The surface forces between platinum, Pt, electrodes and those between the Pt electrode and mica in aqueous HClO4 were measured at various potentials (E) applied to the electrodes using an electrochemical surface forces apparatus (EC-SFA). This apparatus uses the twin-path surface forces apparatus, recently developed for opaque samples. The influence of the proton adsorption on the surface interactions was studied. The Pt electrodes were prepared by the template-stripping procedure using glass templates. The electrode surfaces were smooth (RMS roughness: 0.26 nm for a 5 μm × 5 μm area) and polycrystalline based on the atomic force microscopy and cyclic voltammetry results, respectively. When the applied potential E was decreased from 0.5 to 0.2 V (vs Ag/AgCl), the electric double layer (EDL) repulsion between the Pt electrodes decreased. The absolute values of the surface potentials, |0|, calculated using the EDL theory were 58 and 43 mV at E = 0.5 and 0.2 V, respectively. The EDL force at E = 0.2 V was the local minimum, suggesting that the potential of the zero charge (PZC) of the Pt electrode was around 0.2 V in the 1 mM HClO4 solution. With the further decreasing potential E from 0.2 to -0.2 V, the EDL repulsion remained similar in amplitude, took another minimum, |0| = 40 mV, at E = -0.1 V, and started to increase again at E = -0.1 V. These behaviors could be caused by proton adsorption on the Pt surface (Ptδ-···H+), the electrochemical hydrogen adsorption (Pt-H), and the subsequent hydrogen evolution (H2). The possibility for characterizing the hydrogen evolution processes on the Pt electrodes based on the surface forces measurement is discussed for the first time.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films