Efficient design and preparation of cost-effective and binder-free bifunctional electrocatalysts to accelerate the hydrogen and oxygen evolution reaction (HER and OER) are critical for overall water splitting. In this work, 3D hierarchical NiFe-LDH/FeCoS2/CFC electrodes were synthesized for the first time. The carboxyl groups derived from acid treating promote the homogeneously coated FeCoS(2)on CFC, giving rise to the strongly coupled FeCoS2/CFC hybrid. The NiFe-LDH exhibited the vertical growth feature on the FeCoS2/CFC composite, which can efficiently expose the active edges sites. Due to unique structure and synergistic effect between the components, the NiFe-LDH/FeCoS2/CFC exhibits significant electrocatalytic activity and stability under alkaline environments, with overpotentials of 190 and 308 mV to achieve 10 mA cm(-2)for OER and HER, respectively, providing it as a promising electrocatalyst for water splitting reaction. In addition, we deeply studied the synergistic catalytic mechanism of NiFe-LDH/FeCoS2/CFC, explaining the reasons leading to the improved catalytic performance of HER and OER. Graphic abstract