▎ 摘　　要

Nanoparticles (NPs) of Pt, Ni or NiO, deposited on few-layered graphene using pulsed laser ablation catalyze the in-situ formation of graphitic shells from graphene. These shells encapsulate the NPs as their cores. High substrate temperature (>450 degrees C) was necessary for this unique transformation. Size distribution of the core-shell NPs could be adjusted by varying the deposition parameters. The composite of graphene and core-shell Ni NPs was found to be more stable than bare unsupported Ni NPs in corrosive acid and iodine based solutions. The composite survived for about an hour inside the acid and for around 3.5 months in iodine solution. These core-shell composite materials with longer life could be instrumental in eliminating the use of precious metals in several industrial processes and commercial devices. We found them to be highly effective as catalyst in dye sensitized solar cells, surpassing conventionally used Pt thin films in some cases. (C) 2015 Elsevier Ltd. All rights reserved.