Elucidating the Bulk Morphology of Cellulose-Based Conducting Aerogels with X-Ray Microtomography

Conducting cellulose composites are promising sustainable functional materials that have found application in energy devices, sensing and water purification. Herein, conducting aerogels are fabricated based on nanofibrillated cellulose and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, using the ice templating technique, and their bulk morphology is characterized with X-ray microtomography. The freezing method (−20 °C in a freezer vs liquid nitrogen) does not impact the mean porosity of the aerogels but the liquid-N₂ aerogels have smaller pores. The integration of carbon fibers as addressing electrodes prior to freezing results in increased mean porosity and pore size in the liquid-N₂ aerogels signifying that the carbon fibers alter the morphology of the aerogels when the freezing is fast. Spatially resolved porosity and pore size distributions also reveal that the liquid-N2 aerogels are more inhomogeneous. Independent of the freezing method, the aerogels have similar electrochemical properties. For aerogels without carbon fibers, freezer-aerogels have higher compression modulus and are less stable under cycling compression fatigue test. This can be explained by higher porosity with larger pores in the center of liquid-N₂ aerogels and thinner pore walls. This work demonstrates that micro-CT is a powerful tool for characterizing the morphology of aerogels in a non-destructive and spatially resolved manner.