| 研究実績の概要 |
The scale of carbon foam production has been increased from 0.5 g to >5 g, by utilization of a box furnace with N2 gas flow. The surface area of carbon foam has been increased from 1500 m2/g to >2500 m2 by optimization of the pyrolysis temperature, heating rate, and gas flow rates.
Various nitrogen-containing precursors have been investigated, namely ethanolamine, diethanolamine, and triethanolamine. Triethanolamine was found to give the most consistent products with the highest yield. A new technique for synthesis of the nitrogen-doped carbon foam has been developed. Previously, Na was reacted with alcohol at high temperature and pressure. Now, the Na is kept under ether, and the reactant is added dropwise until the sodium is consumed. The ether is removed by rotary evaporation and the product is then pyrolysed. This new technique is highly scalable and safer. The surface area of nitrogen-doped carbon foam has been increased from ~700 m2/g to >2000 m2 by optimization of the pyrolysis temperature, heating rate, and gas flow rates.
The physical and chemical structure of the samples have been characterized in detail via X-ray spectroscopy, electron microscopy, combustion analysis, gas adsorption techniques etc. The electrochemical performance for the oxygen reduction reaction (ORR) has been investigated by cyclic and linear sweep voltammetry. The ORR current density, turn on voltage, mass activity and electron transfer number have been evaluated.
In future work, Fe decoration will be achieved by heat treatment in iron acetate, and the impact on the ORR will be investigated.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
2: おおむね順調に進展している
理由
We have made excellent progress in terms of materials development beyond our initial expectations. For example the surface areas, scale, and yield we have achieved through this simple process have been much higher than expected. However, the electrochemical properties have been lower than expected. To remedy this much higher pyrolysis temperatures will be utilized (e.g. 1400C) most likely at the cost of surface area and yield.
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| 今後の研究の推進方策 |
The electrochemical activity of nitrogen-doped carbon foam will be optimized by increasing pyrolysis temperature (and therefore conductivity). Electrochemical durability tests will be performed in both acid and alkaline. Synthesis and characterization of iron-decorated carbon foam and iron-decorated nitrogen-doped carbon foams will be undertaken. These new materials will be tested for their ORR capability and durability. Membrane electrode assemblies (MEAs) will be fabricated to explore how these electrocatalysts behave under realistic fuel cell conditions. Advanced electrochemical techniques will be performed to clarify the role of nitrogen and iron in 4-electron ORR in the four types of sample. High temperature ORR measurements will be performed to elucidate for the first time the reaction kinetics of nitrogen-doped carbons over a wide temperature range (e.g. 90 to 300˚C). These will be undertaken by: (a) using PBI as a high temperature proton conductor (up to 180˚C); (b) replacing aqueous electrolyte with proton-conducting ionic liquids (up to 250˚C); and (c) replacing the aqueous electrolyte with solid ceramic proton conductors (up to 450˚C). This will give new insights into the kinetics of the ORR in Pt-free catalysts, and will determine the usefulness of such catalysts at high temperature, where the kinetic rates are faster, and the need for highly active catalysts such as platinum is drastically reduced.
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