Platinum group metals (PGMs) are used as oxygen reduction reaction (ORR) electrocatalysts at cathodes in polymer electrolyte fuel cells (PEFCs). For mass-production of PEFCs, ORR electrocatalysts with high catalytic activity and low amounts of expensive PGMs should be developed. Alloying Pt with other metals such as Ni reduces Pt amounts used and enhances ORR catalytic activity, caused by the lattice strain and ligand effects ^{[1, 2]}. Pt-Ni alloy nanoparticles are usually prepared by wet chemical methods using organic solvents and/or surface modifiers^{[3, 4]}. The use of organic compounds causes contamination of organic impurities, leading to deactivation of Pt-Ni alloy nanoparticles for the ORR. In contrast, dry methods need no organic solvent or surface modifier and will allow us to prepare Pt-Ni alloy nanoparticles with high ORR activity.

Herein, we report Pt-Ni alloy electrocatalysts prepared by using an arc-plasma deposition (APD) method and their electrocatalytic activity for the ORR. The APD is a physical vapor deposition and gives highly dispersible metal nanoparticles under high vacuum ^{[5, 6]}.In this work, Pt and Ni nanoparticles were co-deposited on a glassy carbon (GC) substrate by using the APD method. Linear sweep voltammograms of Pt-Ni electrocatalysts prepared by the APD showed reduction currents in 0.1 M HClO₄under oxygen, indicating that Pt-Ni electrodes are electrochemically active for the ORR (Fig. 1). Pt-Ni electrodes showed higher ORR activity than Pt electrodes prepared by the APD of Pt nanoparticles on GC, suggesting that the synchronized APD of Pt and Ni nanoparticles resulted in the formation of Pt-Ni alloy nanoparticles. The ORR activity of Pt-Ni electrodes that we prepared depended on APD conditions of substrate temperatures and the APD order of Pt and Ni nanoparticles. The ORR activity increased with increasing the substrate temperature (Fig. 1). The APD of Ni nanoparticles followed by the APD of Pt nanoparticles on the GC gave the Pt-Ni electrocatalyst, which showed higher ORR activity than that prepared by the synchronized APD of Pt and Ni nanoparticles.

Acknowledgments

This work was supported by NEDO.

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