Lignin-Derived Ionic Hydrogels for ThermoelectricEnergy Harvesting

Thermoelectric materials are attracting attention for their ability to convert heat into electricity, traditionally assessed through a figure of merit (<i>ZT</i>) depending on the electrical conductivity, Seebeck coefficient, and thermal conductivity. Developing efficient ionic thermoelectric materials presents challenges as they cannot integrate directly into standard generators. However, they can utilize the ionic thermoelectric effect to charge supercapacitors. This study investigates lignin, an abundant plant-based waste, as a basis for ionic thermoelectric systems, combining sustainability and thermoelectric efficiently. Lignin-based hydrogels with varying compositions were examined for their thermoelectric properties, revealing gigantic ionic Seebeck coefficients of up to 30.4 mV K^–1 and good conductivity, reaching 5.87 S m^–1. The optimal hydrogel composition displayed a high-power factor of 4187 μW m^–1 K^–2, and an impressive ionic i<i>ZT</i> value of 3.5, showcasing the potential of lignin-based hydrogels for ionic thermoelectric systems. This research suggests a promising avenue for addressing environmental and economic challenges in energy production.