Abstract
One of the applications of Pt‐based nanoparticles on high surface area carbon (HSAC) support composites is as a catalyst in polymer electrolyte membrane fuel cells (PEMFC) [1]. Yet the full commercial implementation of the technology has been hindered by the composite cathode which exhibits a low catalytic activity for oxygen reduction reaction (ORR), a poor stability in electrochemical environment and is expensive due to use of Pt. One solution to those issues is to alloy Pt with other transitional metals, which will not only reduce the composite costs, but also increase the catalytic activity for ORR [2]. Chemical ordering of the Pt‐M/HSAC (M=Metal) composite has shown to improve the stability of the nanoparticles, as well as to enhance the catalytic activity for ORR. [3]. Recent work has shown that adding a small amount of gold can improve the durability of Pt and Pt‐based nanoparticles [4,5], as well as inhibit the oxidation of HSAC support [5]. We have used Aberration Corrected Scanning Transmission Electron Microscopy (AC‐STEM) to study the effect of gold on the Pt‐skin partially ordered intermetallic PtCu 3 /HSAC composite. Au doped PtCu 3 /C and PtCu 3 /C composites were compared side to side, before and after an electrochemical cycling treatment. Fig. 1 shows scanning transmission electron microscopy annular dark filed images and energy dispersive x‐rays maps of the two composites after 200 cycles of electrochemical activation (EA, 0.05 – 1.35 V RHE , 300 mVs ‐1 ). Less porous nanoparticles and lower Cu dissolution are observed in the Au doped PtCu 3 /C composite. Surface modifications were also observed in non‐porous nanoparticles after performing 10 000 cycles of severe degradation (0.4 – 1.4 V, 1 Vs ‐1 ): (1) thickening of the Pt skin, (2) faceting and (3) surface dislocations (Fig. 2). These surface modifications may have influence on stress and nanoparticle stability. Overall, the Au doped PtCu 3 /C composite exhibited higher Cu retention and better durability compared to its binary analogue.
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