Lignin-derived ionic conducting membranes for low-grade thermal energy harvesting

Wood-based ionic conductive membranes have emerged as a new paradigm for low-grade thermal energy harvesting applications due to their unique and tailorable structures. Herein, a lignin-derive dionic conducting membrane with hierarchical aligned channels is synthesized via a double network crosslinking approach. Their excellent thermal stability and superior swelling ratio allow their optimization as low-grade heat recovery technologies. Several vertically aligned nanoscale confinements are found in the synthesized membranes, contributing toward enhanced ionic diffusion. Among all the combinations, the membrane comprising69.2 wt.% of lignin and infiltrated with 0.5 m KOH exhibits an exceptional ionic figure of merit (ZTi) of 0.25, relatively higher ionic conductivity(51.5 mS cm‒1), lower thermal conductivity(0.195 W m‒1·K), and a remarkable ionic See beck co-efficient of 5.71 mV K‒1 under the application of an axial temperature gradient. A numerical model is also utilized to evaluate the veracity of experimental observations and to gain a better understanding of the fundamental mechanisms involved in attaining such values. These results display the potential of lignin-based membranes for future thermal energy harvesting applications and are a new facet in thermoelectric energy conversion which is certain to pave the way for further investigations on sustainable ionic conductive membranes.