Influence of the Working and Counter Electrode Surface Area Ratios on the Dissolution of Platinum under Electrochemical Conditions

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• 作者：Min Tian ; Christine Cousins ; Diane Beauchemin ; Yoshihisa Furuya ; Atsushi Ohma ; Gregory Jerkiewicz
• 刊名：ACS Catalysis
• 出版年：2016
• 出版时间：August 5, 2016
• 年：2016
• 卷：6
• 期：8
• 页码：5108-5116
• 全文大小：462K
• 年卷期：0
• ISSN：2155-5435

文摘

The potential variation of a Pt counter electrode (CE) in a three-electrode configuration is monitored as the potential of a Pt working electrode (E_WE) follows a triangle-shaped program in 0.5 M aqueous H₂SO₄. The spontaneously adopted CE potential (E_CE) is reported for different values of the ratio of geometric surface areas of WE and CE (A_geom,WE/A_geom,CE). The E_CE versus time (t) transients are nonlinear and resemble charging/discharging curves. In the case of A_geom,WE > A_geom,CE, E_CE adopts higher values than E_WE and vice versa. In the case of A_geom,WE/A_geom,CE = 10/1, the values of E_CE are 0.3–0.4 V higher than the highest values of E_WE. The high E_CE values give rise to the development of a thick surface oxide that undergoes subsequent dissolution. A novel three-compartment electrochemical cell is employed to examine simultaneously the dissolution of WE and CE and to monitor their potentials; the amount of dissolved Pt is quantitatively analyzed using inductively coupled plasma mass spectrometry. The magnitude of the A_geom,WE/A_geom,CE ratio has a significant impact on the CE oxidation and dissolution. The oxidation and dissolution of CE depend on the lower potential limit of WE; the amount of surface oxide and the quantity of dissolved Pt significantly increase as the WE potential limit is reduced from 0.50 to 0.05 V because CE adopts a high potential. The presence of dissolved O₂ also affects the dissolution of CE but to a lesser extent than the A_geom,WE/A_geom,CE ratio or the lower potential limit of WE. Field emission scanning electron microscopy analysis of the CE morphology following prolonged potential cycling in the presence of dissolved O₂ reveals a thick surface oxide that has a dry mudlike structure. The slightly higher dissolution of CE under these conditions is attributed to physical detachment of some of the cracked surface oxide. This research advances the understanding of Pt dissolution, with some of the new knowledge being applicable to fuel cells.