▎ 摘　　要

electrocatalystsThe development of cheap and efficient electrocatalysts for promoting full water splitting is still challenging. Here, we report a composite architecture that consists of onion-like ultrathin graphene shells encapsulating uniform metallic nickel nanoparticles (Ni@graphene) derived by a straightforward thermal treatment of a Ni-based metal organic framework in an inert atmosphere. The resulting Ni@graphene is highly catalytically active for both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) in 1.0 M KOH solutions. It only requires relatively low overpotentials (OER 370 mV; HER 240 mV) to yield a catalytic current of 10 mA/cm(2), which compares favorably to most previously reported Ni-based elecrocatalysts for water splitting. The excellent performance would be attributed to the catalytic sites of metallic Ni and the intact metal protection effect of the outer graphene layers.