Summarising, the EQCM results illustrate that the charging mechanism significantly changes as the cation size is increased from TEA + to THA + . Furthermore, these results support the hypothesis from electrochemical measurements of porosity saturation in Cu 3 (HHTP) 2 when charging with larger TAA + cations, with a significantly lower available pore volume following cation adsorption forcing the solvent to participate in the charge storage mechanism. This surprising change has not been observed in other supercapacitor systems. Together with the three-electrode measurements, this demonstrates that porosity saturation can occur in Cu 3 (HHTP) 2 electrodes with large electrolyte ions, resulting in both asymmetric charging and lower capacities. This is perhaps unsurprising given the comparatively lower total pore volume of layered MOF composite films compared to those of most traditional porous carbons. As a result, electrolytes with small ion sizes should be used to maximise the performance of MOF-based supercapacitors. Additionally, this work also demonstrates the crucial significance of operando EQCM in elucidating ion transport mechanisms under nanoconfinement.