Surface Optimisation of Regenerated Cellulose Membranes for development of a sustainable and efficient low-grade waste heat harvester

ABSTRACT: Around 70% of global energy generated is lost as waste heat. Hence an efficient and sustainable technology is required to convert low-grade heat (≤ 100 °C) into a useful form of energy. Conventional technology does not allow efficient conversion of low-grade heat into useful forms of energy, such as electricity. The selective movement of ions in nanoscale channels, driven by a temperature gradient (ΔT), can be utilised to generate electricity from low grade waste heat1. This presentation describes surface functionalised, sustainable, and biocompatible regenerated cellulose membranes as components for ionic thermoelectric energy harvesters, capable of generating electricity under a moderate temperature gradient. Membranes were functionalised with appropriate organic moieties, such as negatively charged TEMPO (2,2,6,6-tetramethylpiperidin-1-oxyl) and positively charged CHMAC (3-chloro-2-hydroxypropyl)trimethylammonium chloride), to enhance their pore wall charge densities and maximise their ability to convert thermal energy into electrical energy. Successful functionalisation of the membrane channels is confirmed by infrared spectroscopy, contact angle measurements and scanning electron microscopy, as well as various electrochemical characterisation techniques such as linear sweep voltammetry (LSV). Functionalization enhanced the charge density of TEMPO cellulose by over 11 times, resulting in a 250-fold increase in ionic conductivity. With CHMAC functionalisation, the ionic conductivity increased around 600 times than that of the pristine. These functionalised and electrolyte-filled membranes are being investigated for ionic thermoelectrics. A thermovoltage of -3.68 mV K-1 was achieved with CHMAC functionalised cellulose membranes. Reference1. Li, T., Zhang, X., Lacey, S.D. et al. Cellulose ionic conductors with high differential thermal voltage for low-grade heat harvesting. Nat. Mater. 18, 608–613 (2019). https://doi.org/10.1038/s41563-019-0315-6