Platinum dissolution

Platinum has also had its share of attention in recent years. The effect of phosphoric acid concentration on the oxygen evolution reaction kinetics at a platinum electrode using 0-7 m-17-5 m phosphoric acid at 25°C has been studied with a rotating disc electrode . The characteristics of the ORR are very dependent on phosphoric acid concentration and H2O2 is formed as an intermediate reaction. Also, platinum dissolution in concentrated phosphoric acid at 176 and 196°C at potentials up to 0-9 (SHE) has been reported . 

Bindra P, Clouser SJ, Yeager E. 1979. Platinum dissolution in concentrated phosphoric-acid. J Electrochem Soc 126 1631-1632. 

Dam VAT, de Bmijn FA. 2007. The stability of PEMFC electrodes—Platinum dissolution vs. potential and temperature investigated by quartz crystal microbalance. J Electrochem Soc 154 B494-B499. 

Darling RM, Meyers JP. 2003. Kinetic model of platinum dissolution in PEMPCs. J Electrochem Soc 150 A1523-A1527. 

Wang XP, Kumar R, Myers DJ. 2006. Effect of voltage on platinum dissolution relevance to polymer electrolyte fuel cells. Electrochem Solid State Lett 9 A225-A227. 

Yasuda K, Taniguchi A, Akita T, loroi T, Siroma Z. 2006a. Characteristics of a platinum black catalyst layer with regard to platinum dissolution phenomena in a membrane electrode assembly. J Electrochem Soc 153 A1599-A1603. 

Error bars in Fig. 2 for the data at the lowest potentials are indicated, reflecting the limits for the gravimetric analyses but also it is realized that at the 0.65 V operating potentials of the PAFC, platinum dissolution will still occur with a projected equilibrium solubility of 1 x 10 10 moles... 

Wang, X., Kumar, R., and Myers, D.J., Effect of voltage on platinum dissolution, Electrochem. Solid-State Lett., 9, A225, 2006. 

R. M. Darling, and J. P. Meyers, Kinetic model of platinum dissolution in PEM fuel cells in E. Society (Ed.), Proton Conducting Membrane Fuel Cells III, 2005, p. 44. 

R. M. Darling and J. P. Meyers, "Kinetic Model of Platinum Dissolution in PEMFCs," Journal of the Electrochemical Society, 150 (2003) A1523-A1527. 

Thus, in presence of chlorine ions, aetivation energy of platinum dissolution is sharply lowered. The same statement can be related to the ease of carbon compound oxidation, for example methanol, where CO forms strong eomplexes with Pt ions with the low activation energy of desorption. 

Platinum dissolution is neghgible. Sn equilibrium potential is —0.138 vs. SHE and that of hydrogen, e°, is 0.00 vs. SHE. Assume that platinum dissolution is... 

Assuming that only tin is dissolving (platinum dissolution in acidic solution is negligible), the anodic Tafel equation is ... 

Figure 1.2 shows the thermodynamic equilibrium for mobile platinum versus potential for an acidic solution in equilibrium with an exposed platinum surface and a lower branch of equilibrium concentration at potentials more positive than approximately 1.1 volts relative to a hydrogen electrode, where the plotted concentration denotes the concentration of mobile species in equilibrium with a platinum oxide layer covering the surface. This shows that excursions to higher potential can rapidly increase the rate of platinum dissolution prior to passivation of the surface. Once the surface is passivated, the dissolution stops and redeposition can occur, albeit incomplete redeposition, as the platinum, once rendered mobile, is free to redeposit on larger particles or diffuse away from the catalyst layer altogether [32]. 

Platinum dissolution at high potentials and redeposition on larger particles (Ostwald ripening). 

The rate of platinum dissolution increases with potential, decreasing pH and increasing temperature. Potential cycling and extended periods at high potential have been found to be particularly detrimental. 

As a consequence of platinum dissolution, the electrode region next to the membrane carrying most of the current during phases of high load is depleted from platinum (Fig. 14.11). 

There is growing evidence that platinum dissolution plays a major role in the ECSA loss, especially of the cathode catalyst, where high potentials are encountered [118]. Oxidized platinum can then either deposit on existing platinum particles to form larger particles [117] or diffuse into electrochemically inaccessible portions of the MEA (i.e., sites not fulfilling the requirements of gas, electron, and proton access in the three phases region). 

The most commonly used working electrode material is platinum, sometimes alloyed with a few per cent of iridium. Two difficulties can arise. First, in chloride media, the Pt anode may dissolve and codeposit with the intended metal on the cathode platinum dissolution can be suppressed using a depolarizer such as hydrazine sulfate. Second, electrode cleaning is difficult when the deposited metal alloys with platinum. This arises with Bi, Cd, Ga, Hg, Pb, Sn, and Zn but can be prevented by precoating Pt with Cu or Ag. 

Pt/C and PtCo/C catalysts High temperature operation effect on carbon corrosion, platinum dissolution, and sintering Arico et ai, 2008... 

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