Elaboration and properties of nanofibrillated cellulose composites with polypyrrole nanotubes or their carbonized analogs

Flexible electrically conductive composites based on renewable resources have attracted a growing interest for the development of high performance sustainable electronic and energy storage devices. In this study, electrically conductive flexible composite films based on nanofibrillated cellulose (NFC) and conductive nanotubular fillers were elaborated using environmentally friendly approach. Three conductive fillers were tested, specifically polypyrrole nanotubes (PPy-NT), carbonized polypyrrole nanotubes (C-PPy-NT) and commercially available multi-walled carbon nanotubes (MWCNT) for comparison. The prepared films were assessed for potential applications as electrodes for energy storage devices or protective shields for electromagnetic interference (EMI) shielding in the microwave region. Electrical conductivity measurement revealed that NFC films loaded with PPy-NT (PPy-NT/NFC) exhibited the highest conductivity (1.16 S cm-1) compared to those loaded with C-PPy-NT or MWCNT. PPy-NT/NFC displayed the highest gravimetric capacitance among all tested films reaching 209.7 F g-1 at 10 mV s-1 in a stable potential window (from -0.5 to 0.15 V vs. MSE). When larger potential window (from -0.5 to 0.5 V vs. MSE) was applied, PPy-NT/NFC exhibited fast capacitance decay (to 80% of initial value in 50 cycles). The promising properties of PPy-NT/NFC electrode material were further confirmed in full-cell measurements in symmetric arrangement providing stable performance and 74 F g-1. Meanwhile, C-PPy-NT/ NFC and MWCNT/NFC displayed significantly lower capacitances (below 20 F g-1 at 10 mV s- 1) but better cycling stability in a larger potential window. The highest shielding efficiency of all NFC-based composites was observed in case of PPy-NT/NFC, reaching 75% in the C-band region.