title: Spectroscopicin situMeasurements of the Relative Pt Skin Thicknesses and Porosities of Dealloyed PtMn(Ni, Co) Electrocatalysts.
abstract: X-ray adsorption near edge structure (XANES) data at the Co or Ni K-edge, analyzed using the Δμdifference procedure, are reported for dealloyed PtCoxand PtNixcatalysts (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 mgPt-1), but exhibit varying activities and durabilities. The variance factors include different initial precursors, dealloying in HNO3vs H2SO4, if a postdealloying thermal annealing step was performed, and different morphologies (some with a multi PtMxcore and porous Pt skin, some single core with nonporous skin). Data are obtained at the initial beginning of life (BOL, ~200 voltage cycles) and after 10k and 30k (end of life, EOL) voltage cycles following DOE protocol (0.6-1.0 V vs reversible hydrogen electrode). The Δμdata are used to determine at what potential (Vpen) 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 theVpenat BOL. The data indicate that cycling produces a "characteristic" Pt skin robustness (porosity or thickness). When the Pt skin at BOL is "thin" (Vpen< 0.9 V) it grows to a "characteristic" thickness consistent with aVpenof ≈1.1 V, and if it begins very thick, it thins to the same "characteristic" thickness. Particles dealloyed in H2SO4appear 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 highVpen, but not necessarily thicker. Furthermore, the PtM3catalysts exhibited a fast skin "healing" 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 firstin situXAS 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.
authors.affiliation: Department of Chemistry, George Washington University, Washington, District of Columbia 20052, United States.
authors.forename: Keegan M
authors.initials: KM
authors.lastname: Caldwell
authors.affiliation: Department of Chemistry, George Washington University, Washington, District of Columbia 20052, United States.
authors.forename: David E
authors.initials: DE
authors.lastname: Ramaker
authors.affiliation: Department of Chemistry and Chemical Biology, Northeastern University, Boston, Massachusetts 02115, United States.
authors.forename: Qingying
authors.initials: Q
authors.lastname: Jia
authors.affiliation: Department of Chemistry and Chemical Biology, Northeastern University, Boston, Massachusetts 02115, United States.
authors.forename: Sanjeev
authors.initials: S
authors.lastname: Mukerjee
authors.affiliation: Electrochemical Energy Research Laboratory, General Motors Central Research and Development, Warren, Michigan 48090, United States.
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Ziegelbauer
authors.affiliation: Electrochemical Energy Research Laboratory, General Motors Central Research and Development, Warren, Michigan 48090, United States.
authors.forename: Ratandeep S
authors.initials: RS
authors.lastname: Kukreja
authors.affiliation: Electrochemical Energy Research Laboratory, General Motors Central Research and Development, Warren, Michigan 48090, United States.
authors.forename: Anusorn
authors.initials: A
authors.lastname: Kongkanand