Investigation of the kinetic and mass transport limitations in thermoelectrochemical cells with different electrode materials.

Thermoelectrochemical cells (TECs) have the potential to offer a continuous renewable electricity supply from a variety of thermal energy sources. Because of the thermal gradient, the device characteristics are a complex function of temperature dependent electrolyte transport properties, electrode electro-catalytic properties and the Seebeck coefficient of the redox couple. Understanding the interplay between these functions is critical to identifying the limiting factors that need to be overcome to produce more advanced devices. Thus, in this work we have developed a theoretical model for TECs and have measured a range of properties required by the model. We focused attention on the Co(n)(bpy)3(NTf2)n in a [C2mim][B(CN)4] ionic liquid electrolyte as one of the optimal systems for >100 °C operation. The exchange current densities on a range of electrode materials were measured in order to explore the role of electrode function in the simulation. Alternatives to platinum electrodes (maximum output power, Pmax = 183 mW m(-2)), including platinized stainless steel, Pt-SS (Pmax = 188 mW m(-2)) and poly(3,4-ethylenedioxythiophene) deposited on stainless steel, PEDOT-SS (Pmax = 179 mW m(-2)), were shown to be viable options. From the simulations we conclude that for further development of ionic liquid TECs, modifications to the redox couple to increase the Seebeck coefficient, and increasing the rate of diffusion of the redox couple to minimize mass transport resistance, will yield the greatest improvements in device performance.

Electrochemical surface-enhanced Raman spectroscopy (E-SERS) of novel biodegradable ionic liquids.

Electrochemical SERS (E-SERS) was used for the first time to study the interfacial behavior of a class of pyridinium-based biodegradable ionic liquids at a silver nanoparticle (AgNP) electrode surface. An isomeric series of ionic liquids (IL) based on 3-butoxycarbonyl-1-methylpyridinium bis(trifluoromethanesulfonyl)imide were prepared, which have demonstrable biodegradability. It was found that all four of the isomeric ionic liquids studied exhibited excellent electrochemical stability as binary mixtures combined with methanol, with the absence of any specific redox processes occurring over nearly 3.0 V of applied potential. Normal Raman measurements of the neat isobutyl IL showed a signal rich in vibrational features, with strong contributions from both the anion and the bulky organic cation. E-SERS of the neat isobutyl IL was shown to exhibit excellent potential stability, with no potential-induced orientational change at the metal surface. When the ionic liquids were prepared as methanolic binary mixtures, dissociation of the IL ions was observed, and only the organic cation was shown to adsorb at the Ag/solution interface. The nature of the substituent on the ester group of the IL series was observed to have a significant effect on the orientation of the cation on the metal surface, based on the application of the metal surface selection rules combined with computational data. Notably, the isobutyl and sec-butyl isomers were observed to have an orientation wherein the pyridinium ring was oriented perpendicular to the surface, while the tert-butyl and n-butyl isomers were observed to have an orientation wherein the pyridinium ring was lying flat on the metal surface.

Seebeck coefficients in ionic liquids--prospects for thermo-electrochemical cells.

Measurement of Seebeck coefficients in a range of ionic liquids (ILs) suggests that these electrolytes could enable the development of thermoelectric devices to generate electrical energy from low-grade heat in the 100-150 °C range.