To test these hypotheses, we synthesized a series of hierarchical heterostructures of MoS 2 @NiFeCo-Mo(doped)-LDH and MoS 2 @NiFeCo-LDH using a straightforward hydrothermal method and electrodeposition approach on nickel foam (NF). The as-prepared catalyst MoS 2 @NiFeCo-Mo(doped)-LDH demonstrated exceptional performance towards HER and exhibited a low IR-corrected overpotential of 61 mV at 10 mA cm -2 under light illumination, which is lower than that of the benchmark Pt/C (73 mV). The MoS 2 @NiFeCo-LDH electrodes exhibited very good OER performance and have a low IR-corrected overpotential of 156 mV at 10 mA cm -2 under light illumination, which is lower than that of the benchmark RuO 2 catalysts (303 mV) at 10 mA cm -2 . Furthermore, we used MoS 2 @NiFeCo-Mo(doped)-LDH and MoS 2 @NiFeCo-LDH as the HER and OER electrodes, respectively, in a two-electrode water-splitting cell. This electrolytic cell was shown to be stable and to achieve a low cell voltage of 1.46 V for OWS at a current density of 10 mA cm -2 . The MoS 2 @NiFeCo-Mo(doped)-LDH and MoS 2 @NiFeCo-LDH electrodes were shown to be stable at high, industrially relevant current densities of 500 and 1000 mA cm -2 . Density functional theory (DFT) calculations allowed us to rationalize how and why each component of the complex, hierarchical LDH heterostructure contributes to the HER and OER activity. Overall, our work provides a facile and rational way to fabricate and design highly efficient, low-cost, and stable heterostructure catalysts for (photo)electrocatalytic water splitting. Given the modular synthesis approach of the LDH heterostructure, we expect that the design principles applied herein can be used for optimizing LDH-based electrocatalysts for various electrocatalytic processes.