Dealloying of platinum-aluminum thin films: Electrode performance

Highly porous Pt/Al thin film electrodes on yttria-stabilized zirconia electrolytes were prepared by dealloying of co-sputtered Pt/Al films. The oxygen reduction capability of the resulting electrodes was analyzed in a solid oxide fuel cell setup at elevated temperatures. During initial heating to 523 K, exceptionally high performances compared to conventional Pt thin film electrodes were measured. This results from the high internal surface area and large three phase boundary length obtained by the dealloying process. Exposure to elevated temperatures of 673 or 873 K gave rise to degradation of the electrode performance, which was primarily attributed to the oxidation of remaining Al in the thin films.

Figure 1

(a) FIB-polished crosssection of a nanoporous Pt${}_{0.72}$Al${}_{0.28}$ film on YSZ fabricated by dealloying. (b) Morphology after annealing at 673 K for 10 h and 873 K for 14 h in air.

Figure 2

Porosity of Pt${}_{0.72}$Al${}_{0.28}$ films on YSZ plotted as a function of film height perpendicular to the film/substrate interface. Data for as-dealloyed films (partially filled circles) as well as films subjected to annealing at 673 K for 10 h and 873 K for 14 h in air (open circles) is shown.

Figure 3

GIXRD patterns of nanoporous Pt${}_{0.72}$Al${}_{0.28}$ films measured directly after dealloying or after additional annealing at 673 K for 10 h and 873 K for 14 h in air. Reflections are indexed as belonging to the structure group $Fm-3m$. The black line corresponds to a Pearson VII distribution fitted to the original data shown in gray.

Figure 4

(a) ASR of nanoporous Pt${}_{0.72}$Al${}_{0.28}$ films on YSZ plotted as a function of temperature $T$. Data of as-dealloyed films heated for the first time (partially filled circles) and films cooled after subsequent annealing at 673 K for 10 h and 873 K for 14 h in air (open circles) is compared. The dashed lines correspond to Arrhenius fits. Literature data for Pt thin film electrodes is shown in gray, $x$,[19] $y$,[20] $z$.[21] (b) Temperature-induced increase of the ASR at 673 K (tilted squares) and 873 K (hexagons) plotted as a function of time $t$. The dashed line and the exponent $c$ correspond to fitting of the data using a power law specified by Eq. (3).