Earth-abundant and highly efficient electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are desired for water-splitting to produce hydrogen. Some nickel-based materials are usually used in water-alkaline electrolysis, but their composition and structure are still not optimized. In this work, porous aligned flake arrays of Ni-embedded NiO (Ni/NiO) and single-crystalline NiFe layered double hydroxide (LDH) are proposed to be HER and OER electrocatalysts to produce H-2 and O-2, respectively. The former catalyst, fabricated by non-contact Al-reduction of nickel hydroxide precursors, showed high HER activity, approaching that of commercial Pt/C. The latter catalyst, prepared by the fluorinion-assisted hydrothermal method, possessed higher activity for the OER than the well-known RuO2. The water-alkaline electrolyser assembled by the arrays of Ni/NiO and NiFe LDH in 1 M NaOH exhibits an ultra-small cell voltage of 1.52 V at a current density of 20 mA cm(-2) at room temperature, as well as good long-term stabilities. These high performances of our nickel-based arrays result from their improved charge transfer and mass transport, and faster kinetics of catalytic reactions. So the arrays of Ni/NiO and NiFe LDH are promising in the application of water-splitting devices.