Characterization of electrochemical properties of a micro-nanochannel integrated system using computational impedance spectroscopy (CIS)

The integration of a microchannel with an ion-selective nanochannel exhibits nonlinear current-voltage characteristics owing to the concentration polarization effects. In this paper, an efficient computational impedance spectroscopic technique (CIS) is developed using an area averaged multi-ion transport model (AAM). Using this technique, we investigate the ion transport dynamics in the Ohmic and non-Ohmic regions. Under no external DC bias and in the Ohmic regime, we observe two distinct arcs. The low frequency diffusional arc characterizes the diffusion-transport and the electrical double layer (EDL) charging effects at the interface of the micro-nanochannel, while the high frequency geometric arc characterizes the electric migration and displacement current effects inside the nanochannel and in the microchannel. Further, we observe an anomalous inductive arc at low frequencies (fL² _m/D ≤ 1), in the overlimiting regime. This arc is primarily attributed to the phase effects between the first harmonic contribution of the total ionic concentration and the electric field in the induced space charge region. The microscopic diffusion boundary layer (DBL) lengths observed in the microchannel are also efficiently characterized from the impedance spectrum. Equivalent circuit models are designed to interpret the impedance response.