Effect of pH and Water Structure on the Oxygen Reduction Reaction on platinum electrodes

Abstract

The oxygen reduction reaction (ORR) at different pH values has been studied at platinum single crystal electrodes using the hanging meniscus rotating disk electrode (HMRDE) configuration. The use of NaF/HClO4 mixtures allows investigating the reaction up to pH = 6 in solutions with enough buffering capacity and in the absence of anion specific adsorption. The analysis of the currents shows that the kinetic current density measured at 0.85 V for the Pt(111) electrode follows a volcano curve with the maximum located around pH = 9. This maximum activity for pH = 9 can be related to the effects of the electrode charge and/or water structure in the ORR. On the other hand, the catalytic activity for the other basal planes shows a monotonic behavior with a small dependence of the activity with pH. For stepped surfaces with (111) terraces, the behavior with pH changes gets closer to that of the Pt(111) surface as the terrace length increases. Additionally, the ORR curves show a dependence of the limiting diffusion current with pH. It is observed that the limiting current density diminishes as the pH increases in a potential region where hydrogen peroxide is readily reduced. These results suggest the existence of a bifurcation point in the mechanism previous to peroxide formation, in which OOH • is proposed as the bifurcation intermediate. The reduction of OOH • requires proton addition and would be more difficult at neutral pH values, justifying the diminution of the limiting currents.

The behavior of chemical and electrochemical Ag deposition on FeNi‐mesh cathodes in Al‐air battery

“…As is known, aluminium is oxidized in the anodic direction, oxygen (Equation 3.8) and/or H+ ions (Equation 3.9) are reduced in the cathodic direction. 24 The oxygen reduction is preliminary in the cathodic polarization curves from −0.2 V to −1.35 V vs Ag/AgCl for FeNi mesh. After these values, the sudden increase of the currents shows that the H + is reduced.…”

“…In this interaction, the effect of pH can be shown according to Equation . The studies have shown that as the basicity increases (pH), the oxygen reduction region shifts to the negative …”

“…The polarization curves taken from the −0.2 V vs Ag/AgCl potential to the cathodic directions are shown in Figure . As is known, aluminium is oxidized in the anodic direction, oxygen (Equation ) and/or H+ ions (Equation ) are reduced in the cathodic direction …”

“…The studies have shown that as the basicity increases (pH), the oxygen reduction region shifts to the negative. 24 When we adjust it according to the pH of the basic medium, the equation becomes as follows: HO 2 − , ad at pH > 11.63. 22,25…”

Corrosion Behaviors of Q345R Steel at the Initial Stage in an Oxygen-Containing Aqueous Environment: Experiment and Modeling

“…Considering the mixed mass transfer and charge transfer control of the cathodic reaction rate, the effect of mass transfer on net current density $j_{\mathrm{net}}$ can be theoretically derived by Equation (1) (All the explanation about parameters, variables and constants in the modeling are summarized in Table 1, the same hereinafter): $\frac{1}{j_{\mathrm{net}}}=\frac{1}{j_{\mathrm{ct}}}+\frac{1}{j_{\lim }}$ where $j_{\mathrm{ct}}$ is the current density controlled by charge transfer and $j_{\lim }$ is the limiting current density controlled by mass transfer. The equation has been widely used in elementary mechanistic models of corrosion [23,24,25]. …”