Structure–performance relationship in copper phthalocyanine-based supercapacitor electrodes: influence of substituent geometry from molecular design to electrochemical function

Abstract

This work investigates how the substituent position governs the structure–performance relationship of copper phthalocyanine (CuPc) derivatives used as supercapacitor electrodes. Two positional isomers bearing the same (3,4,5-trimethoxybenzyl)oxy substituent, namely the peripheral derivative (TMe-Cu) and the non-peripheral derivative (n-TMe-Cu), were synthesized and characterized by spectroscopic and structural techniques. Electrochemical evaluation in 1 M H₂SO₄ using cyclic voltammetry, galvanostatic charge–discharge, electrochemical impedance spectroscopy, and scan-rate-dependent kinetic analyses revealed a pronounced performance advantage for n-TMe-Cu, which delivered a specific capacitance of up to 360 F g⁻¹ at 1 A g⁻¹ and retained 80% of its initial capacitance after 5000 cycles. Dunn analysis showed that n-TMe-Cu exhibits a substantially higher surface-controlled contribution than TMe-Cu, indicating that a larger fraction of charge storage proceeds through rapidly accessible interfacial pathways. In conjunction with the observed morphological differences between the two electrodes, these results suggest that non-peripheral substitution promotes a more electrochemically accessible electrode architecture and more favourable charge-storage kinetics. Overall, this study demonstrates that substituent geometry is a key molecular design parameter for regulating electrochemical utilization and rate performance in CuPc-based organic electrode materials.