Polycrystalline polythiophene-boron doped rGO composite exhibiting a unique charge storage mechanism and exceptional stability: A rigorous EIS investigative model to explore the material's integrity

Abstract

We report on the electrochemical behavior and device performance of highly crystalline unsubstituted polythiophene (PTh) and polythiophene: boron-doped reduced graphene oxide (PTh:B-rGO) composite in the context of electrochemical charge storage. Both PTh and PTh:B-rGO display interesting charge-storage mechanisms, remarkable performance, and exceptional material integrity. The PTh-electrode exhibits an increase in capacitive share from 8.6 % to 22.4 % through long charge–discharge cycling and attributed to internal rearrangement of polymeric molecules within the material matrix. On the contrary, there is no such change in the case of PTh:B-rGO composite, where it remains constant at an average value of 9.5 % even after the electrodes have undergone 10,000 continuous galvanostatic charge–discharge (GCD) cycles. The PTh-device delivers energy and power densities of 3.22 Wh kg−1 and 11.24 kW kg−1, respectively, at an applied current density of 1.0 A g−1. PTh: B-rGO-device delivers energy and power densities of 5.2 Wh kg−1 and 9.23 kW kg−1, respectively. In addition, we developed a rigorous electrochemical impedance spectroscopy (EIS) investigative model to evaluate the material's integrity through long cycling tests. The solution resistance (R<inf>s</inf>) and heterogeneity factor (n-values) show minimal or no significant change, indicating that both materials possess remarkable chemical robustness and electrochemical stability. The feasibility of the formation of the standalone PTh and PTh:B-rGO composite, their thermodynamic properties, and interaction energies (IE) are evaluated using DFT calculations and correlated with the stability and integrity of the material. Nevertheless, the Warburg component is absent, suggesting the charge storage mechanism is dominated by surface redox pseudocapacitive processes. We propose that rigorous EIS experimentation should be adopted as an essential test to validate the material's integrity, in addition to the conventional methods of CV and GCD. © 2025 Elsevier B.V., All rights reserved.