Covalent Triazine-Based Polymers with Controllable Band Alignment Matched with BiVO₄ To Boost Photogeneration of Holes for Water Splitting

To promote the charge carrier utilization for efficient photoelectrochemical (PEC) water splitting, we design novel covalent triazine-based polymers (CTPs) with a controllable energy band alignment to construct hybrid heterojunction photoanodes with BiVO4 based on energy band matching conception. The energy bands of CTPs with the same triazine backbone can match well with BiVO4 by lengthening the aryl groups as electron donors through a convenient aromatic nucleophilic substitution reaction to enhance charge separation and transfer capacity. Typically, a CTP with a naphthyl group, that is, CTP2 hybridized with BiVO4 indicates a distinctly reinforced PEC performance profiting from the quick hole extraction from BiVO4 via an efficient built-in electric field. Accordingly, the hybrid BiVO4/CTP2 electrode with the aid of iron/nickel hydroxyl oxide realizes a prominent photocurrent density of 4.05 mA cm–2 and the corresponding H2/O2 amounts of 676/338 μmol cm–2 after the stability test of 10 h at 1.23 V versus a reversible hydrogen electrode, which is ca. sevenfold as large as the pristine BiVO4 electrode. Hence, the energy band modulation and matching could be one of the conducive references to design hybrid heterojunctions from the aspect of organics.