Ordered Intermetallic PtCu Catalysts Made from Pt@Cu Core/Shell Structures for Oxygen Reduction Reaction.

ABSTRACT

Platinum-based ordered intermetallic compounds are promising low-Pt catalysts toward the oxygen reduction reaction (ORR) for high-performance fuel cells. However, the synthesis of ordered intermetallic catalysts usually requires high-temperature annealing to overcome the energy barrier for atom diffusion, which leads to inevitable sintering of catalysts and greatly reduced mass-specific activity. Herein, we developed a new strategy to synthesize PtCu-ordered intermetallic catalysts by the generation of the Pt@Cu core/shell nanoparticles (Pt@Cu NPs) by Pt-assisted H2 reduction of Cu2+ with subsequent annealing at 500-1000 °C. Compared to the commonly used wet-impregnation method, the core/shell structure starts to form ordered PtCu alloys at a lower annealing temperature (500 °C). The Pt@Cu core/shell structure avoids the necessary process of Cu atoms diffusing to Pt NPs across the carbon supports occurred during high-temperature annealing in the wet-impregnation method, which ensures the formation of PtCu NPs with higher ordering degree while annealing at the same temperature. The highly ordered small-sized PtCu catalysts prepared by the core/shell strategy exhibit higher mass activity and specific activity compared to those prepared by the wet-impregnation method. Moreover, a positive correlation between the ORR activity and the ordering degree of the intermetallic PtCu NPs is identified, which could be associated with the increase of compressive strain with the ordering degree.