Bacterial cellulose-based hydrogel thermocells for low-grade heat harvesting

The hydrogel thermoelectrochemical cells (thermocells, TECs) are a simple, efficient, and inexpensive technology for harvesting low-grade heat from the environment. For the current development, higher mechanical properties and relatively simple and mature production processes are highly desirable and challenging. Herein, readily available bacterial cellulose (BC)-based TECs with Fe(CN)63−/4− redox couple and Fe2+/3+ redox couple as n, p-type cellulose hydrogel electrolyte via a simple impregnation process are prepared. The Seebeck coefficient can reach 4.5 mV∙K−1 for n-type TEC and 0.72 mV∙K−1 for p-type TEC. The proof-of-concept thermoelectric device, connecting in series with 3 pairs of units, can generate 0.82 V voltage and 4.5 μW peak power. The bacterial cellulose matrix is commercially available and can be produced in a large area, demonstrating the hope of being an energy carrier of thermoelectric ions for thermoelectric energy conversion. The bacterial cellulose-based TECs have potential applications in wearable electronic devices, energy storage devices, temperature sensing devices and so on.