Molten-based defect engineering polymeric carbon nitride quantum dots with enhanced hole extraction: An efficient photoelectrochemical cell for water oxidation

Abstract

Polymeric carbon nitride (g-C3N4) has emerged as a promising material for energy-related applications. However, the utilization of g-C3N4 in photoelectrochemical cells is still limited by poor exciton mobility, sluggish hole extraction, and short electron diffusion length. Here, we report a molten-based defect engineering strategy to prepare nitrogen-deficient g-C3N4 quantum dots (SxCNQD) for photoelectrochemical water splitting. This novel strategy requires no chemical etching or secondary treatments like recent state-of-the-art defect introduction methods, and for the first time achieves the in-situ integration of nitrogen-vacancy defects (NVs) during the polymerization of g-C3N4. Theoretical evaluation and experimental validation identified that the involved structural NVs redistribute the electrons on the delocalized π-conjugated networks of g-C3N4 and creates an additional sub-band on the optical bandgap, which can effectively improve carrier separation, facilitate charge transport dynamics, and boost hole extraction. Beneficial from its featured topological structures and electronic properties, the S600CNQD@ZnO photoanode exhibits a markedly high photocurrent density of 193.8 μA cm−2 at 1.23 V vs. RHE, long-term durability, as well as an impressive IPCE value in an alkaline solution in the absence of sacrificial agent under visible light illumination.