Optimization of diffusion dynamics in Mn-doped Co3O4/rGO hybrid electrodes for efficient energy storage in asymmetric supercapacitors

Abstract

Efficient electrode materials are crucial to meet the growing modern-day energy storage needs. In this context, a series of electrodes composed of Co₃O₄ with varying levels of Mn doping (4% and 8%) and varying rGO contents (4% and 8%) were prepared using a combination of hydrothermal and solvothermal methods. The samples were labeled as Co₃O₄ (CoO), Co_2.96Mn_0.04O₄ (MDCoO-I), Co_2.92Mn_0.08O₄ (MDCoO-II), Co_2.92Mn_0.08O₄@4%rGO (MDCoO-III), and Co_2.92Mn_0.08O₄@8%rGO (MDCoO-IV). Various tests confirmed the formation of the desired phase, with X-ray diffraction showing a cubic structure that remained consistent throughout the series. Following this survey, comprehensive electrochemical testing of all samples was conducted in a three-electrode setup to identify the best candidate for practical device applications. For example, MDCoO-IV showed enhanced ion transport properties, including ion conductivity (0.62 S cm⁻¹), transference number (0.45), rate constant (2.21 × 10⁻⁷ cm s⁻¹), exchange current density (0.021 A g⁻¹), and a notable value of diffusion coefficient (5.51 × 10⁻¹³ m² s⁻¹), due to efficient coupling of conduction mechanism facilitated by 8% rGO inclusion across the pseudocapacitive enriched surface-active chemistry of Co_2.92Mn_0.08O₄. Owing to the efficient ion-transport characteristics, an asymmetric assembly with full device testing using MDCoO-IV was subsequently established, demonstrating good rate performance with a specific capacitance of about 833.25 F g⁻¹ and an energy density of 57.86 Wh kg⁻¹ at 1250 W kg⁻¹, thereby maintaining 87.27% after 10 000 cycles. The discovery of these features suggests that this material has potential for use in future energy storage devices.