Abstract
A large Seebeck coefficient (S e) of 1.9 mV K-1 was recorded for the I-/I3 - thermocell by utilizing the host-guest complexation of hexakis(2,3,6-tri-O-methyl)-α-cyclodextrin (Me18-α-CD) with the oxidized iodide species. The thermocell measurement and UV-vis spectroscopy unveiled the formation of an Me18-α-CD-pentaiodide (I5 -) complex, which is in remarkable contrast to the triiodide complex α-CD-I3 - previously reported. Although the precipitation of the α-CD-I3 - complex in the presence of an electrolyte such as potassium chloride is a problem in thermocells, this issue was solved by using Me18-α-CD as a host compound. The absence of precipitation in the Me18-α-CD and I-/I3 - system containing potassium chloride not only improved the S e of the I-/I3 - thermocell, but also significantly enhanced the temporal stability of its power output. This is the first observation that I5 - species is formed in aqueous solution in a thermocell. Furthermore, the solution equilibrium of the redox couples was controlled by tuning the chemical structure of the host compounds. Thus, the integration of host-guest chemistry with redox couples extends the application of thermocells.
Highlights
Thermo-electric conversion based on the Seebeck effect has attracted much interest due to its potential to retrieve waste heat and convert it to electricity, which provides a promising way to reduce the consumption of fossil fuel
We recently reported the concept of a supramolecular thermocell, which was demonstrated by introducing a-cyclodextrin (a-CD, Fig. S1a†) as a molecular host to the IÀ/I3À thermocell. aCD selectively captured the hydrophobic I3À anion, which led to a signi cant enhancement of Seebeck coefficient (Se) from 0.8 to 1.4 mV KÀ1.18 The addition of KCl as the supporting electrolyte resulted in the precipitation of the a-CD–I3À complex in the lower-temperature cells, which further increased the Se value to ca. 2 mV KÀ1
The Voc values were proportional to the temperature difference (DT), where the slope of the line corresponds to the Seebeck coefficient
Summary
Thermo-electric conversion based on the Seebeck effect has attracted much interest due to its potential to retrieve waste heat and convert it to electricity, which provides a promising way to reduce the consumption of fossil fuel. ACD selectively captured the hydrophobic I3À anion, which led to a signi cant enhancement of Se from 0.8 to 1.4 mV KÀ1.18 The addition of KCl as the supporting electrolyte resulted in the precipitation of the a-CD–I3À complex in the lower-temperature cells, which further increased the Se value to ca.
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