Green Synthesis of Chlorophyta Seaweed Mediated Mn₃O₄ Nanoparticles: Electrochemical Applications and Evaluation of Capacitive and Diffusive Contributions

Abstract

This study focuses on the sustainable synthesis of Mn₃O₄ nanoparticles using Chlorophyta seaweed extracts for electrochemical capacitor applications. X-ray diffraction (XRD), ultraviolet-visible (UV–Visible) spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and Fourier-transform infrared (FTIR) spectroscopy were used to evaluate the produced nanoparticles to determine their crystallinity, structure, shape, and elemental composition. The XRD results showed diffraction peaks that correspond to the Hausmannite Mn₃O₄ phase, with a 24.4 nm-sized average crystallite. The electrochemical properties were examined through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). When compared to a bare Ni electrode, the electrochemical analysis showed a voltammetric response that was 17-fold higher. For the kinetics of the electrochemical reaction, the charge transfer coefficient (α_a) and apparent electron transfer rate constant (k_s) were determined to be 4.0 s⁻¹ and 0.33, respectively. The diffusion coefficient, as evaluated using the Randles-Sevcik equation, was 1.78 × 10⁻⁶ cm²/s. The analysis conducted at various scan rates revealed a diffusive contribution of 90.6% at 5 mV/s and 67.7% at 100 mV/s. In contrast, at a scan rate of 100 mV/s, the capacitive contribution increased from 9.4 to 32.3%. The change in the time for the interaction between ions and electrode material is responsible for the reduction in the diffusive component and the increase in the capacitive component.

Keywords:

• Chlorophyta
• diffusion coefficient
• electrochemical capacitor
• electron transfer rate constant
• green synthesis
• Hausmannite

Acknowledgments

The authors are grateful to the Ministry of Higher Education, Research, Science and Technology of the Gambia for sponsoring studies at the Kwame Nkrumah University of Science and Technology.

Disclosure statement

No potential conflict of interest was reported by the authors.