Ultrathin Graphene Layers Encapsulating Nickel Nanoparticles Derived Metal–Organic Frameworks for Highly Efficient Electrocatalytic Hydrogen and Oxygen Evolution Reactions

The 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/cm², 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.