Defect-Conjugation Coupling in Sulfur and Carbon Co-doped Poly(triazine imide) for Visible-Light-Driven H ₂ O ₂ Production

Crystalline poly(triazine imide) (PTI) is a promising semiconductor for solar-driven oxygen (O 2 ) reduction to hydrogen peroxide (H 2 O 2 ). However, its performance is constrained by limited visible-light absorption and inefficient charge transport arising from unfavorable defect-mediated recombination. Here, we report a molten-salt strategy to synthesize sulfur (S) and carbon (C) co-doped PTI (S, C-PTI), enabling precise modulation of its optoelectronic properties while preserving the intrinsic crystalline framework. The resulting S, C-PTI exhibits enhanced visible-light absorption and a narrowed band gap arising from the synergistic effect of S-induced defect states and extended C-driven π-conjugation. Spectroscopic and structural analyses reveal that codoping reorganizes the local electronic environment, suppresses radiative exciton recombination, and generates catalytically active sites for selective O 2 reduction. Density functional theory (DFT) calculations further show that S and C co-doping stabilizes the key *OOH intermediate by reducing its formation free energy relative to pristine PTI, thereby promoting H 2 O 2 generation. As a result, S, C-PTI achieve a 7-fold and 16-fold higher H 2 O 2 generation rate compared to pristine PTI and polymeric carbon nitride, respectively. This work establishes non-metal co-doping as a general effective strategy to regulate the crystallinity and optoelectronics relationships in PTI, advancing the rational design of crystalline photocatalysts for solar-to-chemical conversion.