Electrochemical Investigation of Slurry Electrode-Electrolyte for Electrical Energy Storage Systems

Electrical Energy Storage (EES) is projected to play an important role in the integration of large-scale renewable energy sources with electricity grid or off-grid. Grid-scale EES, particularly for renewable energy applications, has been a challenging task due to its high capital cost. Electrochemical-based EES systems, specifically redox flow batteries (RFBs) among other options, are uniquely suited for large-scale EES due to many advantages they have over conventional sealed batteries (e.g., lead-acid and Li-ion batteries). Flow batteries can meet a wide range of commercial-scale EES applications with varying power-to-energy ratios. Flow batteries have excellent energy efficiency and competitive life-cycle cost. The present work focuses on electrochemical investigations of slurry electrodes for flow cell (e.g. flow batteries) applications, aiming at improving the energy density of the system. The investigation includes; development of slurry electrode-electrolyte composites and slurry property characterization, electrochemical studies of slurry electrode-electrolyte (three-electrode cell configuration), cell design, subscale cell performance evaluation. The findings revealed that; in terms of conductivity, reduction of charge transfer resistance when carbon particles are dispersed in electrolyte/redox solution is mainly due to carbon nature. In addition, increase in carbon particles loading leads to increase in conductivity. The corrosion/carbon oxidation largely depends on the number of defect sites on carbon surfaces, which is directly related to carbon surface area (BET surface area). Among all the carbons studied, Black Pearls carbon demonstrated the best redox kinetics in V⁺²/V⁺³, V⁺⁴/V⁺⁵, Fe²⁺/Fe³⁺, and S^2-/S⁰ redox couples. The kinetics of slurry electrodes in acid and alkaline media mainly depend on surface chemistries of the carbons. The performance of slurry electrodes at cell level is a function of; slurry conductivities, channel dimensions, slurry percolation (particle-to-particle interaction) and type of membrane.