Investigating the internal processes of thermo-electrochemical cells using in-situ magnetic resonance imaging

Thermo-electrochemical cells are emerging as a promising and efficient method to convert waste heat to electricity. In addition to developing novel redox electrolyte materials to increase the energy densities, it is crucial for future developments to understand the internal chemical and thermodynamical processes happening inside the thermo-electrochemical cell while it is under operating conditions. Although the temperature and concentration distributions between the electrodes and the variations of the convection currents with cell orientation have been modelled mathematically, it has been a challenge to study these internal processes using experimental techniques. Magnetic resonance imaging (MRI) is a non-invasive and well-established diagnosis technique in medical research to investigate physiology, but it also has the capability to study spatial properties of materials, chemical and thermodynamic processes in energy storage devices using different image contrast options including spin density, relaxation time and velocity [1]. The goals of this study are to develop an MRI method to study the internal chemical and thermodynamic processes within a functioning thermo-electrochemical cell, and understanding how these are affected by the electrolyte, the cell geometry and the orientation of the thermal gradient. A cobalt redox couple based electrolyte, which has been shown to be a promising candidate for thermo-electrochemical cells [2], was used for the in-situ experiments inside specialised cells custom built for MRI experiments, and temperature and concentration dependent 1H nuclear magnetic resonance spin-lattice relaxation time (T1) measurements were used to interpret the 1H T1 weighted MRI images of the working cells. References [1] Britton M. M., MRI of chemical reactions and processes, Progress in Nuclear Magnetic Resonance Spectroscopy, 101 (2017) 51-70. [2] Dupont M. F., MacFarlane D. R., Pringle J. M., Thermo-electrochemical cells for waste heat harvesting – progress and perspectives, Chem. Commun., 53 (2017) 6288-6302.