(41h) Novel Energy Sources Based on Excess Thermopower and Carbon Nanotube Fibers

As cylindrical forms of graphene sheets, carbon nanotubes are unique in their high surface area for molecular adsorption and exceptional electrical conductivity. The theory describing so called thermopower waves, self-propagating reaction waves that generate electrical current from a thermally driven wavefront, explains the resulting power as arising from two additive components: the thermoelectric effect and the chemical potential gradient across the reaction front or excess thermopower. In this work, we validate this theory and generate unique power sources by creating conduits driven by only excess thermopower. Electrical current (11.9 µA/mg) is reversibly produced across a carbon nanotube fiber by localized chemical doping with acetonitrile. We show that the voltage is driven by a spatial gradient in the Fermi energy across the carbon conduit and can reach an unprecedented 525 mV in magnitude. Chemical modification of the nanotube surface, specifically, oxidation of the conduit is shown to enhance the effect. Closed circuit experiments further reveal an inverse length-scaling of the maximum power as L^-1.03. The resulting specific powers as large as 30.0 kW/kg for oxidized nanotubes highlight the potential for microscale energy generation and harvesting. These results constitute a strong validation of Excess Thermopower theory and may enable unique power sources capable of continual operation based on repeated solvent exposure.