1 research outputs found
Evolution of Structure and Activity of Alloy Electrocatalysts during Electrochemical Cycles: Combined Activity, Stability, and Modeling Analysis of PtIrCo(7:1:7) and Comparison with PtCo(1:1)
This
study explores the changes in bulk composition/structure and
oxygen reduction activity of two alloys, Pt<sub>7</sub>IrCo<sub>7</sub> and PtCo, caused by Co leaching during electrochemical cycles and
as a result of membrane electrode assembly (MEA) fabrication procedures.
Exposure to liquid electrolyte and electrochemical cycles in a rotating
disc electrode (RDE) environment resulted in substantial Co loss and
no stabilization from the low levels of Ir used in the ternary material.
The true composition of the ternary material was determined as Pt<sub>8</sub>IrCo<sub>3</sub> following initial exposure to 0.1 M HClO<sub>4</sub> (before cycling) and Pt<sub>11</sub>IrCo<sub>4</sub> after
5000 cycles. Density functional theory (DFT) modeling of the cycled
catalyst compositions indicated that structures with Pt-rich upper
layers would show the highest stability; however, addition of 0.25
ML oxygen adsorption favored Co segregation from second and third
atomic layers. The high initial activities (>0.44A/mgPt) achieved
in the RDE environment decreased with cycles and were not reproduced
in MEAs. X-ray diffraction (XRD) analysis revealed a measurable increase
in lattice parameter caused by the MEA preparation procedure, consistent
with Co (and some Ir) leaching into the ionomer phase and relaxation
of the lattice. MEA fabrication procedures and cycling in 1 M H<sub>2</sub>SO<sub>4</sub> at 80<sup>â—¦</sup>C showed greater changes
to catalyst structure and increased Ir and Co loss compared to exposing
the catalyst to RDE like conditions (0.1 M HClO<sub>4</sub>, RT) explaining
the observed discrepancy in activity between RDE and MEA