Electrochemical charge storage properties of vertically aligned carbon nanotube films: Effects of thermal oxidation

Vertically aligned carbon nanotube (VACNT) films were synthesized and investigated in vitro for their potential use as a neural stimulation electrode. Materials and electrochemical (EC) characterization (cyclic voltammetry, electrochemical impedance spectroscopy, and high-rate potential transient measurements) were performed before and after flash oxidation in O 2 at various temperatures and over a wide frequency range. The results showed distinct EC behavior within three ranges of treatment temperature. Oxidative thermal treatments that did not visibly etch the VACNT film caused a significant improvement in electrode performance compared to the as-deposited electrode. Surprisingly, flash oxidation within a narrow temperature range (400 < T ≥ 450 °C) selectively increased capacitance/charge injection at high frequencies (10 ²-10 ⁴ Hz). A phenomenological model is proposed to explain the temperature-dependent behavior and indicates the importance of modifying a porous coating to increase the charging rate rather than maximizing the total charge accumulated at long times for high-rate charge storage applications. © 2012 American Chemical Society.

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