Spectroscopic in situ Measurements of the Relative Pt Skin Thicknesses and Porosities of Dealloyed PtMn (Ni, Co) Electrocatalysts

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• 作者：Keegan M. Caldwell ; David E. Ramaker ; Qingying Jia ; Sanjeev Mukerjee ; Joseph M. Ziegelbauer ; Ratandeep S. Kukreja ; Anusorn Kongkanand
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：January 8, 2015
• 年：2015
• 卷：119
• 期：1
• 页码：757-765
• 全文大小：398K
• ISSN：1932-7455

文摘

X-ray adsorption near edge structure (XANES) data at the Co or Ni K-edge, analyzed using the 螖渭 difference procedure, are reported for dealloyed PtCo_x and PtNi_x catalysts (six different catalysts at different stages of life). All catalysts meet the 2017 DOE beginning of life target Pt mass activity target (>0.44 A mg_Pt^鈥?), but exhibit varying activities and durabilities. The variance factors include different initial precursors, dealloying in HNO₃ vs H₂SO₄, if a postdealloying thermal annealing step was performed, and different morphologies (some with a multi PtM_x core and porous Pt skin, some single core with nonporous skin). Data are obtained at the initial beginning of life (BOL, 鈭?00 voltage cycles) and after 10k and 30k (end of life, EOL) voltage cycles following DOE protocol (0.6鈥?.0 V vs reversible hydrogen electrode). The 螖渭 data are used to determine at what potential (V_pen) the Pt skin is penetrated by O. The durability, related to a drop in the electrochemical surface areas (ECSAs) after extensive voltage cycling, directly correlates with the V_pen at BOL. The data indicate that cycling produces a 鈥渃haracteristic鈥?Pt skin robustness (porosity or thickness). When the Pt skin at BOL is 鈥渢hin鈥?(V_pen < 0.9 V) it grows to a 鈥渃haracteristic鈥?thickness consistent with a V_pen of 鈮?.1 V, and if it begins very thick, it thins to the same 鈥渃haracteristic鈥?thickness. Particles dealloyed in H₂SO₄ appear to have a thicker Pt skin at BOL than those dealloyed in HNO₃, and a postdealloying annealing procedure appears to produce a particularly nonporous skin with high V_pen, but not necessarily thicker. Furthermore, the PtM₃ catalysts exhibited a fast skin 鈥渉ealing鈥?process whereby the initial porous skin appears to become more nonporous after holding the potential at 0.9 V. This work is believed to be the first in situ XAS study to shed light on the nature of the Pt skin, its thickness, and/or porosity, and how it changes with respect to operating electrochemical conditions.