Improving Electrochemical Activity in a Semi-V-I Redox Flow Battery by Using a C–TiO2–Pd Composite Electrode

This study developed composite electrodes used in a semi-vanadium/iodine redox flow battery (semi-V-I RFB) system and designed semi-V-I RFB stacks to provide performance comparable to that of an all-vanadium redox flow battery (all-VRFB) system. These electrodes were modified using the electroless plating method and sol-gel process. The basic characteristics of the composited electrodes, such as the surface structural morphology, metal crystal phases, and electrochemical properties, were verified through cyclic voltammetry, field emission-scanning electron microscopy, energy-dispersive X-ray spectrometry, and X-ray diffraction. The results show that the sintering C–TiO2–Pd electrode improved the electrocatalytic activity of the semi-V-I RFB system, thereby effectively increasing the energy storage ability of the system. The C–TiO2–Pd electrode was used as a negative electrode in a single semi-V-I RFB and exhibited excellent cyclic performance in a charge-discharge test of 50 cycles. The average values for coulomb efficiency, voltage efficiency, and energy efficiency were approximately 96.56%, 84.12%, and 81.23%, respectively. Moreover, the semi-V-I RFB stacks were designed using series or parallel combination methods that can effectively provide the desired operating voltage and linearly increase the power capacity. The amount of vanadium salt required to fabricate the semi-V-I RFB system can be reduced by combining large stack modules of the system. Therefore, this system not only reduced costs but also exhibited potential for applications in energy storage systems.