Hierarchical Microcellular Microporous Carbon from Polyamic Acid Cryogel and its Electrochemical Capacitance

The obtainment of a high specific surface area (SSA) without disrupting the conductivity of carbon is very challenging. Herein, an as-synthesized polyamic acid (PAA) derivative dissolved in 1,4-dioxane solvent was freeze dried to prepare a PAA cryogel, which allowed homogenous shrinkage of the texture and a high carbon yield upon carbonization. This work presents the successful template-free preparation of a high-surface area microporous carbon with a unique microcellular structure by simple carbonization treatment of a PAA cryogel. Upon increasing the carbonization temperature, the N content decreased, which was unfavorable for capacitance, but simultaneously, both the surface area and the crystallinity increased, which was beneficial in increasing the capacitance; these results are indicative of an interesting trade-off relationship between surface area, conductivity, and the N content of the carbon. In particular, C-PAA(1000) prepared by carbonization at 1000°C from the PAA cryogel showed a high porosity of approximately 90.8% and a remarkably high SSA of 2038 m²g^-1 along with high crystallinity and effective N doping favorable for good conductivity; this material thus illustrates a high specific capacitance of 248 Fg^-1 at 0.5 Ag^-1 and excellent stability in inorganic electrolyte.