Challenges in the theory of electron transfer at passive interfaces

Oxidation of hydrogen on oxidized platinum

“…As noted elsewhere [29,30], the quantum mechanical tunneling-point defect model (QMT-PDM) developed here has significant advantages over conventional techniques for measuring the thickness of thin oxide films, such as ellipsometry [4], capacitance measurements, and galvanostatic charging (oxidation/reduction) [5,6,8,10,35]. These methods require that the surface roughness be significantly less than the thickness of the film (ellipsometry), or require knowledge of the true surface area (capacitance and galvanostatic charging methods), and hence become problematic when the film is very thin (<1 nm).…”

“…Furthermore, we show how the current for the HOR, measured in the oxide formation region, can be used to determine the tunneling constant [23,[29][30][31] and the ''true'' thickness of the thin oxide layer.…”

Facile chromaticity approach for the inspection of passive films on austenitic stainless steel

“…Previous studies [12,[22][23][24] reported that the capacitance response in the p-type and n-type regions are controlled by the inner Cr-rich oxides and outer Fe-rich oxides in passive films, respectively, thereby suggesting the dual semiconducting properties of the films. According to point defect theory [25,26], doping density is an indicator of non-stoichiometric defects (vacancies or cation interstitials) in the space charge region of passive films. A decrease in doping density indicates a depletion in defects [22][23][24][25][26][27].…”

“…According to point defect theory [25,26], doping density is an indicator of non-stoichiometric defects (vacancies or cation interstitials) in the space charge region of passive films. A decrease in doping density indicates a depletion in defects [22][23][24][25][26][27]. Therefore, the evolution of porosity and point defects in the passive films during air exposure and chemical passivation can be revealed by the relationship between a à value and doping density.…”

Kinetics of the Hydrogen Electrode Reaction on Platinum in Alkaline Solutions at Elevated Temperatures

“…It is seen that the hydrogen oxidation and evolution currents increase sharply at low overpotentials, and the oxidation current quickly goes to a plateau indicating the mass transfer control of the reaction. Upon further increasing of the overpotential, the reaction rate decreases exponentially with increasing voltage, resulting in the so called "inverse Tafel's Law" phenomenon (29), which can be accounted for by quantum mechanical tunneling theory in that charge carriers must tunnel across a passive oxide layer whose thickness increases linearly with the applied voltage (26,30). The passive oxide layer is the anodic oxide film of platinum.…”