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 (O2) reduction to hydrogen peroxide (H2O2). 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 O2 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 H2O2 generation. As a result, S, C-PTI achieve a 7-fold and 16-fold higher H2O2 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.