Porosity saturation is further supported by examining the mass change in the potential range from -0.05 V to +0.22 V vs. Ag. In this region, a steep mass drop is observed (purple box; Fig. ). This behaviour is not seen with TEA + , and is once more indicative of overcrowding of the electrode pores with THA + . One potential explanation for this unexpected mass drop is a conformational change of the large THA + cations upon a change in polarisation at high accumulated charges. At the start of the cathodic scan (Fig. ; stage 1), THA + cations with long flexible alkyl chains start to accumulate in the pores, resulting in a significant increase in the in-pore cation density. As a result, the tightly packed THA + cations become electrostricted at high negative polarisations. However, when the polarisation is reversed at -0.05 V (Fig. ; stage 2 to 3), the release of electrostatic force drives a change in conformation of the electrostricted THA + cations from a compact packing to a looser packing arrangement. Similar behaviour is observed in surface-active ionic liquids with analogous structures. This conformational change is accompanied by an increase in volume of the in-pore cations, resulting in an expulsion of solvent molecules from the saturated MOF pores and a sudden mass decrease. At the maximum accumulated charge (Fig. ; stage 3), the in-pore cation population reaches a maximum and the in-pore solvent number reaches minimum. This results in a highly concentrated in-pore ion population, leading to considerable steric hindrance between the long alkyl chains of THA + and thus slower ion kinetics, evidenced by the resistive current response from stage 2 to 4 (purple box; Fig. ). Poorer kinetic performance with THA + is also seen in both rate capability and electrochemical impedance spectroscopy (EIS) measurements on three-electrode cells (SI Fig. , S10), supporting lower ion mobility of the larger TAA + cations.