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

Nanocarbon based electrodes have led to remarkable improvements in the performance of thermo-electrochemical 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/m(2) at a small temperature difference of 22 degrees C. The output power with 3-layer DWCNT sheets can be further improved to 200 mW/m(2) 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. (C) 2019 Elsevier Ltd. All rights reserved.