Abstract Developing cost‐effective, durable bifunctional electrocatalysts is crucial but remains challenging due to slow hydrogen/oxygen evolution reaction (HER/OER) kinetics in water electrolysis. Herein, a combined engineering strategy of phosphorous vacancy (V p ) and spontaneous built‐in electric field (BIEF) is proposed to design novel highly‐conductive Co‐doped MoP@MXene heterostructures with phosphorous vacancy (V p ‐Co‐MoP@MXene). Wherein, Co doping regulates the surface electronic structure and charge re‐distribution of MoP, V p induces more defects and active sites, while BIEF accelerates the interfacial charge transfer rate between V p ‐Co‐MoP and MXene. Therefore, the synergistic integration of V p ‐Co‐MoP/MXene efficiently decreases activation energy and kinetic barrier, thus promoting its intrinsically catalytic activity and structural stability. Consequently, the V p ‐Co‐MoP@MXene catalyst displays low overpotentials of 102.3/196.5 and 265.0/320.0 mV at 10/50 mA cm −2 for HER and OER, respectively. Notably, two‐electrode electrolyzers with the V p ‐Co‐MoP@MXene bifunctional catalysts to achieve 10/50 mA cm −2 , only need low‐cell voltages of 1.57/1.64 V in alkaline media. Besides, experimental and theoretical results confirm that the hetero‐structure effectively reduces hydrogen adsorption free energy and rate‐determining‐step energy barrier of OER intermediates, thereby greatly boosting its intrinsically catalytic activity. This work verifies an effective strategy to fabricate efficient non‐precious bifunctional electro‐catalysts for water splitting via combination engineering of phosphorous vacancy, cation doping, and BIEF.

Phosphorous Vacancy and Built‐In Electric Field Effect of Co‐Doped MoP@MXene Heterostructures to Tune Catalytic Activity for Efficient Overall Water Splitting