Polycarbazole– <scp>NiOOH</scp> Interfacial Engineering of <scp> BiVO ₄ </scp> Photoanodes for Efficient and Stable Solar Water Splitting

Photoelectrochemical (PEC) water splitting is a promising strategy for sustainable hydrogen and chemical production. Among candidate photoanodes, bismuth vanadate (BVO) offers a suitable band gap (~2.4 eV) and favorable band‐edge alignment for water oxidation, yet its performance remains limited by inefficient charge separation, severe surface recombination, and sluggish interfacial kinetics. Here, these challenges are addressed through the electro‐polymerization of a π‐conjugated carbazole (p‐CBZ) layer on BVO, forming a p–n heterojunction that enhances the built‐in electric field, accelerates hole transport, and passivates surface defects. The subsequent deposition of NiOOH as an oxygen evolution co‐catalyst further promotes charge transfer and catalytic activity. The resulting BVO/p‐CBZ/NiOOH hybrid photoanode achieves a photocurrent density of 5.6 mA cm −2 at 1.23 V versus RHE under 1 sun illumination and maintains stable water oxidation for over 72 h. Further mechanistic insights using electrochemical impedance (EIS) and light‐modulated spectroscopies (IMPS/IMVS) confirm that p‐CBZ markedly improves charge separation and carrier diffusion, while NiOOH facilitates oxygen evolution. This synergistic design significantly enhances PEC performance, highlighting π‐conjugated carbazole polymers as effective hole extraction and passivation layers in BVO‐based photoanodes for efficient and durable solar‐driven water splitting.