Cellulose ionic gel and its sustainable thermoelectric devices – Design, applications and prospects

Thermoelectric materials, which can convert thermal behaviors into electrical properties, are widely used in thermoelectric power generation, friendly refrigeration, and wearable electronic devices. Compared to synthetic polymer materials, cellulose is one of the most sought-after natural polysaccharide polymers, mainly found in plants and some biological colonies. Cellulose can be designed as a flexible, ion/electron conductive ionogel material with robust mechanical properties through molecular-scale physical treatment, chemical-group substitution, topological network regulation, etc. Cellulosic functional materials, such as ionogels, show promising thermoelectric applications due to their structural/functional designability, rapid thermoelectric conversion, and good sustainability. In this review, we briefly introduced the structural characteristics, functionalization methods, and advanced thermoelectric applications of cellulose. Then, we discussed the design concept, current status, and application prospects (such as smart watches, electronic skins, health detectors, etc.) of cellulose ionogels for developing thermoelectric cells, sensors, and refrigerating units. Finally, we highlighted some key technologies and strategies to broaden the application prospects of cellulose-based gels for thermoelectricity and intelligent electronics.