Structure-Performance Relationship in Copper Phthalocyanine-Based Supercapacitor Electrodes: Influence of Substituent Geometry from Molecular Design to Electrochemical Function

Abstract

This work investigates how 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 to360 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.