electrode assemblies were prepared using the decal method such that the effect of different anode backing layers could be studied with the same anode catalyst layer, the same membrane and the same cathode. We found that a too thin anode backing layer resulted in lower cell voltages in the entire current density region, whereas a too thick backing layer led to a lower limiting current density. The reduced cell performance as a result of thinning the backing layer may be attributed mainly to the increased under-rib mass transport polarization as a result of weaker under-rib convection in a thinner backing layer. The experimental results also showed that the use of a PTFE-treated backing layer resulted in a lower limiting current density, attributing primarily to the increased mass transfer resistance as a result of the PTFE treatment.     

On a possible role for electrochemical oxidation in coal liquefaction

The feasibility of coal conversion via electrochemical liquefaction has been investigated. Because of the complicating presence of inorganic materials in coals, humic acids extracted from lignites have been used as model substrates. Considerable reductions in molecular mass, as revealed by size exclusion chromatography, were achieved by anodic oxidation at 1.7 V for slurries in acid, and more especially for solutions in alkali. NMR spectroscopy of methylated humic acids before and after oxidation suggests cleavage of ether linkages between aromatic clusters, with generation of carboxyl groups.     

温度、接触压力与时间对燃煤飞灰固体桥力的影响规律

在所开发的用于在高温条件下(最高使用温度可达1600℃)测量灰的固体桥力的实验系统上,研究了温度、接触压力及接触时间对燃煤飞灰的固体桥力的影响规律。结果显示,燃煤飞灰的脖颈抗拉强度与温度之间呈现出双峰分布曲线的关系。这是由于随着温度的变化,燃煤飞灰的物相状态发生改变,玻璃体成分的含量也随之变化。在温度不变的情况下,燃煤飞灰的烧结脖颈抗拉强度随接触时间和接触压力的增加而增大。     

Performance of a direct methanol fuel cell

The performance of a direct methanol fuel cell based on a Nafion® solid polymer electrolyte membrane (SPE) is reported. The fuel cell utilizes a vaporized aqueous methanol fuel at a porous Pt–Ru–carbon catalyst anode. The effect of oxygen pressure, methanol/water vapour temperature and methanol concentration on the cell voltage and power output is described. A problem with the operation of the fuel cell with Nafion® proton conducting membranes is that of methanol crossover from the anode to the cathode through the polymer membrane. This causes a mixed potential at the cathode, can result in cathode flooding and represents a loss in fuel efficiency. To evaluate cell performance mathematical models are developed to predict the cell voltage, current density response of the fuel cell.     

Template synthesis of microporous carbon for direct methanol fuel cell application

Ordered microporous carbon with a structure of amorphous carbon core and graphitic carbon shell was prepared using hydrogen-form zeolite Y as the template. Impregnation and chemical vapor deposition methods were employed to infiltrate carbon in the pores of the template. Physical adsorption of nitrogen, X-ray diffraction, thermogravimetric analysis, field-emission scanning electron microscope, and field-emission transmission electron microscope techniques were employed to study the structural and morphological properties of the samples. The electrochemical properties of Pt supported on the carbon samples were examined and compared with a commercial catalyst. It was observed that Pt catalyst supported on a carbon with a core/shell structure has a higher specific activity for room-temperature methanol oxidation than the commercial catalyst.     

Effect of a GDL based on carbon paper or carbon cloth on PEM fuel cell performance

A commercially available GDL based on carbon paper or carbon cloth as a macroporous substrate was characterized by various physical and electrochemical measurements: mercury porosimetry, surface morphology analysis, contact angle measurement, water permeation measurement, polarization techniques, and ac-impedance spectroscopy. SGL 10BB based on carbon paper demonstrated dual pore size distribution and high water flow resistance owing to less permeable macroporous substrate, and more hydrophobic and compact microporous layer, as compared to ELAT-LT-1400 W based on carbon cloth. The membrane-electrode-assembly fabricated using SGL 10BB showed an improved fuel cell performance when air was used as an oxidant. The ac-impedance response indicated that a microporous layer which has high volume of micropores and more hydrophobic property allows oxygen to readily diffuse towards the catalyst layer due to effective water removal from the catalyst layer to the gas flow channel.     

Influence of hot-pressing temperature on physical and electrochemical performance of catalyst coated membranes for direct methanol fuel cells

The physical and electrochemical performance of a direct methanol fuel cell (DMFC) are improved by optimizing the hot-pressing temperature for fabricating the catalyst coated membrane (CCM) through the decal transfer method. SEM and XRD tests show that the morphology of the catalyst layer and the growth of Pt particles can be greatly influenced by the hot-pressing temperature. The CCM hot-pressed at 185 °C displays the best output performance due to the increase in electrochemical surface area (ESA), and the improved contact between the catalyst layer and the membrane. Although high hot-pressing temperature favors decreased methanol crossover, the performance of the CCM is subject to serious Pt agglomeration and slow mass transport.     

Formic acid oxidation by carbon-supported palladium catalysts in direct formic acid fuel cell

The oxidation of formic acid by the palladium catalysts supported on carbon with high surface area was investigated. Pd/C catalysts were prepared by using the impregnation method. 30 wt% and 50 wt% Pd/C catalysts had a high BET surface area of 123.7 m²/g and 89.9 m²/g, respectively. The fuel cell performance was investigated by changing various parameters such as anode catalyst types, oxidation gases and operating temperature. Pd/C anode catalysts had a significant effect on the direct formic acid fuel cell (DFAFC) performance. DFAFC with Pd/C anode catalyst showed high open circuit potential (OCP) of about 0.84 V and high power density at room temperature. The fuel cell with 50 wt% Pd/C anode catalyst using air as an oxidant showed the maximum power density of 99 mW/cm². On the other hand, a fuel cell with 50 wt% Pd/C anode catalyst using oxygen as an oxidant showed a maximum power density of 163 mW/cm² and the maximum current density of 590 mA/cm² at 60 °C.     

直接燃烧法快速测定煤及煤灰中总汞含量的方法研究

探讨直接燃烧法快速测定煤及煤灰中总汞含量方法的主要性能指标,方法的精密度和正确度。结果表明,采用直接燃烧法快速测定煤及煤灰中总汞含量的方法可获得较好的准确度,其方法精密度与ASTM D6722—11中规定的精密度无显著性差异,可直接采用ASTM D6722—11中规定的精密度作为本方法的精密度。方法最佳称样量为(80±10) mg,煤灰样品最佳粒度为0.1 mm,方法检出限为0.016μg/g。