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 (BiVO₄) 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 BiVO₄. 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-BiVO₄ 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 Ni²⁺ into active, defect‑free Ni³⁺ sites. The phosphonate group further stabilizes these Ni³⁺ centers. The resulting SAM-NiO_x-BiVO₄ 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.