An Fe-doped CoP nanoarray behaves as a robust 3D monolithic multifunctional catalyst for electrolytic and hydrolytic hydrogen evolution with high activity. Its two-electrode electrolyzer needs a cell voltage of only 1.60 V for 10 mA cm−2 water-splitting current. It also catalyzes effectively NaBH4 hydrolysis with a low activation energy of ≈39.6 kJ mol−1 and a hydrogen generation rate of 6.06 L min−1 g−1.