The Relationship between Shunt Currents and Edge Corrosion in Flow Batteries
Shunt currents occur in electrochemical reactors like flow batteries, electrolyzers, and fuel cells where many bipolar cells that are connected in series electrically contact a mobile electrolyte through one or more common fluid distribution manifolds. Shunt currents reduce energy efficiency, and can cause unwanted side reactions including corrosion and gas generation. Equivalent-circuit models have been widely used to examine shunt currents in multi-cell electrochemical reactors. However, a detailed investigation of the interesting electrochemical processes occurring at the edges of the active areas has not been presented. In this work, the generation of shunt currents and their tendency to drive corrosion at the edges of positive electrodes in the most positive cells in a reactor stack are investigated with a comprehensive numerical model. An analytical model based on the penetration of current into a semi-infinite electrode, that can be used in conjunction with traditional equivalent-circuit models to assess the tendency for shunt currents to drive corrosion, is developed and compared to the numerical model. The models provided here can be used to set requirements on maximum allowable port currents in order to achieve a particular durability goal.