Pt oxidation

The break in the plot log I vs coincides with the observed inflection in rH2 and r0, and corresponds to the onset of Pt oxide formation.6 As shown in Fig. 10.3 the, predominantly catalytic, rates rH2 and r0 depend exponentially on catalyst potential Uriie, as in studies with solid electrolytes with slopes comparable with the Tafel slopes seen here. This explains why the observed magnitude of the faradaic efficiency A (-2-20) is in good agreement with 2F rc° /I0 (rc° is the open-circuit catalytic rate and I0 is the exchange current) which is known to predict the expected magnitude of A in solid-electrolyte studies. 

The second is a neat idea coming from Johnson Ma tthey. They invented the so-called continuously regenerating trap (CRT) consisting of a monolithic preoxidizer and a particulate trap, see Figure 9.3 [24]. The first monolith (containing Pt) oxidizes hydrocarbons and CO to CO2 and NO into NO2, which is very reactive... 

A study of the area of the L absorption edge resonance shows a correlation with chemical activity. This implies a correlation with the number of d-band vacancies. This occurred when Pt oxide was reduced by hydrogen or when the particle size was decreased (13). 

In the Pt bulk oxide range of the phase diagram, which is relevant provided that (5.26) is fulfilled, the bulk electrode is Pt oxide and no longer pure Pt. Therefore the corresponding term in (5.28) that accounts for the bulk electrode reservoir now has to involve Since the bulk electrode should be in thermodynamic equihbrium with the surroundings. 

Jacob T. 2007b. Theoretical investigations on the potential-induced formation of Pt-oxide surfaces. J Electroanal Chem 607 158-166. 

At near-saturation coverages, the oxidation peak potential is displaced to approximately 1.03 V. There is a second oxidation process at 1.1 V that involves desorption of Te adatoms, which has been ascribed to the displacement of the Te(IV) oxide by surface Pt oxide. 

Studies have shown that the Pt oxides are not hydrated [Birss et al., 1993 Harrington, 1997 Jerkiewicz et al., 2004]. Electrochemical quartz crystal microbalance [Birss et al., 1993] and nanobalance [Jerkiewicz et al., 2004] experiments... 

Harrington DA. 1997. Simulation of anodic Pt oxide growth. J Electroanal Chem 420 101-109. 

Figure 12.5 CO stripping voltammogram with a CO- tee 0.1 M H2SO4 electrolyte. Compare the data in Fig. 12.4 the CO oxidation region begins at V = 0.43 V. After CO stripping, hydrogen adsorption/desorption peaks and the beginning of the Pt oxidation range are shown.

Figure 10.5. Comparisons of the conversion obtained on Ag/alumina in combination with Pt oxidation catalyst in the presence of hydrogen. 500 ppm NO, 375 ppm C8H18, 1 vol.% H2, 6 vol.% 02, 10vol.% C02, 350ppm CO, 12vol.% H20 in He. GHSV = 60000h 1 (reproduced with permission from Ref. [72]).

Figure 4. Reflection infrared spectra of aniline films (a) aniline multilayer adsorbed on Ni(111) at 165 K (b) poly(aniline) monolayer on Ni(111) at 400 K (c) electrochemically grown poly(aniline) on Pt oxidized at 0.8 V vs. Ag/AgCI(1M) (d) electrochemically grown poly(aniline) on Pt reduced at 0.35 V vs. Ag/AgCI(1M) (e) electrochemically grown poly(aniline) on Pt reduced at 0.0 V vs. Ag/AgCI(1M)...

The kinetics of CO oxidation from HClOi, solutions on the (100), (111) and (311) single crystal planes of platinum has been investigated. Electrochemical oxidation of CO involves a surface reaction between adsorbed CO molecules and a surface oxide of Pt. To determine the rate of this reaction the electrode was first covered by a monolayer of CO and subsequently exposed to anodic potentials at which Pt oxide is formed. Under these conditions the rate of CO oxidation is controlled by the rate of nucleation and growth of the oxide islands in the CO monolayer. By combination of the single and double potential step techniques the rates of the nucleation and the island growth have been determined independently. The results show that the rate of the two processes significantly depend on the crystallography of the Pt surfaces. 

Since it is known that the tetranuclear mixed-valent platinum-blue complexes such as 19 and 57 undergo disproportionation and reduction by water as Eqs. (1)—(3) and (7)—(9) show (106, 113), all the species appearing in Eqs. (1)—(3) and (7)—(9) are present in the solution. However, only one or several of the four species in the solution may in fact be resposible for the catalytic olefin oxidation. To clarify this point, the effect of the Pt oxidation state in the platinum complexes was compared. The results are summarized in Table VII, which... 

Complex Ptl—Pt2 Pt2—Pt3 Pt3-Pt4 Colour Average Pt oxidation state Reference... 

One further degradation mode related to catalysis is a consequence of operating at low current densities typical of portable power application. Under these conditions, overoxidation of the Pt cathode catalyst occurs, reducing cathode and overall MEA performance. Zelenay has shown that starving the cathode of air flow lowers the cathode potential to low values, causing reduction of Pt oxides and restoring cathode activity. ... 

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