Atomic Replacement of PtNi Nanoalloys within Zn-ZIF-8 for the Fabrication of a Multisite CO2 Reduction Electrocatalyst

Exploring the transformation/interconversion pathways of catalytic active metal species (single atoms, clusters, nanoparticles) on a support is crucial for the fabrication of high-efficiency catalysts, the investigation of how catalysts are deactivated, and the regeneration of spent catalysts. Sintering and redispersion represent the two main transformation modes for metal active components in heterogeneous catalysts. Herein, we established a novel solid-state atomic replacement transformation for metal catalysts, through which metal atoms exchanged between single atoms and nanoalloys to form a new set of nanoalloys and single atoms. Specifically, we found that the Ni of the PtNi nanoalloy and the Zn of the ZIF-8-derived Zn₁ on nitrogen-doped carbon (Zn₁-CN) experienced metal interchange to produce PtZn nanocrystals and Ni single atoms (Ni₁-CN) at high temperature. The elemental migration and chemical bond evolution during the atomic replacement displayed a Ni and Zn mutual migration feature. Density functional theory calculations revealed that the atomic replacement was realized by endothermically stretching Zn from the CN support into the nanoalloy and exothermically trapping Ni with defects on the CN support. Owing to the synergistic effect of the PtZn nanocrystal and Ni₁-CN, the obtained (PtZn)_n/Ni₁-CN multisite catalyst showed a lower energy barrier of CO₂ protonation and CO desorption than that of the reference catalysts in the CO₂ reduction reaction (CO₂RR), resulting in a much enhanced CO₂RR catalytic performance. This unique atomic replacement transformation was also applicable to other metal alloys such as PtPd.