Abstract
A thermo-electrochemical cell (thermocell) is an electrochemical system with two identical electrodes placed at different temperatures in an electrolyte solution. The ion migration between the electrodes due to the temperature gradient leads to thermoelectric conversion. Such systems represent a promising pathway to utilise dynamic heat as power source. A possible thermo-electrochemical cell with molten carbonate electrolyte and gas electrodes was recently reported [1,2]. The change in Seebeck coefficient (thermoelectric power) with electrode materials, electrode gas mixture, electrolyte composition and electrolyte support materials was studied [2]. Addition of support material (solid oxide) in the molten carbonate electrolyte, may reduce the thermal conductivity and maintain the temperature gradient between the electrodes. Thermal boundary layers may arise due to the electrode gas flow; slow flow rate seems to be preferred for obtaining a high value in thermoelectric power. In this study the system is further optimised with respect to the composition of electrolyte and supporting materials as well as electrode gas flow rate. The thermoelectric power is measured with various ratios of ((Li,Na)2CO3) molten carbonate to support (MgO) solid oxide in the electrolyte mixture and also with different gas flow rates at the electrode-electrolyte interface.
Highlights
Thermoelectric systems converting heat into electricity are well known since their discovery of the Seebeck effect in 1821.1 The thermoelectric power was first demonstrated for aqueous thermogalvanic cells, Quickenden et al summarized many similar systems in a review.[2]
Homogeneity of the electrolyte mixture.—The X-ray diffraction results of the electrolyte samples of Cells D and G, collected from various regions in the cell after the experiments are shown in Figures 2a and 2b
Reversibility of the electrodes.—We have further found by inspecting the raw data, like the ones pictured in Figure 3a and processes in Figure 3b, that the thermoelectric potential measurement could be reversed by reversing the temperature difference, and that there was no bias potential between the gold electrodes at moderate flows of gas to the electrode
Summary
The use of an ion-conducting electrolyte and gas electrodes offers possibilities of achieving high Seebeck coefficients.[4,5,6] Electrolytes such as ionic liquids and molten salts offer possibilities of higher stable operating temperatures and larger Seebeck coefficients than semiconductor thermoelectric materials.[7,8] Experimental studies of electrochemical cells with inexpensive components such as molten carbonate electrolyte and CO2|O2 gas electrodes have been reported earlier. The so-called “figure of merit” is related to the thermoelectric power generation efficiency It increases with an increasing Seebeck coefficient, a decreasing thermal conductivity and a decreasing electrical resistivity.[2] The use of non-critical and non-poisonous materials and the prospective of a high thermoelectric efficiency, as well as the availability of CO2 gas, may be advantageous for the thermocell compared to semiconductor thermoelectric devices. The change in the Seebeck coefficient for similar thermocells with different carbonate melt compositions, electrode gas mixture, current collector, solid-state oxide and various average cell
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
