At an electrified interface of metal and electrolyte, ion concentration in the diffuse layer is different from the bulk and is impacted by metal charge. The double-layer structure can significantly enhance local ionic conductivity. Understanding the conductivity enhancement with conventional electrochemical measurements is challenging; however, electrokinetic experiments can be more useful in probing local ionic conductivities. We used streaming-current experiments for a range of pH values to measure ζ-potential at metal-electrolyte interfaces. We extend the method by incorporating a three-electrode electrochemical cell where the potential of the metal can be varied. By using a range of applied potentials between -200 and 800 mV (vs standard hydrogen electrode), we explored how surface charging of Au electrode affects ζ-potential. An inflection point is observed on the plot of ζ-potential against applied potential, and this point is believed to be a potential of zero charge of the electrode. Using the Gouy-Chapman-Stern-Grahame model, we correlate measured ζ-potential values to metal surface charge and calculate ionic distribution and conductivity within the microchannel. Finally, ionic conductivity is calculated as a function of metal surface charge, and as expected, Gouy-Chapman theory shows a parabolic relationship.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films