(438b) Excess Thermopower in Carbon Nanotubes Using Thermopower Waves

The nonlinear coupling between an exothermic chemical reaction and a nanowire or nanotube with large axial heat conduction results in a self-propagating thermal wave guided along the nano-conduit. The reaction wave induces a concomitant thermopower wave of high power density, resulting in an electrical current in the same direction. Thermopower waves also tend to produce monopolar voltage pulses, although conventional thermoelectric theory clearly predicts bipolar voltage, and they propagate in materials with both high electrical and thermal conductivity. 
Temperature and voltage measurements of thermopower waves on single-walled carbon nanotubes (SWNTs) show that they can generate voltage and power in excess of the predictions of the Seebeck effect for the temperature gradient, as much as four times greater power. We hypothesize that the excess thermopower stems from a chemical potential gradient across the SWNTs with a new model that describes the electrical properties of the waves. The fuel (prototypically picramide) and ambient oxygen adsorb and dope the SWNTs ahead of the wave, and desorb and react in the hot zone behind the wave front. Raman spectroscopy confirms that picramide dopes SWNTs. Furthermore, the excess thermopower depends on the mass of fuel added (relative to SWNT mass), and the chemical potential difference matches the magnitude of the excess thermopower. This model relies on SWNT property data measured in the literature rather than fit parameters. Thermopower waves thus provide an exciting new class of highly scalable, stable energy storage devices, and offer the possibility of greatly exceeding the power limitations of conventional thermoelectric devices.