Potential holding

Modifying this procedure, another potential holding period was set after removing the adsorbates. This potential should not cause methanol oxidation and be low enough to facilitate the reconstruction. 

Fig. 3-17 Cuirent density and coverage of platinum electrodes with strong adsorbates during a potential holding in 5M H2SO4 with 0.1 MCH30H.

Fig. 3-21 Methanol oxidaticm current density diiiing potential holding in 5 M H2SO4 with 0.1 M CH3OH at 500 mV. 

Fig. 3-22 Methanol oxidation corrent density of platinum during potential holding at 600mV in various concentration of H2SO4 at 25 °C with 0.1 M CH3OR...

Fig. 3-24 Iiifethanol oxidation current density of platinum after 2 min, of potential holding at 600 mV in various concentration of H2SO4 with 0.1 M CH3OH. ESach curve is extrapolated to the boiling point of the respective solution (black points). 

Fig. 3-27 Coverage of platiniim electrode by a rbates during potential holding at GOOxnV in 3 M of adds with 0.1 M CH3OH at 25°C. 

Fig. 3-28 Methanol oxidation current after 2 min. of potential holding at 600mV with 0.1 M CH3OH at 25 C. 

Fig. 3-39 Methanol oxidation current during potential holding after cleaning steps on platinum Nafion SPE and chemically platinized Pt electrodes. 

Fig. S-40 Hydrogen adsorption-desorption features of Nafion SPE Pt and platinized Pt electrodes b ore and after 24 hour potential holding at GOOmV.

Figures 3-41 shows the oxidation current after 2 min. of potential holding at 500 mV for both gas feeding (saturated at room temperature 15%) and electrolyte feeding (0.1, 0.5 and 1.0 M). The gas feeding showed the intermediate characteristics between 0.5 M and 1 M electrolyte feedings and slightly larger temperatiu e dependence. Otherwise, no significant difference was foimd.

Fig. 3-41 Temperature dependance of methanol oxidation current denai after 2 min. potential holding at 500 mV for Nafion SPE platinum electrode at various methanol concentration in the electrolyte or in the feed gas. 

Fig. 3-42 Methanol oxidation current of Nafion SFE Pt electrode after 2 min. cf potential holding at 500 mV or 600 mV atTff C. Methanol was fed throu gas phase at various partial pressures, water vapor pressure 0, electrolyte 3 M H2S04...

Fig. 4-3 Cyclic voltammograms of a smooth Pt-Ru electrode in 3M H2SO4 after Ru stripping by anodic potential holding. 

Potential holding measurements were conducted to examine the sustained current. The surface cleaning steps used for pure platinum were not applied on Pt-Ru electrode because the high potential causes the removal of ruthenium. Instead, the potential was stepped to 800 mV for 5 s for cleaning and stepped to the potential to examine the oxidation current... 

From a practical point of view, data obtained by CA methods are more useful. Figure 15.8 shows examples of the CA curves obtained in 0.5 M ethanol solution in 0.1 M HCIO4 at an anodic potential of 600 mV vs. SCE. In both of the CA curves there is a sharp initial current drop in the first 5 min, followed by a slower decay. The sharp decrease might be related to a double layer thus indicating that the catalysts differ mainly in their active area based on the above CV experiments in acid solution. In longer runs it was found that the current (j after 30 min polarization at 600 mV vs. SCE) obtained on PtSn-1 electrodes is higher than that on PtSn-2. The quasi-steady-state current density stabilized for both the catalysts within 0.5 h at the potential hold. The final current densities on PtSn-1 and PtSn-2 electrodes after holding the cell potential at 600 mV vs. SCE for 30 min were 3.5 and 0.3 mA, respectively. 

Enhancement of the activity of Ag has been observed upon continuous potential cycling [265], as well as with more complex potential sequences including potential holding at some cathodic values [266] and pulsating overpotential [267]. The enhancement cannot be explained only in terms of surface area increase, so that the creation of especially active Ag sites has been postulated [266]. 

Finally, it should be stressed that the case of william is presented to illustrate the potential of self-reporting of hypnotic depth. The effects of subtle factors in my laboratory, demand characteristics, and william s uniqueness must be assessed in the course of replication and extension of this work by others to establish how much of this potential holds up and becomes practically and theoretically useful. 

The second and third terms on the right hands side of Eq. 9.8 remain constant for a given electrode-electrolyte system, and hence the electrode potential is a linear function of the interfacial potential A MIS of the electrode. This definition of the electrode potential holds valid for all electronic and ionic electrodes, whether the electrode reaction is in equilibrium or non-equilibrium. The potential defined by Eq. 9.8 is called the absolute electrode potential. 

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