Polycarbazole–NiOOH Interfacial Engineering of BiVO4 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.