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La Chaux-de-Fonds, Switzerland

Uhl S.,Haute Ecole Arc Ingenierie HESSO | Laux E.,Haute Ecole Arc Ingenierie HESSO | Journot T.,Haute Ecole Arc Ingenierie HESSO | Jeandupeux L.,Haute Ecole Arc Ingenierie HESSO | And 2 more authors.
Journal of Electronic Materials | Year: 2014

The unfavourable relationship between electrical and thermal conductivity limits the choice of solid-state materials for thermoelectric generators (TEG). Among ionic liquids (IOL), it appears that a large variety of thermoelectric (TE) materials with promising high Seebeck coefficients have potential for development. Furthermore, the novel solid-on-liquid deposition technology (SOLID) allows the encapsulation of liquid TE materials to create new, highly integrated TEG devices. Following this vision, this paper studies a large number of IOLs looking at TE-relevant parameters such as thermal and electrical conductivity, Seebeck coefficient and temperature-dependent viscosity. We show that positive and negative Seebeck coefficients can be obtained, depending on the molecular structure and the viscosity of the IOL. The properties of single-junction TEGs are presented in terms of I–V characteristics correlated with the IOL properties. We prove that the limiting effect of conversion efficiency is the current density that can be extracted from a device rather than the Seebeck coefficient. © 2014, TMS. Source


Laux E.,Haute Ecole Arc Ingenierie HESSO | Uhl S.,Haute Ecole Arc Ingenierie HESSO | Journot T.,Haute Ecole Arc Ingenierie HESSO | Brossard J.,Haute Ecole Arc Ingenierie HESSO | And 2 more authors.
Journal of Electronic Materials | Year: 2016

The Seebeck coefficient (SE) or thermopower and power output have been measured in a series of 16 ionic liquids (ILs). Thermoelectric current extraction is assisted by a dissolved redox couple (I2/LiI) added to the IL. The experiments were carried out in a thermoelectric cell where the IL is packaged between two electrodes. A large range of Seebeck coefficients and power outputs could be observed. The highest SE was measured for protonic ILs, reaching a value of 968 μV/K. Moreover, the maximal power output of an IL-based thermoelectric generator and the polarity of its electrodes depend on the concentration of the redox-active species in the IL. The power output of the generator increased continuously with the redox concentration up to a maximum value (at 0.4 mol/L) but decayed for higher concentrations. We showed that an IL with high SE [linked to open-circuit voltage (VOC)] does not necessarily lead to high power output; rather, it is carrier transport and extraction that determine the generator power. Surprisingly, the carrier extraction is not highest at the maximum electrode temperature difference; the power output observed for a given electrode temperature difference can be further increased by heating up the cold electrode in spite of the consequent reduction in the total temperature difference between the electrodes. © 2016 European Union Source


Uhl S.,Haute Ecole Arc Ingenierie HESSO | Pellet M.,Haute Ecole Arc Ingenierie HESSO | Tschanz J.,Haute Ecole Arc Ingenierie HESSO | Laux E.,Haute Ecole Arc Ingenierie HESSO | And 3 more authors.
Materials Today: Proceedings | Year: 2015

Recent research in Ionic Liquids as new thermoelectric materials [1,2] demands a suitable implementation in an industrially producible generator. Such a flexible micro generator can harvest electrical energy in order to extent battery lifetime or serve as single energy source for medical and wearable applications. The paper presents the fabrication steps of a new, highly integrated thermoelectric generator (TEG) based on ionic liquids. Furthermore, the applicability of ionic liquids with copper electrodes in thermoelectric devices is shown due to a passivation process at the electrode surface, whichallows the usage of commercially available copper clad laminates. © 2015. Source

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