Transition from core-shell to janus segregation pattern in AgPd nanoalloy by Ni doping for the formate oxidation

Developing the nanoalloys with well-designed chemical ordering and understanding the correlation between the chemical ordering and catalytic property remain a challenge, yet represent an effective strategy to improve the performance of the nanoalloys. Herein, three AgPd-based nanoalloys with different composition-segregation types, namely, alloy (mixed-Ag₁₉Pd₇₂Ni₉), core-shell (core-shell-Ag₄₀Pd₆₀) and janus (janus-Ag₂₀Pd₆₀Ni₂₀) atomic arrangements, are developed via a successive co-reduction method and used in the formate oxidation reaction (FOR). The janus-Ag₂₀Pd₆₀Ni₂₀ nanoalloy exhibits an electrocatalytic activity of 1.31 A mg_Pd⁻¹ and remarkable long-term stability, outperforming the commercial Pd/C catalysts. The FOR activity follows the order of janus-Ag₂₀Pd₆₀Ni₂₀ > core-shell-Ag₄₀Pd₆₀ > mixed-Ag₁₉Pd₇₂Ni₉ nanoalloys. After galvanic replacement and acid treatment, the obtained galvanic-Ag₂₀Pd₆₀Ni₂₀ and acid-Ag₂₀Pd₆₀Ni₂₀ nanoalloys demonstrate 2.31 and 1.44 times higher mass activity than the janus-Ag₂₀Pd₆₀Ni₂₀ nanoalloy. The improvements in the activity and stability can be attributed to largely increased Pd active sites on the surface of AgPd-based nanoalloys with optimal chemical ordering.