Shunt current

Current bypassing the intended electrical path through shared electrolyte channels.

Also called parasitic or leakage current. In a bipolar stack the cells are electrically in series but share common electrolyte manifolds, and because the electrolyte conducts, some current takes a path through those channels instead of through the cells.

Shunt currents reduce Faradaic efficiency, because the diverted charge produces no collectable hydrogen. They also drive localised corrosion where they enter and leave the electrolyte, which can damage manifolds and end plates over time.

They are most significant in alkaline systems with liquid electrolyte, and their relative impact rises at low load, because the shunt path is largely independent of operating current while the useful current falls. This is one of several mechanisms that make part-load operation less efficient than a stack-only view suggests.