Stacked double-walled carbon nanotube sheet electrodes for electrochemically harvesting thermal energy

Abstract

Nanocarbon based electrodes have led to remarkable improvements in the performance of thermoelectrochemical cells (TECs), which are able to electrochemically harvest low-grade waste thermal energy. However, the highly tortuous ionic pathways of the electrodes limit the output current from the TECs by reducing the reaction rate inhibited by a concentration gradient in the electrode. In this work, we investigate an electrode structure that facilitates efficient ion transport by sequentially stacking highly aligned double-walled carbon nanotube (DWCNT) sheets. The performance of the TEC is evaluated with respect to the number of DWCNT stacks and the lamination orientation in a parallel or orthogonal direction. As the number of stacks increases from 1 to 3 layers oriented in parallel, the output power increases from 113 to 187 mW/m2 at a small temperature difference of 22 °C. The output power with 3-layer DWCNT sheets can be further improved to 200 mW/m2 by implementing an orthogonal lamination. The significance of electrode tortuosity presented here would be useful in electrode design as a way to improve energy harvesting performance. The results should also provide a basis for devising electrochemical devices with highly porous nanocarbon electrodes.