Electrochemical experiments on symmetric two-electrode supercapacitors assembled with this series of electrolytes support the above findings (SI Fig. ; SI Table ). Once again, TEA + showed the best energy storage performance with Cu 3 (HHTP) 2 , supporting the conclusion that smaller electrolyte ions are favourable for high capacitive performances with this class of materials. In addition, a large drop in performance was seen between TPA + and TBA + , providing further evidence for porosity saturation with larger TAA + cations. The asymmetric charging behaviour of these systems has additional consequences for symmetric two-electrode cells. For electrolytes with larger cations, differences in capacity between the two oppositely polarised electrodes results in the potential of the negative electrode going outside its stable potential window. This leads to quasi-reversible Faradaic activity at lower cell voltages, resulting in more facile degradation of Cu 3 (HHTP) 2 and reducing the energy density of devices with larger cations (SI Fig. ). This further highlights the superior performance of smaller TAA + cations with Cu 3 (HHTP) 2 . To investigate these results in more detail and better understand the impact of cation ion size on the performance of Cu 3 (HHTP) 2 , EQCM was used to probe the ion flux and charging mechanisms of these systems.