Coordinatively Unsaturated PtCo Flowers Assembled with Ultrathin Nanosheets for Enhanced Oxygen Reduction

Exploring a Pt-based catalyst with a low coordination number is crucial to developefficient oxygen reduction reaction (ORR) catalysts in fuel cells. Herein, an open-structured Pt-rich PtCo nanoflower (NF) catalyst assembled by radial ultrathin nanosheets (similar to 1.5 nm) with alow coordination number (8.65) is synthesized. The Pt-rich PtCo NFs exhibit excellent ORRperformance in aspects of mass and specific activity (2.63 A mgPt-1and 11.23 mA cm-2,respectively), which are 17.5 and 38.7 times that of commercial Pt/C, respectively, and a currentdensity of 1854 mA cm-2is achieved at 0.6 V in a single fuel cell. The superior ORR performanceis mainly attributed to the low coordination number of Pt, which is induced by the optimized catalytic interface, including defectsites, high-index facets, and twin boundary. Also, theoretical calculations reveal that the ORR performance of a low-coordination siteis much higher than that of a high-coordination site, the tendency of which is contrary to the d-band center. This work provides anin-depth understanding of the relationship between coordination number and electrocatalytic performance at the atomic scale, whichis conducive to designing more robust and efficient alloy catalysts.