Tailor-made dual doping for morphology control of polyaniline chains in cellulose nanofiber-based flexible electrodes: electrical and electrochemical performance

The present study revealed the effect of combining one strong-inorganic and weak-organic protonic acid dopants on the electrical conductivity and electrochemical properties of flexible free-standing composite electrodes based on polyaniline and nanofibrillated cellulose (NFC) or its carboxylated analog (CNFC), synthesized using a bottom-up approach. Hydrochloric acid (HCl) served as a low molecular weight inorganic dopant while phytic acid (PhA) and poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAAMPSA) were chosen as the organic dopants. Both PhA and PAAMPSA acted as secondary dopants in the dually doped composites through the molecular conformation changes of PANI chains. Synergistic increase in the electrical conductivity is observed for dually doped PANI-NFC with the combination of PAAMPSA and HCl in comparison with PhA and HCl. Unlike the PhA, the morphological changes induced by PAAMPSA are more favorable for the enhancement of conductivity. Neither the morphological changes, nor the carboxylation of NFC affected the electrochemical properties of the composites as the specific capacitance values were influenced mainly by the type and the strength of the individual acids. The capacitance values per gram of the dually doped composite with PAAMPSA and HCl increased with the decrease in the NFC or CNFC loading reaching values above 200 F·g –1 measured at 50 mV·s −1 of composite for the 80 wt% PANI content. These results highlight the profound impacts of the secondary dopant in PANI on the performance of PANI-based nanocellulose composites. Graphical Abstract