Developing efficient oxygen evolution reaction (OER) electrocatalysts for clean hydrogen production is important for transitioning away from conventional energy resources. Herein, this work presents a metal–organic-framework-derived Ni-doped Co9S8 catalyst confined in nitrogen-doped carbon (Ni-Co9S8@NC), featuring enhanced charge-transfer kinetics due to the large electrochemically active surface area and high conductivity of the conductive carbon. In situ characterization and density functional theory calculations reveal that the Ni-Co9S8 component was reconstructed into the built-in electric field structure (i.e., the extensive catalyst structure: Ni-doped Co(OH)2/CoOOH shell coated on Ni-Co9S8 core) during the OER. This Ni-doped built-in electric field regulated the d-band centers of interface Co sites and optimized the adsorption/desorption energies of OER intermediates, thus enhancing the adsorbate evolution mechanism pathway and obtaining excellent OER performance. The anion exchange membrane electrolyzer of the above as-prepared catalyst achieved a cell voltage of 1.85 V at a high current density of 1 A cm−2, outperforming a noble-metal catalyst-based RuO2‖Pt/C electrolyzer (2.11 V @ 1 A cm−2). This work provides an atomic-level Ni-doping strategy to tailor the built-in electric field for obtaining high-performance noble-metal-free catalysts for scalable green hydrogen production.