Exploring Pyrazine-Based Organic Redox Couples for Enhanced Thermoelectric Performance in Wearable Energy Harvesters.

Area of Science:

• Materials Science
• Electrochemistry
• Energy Conversion

Background:

• Thermoelectric generators (TEGs) utilizing thermogalvanic cells offer a promising route for converting low-temperature waste heat into electricity.
• Organic redox couples are ideal for wearable applications due to their non-toxicity and tunable properties, particularly the ionic Seebeck coefficient.
• Functional group modifications on organic molecules can significantly influence thermoelectric performance.

Purpose of the Study:

• To comparatively analyze pyrazine-based organic redox couples with varying functional groups for thermoelectric applications.
• To investigate the impact of molecular structure on the ionic Seebeck coefficient using computational methods.
• To develop and evaluate a hydrogel-based thermoelectric generator for wearable devices.

Main Methods:

• Cyclic voltammetry was employed to study pyrazine-based redox couples under different temperatures.
• Density functional theory (DFT) calculations were used to determine electrostatic potentials and understand functional group effects.
• A double-network hydrogel incorporating poly(vinyl alcohol) and polyacrylamide was synthesized to host the optimal redox couple (PDCA).

Main Results:

• Significant differences in entropy changes were observed across various pyrazine compounds, identifying 2,5-pyrazinedicarboxylic acid dihydrate (PDCA) as the most promising candidate.
• The champion hydrogel device achieved a high ionic Seebeck coefficient (S_i) of 2.99 mV K^-1, with good ionic and thermal conductivities.
• A thermoelectric generator (TEG) constructed from 36 PDCA-infused hydrogel units demonstrated a power output of ≈0.28 µW, capable of powering a small LED.

Conclusions:

• Pyrazine-based organic redox couples show great potential for efficient thermoelectric energy conversion in wearable devices.
• PDCA stands out as an optimal organic material for enhancing thermoelectric generator performance.
• The developed hydrogel-based TEG demonstrates practical application for powering small electronic components using waste heat.