Redox-enhanced photocatalysis: Boosting hydrogen peroxide production in conjugated triazine frameworks with dihydrophenazine cycling

Solar-driven hydrogen peroxide (H2O2) synthesis is crucial for sustainable solar fuel production. Covalent triazine frameworks (CTFs) are promising photocatalysts for solar-driven H2O2 generation due to their tunable structures. However, the catalytic mechanism is not fully understood, and efficiency remains limited, making it a significant challenge to extend their application to practical H2O2 production. To address this, inspired by the role of dihydrophenazine (DHPZ) as an electron transfer carrier in biochemical reactions, we introduce a dihydrophenazine (DHPZ)-functionalized CTF (TA-DHPZ) designed to facilitate effective electron transfer, leveraging DHPZ's redox cycling to promote the reduction of O2 to H2O2. The DHPZ unit in TA-DHPZ sequentially oxidizes to phenazyl radical (PZ center dot+) and phenazinium salt (PZ2+) during H2O2 synthesis, then photoreduces back to DHPZ, maintaining continuous electron flow and lowering the energy barrier. As a result, TA-DHPZ achieves a remarkable H2O2 production rate of 7787 mu mol g- 1h- 1, outperforming its molecular counterpart TA-AN (anthracene-functionalized CTF), by capitalizing on DHPZ's redox efficiency. This investigation not only introduces a valuable functional moiety for the design of CTFs but also lays the groundwork for innovative approaches in molecular-level design of photocatalysts for efficient solar-to-chemical energy conversion.