Edge-Selective Growth of MCp2 (M = Fe, Co, and Ni) Precursors on Pt Nanoparticles in Atomic Layer Deposition: A Combined Theoretical and Experimental Study

Recent experiments about the selective coating of transition-metal oxide on Pt nanoparticles have aroused great interest in molecular catalysis for the promotion of both activity and stability. In this work, first-principles calculations combined with microkinetic methods are employed to shed to light on the edge-selective growth mechanism of 3d-transition metal oxide on Pt nanoparticles in atomic layer deposition (ALD) from the metal cyclopentadienyl precursors (MCp2, M = Fe, Co, and Ni). The MCp2 decomposition on the surface of Pt nanoparticles exhibits robust preferential growth, following the order of edge > (100) > (111), which indicates that edges are naturally selected to be covered and the (111) facets could survive toward the MCp2 precursors. The preferred deposition on the edge site is attributed to a more favorable splitting path for the precursors. On the other hand, competing reactions make the overall reaction rates of MCp2 precursors on edge sites follow the order of NiCp2 > FeCp2 > CoCp2. Moreover, the reaction rate analysis indicates that the edge selectivity of MCp2 on Pt nanoparticles is temperature dependent, and a high temperature will suppress the selectivity between different sites. FeCp2 could maintain high selectivity in a wide temperature range among the three precursors. The theoretical predictions about the edge-selective growth of MCp2 are confirmed by the Fourier transform infrared measurements of CO signals on successive ALD-coated Pt nanoparticles. The combination of theoretical and experimental study demonstrates the robust edge-selective growth of MCp2 on Pt nanoparticles, which may open up a new avenue for the design of metal-oxide composite catalyst with specific site passivation.