Construction of hierarchical and porous cellulosic wood with high mechanical strength towards directional Evaporation-driven electrical generation

Abstract

Tremendous efforts have been dedicated to harvesting energy from the ubiquitous natural water evaporation process. Inspired by the plant's bioelectric phenomenon during the transport of sap from bottom to top, the hierarchically porous cellulosic wood was engineered as the robust carrier for efficiently capturing and transferring water and moisture by removing lignin and hemicellulose, releasing the microscale pore in the cell wall and nanoscale pores in the middle lamella. A conductive polymer, poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS), was impregnated in the cellulosic wood, which was further lyophilized to increase the specific surface area and improve the charge transport as an evaporation-driven electrical generator (EEG) with high Young’s modulus. This EEG produces a sustained voltage of around 385 mV and current over 11 μA across the porous and conductive cellulosic wood in a saturated NaCl solution. The anisotropic nature of the cellulosic wood leads to a higher output voltage in the growth direction than in the transverse direction. The driving force behind this energy generation is a self-maintained moisture gradient to generate an ion concentration difference between the output electrodes when the system is exposed to water or moisture. Furthermore, the critical factor of energy generation is the coupling between naturally aligned cellulose microfibrils in wood and water molecule. The generated voltage could be increased by elevating the concentration of ions in the aqueous solution and the temperature difference between the output electrodes. These strong and hierarchical cellulosic wood have a significant potential for electric energy collection through water evaporation and waste heat energy.