Abstract
Thermocells represent a promising way to utilize heat as a power source. The aim of this work is to develop a thermocell with identical gas electrodes using molten carbonate-based electrolytes. The cell can generate power from waste heat, and can also utilize the CO2 rich off-gas available in metal producing industries. The flow rate of the gas supply to the electrodes needs to be optimized. Its effect on the Seebeck coefficient was not studied systematically before. The addition of solid oxide to the molten carbonate melt alters also the system's Seebeck coefficient. We report measurements where we vary the content of solid oxide in the liquid eutectic electrolyte mixture as well as the electrode gas flow rate. The Seebeck coefficient is reported for various ratios of eutectic (Li,Na)2CO3 molten carbonate and dispersed solid oxide MgO, and for varying gas (CO2|O2) flow rates to the electrode interfaces.
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
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