SURFACE MODIFIED AND BISMUTH LOADED GRAPHITE FELTS FOR IMPROVEMENT OF ANODE ELECTRODE KINETICS IN IRON CHROMIUM REDOX FLOW BATTERY

Abstract

In this study, anode electrodes were modified and bismuth loaded to enhance chromium redox reaction for iron chromium redox flow batteries. Graphite felt anode electrode surface was modified by two step chemical treatment. Corrosive HF was used as an etchant to increase porosity at the first step and oxidizing H2O2 was used to increase wettability of electrode at the second step. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analyses were used for the physical and chemical characterization of electrode materials. Cyclic voltammetry (CV) and linear sweeping voltammetry (LSV) techniques were conducted to investigate Cr2+/Cr3+ redox reaction kinetics for the modified electrodes with or without bismuth loading. Carbon nanoparticles formed on the surface and oxygen content increased. Contact angle for pristine graphite felt decreased from 132.6° to 128.5°, electrode wettability increased after treatment with HF and H2O2. Dispersion of bismuth particles became more uniform on modified electrode. Compared to untreated felt, the diffusion coefficient for Cr2+ has been almost doubled on modified graphite felt and Cr2+ concentration on the surface increased. When bismuth was in solution, reaction was controlled by charge transfer for modified electrode. In contrast, when bismuth was loaded onto the felt electrodes, reaction became diffusion controlled.