Organic–Inorganic Hybrid Hole‐Selective Layer Interface Engineering for Enhanced Photoelectrochemical Water Oxidation on Bismuth Vanadate Photoanodes

ABSTRACT Due to poor carrier migration and sluggish water oxidation kinetics, bismuth vanadate (BiVO 4 ) photoanodes show limited photoelectrochemical (PEC) performance and stability. Coupling a hole‐selective layer (HSL) can mitigate these issues. Here, we construct an organic‐inorganic hybrid HSL by combining a self‐assembled monolayer (Me‐4PACz) with NiO x on BiVO 4 . Through systematic control experiments that decouple the contributions of the individual layers, we quantitatively reveal a genuine synergy between NiO x and Me‐4PACz. NiO x rapidly extracts holes and provides catalytic sites. The Me‐4PACz adopts a vertical, non‐dense orientation, generating a molecular dipole that forms a continuous SAM‐NiO x ‐BiVO 4 energy cascade and lowers the hole transfer barrier. More importantly, we uncover a “local anchoring and remote activation” mechanism: a single Me‐4PACz binds via P–O–Ni to a surface Ni site (passivating a harmful defect), while its electron‐withdrawing effect propagates through the Ni–O–Ni lattice to convert adjacent Ni 2+ into active, defect‑free Ni 3+ sites. The phosphonate group further stabilizes these Ni 3+ centers. The resulting SAM‐NiO x ‐BiVO 4 photoanode achieves a photocurrent density of 6.90 mA cm −2 at 1.23 V versus reversible hydrogen electrode (RHE) and retains stable performance for over 60 h. This work expands SAM applicability in PEC water oxidation and offers a rational design principle for organic–inorganic hybrid photoanodes.