Year: 2026 | Month: October | Volume: 13 | Issue: 10 | Pages: 222-232
DOI: https://doi.org/10.52403/ijrr.20261020
Composition-Dependent Interfacial Resistance in Ex-Situ rGO/MnO₂ Nanocomposite Electrodes Prepared Using Tea-Stem Extract: An Impedance Spectroscopy Study
Cherin Virginia1, Ngurah Ayu Ketut Umiati1, Agus Subagio1
1Department of Physics,
Faculty of Science and Mathematics, Diponegoro University, Semarang, Indonesia,
Corresponding Author: Cherin Virginia
ABSTRACT
Reduced graphene oxide (rGO) prepared using tea-stem extract as a green reducing agent was blended ex situ with manganese dioxide (MnO₂) at mass ratios of 1:3, 1:1, and 3:1. Impedance spectra collected over the frequency range of 100 kHz to 0.01 Hz were fitted using four equivalent circuits, which were evaluated based on residual error and the Bayesian information criterion (BIC). The classical Randles circuit incorporating a Warburg element was rejected because its residual error was 5.2–60 times greater than that of the modified Randles circuit, in which constant phase elements replaced the double-layer capacitor and the Warburg element. Moreover, the classical circuit yielded a charge-transfer resistance that collapsed to zero for the 1:1 composite. In the modified circuit, the series resistance increased from 39 to 302 Ω as the rGO fraction increased, whereas the charge-transfer resistance varied nonmonotonically, reaching 2.4, 14.8, and 1.8 kΩ for the 1:3, 1:1, and 3:1 composites, respectively. The 1:1 composite also exhibited a relaxation process 16–23 times slower than those of the other two composites. Across the three composites, voltammetric capacitance retention between scan rates of 10 and 100 mV s⁻¹ decreased with increasing series resistance, whereas galvanostatic capacitance retention between current densities of 1 and 10 A g⁻¹ followed the trend in relaxation frequency. The low-frequency admittance of the diffusion-like element also followed the trend in specific capacitance. These findings distinguish ohmic, interfacial, and capacitive limitations and provide an impedance-based framework for designing green-synthesized composite electrodes.
Keywords: interfacial resistance; electrochemical impedance spectroscopy; reduced graphene oxide; manganese dioxide; tea-stem extract; supercapacitor
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