Conductive ionic thermoelectric hydrogel with negative Seebeck coefficient, self-healing and highly sensitive to temperature for photothermoelectric conversion and non-contact sensing device

Abstract

Ionic thermoelectric (i-TE) hydrogels have a high thermal energy utilization rate for low-grade heat, presenting a renewable energy supply option for sustainable global development. Conventional i-TE materials need to be conductive, stable and environmentally friendly, which remains a challenge today. This study presents a highly temperature-sensitive i-TE hydrogel with negative Seebeck coefficient, self-healing properties and conductive for photothermoelectric (PTE) conversion and non-contact sensing. The prepared PSFC-0.5 hydrogel exhibits a negative Seebeck coefficient and features a dual-crosslinked structure of polyacrylamide (PAM) and sodium alginate (SA), which provides the hydrogel with good mechanical strength (>2.7 kPa) and tensile properties (>1300 %). Photothermal (PT) conversion properties is effectively enhanced by combining carbon black/multi-walled carbon nanotubes (CB/MWCNTs) PT materials, and the addition of FeCl₃ provides anions and cations for ionic diffusion. Under a 5 K temperature gradient, the optimized Seebeck coefficient was measured to be −2.01 mV·K⁻¹ and the conductivity was approximately 1.70 mS·cm⁻¹. Moreover, reversible hydrogen bonding interactions provides ionic hydrogels with good mechanical strength and self-healing capabilities. Due to the high sensitivity of PSFC-0.5 hydrogel to temperature, it can be effectively utilized in the field of non-contact sensing for the precise detection of temperature signals. This study presents an effective method for fabricating hydrogels that exhibit exceptional toughness and electric properties, demonstrating its significant potential for applications in PTE conversion and non-contact sensing technologies.