Dynamic response of a thermoelectric cell induced by ion thermodiffusion

Abstract

Aqueous electrolyte solutions under the influence of a temperature gradient can generate thermoelectric fields, which arise from different responses of the positive and negative charges. This is related to the thermodiffusion effect which is quantified by the ionic heat of transport and the thermal diffusion coefficient. When a solution is confined between two metallic electrodes with different temperatures, it is expected to measure the electrostatic potential difference due to the thermoelectric field. We performed experiments in aqueous electrolyte solutions, and our results show that a thermoelectric field appears instantly in the solution as the temperature difference between the electrodes stabilizes. This field arises from the trend to separate both ionic charges in the temperature gradient. The experimental results also show that a slow change in the potential difference is observed, which is related to thermodiffusion in the entire cell. These results are important to understand how the thermoelectric response can be optimized, given the broad interest in the literature to generate thermoelectric energy from thermoelectric cells.

Molecular Dynamics Approach to Calculate the Thermodiffusion (Soret and Seebeck) Coefficients of Salts in Aqueous Solutions

“…Finally, the calculated values for salt thermodiffusion-related coefficients, that is, thermal diffusion D T and Soret S T and Seebeck at fast and slow time regimes, S fast and S slow , respectively, are presented, discussed, and compared with experimental values obtained from optical experiments. 16,42,43 2.1. Ion Hydration.…”

“…The calculated values for S fast obtained from the single-ion Soret coefficient α i (MD/TN) and α i (Agar) are close to the experimental data. 43 S fast (MD/TN) values are in the range of 0.06 to 0.42 × 10 −2 1/K and experimental values are in the range of 0.2 to 0.9 × 10 −2 1/K.…”

“…For S slow (Agar), it can be seen that the values for Na + Cl − (open red triangle) and Na + OH − (solid red triangle) present large deviation with respect to the linear fit (dashed red line) causing a weak correlation between them, but its slope is near 1.0 showing values of 2 and single-ion Soret coefficient α i shown in Table 3, and the experimental data obtained with optical measurements. 43 The color and symbol descriptions are the same as shown in Figure 5. The theoretical approach proposed herein using MD simulations and the scaling factor f i TN between the hydration entropy for ions S i hyd and the single-ion heat of transport Q i * is capable of predicting the Seebeck coefficient and describing the thermodiffusion of salts in aqueous solutions.…”

“…Figure 7. Modules of fast and slow Seebeck coefficients, S fast (left) and S slow (right) (in mV/K), calculated using eqs 7 and 8, respectively, with selfdiffusion coefficients D i shown in Table2and single-ion Soret coefficient α i shown in Table3, and the experimental data obtained with optical measurements 43. The color and symbol descriptions are the same as shown in Figure5.…”