Periodic and complex waveform current oscillations of copper electrodissolution in phosphoric acid in an epoxy-based microchip flow cell

Abstract

We investigate the dynamical behavior of anodic copper dissolution in phosphoric acid in an on-chip integrated microfluidic flow cell. Electrodissolution of copper in the microcell displayed periodic, smooth, and relaxation oscillations. The system displayed complex waveforms with mixed-mode and chaotic oscillations as well. These waveforms appeared when proper external resistance, flow rate, and circuit potential were applied. The oscillations in the Cu-phosphoric acid system exhibited a strong dependence on the flow rate of the electrolyte solution. An increase in flow rate correlated with a decrease in the minimum external resistance required for oscillations. The experiments displayed a considerable “drift” where repeated linear polarization scan measurements resulted in a decrease of current level as well as a shift of the range of oscillations to lower (more negative) potentials. The experiments also indicated that the direction of flow affected the observed dynamics of the microcell flow system. Pushing the flow moved the acid through the channel over the recessed Cu electrode to reservoir accommodating the counter and reference electrode; pulling the flow transferred the acid from the reservoir to the electrode. With pull flow, an increased oscillatory potential range and a greater variety of complex waveform types were observed.