All-Wood Electrochemical Transistor and Energy Storage Electrodes from Electrically Conducting Wood

Using suitable pretreatment, wood serves as an excellent template for electronic and ionic conductivity. To utilize this possibility, we treated wood with the conducting polymer PEDOT:PSS to achieve a conductivity of 69 S/m, while maintaining the good mechanical properties of the balsa wood veneers that served as raw material. SEM and SAXS measurements indicate a thin film of PEDOT:PSS coating the inner surface of the lumen, with slight penetration of conducting polymer in between the wood fibers, while the inner volume of the lumen remains accessible for an ion-conducting electrolyte. Three pieces of this conducting wood were used to create an all-wood, double-gate electrochemical transistor where all three electrodes (drain, source, gate) and the transistor channel were made from the same material. The electric current in the 1 mm thick transistor channel could be modulated with an on/off ratio of up to 50. <br/>Conductive wood also has potential to serve as electrodes for capacitive energy storage. Using a similar procedure, we prepared such electrodes using pine veneers, where the pretreatment was designed to maintain a portion of the wood-native lignin. The lignin increases energy storage capacity due to the redox-based charge storage capacity of its catechol groups. To access lignin inside the wood cell wall, where PEDOT:PSS has limited reach due to its particle size, an additional step was used where the conducting polymer S-PEDOT was <i>in situ</i> polymerized inside the wood. Confocal Raman spectroscopy was used to map the distribution of the two different polymers inside the wood. The synergistic use of these two polymers increased the electrode capacitance by a factor of 7 compared to samples with only PEDOT:PSS, and by a factor of 2 compared to only S-PEDOT, reaching a maximum specific capacitance of 315 mF/cm².