Platinum oxide growth kinetics for cyclic voltammetry

Electric Field-Dependence of Double Layer Capacitances by Current-Controlled Charge-Discharge Steps

Voltage vs. time curves of double layer capacitances (DLCs) by current-controlled charge and discharge steps have been recognized to be composed of triangular waves. They are deviated slightly from triangles from the viewpoint of the time dependence or the constant phase element of the DLC. In order to evaluate the deviation, we measured DLCs of a platinum (Pt) electrode in KCl solution by current-control. Each time-voltage curve was convex rather a line, and was followed by the power law. Even if the time dependence was subtracted from each curve, the enhancement of the DLC was noticeable with an increase in the time well as the voltage. It can be attributed to the electric field effect, in which dipoles of solvents are oriented on an electrode so strongly that the DLC may be increased. The field dependence can be justified with the kinetic theory of interacting dipoles of solvents on an electrode through the observed linearity of the logarithmic DLC with the net voltage. This concept was applied to a commercially available super-capacitor to demonstrate a significant contribution of the field effect.

Kinetically induced irreversibility in electro-oxidation and reduction of Pt surface

A mean field kinetic model was developed for electrochemical oxidations and reductions of Pt(111) on the basis of density functional theory calculations, and the reaction mechanisms were analyzed. The model reasonably describes asymmetric shapes of cyclic voltammograms and small Tafel slopes of relevant redox reactions observed in experiments without assuming any unphysical forms of rate equations. Simulations using the model indicate that the oxidation of Pt(111) proceeds via an electrochemical oxidation from Pt to PtOH and a disproportionation reaction from PtOH to PtO and Pt, while its reduction proceeds via two electrochemical reductions from PtO to PtOH and from PtOH to Pt.

A Coverage-Dependent Study of Pt Spontaneously Deposited onto Au and Ru Surfaces: Direct Experimental Evidence of the Ensemble Effect for Methanol Electro-Oxidation on Pt

Direct experimental evidence that can be unambiguously attributed to the need of an ensemble of a minimum number of neighboring Pt atoms for methanol electro-oxidation has been observed for the first time. This was realized by a Pt coverage-dependent investigation of methanol and CO electro-oxidation on Pt sites generated via spontaneous deposition onto both Au and Ru surfaces. CO stripping voltammograms also show clear evidence of a substantially strengthened CO-Pt bonding for submonolayer Pt deposited on the Au substrate over a range of ca. 0.22 to 0.77, which is in qualitative agreement with the theoretical prediction based on the Hammer-Nørskov d-band center model. However, the degree of the bond strengthening depends on the Pt coverage, being stronger for lower coverage. Additionally, evidence of an Ostwald ripening process for Pt islands formation has also been observed.