Thermoelectric effects in solid-state polyelectrolytes
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2017 Elsevier B.V. Solid-state polyelectrolytes have recently been reported to exhibit extremely high thermally induced voltage in contrast to conventional thermoelectric materials, showing great promise in energy harvesting for wearable and flexible electronics. Nevertheless the thermoelectric behaviors of polyelectrolytes have been barely studied. Here we provide comparative experimental studies about the thermoelectric behaviors of three different types of solid-state polyelectrolytes - cation conductors with negatively charged immobile backbones (Nafion and S-PEEK), conductors with both cations and anions (basic PVA-NaOH and acidic PVA-H3PO4), and an anion conductor (PDDAC). We observed that the proton conductors (Nafion and S-PEEK) exhibited large thermopower values up to 5.5 mV/K. Higher humidity rendered the thermopower of S-PEEK larger but that of Nafion smaller, which is attributed to the opposite thermo-diffusion direction of water. When both cation and anion are thermally diffused (PVA-NaOH and PVA-H3PO4), the absolute values of thermopower was relatively small 11.5 mV/K and independent of humidity. In PDDAC, we observed extremely large thermopower values up to 19 mV/K, which could be attributed to more rigorous dissociation of Cl in the hotter side rather than the thermo-diffusion of Cl. Our experimental results provide useful data for developing practical thermal energy harvesters and storage devices with high output voltages for wearable and flexible electronic devices.
