An n-type ionic thermoelectric hydrogel with confined cation diffusion for boosted low-grade heat harvesting

Abstract

Ionic thermoelectric (i-TE) materials based on the thermodiffusion effect have shown great potential in low-grade heat conversion due to their exceptional heat-to-electricity properties, low cost, and flexibility. However, most current research has focused on p-type i-TE materials, leaving n-type i-TE materials underexplored by comparison. In addition, the current n-type i-TE materials still face some challenges such as unsatisfactory thermoelectric performance and the unclear mechanism of anion transport. Herein, we demonstrate an n-type i-TE hydrogel with hierarchical pathways for anion transport by employing an interpenetrating polymer network composed of sodium polystyrene sulfonate modified polyvinyl alcohol. Due to the coordination and electrostatic interactions between cations and functional groups, the hydrogel displays an n-type behavior with enhanced anion diffusion efficiency. The developed i-TE device not only shows excellent thermoelectric performance with a high thermopower of −16.8 ± 0.5 mV K⁻¹ and an output power density of 47.8 mW m⁻² at a temperature difference of 10 K, but also displays high sensitivity and responsivity to fluctuating heat input. This work provides valuable insights for the design and development of potential n-type i-TE materials and devices for low-grade heat conversion.