Highly efficient and stable earth-abundant metal electrocatalysts are of great significance for improving water splitting systems and rechargeable metal–air batteries, in which the oxygen evolution reaction (OER) plays a central part. Among other strategies, anchoring metal–organic frameworks (MOFs) onto conductive materials has proven fruitful towards enhancing their OER performance. Here we explore two strategies for covalent functionalization of graphene flakes as templates for in situ growth of a bimetallic MOF (NiCo-H2bpydc) that is formed using 2,2′-bipyridine-5,5′-dicarboxylic acid as the organic linker, and Ni2+/ Co2+ (1:1) as the metal nodes. The graphene template modified with low density functional groups preserves the original octahedral shape of 3D NiCo-H2bpydc, while functionalization with high density functional groups transforms the MOF octahedra into nanoflowers with ‘desert rose’ morphology, leading to increased accessible active sites, electric conductivity and enlarged active surface area, thus boosting the OER performance with a small overpotential (241 mV) at 10 mA cm−2 in alkaline solution. This synthetic strategy therefore presents an efficient pathway towards controlling morphology and properties of graphene supported electrocatalytic materials with excellent OER performance.