Earth-abundant and highly efficient electrocatalysts for the hydrogen evolution reaction (HER) are desired for hydrogen production from water-splitting. Here, Co nanoparticles were embedded in the 3D CoO matrix via a template-free method, including cobalt hydroxy-carbonate nanowire arrays grown on Ni foam and the following non-contact Al-reduction process. The as-prepared 3D hierarchical structured Co/CoO nanowires possess good charge transfer and mass transport properties, and a synergistic effect at the Co/CoO interface can hugely facilitate the HER kinetics. A suitable balance between Co and CoO in the catalyst is crucial for high catalytic activity. And the optimal Co/CoO array exhibited outstanding HER activities in 1 M NaOH, achieving nearly zero onset potential, and a current density of 100 mA cm(-2) with a small overpotential of 167 mV. They also showed good long-term stabilities. This hybrid Co/CoO nanowire array is a promising material for large-scale hydrogen production from water-splitting.