Humic Acids: A Material from Renewable Sources with the Potential for Making Supercapacitors

Abstract

This paper examines the electrochemical performance of humic acids extracted from natural water and fertile soil, like electrode materials for supercapacitors, as proposed and evaluated. Humic acids come from the decomposition of organic matter in the humus formation process, therefore they are considered renewable resources. The humic acids are characterized by Fourier transform infrared spectroscopy, UV–vis spectroscopy, optical microscopy, and scanning electron microscopy with energy-dispersive X-ray spectroscopy. Electrochemical techniques are used to evaluate the behavior of humic acids like electrode materials for supercapacitors. Cyclic voltamperometry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy are performed in H2SO4 0.5 mol L−1. The highest capacitance, energy, and power values are found with humic acids from the soil. Thus, the specific capacitance of 87.15 F g−1 at 0.040 A g−1, maximum power of 32680 W kg−1, and energy of 60.52 W h kg−1 are obtained. The humic acids from soil have good cycling stability and high energy efficiency, placing them as promising materials in energy storage.