Electric Double Layer at the Polycrystalline Platinum-Electrolyte Interface Probed by the Electrokinetic Streaming Current Method

Interfacial charging and ionic conductivity in the diffuse layer of polycrystalline platinum (poly-Pt)- nonadsorbing electrolyte interface were studied using a combined electrochemical-electrokinetic method. Assuming no specific adsorption of ions, the electronic charge on the metal (metal charge) was found to increase monotonically for acidic, neutral, and basic pH, with the applied potential up to 0.95 V versus SHE. Nonmonotonic metal charging was not observed; however, the metal charge was found to saturate to a near-constant positive value at higher applied potentials, possibly due to ion crowding in the diffuse layer. With respect to the potential of zero free charge of Pt, the potential at which the zeta potential was 0 was found to be lower in acidic pH, higher in basic pH, and almost equal in neutral pH. In addition, oxide coverage was calculated from cyclic voltammetry, and H-coverage was calculated from Frumkin adsorption isotherms. They were added to the metal charge to calculate the total charge and were compared with the CO displacement results for P4111) from the literature. The results from these two methods showed good agreement, with the electrokinetic method being applicable for a larger potential window (V > 0.75 V). Ionic conductivity in the diffuse layer was found to be minimum at applied potentials where the zeta potential is 0, and its value was equal to the bulk ionic conductivity of the electrolyte. For all the other applied potentials, diffuse layer ionic conductivity was higher.

Automated summary

The study investigated interfacial charging and ionic conductivity in the diffuse layer of polycrystalline platinum (poly-Pt) interface with a nonadsorbing electrolyte using an electrochemical-electrokinetic method. The results showed an increase in metal charge with applied potential, saturating at higher potentials. Ionic conductivity in the diffusive layer was found to be minimum when the zeta potential was 0, and increased at other potentials.