Charge migration model for the impedance response of DI water

A charge migration model is proposed to model the impedance response of water, containing intrinsic (auto dissociated) and extrinsic ions (from dissolved gases), measured in the frequency range 1mHz − 30MHz with stainless steel electrodes. The observed response may be broadly classified into two frequency regions (region I: 10 kHz < f < 20 MHz and region II: 200μ Hz < f < 10 kHz). Region I may be characterized by bulk conduction and geometric capacitance leading to a relaxation-like response and a dispersion-free conductivity. Region II may be characterized by dispersive effects associated with space-charge layer in the vicinity of the electrodes. The proposed model is built on the notion that the process of space charge formation is mutually exclusive from the process of ionic conduction. Accordingly, it assumes that a fraction of the charge carriers participates in the conduction process and the remaining fraction contributes to the capacitance associated with space charge formation. When fitted to the observed impedance response, through equivalent circuit models, the charge concentration fraction exhibits a power law dependence on the frequency. The model is fairly general in its scope and may provide an alternate route to understand the internal processes and prompt further investigations.