多壁纳米碳管空气电极的交流阻抗研究

研究了多壁纳米碳管、活性炭和石墨等空气电极的交流阻抗特性.结果表明,纳米碳管空气电极的阻抗谱由两个半圆组成,高频区半圆对应欧姆极化阻抗,低频区半圆对应电化学极化阻抗.催化剂Pt以纳米颗粒的形式沉积在碳管的外表面,明显减小了电极的欧姆阻抗和电化学极化阻抗,提高了氧还原反应的电催化活性.活性炭电极除存在电化学阻抗外,还存在薄液膜扩散阻抗(Nernst扩散),石墨电极形成的薄液膜反应区域较小,电极反应呈Warburg扩散阻抗特征,相应的电催化活性较低.采用交流阻抗等效电路分析方法,对拟合的动力学数据进行了解释.

AC Impedance Studies on Multi-walled Carbon Nanotubes Air Electrode

The AC impedance properties of the air electrodes using multi-walled carbon nanotubes, active carbon and graphite particles as catalyst layer material were investigated. The results showed that the AC impedance diagram of carbon nanotubes consisted of two semi-circles, in which the high frequency zone was ascribed to the ohmic process within porous structure and the low frequency zone to the kinetic impedance of electrochemical reaction. The Pt nanoparticles deposited on the exterior surface of carbon nanotubes decreased greatly ohmic and electrochemical impedance, so increased electro-catalytic activity of oxygen reduction. However, for the air electrode prepared by active carbon, the thin film diffusion impedance was appreciably observed in addition to ohmic impedance. The low catalytic activity in the graphite air electrode appeared as a consequence of the decreased thin film reaction sites and the mass transport process was dominated by Warburg diffusion. Finally, the equivalent circuit of air electrode was proposed and the simulated kinetic data were also discussed.