A thermally rechargeable electrochemical oscillator for harvesting near room temperature ultra-low grade waste heat*

We present Soret effect-driven electrochemical devices that generate 1.02 V with a mere 10 K temperature difference with the cold end at room temperature, i.e., a Seebeck coefficient of 102 mV/K, which is almost four times the previously reported highest value (24 mV/K)¹ for cells with cellulose based separators. The Seebeck coefficient was found to depend not only on the electrolyte composition but also on the electrode porosity and microstructure (a neglected area of study). Interestingly, during galvanostatic discharge (with and without the temperature gradient), we observed novel voltage oscillations for both porous and non-porous electrodes. We conclusively prove (via models and experiments) that interplay between ionic diffusion and ionic migration within the electric double layer at the electrode-electrolyte interface is the root cause for voltage oscillations. We demonstrate that the oscillations can be controlled by changing the electrode porosity and the discharge current. Using up to 4 cells in series, we powered a calculator and performed basic calculations in real time. The presence of voltage oscillations indicates potential for novel applications. 

 

Reference: 

 

1. 1. Li, Tian, et al. Nature materials 18.6 (2019): 608-613.