Abstract
Thermo-electrochemical cells (thermocells) convert temperature difference to electricity with no moving parts and is an inexpensive technology to harvest waste heat. However, low power conversion efficiency and power output has limited its use from being a commercial application. In a thermocell, when a temperature difference is applied at the electrodes, oxidation and reduction takes place at the hot and cold electrodes respectively. The electron released at the hot electrode (anode) due to oxidation of ion passes through the external circuit, while the oxidized ion moves towards the cold electrode (cathode) where it is reduced and the cycle repeats. To minimize the over potentials at the electrode/electrolyte interface (interfacial charge transfer resistance) due to electronic transport, concentration polarization near the electrode interface (mass transfer resistance) due to ions, transport of ions in the bulk fluid (ohmic resistance) are the primary requirements for high energy conversion efficiency.1 Increasing the flux of charge carriers to flux of heat flowing between the electrodes is also needed. In this work, the effect of mixing carbon nanotubes (CNT) and poly (3,4-ethylenedioxythiophene)−poly(styrenesulfonate) (PEDOT:PSS) composite in aqueous potassium ferri/ferrocyanide electrolyte is characterized using electrochemical impedance spectroscopy. Here we report a 10% decrease in ohmic resistance and 5-fold decrease in interfacial charge transfer resistance. The decrease is ohmic resistance is attributed to increase in PEDOT:PSS ions and interfacial polarization2 due to CNT present in the electrolyte. While the decrease in interfacial charge transfer resistance is attributed to composite increasing the contact area at the electrode/electrolyte interface.3, 4 The composite electrolyte improved the power performance of the standard electrolyte by about 30% and gave a stable output over a 30 day period suggesting that it can be used for long term operation. 1. T. Quickenden and C. Vernon, Solar Energy, 1986, 36, 63-72. 2. P. F. Salazar, S. T. Stephens, A. H. Kazim, J. M. Pringle and B. A. Cola, Journal of Materials Chemistry A, 2014, 2, 20676-20682. 3. T. Kato, T. Kado, S. Tanaka, A. Okazaki and S. Hayase, Journal of the Electrochemical Society, 2006, 153, A626-A630. 4. C. P. Lee, K. M. Lee, P. Y. Chen and K. C. Ho, Solar Energy Materials and Solar Cells, 2009, 93, 1411-1416.
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