On the time-dependent electrolyte Seebeck effect

Area of Science:

• Physical Chemistry
• Electrochemistry
• Materials Science

Background:

• Single-ion Soret coefficients (αᵢ) quantify ion movement in thermal gradients.
• Differences in cation and anion Soret coefficients can generate electric fields (electrolyte Seebeck effect).
• Previous models often neglect the role of electrode boundary layers in thermoelectric field generation.

Purpose of the Study:

• To derive a time-dependent Seebeck coefficient (S(t)) model for binary electrolytes under time-dependent thermal gradients, enforcing local electroneutrality.
• To experimentally measure S(t) for various electrolytes near titanium electrodes.
• To compare experimental findings with theoretical predictions and literature values for Soret coefficients.

Main Methods:

• Theoretical derivation of S(t) for binary electrolytes, incorporating local charge neutrality at boundaries.
• Experimental measurement of S(t) for five different acids, bases, and salts using titanium electrodes.
• Fitting the derived S(t) expression to experimental data, treating αᵢ as adjustable parameters.

Main Results:

• The derived model accounts for the time-dependent thermoelectric field generation in electrolytes.
• Experimental steady-state Seebeck coefficients (S) were approximately 2 mV K⁻¹, an order of magnitude higher than literature predictions.
• Fitted αᵢ values were consistently larger than those reported in existing literature.

Conclusions:

• The electrolyte Seebeck effect is significantly influenced by boundary phenomena, not solely a bulk effect.
• Existing literature values for single-ion Soret coefficients may underestimate their contribution to thermoelectric effects in electrolytes.
• The developed model and experimental validation provide a more accurate understanding of thermoelectric phenomena in electrolyte solutions.