Beyond this concentration, both σ″ and f0 decrease, becoming gradually lower towards 20 mol•kg -1 . Most likely, at an open circuit voltage of around 30 mV, the stainless-steel rod current collector could be treated as a blocking (non-reactive) electrode. Thus, the f0 of the σ″ spectrum can be related to EDL capacitance, CEDL, and equivalent series resistance RS, as expressed in equation 1. The values of Z′ at 1 MHz correspond to RS.