Carbonization temperature dependence of hydrovoltaic conversion of natural wood

Hydrovoltaic effect is emerging as a potential way to acquire electric energy from water. Some carbon materials, such as carbon nanotubes, graphene or porous carbon, have revealed featured water-electric process due to their typical double electric layer (DEL) behavior. In this work, the carbonized wood (CW) was demonstrated to exhibit a considerable hydrovoltaic performance as water flows in its vertical-pores. Electrochemical studies verified that the maximum open-circuit voltage and short-circuit current achieved ~ 0.27 V and ~ 0.62 μA in 0.5 M NaCl solution, respectively. Further research manifested that carbonization temperature featured prominently on the hydrovoltaic performance owing to the evolution of pyrolytic carbon. At different heat treatment temperatures from 500 to 800 °C, the organic matters of wood were gradually transformed into stacked polyaromatic hydrocarbon, organic mesophase and amorphous carbon through process of thermopolymerization and pyrolyzation. The structure and specific surface area of the amorphous carbon involved played a pivotal role on the water-induced voltage resulting from the DEL effect and electron drag process between water and carbon atoms. The lower resistance of amorphous carbon also enhances the short-circuit current of the CW device. This work is mainly dedicated to provide a potential strategy to get water-induced energy from biochar materials.