Large-scale bismuth vanadate (BiVO4) photoanodes are critical to the practical application of photoelectrochemical (PEC) water splitting devices. However, the lack of interface-modified coatings with simultaneous low cost, scalability, high hole transport efficiency, low impedance, and photocorrosion resistance is a major challenge that prevents the practical application of large-size photoanodes. Here, we present a scalable nickel-chelated polydopamine (PDA-Ni) conformal coating for modifying BiVO4 (BiVO4@PDA-Ni, BPNi), achieving over 500 hours of stable water oxidation. The excellent stability is attributed to the chelated Ni acting as hole oxidation sites for PDA, thereby suppressing the accumulated-holes-induced PDA decomposition. Additionally, the in situ generation of Ni(Ⅳ) facilitates the structural reorganization of PDA in the PEC system, further enhancing the stability of the PDA matrix. The findings of PDA photodegradation, its autonomous metal ion capture within PEC systems, and the rapid deactivation of BPNi photoanodes caused by vanadium (V) ions have all provided significant guidance for the enhancement of PDA. Our study demonstrates that PDA-Ni can be applied to large-scale BiVO4 photoanodes to facilitate oxygen evolution. This will promote the development of large-scale photoanodes suitable for PEC devices.