For ACC-15 soaked with 1 M TEABF4 (ACN), the effective anionic in-pore diffusion coefficient decreases with increasing diffusion time (Figure ). This contrasts with the case of neat electrolyte (Figure ) where the diffusion coefficient stays constant. Here, we consider in-pore diffusion in two limiting cases: (i) at a low diffusion time (D " ), and (ii) at long diffusion times (D ! ). Because of the finite strength of the pulsed field gradients that cannot capture slow diffusion processes at very low diffusion times, D " and D ! are obtained by fitting the data with a decaying exponential. The effective diffusion coefficient of anions at short diffusion time D " (1.5 x 10 -10 m 2 .s -1 , Figure ) was found to be one order of magnitude below that of anions in bulk electrolyte (1.5 x 10 -9 m 2 .s -1 , Figure ). This captures the anionic adsorption of anions and solvent molecules within the pores which slows down anionic diffusion. Over long diffusion times, ionic transport occurs across a larger pore network, which is measured by the effective long-range diffusion coefficient D ! and is expected to be hindered by the size of the constrictions connecting the pores and the degree of interconnectivity between them, both of which determine porosity accessible to the electrolyte and contribute to the long-range diffusion coefficient at long diffusion times. Indeed, a D ! of 5.8 x 10 -12 m 2 .s -1 was found for BF4 -ions diffusing in the pores of ACC-15, which is much lower than the D " value (1.5 x 10 -10 m 2 .s -1 ).