Stable ionic thermopower materials for waste heat recovery above 100 °C†

Ionic thermoelectric materials (i-TEs) face challenges including low thermal stability, humidity sensitivity, and low conductivity, limiting their use in harvesting waste heat above 100 °C. To address this, developing new i-TEs with improved stability and conductivity is essential. This study presents a phosphoric acid (PA)-doped poly(4,4′-diphenylether-5,5′-bibenzimidazole) (OPBI) material with an impressive ionic conductivity of 67.2 ± 0.5 mS cm⁻¹ at 120 °C and 0% relative humidity. The hydrogen bonding networks in PA/OPBI enable efficient proton conduction through “hopping”, ensuring high conductivity at elevated temperatures. These composites can work stably at 120 °C. Moreover, an assembly of an ionic thermoelectric capacitor with PA/OPBI membranes achieved an energy density of 0.22 μW m⁻² at a load resistance of 100 kΩ. The ease of preparation, high thermal tolerance, and reliable output of ionic thermoelectric potential make PA/OPBI materials an optimal choice for large-scale waste heat applications, particularly those utilising industrial waste heat.