Trimetallic Pt-Pd-Ni octahedral nanocages with subnanometer thick-wall towards high oxygen reduction reaction

摘要

Precisely engineering the composition and structure of nanomaterials can effectively tune their activity and stability towards oxygen reduction reaction (ORR), a key process in fuel cells. Here, a highly active and stable electrocatalyst for ORR is fabricated by alloying Ni atoms with octahedral N-Pd nanocages with ultrathin walls and exposed (111) facets. The specific activity (3.8 mA/cm(2)) and mass activity (1.17 A/mg(Pt) ) of the octahedral N-Pd-Ni nanocages represent a performance enhancement by a factor of 25 and 10 compared to commercial Pt/C, respectively. In addition, the ORR activity of octahedral N-Pd-Ni nanocages significantly outperforms the octahedral N-Pd nanocages (1.89 mA/cm(2) and 0.73 A/mgp, in specific and mass activity). The ligand effect and compressive strain, confirmed by the X-ray absorption fine structure (XAFS) analysis and density functional theory (DFT) calculations, accounts for the enhanced activity by weakening the adsorption energy of hydroxyl groups. Particularly, it shows robust stability with only 16% decay in the mass activity after accelerating degradation tests (ADTs), rationalized by its structural stability and high vacancy formation energy. This work provides a new class of N based nanocatalysts with high activity and stability for ORR.