Metal Oxide Coatings on Carbon Electrodes with Large Mesopores for Deeply Charged Zinc Bromine Redox Flow Batteries

Abstract

Carbon nanofibers with various large mesopores (>10nm) were made and tested as active cathode materials for zinc bromine redox flow batteries. The largest mesopores demonstrated improvements over activated carbon in coulombic efficiency as well as rate capability up to 30mA/cm2. Afterwards, the mesoporous carbon nanofibers were coated with four amorphous metal oxides made from liquid precursors to form a protective coating, and their protective nature was examined through deep and shallow charge cycles. The effect of the coating on battery performance was then analyzed through galvanostatic testing, cyclic voltammetry, and electrochemical impedance spectroscopy. It was determined that the metal oxide coatings improved rate capability and voltaic efficiency by adsorbing the bromine complex more readily, while the large mesopores aided performance from a combination of absorption and more efficient diffusion.