Investigation on the applicable pore size of nanoporous carbon for electrochemical double-layer formation at different current densities

Considering the wide application of nanoporous carbon material in electrochemical double-layer capacitors (EDLCs), the investigation of the structure-performance relationship is critical to constructing suitable nanostructure for high performance EDLCs. Herein, we focus on an important but neglected issue of different applicable pore sizes for electrochemical double-layer (EDL) formation at different current loadings. Small-sized pores with different sizes/distributions are introduced for energy storage while a developed 3D large meso/macroporous structure is constructed for guaranteeing rapid mass transfer. An interesting result is obtained that the applicable pore size greatly depends on the current loadings. For instance, pores larger than 0.59 nm are responsible for EDL formation at a low current density of 0.1 A g−1 in aqueous electrolyte. As increasing the current density to 1 and 10 A g−1, the most effective pore size increases to larger than 0.73 and 0.93 nm, respectively, which is attributed to the insufficient time of solvent shell removing, squeezing behavior of solvated ions and charge arrangement at higher current densities. These encouraging results may raise concerns about constructing suitable pore size more precisely to realize a target oriented use, particularly those targeting higher power EDLCs applications.