High capacitance B/C/N composites for capacitor electrodes synthesized by a simple method
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概要
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The B/C/N composites were synthesized by a very simple method, that is, carbonization at HTT = 800-1200℃ of the precursor prepared by drying a solution mixture of polyacrylamide and boric acid, followed by boiling in water to remove borate by-products. The amount of insoluble B species in the composite increased linearly from 4.8 to 18.6 mass% with raising HTT. The XRD and FT-IR revealed that turbostratic h-BN started to form at around 1000℃ as a by-product. By XPS, major B and N components in the composite were >B-N< bond, C-B-O type B, pyridinic N, pyrrolic N, and quaternary N. A fraction for >B-N< bond including h-BN in the total B or N components increased with raising HTT and it exceeded 50 at% between 900 and 1000℃. It was suggested that in the composites formed at HTT > 1000℃ the amounts of h-BN increased, leading to reduction in other B and N components. The S_[BET] was almost unchanged up to 1000℃, 410-420 m2 g^[-1]. Large and broad redox peaks arisen from plural reactions appeared in the cyclic voltammogram (CV) measured in 1 mol dm^[-3] H2SO4 for the composites formed at HTT ≤ 1000℃. These peaks disappeared in 1 mol dm^[-3] solutions of Na2SO4 and Li2SO4. By comparing CV with that for C/N composite formed from PAA by the MgO template method, the pseudocapacitance owing to reactions of >B-N< and C-B-O components with protons was found to be added to commonly observed pseudo-capacitance for nitrogen-doped carbons. The capacitances for the composites formed at 850-950℃ exceeded 300 Fg^[-1] at 2 mV s^[-1] in the acid electrolyte and the retention at 50 mV s^[-1] was 78-80%. The shape of CV in the neutral electrolytes was trapezoid and the current density increased with lowering potential, suggesting adsorption and desorption of Na+ and Li+ ions. This was considered to be due to doped nitrogen, indicating the development of pseudo-capacitance. The capacitance per S_[BET] was 0.33-0.74 F m^[-2] and 0.17-0.32 F m^[-2], larger for lower HTT, in the acid and neutral electrolytes, respectively.
- 2010-03-15
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