MoS2 has emerged as an attractive electrocatalyst for hydrogen evolution reaction (HER) although its performance still needs to be further enhanced, especially in alkaline solution due to inferior ability for water dissociation. Herein, we discover that coupling water-dissociation-active FeOOH with MoS2 grown on Ni3S2 nanowire arrays to achieve a core-shell Ni3S2@MoS2/FeOOH heterostructure can not only significantly accelerate the HER of MoS2, but also appreciably promote the OER activity of the catalyst. Systematic investigations on Ni3S2@MoS2/FeOOH and a series of delicately designed control catalysts reveal that such synergistically enhanced electrocatalytic performance for both OER and HER should be ascribed to the coupling effect and electronic modulation between FeOOH and MoS2. As a result, the prepared Ni3S2@MoS2/FeOOH exhibits small overpotentials of 95 mV for HER and 234 mV for OER at 10 mA cm(-2). The alkaline electrolyzer using it as both anode and cathode only need a cell voltage of 1.57 V to output a stable current density of 10 mA cm(-2), enabling it as an efficient bifunctional electrocatalyst for alkaline overall water splitting. The present strategy opens up opportunities to develop new efficient electrocatalysts for diverse applications by coupling OER-active electron-modulating component with highly-active HER electrocatalyst or vice versa.