Sustainable D-A structured lignin-based ionic thermoelectric hydrogel for high-efficiency photothermoelectric conversion and wearable self-powered sensing.

As a major byproduct of the pulp and paper industry, lignosulfonates can be converted into photothermoelectric gels via their inherent structural advantages, offering an effective pathway for high-value utilization of agricultural and forestry wastes, source reduction of plastic pollution, and circular economy development. Herein, a self-healing, flexible and robust lignin-based ionic thermoelectric hydrogel (PSSLS@DAC) is constructed using sulfopropyl-modified lignosulfonate (PSSLS) with a donor (aromatic ring)-acceptor (sulfonic acid) (D-A) structure. The introduced sulfopropyl group weaken intermolecular hydrogen bonds, accelerate non-radiative relaxation, and narrow the bandgap to increase PSSLS's photothermal conversion efficiency to 69.9%. Na+ thermodiffusion drived thermal gradients generation under the light irradiation serve as the core iTE mechanism. Thus, PSSLS@DAC delivers a high Seebeck coefficient of 3.29 mV/K and a power factor of 45.09 μW/m·k2. A maximum output value of 394 mV can be achieved at a ΔT of 107.2 K under NIR irradiation. Finally, a self-powered wearable sensor is assembled to distinguish three typical human motions, and a solar-thermoelectric signal conversion system is achieved via a hand exposure strategy. This work develops sustainable biobased iTE material with high photothermalelectric properties as candidate for practical applications in next-generation smart wearables electronics.