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

Abstract

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 Coⁿ(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, P_max = 183 mW m⁻²), including platinized stainless steel, Pt-SS (P_max = 188 mW m⁻²) and poly(3,4-ethylenedioxythiophene) deposited on stainless steel, PEDOT-SS (P_max = 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.