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Developing highly active and low-cost electrocatalysts with superior durability for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is a grand challenge to produce hydrogen by electrolysis of water. Here, we report on a facile and scalable approach to fabricate highly efficient three-dimensional (3D) bulk catalysts of core–shell nanostructures, in which few-layer NiFe layered double hydroxide (LDH) nanosheets are grown on Cu nanowire cores supported on Cu foams, toward overall water splitting. Remarkably, benefiting from the 3D hierarchical nanoarchitecture with large surface areas, fast electron transport, and open-channels for effective gas release, the resulting 3D self-standing catalysts exhibit outstanding OER activity as well as excellent HER performance in an alkaline medium. Using them as bifunctional catalysts for overall water splitting, a current density of 10 mA cm−2 …