Chapter 9 - Iron perchlorate electrolytes and nanocarbon electrodes related to the redox reaction

Abstract

Thermocell can effectively tap two thirds of the total energy produced that is discharged as waste heat for the purpose of converting the waste energy to electricity. Here we discuss an aqueous electrolyte for the thermocell that compliments and outperforms the electrolyte of ferric/ferrous cyanide that has been the benchmark in thermocell research. The new electrolyte of iron perchlorate (Fe2+/Fe3+), an n-type electrolyte, provides a high ionic Seebeck coefficient of -1.76 mV/K, which is complementary to the cyanide electrolyte (Fe(CN)63-/Fe(CN)64-) with the coefficient of +1.42 mV/K, a p-type electrolyte. This feature should make it possible to connect the TECs in series in a flip-flop configuration for p-n TECs, as in p-n thermoelectrics. The electrolyte power factor and figure of merit for this new electrolyte of iron perchlorate are higher by 28% and 40%, respectively, than those for the cyanide electrolyte. In terms of device performance, the TEC using the perchlorate electrolyte provides a power density of 687 mW/m2 that is 45% higher compared to the same device but with the cyanide electrolyte for a small temperature difference of 20°C. In view of the tremendous progress made in the thermocell performance with the introduction of the cyanide electrolyte, the proposed electrolyte bodes well for the significant advances that could be made with its introduction.